,transcriber's ,note3 ,italic text is   
enclosed in underscores2 boldface  text 
on the last page of the book is enclosed
 in equals signs4 ,other  notes will be 
found after the footnotes4              
,,university ,,of ,,illinois ,,bulletin 
,,issued ,,weekly            ,vol4 ,,xi 
,,march #af1 #aiad              ,no4 #bi
      ,entered as second-class matter   
,dec4 #aa1 #aiab1 at the ,post ,office  
at               ,urbana1 ,ill41 under  
the ,act of ,aug4 #bd1 #aiab4           
,,acoustics ,,of ,,auditoriums          
,,by                                ,f4 
,r4 ,,watson                            
,illustration3 ,,university ,,of        
,,illinois4                             
,,chartered #ahfg4                      
,,bulletin ,no4 #gc                     
,,engineering ,,experiment ,,station    
,,published ,,by ,,the ,,university ,,of
 ,,illinois1 ,,urbana                   
,,price3 ,,twenty ,,cents               
,,european ,,agent                      
,,chapman ,,and ,,hall1 ,,ltd41 ,,london

          ,the ,engineering ,experiment 
,station was established by act of the  
,board of ,trustees1 ,december #h1      
#aijc4 ,it is the purpose of the        
,station  to carry on investigations    
along various lines of engineering and  
to study problems of importance to      
professional engineers and to  the      
manufacturing1 railway1 mining1         
constructional1 and industrial          
interests of the ,state4    ,the control
 of the ,engineering ,experiment        
,station is vested in the  heads of the 
several departments of the ,college of  
,engineering4 ,these  constitute the    
,station ,staff and1 with the ,director1
 determine the  character of the        
investigations to be undertaken4 ,the   
work is carried  on under the           
supervision of the ,staff1 sometimes by 
research fellows as  graduate work1     
sometimes by members of the             
instructional staff of the  ,college of 
,engineering1 but more frequently by    
investigators belonging  to the ,station

 corps4    ,the results of these        
investigations are published in the form
 of  bulletins1 which record mostly the 
experiments of the ,station's own  staff
 of investigators4 ,there will also be  
issued from time to time  in the form of
 circulars1 compilations giving the     
results of the  experiments of          
engineers1 industrial works1 technical  
institutions1 and  governmental testing 
departments4    ,the volume and number  
at the top of the title page of the     
cover are  merely arbitrary numbers and 
refer to the general publications of the
  ,university of ,illinois2 either above
 the title or below the seal  is given  
the number of ,engineering ,experiment  
,station bulletin or  circular1 which   
should be used in referring to these    
publications4    ,for copies of         
bulletins1 circulars1 or other          
information address the  ,engineering   
,experiment ,station1 ,urbana1          
,illinois4    ,illustration3 ,,fig4 #a4 
,,auditorium1 ,,university ,,of         

,,illinois4          ,,acoustics ,,of   
,,auditoriums    ,,an ,,investigation   
,,of ,,the ,,acoustical ,,properties    
,,of ,,the ,,auditorium ,,at ,,the      
,,university ,,of ,,illinois4           
,i4 ,,introduction4      ,much concern  
has arisen in late years in the minds of
 architects  because of the faulty      
acoustics that exist in many            
auditoriums4 ,the  prevalence of echoes 
and reverberations with the consequent  
difficulty  in hearing and understanding
 on the part of the auditor defeats the 
purpose of the auditorium and diminishes
 its value4    ,the ,auditorium at the  
,university of ,illinois presents such a
 case4 ,the  building is shaped nearly  
like a hemisphere1 with several large   
arches  and recesses to break up the    
regularity of its inner surface4 ,the   
original plans of the architect were    
curtailed because of insufficient  money
 appropriated for the construction4 ,the
 interior of the hall1  therefore1 was  
built absolutely plain with almost no   

breaking up of the  large1 smooth wall  
surfaces2 and1 at first1 there were no  
furnishings  except the seats and the   
cocoa matting in the aisles4 ,the       
acoustical  properties proved to be very
 unsatisfactory4 ,a reverberation or    
undue  prolongation of the sound        
existed1 and in addition1 because of the
  large size of the room and the form   
and position of the walls1 echoes  were 
set up4    ,if an observer stood on the 
platform and clapped his hands1 a       
veritable  chaos of sound resulted4     
,echoes were heard from every direction 
and  reverberations continued for a     
number of seconds before all was still  
again4 ,speakers found their utterances 
thrown back at them1 and  auditors all  
over the house experienced difficulty in
 understanding  what was said4 ,on one  
occasion the ,university band played a  
piece which  featured a xylophone solo  
with accompaniment by the other         
instruments4  ,it so happened that the  
leader heard the echo more strongly than

 the  direct sound and beat time with   
it4 ,players near the xylophone kept    
time to the direct sound1 while those   
farther away followed the echo4  ,the   
confusion may well be imagined4    ,thus
 it seemed that the ,auditorium was     
doomed to be an acoustical  horror2 that
 speakers and singers would avoid it1   
and that auditors  would attend         
entertainments in it only under protest4
 ,but the apparent  misfortune was in   
one way a benefit since it provided an  
opportunity  to study defective         
acoustics under exceptionally good      
conditions  and led to conclusions that 
not only allowed the ,auditorium to be  
improved but also indicate some of the  
pitfalls to be avoided in future        
construction of other halls4            
,illustration3 ,,fig4 #b4 ,,photograph  
,,of ,,interior4 ,,view ,,of ,,stage4   
,illustration3 ,,fig4 #c4 ,,photograph  
,,of ,,interior4 ,,view ,,toward        
,,balcony4    ,an investigation of the  
acoustical properties of the ,auditorium

 was  begun in #aijh and has continued  
for six years4 ,it was decided at the   
outset not to use 8cut and try0 methods 
of cure1 but to attack the  problem     
systematically so that general          
principles could be found1 if  possible1
 that would apply not only to the case  
being investigated but  to auditoriums  
in general4 ,this plan of procedure     
delayed the solution  of the problem1   
since it became necessary to study the  
theory of sound  and carry out          
laboratory investigations at the same   
time that the  complex conditions in the
 ,auditorium were being considered4 ,the
 author  spent one year of the six      
abroad studying the theory of acoustics 
and  inspecting various auditoriums4    
,the main echoes in the ,auditorium were
 located by means of a new method  for  
tracing the path of sound1 the time of  
reverberation was determined  by        
,sabine's method1 and a general         
diagnosis of the acoustical defects  was
 made4 ,hangings and curtains were      

installed in accordance with the        
results of the study so that finally the
 acoustical properties were  improved4  
,acknowledgment4--,the author desires to
 express his great appreciation  of the 
advice and encouragement given by       
,president ,e4 ,j4 ,james1  ,supervising
 ,architect ,j4 ,m4 ,white1 and         
,professor ,a4 ,p4 ,carman of  the      
,physics ,department4 ,he desires also  
to acknowledge the material  assistance 
cheerfully rendered by the workmen at   
the ,university1 which  contributed in  
no small degree to the successful       
solution of the  problem4          ,,ii4
 ,,behavior ,,of ,,sound ,,waves ,,in ,a
 ,,room4      ,when a speaker addresses 
an audience1 the sounds he utters       
proceed in  ever widening spherical     
waves until they strike the boundaries  
of the  room4 ,here the sound is partly 
reflected1 partly transmitted1 and the  
rest absorbed4 ,the amounts of          
reflection1 absorption and transmission 
depend on the character of the walls4 ,a

 hard1 smooth wall reflects most  of the
 sound so that but little is transmitted
 or absorbed4 ,in the case  of a porous 
wall or a yielding wall1 the absorption 
and transmission  are greater1 and the  
reflection is less4 ,after striking a   
number of  reflecting surfaces1 the     
energy is used up and the sound dies    
out4    ,the reflection of sound        
produces certain advantages and         
disadvantages  for the acoustics4 ,when 
it is considered that sound travels     
about #aajj  feet a second it may be    
seen that a room of ordinary size is    
almost  immediately filled with sound   
because of the many reflections4 ,in a  
room #dj feet square1 for instance1 the 
number of reflections per second        
between opposite walls is #aajj  #dj1 or
 approximately #bg4 ,the number is      
really greater than this1 since the     
sound that goes into the corners  is    
reflected much more frequently than out 
in the middle where the  distances      
between walls are greater4 ,the result  

is that the sound mixes  thoroughly in  
all parts of the room so as to give the 
same average  intensity2 that is1 the   
sound is of the same average loudness   
for all  auditors1 even for those in the
 remotest corners4    ,though the       
reflection of sound has the advantage of
 fulfilling the  conditions for         
loudness1 it introduces at the same time
 possibilities  for setting up defective
 acoustics4 ,for instance1 when the     
walls of the  room are hard and smooth  
very little energy is lost at each      
impact of  the sound and many           
reflections take place before it finally
 dies out4  ,this slow decadence of the 
sound1 or reverberation as it is called1
  is the most common defect in          
auditoriums4    ,if a speaker talks in  
such a hall the auditors have difficulty
 in  understanding4 ,each sound1 instead
 of dying out quickly1 persists for     
some time so that the succeeding words  
blend with their predecessors  and set  
up a mixture of sounds which produces   

confusion4 ,the cure for  the trouble is
 brought about by the introduction of   
materials such as  carpets1 tapestries1 
and the like1 which act as absorbers of 
sound and  reduce the time of           
reverberation4    ,when music is played 
in an auditorium with a prolonged       
reverberation1  the tones following one 
another blend and produce the same      
effect as  that of a piano when played  
with the loud pedal in use4 ,a          
reverberation  is more advantageous for 
music than for speech1 since the        
prolongation  and blending of the       
musical tones is desired1 but the mixing
 of the  words in a speech is a distinct
 disadvantage4 ,when curing this defect 
for halls used for both music and       
speaking1 a middle course must be       
steered1 so that the reverberation is   
made somewhat long for speaking  and    
somewhat short for music1 yet fairly    
satisfactory for both4    ,going back to
 the consideration of the reflection of 
sound1 it is found  that another defect 

may be produced1 namely1 an echo4 ,this 
is the  case when a wall at some        
distance reflects the sound to the      
position  of the auditor4 ,he hears the 
sound first from the speaker1 then later
  by reflection from the wall4 ,the time
 interval between the direct and        
reflected sound must be great enough to 
allow two distinct impressions  to be   
made4 ,this time is about #a_/ae of a   
second1 but varies with the  acuteness  
of the observer4 ,the farther off the   
wall is1 the greater is  the time       
interval and the more pronounced is the 
echo4 ,if the wall is  not very distant1
 the time interval is too short to allow
 two distinct  impressions to be made1  
and the effect on the auditor is then   
much the  same as if his neighbor at his
 side speaks the words of the discourse 
in his ear at the same time that he gets
 them directly from the  speaker4 ,in   
case the reflecting wall is curved so as
 to focus the sound  the echoes are much
 more pronounced4 ,a curved wall        

wherever it may be  placed in an        
auditorium is thus always a menace to   
good acoustics4    ,there are other     
actions of the sound that may result in 
acoustical  defects4 ,the phenomena of  
resonance1 for instance1 may cause      
trouble4  ,suppose that the waves of    
sound impinge on an elastic wall1 not   
too  rigid4 ,if these waves are timed   
right they set the wall in vibration in 
the same way that the bell ringer causes
 a bell to ring by a succession  of     
properly timed pulls on the bell rope4  
,the wall of the room will  then vibrate
 under the action of this sound with    
which it is in tune  and will reinforce 
it4 ,now suppose a band is playing in a 
room4 ,certain  tones are reinforced1   
while the others are not affected4 ,the 
original  sound is then distorted4 ,the 
action is the same on the voice of the  
speaker4 ,the sounds he utters are      
complex and as they reach the walls     
certain components are reinforced and   
the quality of the sound is  changed4   

,this action of resonance may also be   
caused by the air in a  room4 ,each room
 has a definite pitch to which it       
responds1 the smaller  the volume of the
 room the higher being the pitch4 ,a    
large auditorium  would respond to the  
very low pitch of the bass drum4 ,in    
small rooms  and alcoves the response is
 made to higher pitched tones1 as may be
  observed by singing the different     
notes of the scale until a resonance  is
 obtained4    ,another action of sound  
causes the interference of waves4 ,thus 
the  reflected waves may meet the       
oncoming ones and set up concentrations 
of  sound in certain positions and a    
dearth of sound in others4    ,summing  
up1 it is seen that the effects of sound
 which may exist in  a room are         
loudness1 reverberation1 echoes1        
resonance1 and  interference1 and that  
the most common defects are             
reverberation and  echoes4 ,we now turn 
to the discussion of the methods of     
cure4          ,,iii4 ,,methods ,,of    

,,improving ,,faulty ,,acoustics4       
,a4 ,,reverberation ,,and ,,its ,,cure4 
,everyone has doubtless observed that   
the hollow reverberations in  an empty  
house disappear when the house is       
furnished4 ,so1 in an  auditorium1 the  
reverberation is lessened when curtains1
 tapestries1  and the like are installed
 in sufficient numbers4 ,the reason for 
this  action is found when we inquire   
what ultimately becomes of the sound4   
,sound is a form of energy and energy   
can not be destroyed4 ,when it  finally 
dies out1 the sound must be changed to  
some other form of  energy4 ,in the case
 of the walls of a room1 for instance1  
it has been  shown in a preceding       
paragraph that the sound may be changed 
into  mechanical energy in setting these
 walls in vibration4 ,again1 some  of   
the sound may pass out through open     
windows and thus disappear4  ,the rest  
of the sound1 according to ,lord        
,rayleigh1 is transformed by  friction  
into heat4 ,thus#a a high pitched sound1

 such as a hiss1  before it travels any 
great distance is killed out by the     
friction of  the air4 ,lower pitched    
sounds1 on reaching a wall1 set up a    
friction  in the process of reflection  
between the air particles and the wall  
so  that some of the energy is converted
 into heat4#b ,the amount of sound      
energy thus lost is small if the walls  
are hard and smooth4 ,the case is  much 
different1 however1 if the walls are    
rough and porous1 since it  appears that
 the friction in the pores dissipates   
the sound energy into  heat4 ,in this   
connection1 ,lamb#c writes3 8,in a      
sufficiently narrow  tube the waves are 
rapidly stifled1 the mechanical energy  
lost being  of course converted into    
heat4 99 99 99 99 ,when a sound wave    
impinges on a  slab which is permeated  
by a large number of very minute        
channels1 part  of the energy is lost1  
so far as the sound is concerned1 by    
dissipation  within these channels in   
the way just explained4 ,the interstices

 in  hangings and carpets act in a      
similar manner1 and it is to this cause 
that the effect of such appliances in   
deadening echoes in a room is  to be    
ascribed1 a certain proportion of the   
energy being lost at each  reflection4  
,it is to be observed that it is only   
through the action of  true dissipative 
forces1 such as viscosity and thermal   
conduction1 that  sound can die out in  
an enclosed space1 no mere modifications
 of the  waves by irregularities being  
of any avail40    ,it should be pointed 
out in this connection that any         
mechanical  breaking up of the sound by 
relief work on the walls or by obstacles
 in  the room will not primarily        
diminish the energy of the sound4 ,these
  may break up the regular reflection   
and eliminate echoes1 but the sound     
energy as such disappears only when     
friction is set up4    ,the following   
quotation from ,rayleigh#d emphasizes   
these conclusions3  8,in large spaces1  
bounded by non-porous walls1 roof1 and  

floor1  and with few windows1 a         
prolonged resonance seems inevitable4   
,the  mitigating influence of thick     
carpets in such cases is well known4    
,the  application of similar material to
 the walls and roof appears to offer    
the best chance of further improvement40
    ,experimental ,work on ,cure of     
,reverberation4--,the most important    
experimental work in applying this      
principle of the absorbing power of     
carpets1 curtains1 etc41 has been done  
by ,professor ,wallace ,c4 ,sabine  of  
,harvard ,university4#e ,in a set of    
interesting experiments lasting  over a 
period of four years1 he was able to    
deduce a general relation  between t1   
the time of reverberation1 ,v1 the      
volume of the room1  and a1 the         
absorbing power of the different        
materials present4 ,thus3               
t  #j4afd ,v  a 7#a7    ,for good       
acoustical conditions1 that is1 for a   
short time of  reverberation1 the volume
 ,v should be small and the absorbing   

materials1 represented by a1 large4     
,this is the case in a small room  with 
plenty of curtains and rugs and         
furniture4 ,if1 however1 the volume  of 
the room is great1 as in the case of an 
auditorium1 and the amount  of absorbing
 materials small1 a troublesome         
reverberation will result4    ,professor
 ,sabine determined the absorbing powers
 of a number of  different materials4   
,calling an open window a perfect       
absorber of  sound1 the results obtained
 may be written approximately as        
follows3        ,one square meter of    
open window space             #a4jjj    
,one square meter of glass1 plaster1 or 
brick       4#jbe      ,one square meter
 of heavy rugs1 curtains1 etc4     4#be 
,one square meter of hair felt1 #a inch 
thick        4#ge      ,one square meter
 of audience                       4#if 
,these values1 together with the        
formula1 allow a calculation to be made 
in advance of construction for the time 
of reverberation4 ,this pioneer  work   

cleared the subject of architectural    
acoustics from the fog of  mystery that 
hung over it and allowed the essential  
principles to be  seen in the light of  
scientific experiment4    ,in a later   
investigation#f ,sabine showed that the 
reverberation  depended also on the     
pitch of sound4 ,as a concrete example1 
the high  notes of a violin might be    
less reverberant with a large audience  
than the lower tones of the bass viol1  
although both might have the  same      
reverberation in the room with no       
audience4 ,again1 the voice of  a man   
with notes of low pitch might give      
satisfactory results in an  auditorium  
while the voice of a woman with higher  
pitched notes would  be unsatisfactory4 
,these considerations show that the     
acoustics in an auditorium vary with    
other factors than the volume of the    
room and the amount of absorbing        
material present4 ,the audience may be  
large or small1 the speaker's  voice    
high or low1 the entertainment a musical

 number or an address4  ,the best       
arrangement for good acoustics is then a
 compromise where the  average          
conditions are satisfied4 ,the solution 
offered by ,professor  ,sabine is such  
an average one1 and has proved          
satisfactory in practice4    ,the       
problem of architectural acoustics has  
been attacked experimentally  by other  
workers4 ,stewart#g proposed a cure for 
the poor acoustical  conditions in the  
,sibley ,auditorium at ,cornell         
,university4 ,his  experiments confirmed
 the work of ,sabine4 ,marage#h1 after  
investigating the properties of six     
halls in ,paris1 approved ,sabine's     
results and advocated a time of         
reverberation of from  to #a second for 
the case of speech4    ,formulae for    
,reverberation of ,sound in a           
,room4--,on the theoretical  side1      
,sabine's formula has been developed by 
,franklin1#i who obtained  the relation 
t  #j4afbe ,v  a1 an interesting        
confirmation1 since  ,sabine's          

experimental value for the constant was 
#j4afd4    ,a later development has been
 given by ,jger1#aj who assumes for a   
room  whose dimensions are not greater  
than about #fj feet1 that the sound1    
after filling the room1 passes equally  
in all directions through any  point1   
and that the average energy is the same 
in different parts of  the room4 ,by    
using the theory of probability and     
considering that a  beam of sound in any
 direction may be likened to a particle 
with a  definite velocity1 he was able  
to deduce ,sabine's formula and write   
down the factors that enter into the    
constants4 ,applying his results to  the
 case of reflection of sound from a     
wall1 he showed that sound would  be    
reflected in greater volume when the    
mass of the wall was increased  and the 
pitch of the sound made higher4 ,he     
showed also that when sound  impinges on
 a porous wall1 more energy is absorbed 
when the pitch of  the sound is high    
than when it is low1 since the          

vibrations of the air  are more         
frequent1 and more friction is          
introduced in the interstices  of the   
material4      ,b4 ,,echoes ,,and       
,,their ,,remedy4    ,an echo is set up 
by a reflecting wall4 ,if an observer   
stands some  distance from the front of 
a cliff and claps his hands1 or shouts1 
he  finds that the sound is returned to 
him from the cliff as an echo4 ,so1  in 
an auditorium1 an auditor near the      
speaker gets the sound first  directly  
from the speaker1 then1 an instant      
later1 a strong repetition  of the sound
 by reflection from a distant wall4     
,this echo is more  pronounced if the   
wall is curved and the auditor is at the
 point where  the sound is focused4     
,to cure such an echo1 two methods may  
be considered4 ,one method  consists in 
changing the form of the wall so that   
the reflected sound  no longer sets up  
the echo4 ,that is1 either change the   
angle of the  wall1 so that the         
reflected sound is sent in a new        

direction where it  may be absorbed or  
where it may reinforce the direct sound 
without  producing any echoes1 or else  
modify the surface of the wall by relief
  work or by panels of absorbing        
material1 so that the strong reflected  
wave is broken up and the sound is      
scattered4 ,the second method is to     
make the reflecting wall a 8perfect0    
absorber1 so that the incident  sound is
 swallowed up and little or none        
reflected4 ,these methods  have been    
designated as 8surgical0 and 8medicinal0
 respectively4 ,each  method has its    
disadvantages4 ,changing the form of the
 walls in an  auditorium is likely to do
 violence to the architectural design4  
,on  the other hand1 there are no       
perfect absorbers1 except open windows1 
and these can seldom be applied4 ,the   
cure in each case is1 then1 a  matter of
 study of the special conditions of the 
auditorium4 ,usually  a combination of  
the surgical and the medicinal cures is 
adopted4 ,for  instance1 coffering a    

wall so that panels of absorbing        
material may be  introduced has been    
found to work well in bettering the     
acoustics1 and  also1 in many cases1 it 
fits in with the architectural features4
      ,c4 ,,popular ,,conception ,,of   
,,cures4--,,use ,,of ,,wires ,,and      
,,sounding ,,boards4    ,a few words    
should be written concerning the popular
 notion that  wires and sounding boards 
are effective in curing faulty          
acoustics4  ,experiments and            
observations show that wires are of     
practically no  benefit1 and sounding   
boards can be used only in special      
cases4 ,wires  stretched in a room      
scarcely affect the sound1 since they   
present too  small a surface to disturb 
the waves4 ,they have much the same     
effect on  sound waves that a fish line 
in the water has on water waves4 ,the   
idea  has1 perhaps1 grown into          
prominence because of the action of a   
piano  in responding to the notes of a  
singer4 ,the piano has every advantage  

over a wire in an auditorium4 ,it has a 
large number of strings tuned  to       
different pitches so that it responds to
 any note sung4 ,it also has  a sounding
 board that reinforces strongly the     
sound of the strings4  ,finally1 the    
singer is usually near the piano4 ,the  
wire in the  auditorium responds to only
 one tone of the many likely to be      
present1  it has no sounding board1 and 
the singer is some distance away4 ,but  
little effect1 therefore1 is to be      
expected4    ,the author has visited a  
number of halls where wires have been   
installed1 and has yet to find a case   
where pronounced improvement has        
resulted4#aa ,sabine#ab cites a case    
where five miles of wire were  stretched
 in a hall without helping the          
acoustical conditions4 ,it is  curious  
that so erroneous a conception has grown
 up in the public mind  with so little  
experimental basis to support it4       
,sounding ,boards4--,sounding boards or1
 more properly1 reflecting  boards1 have

 value in special cases4 ,some          
experiments are described  later where  
pronounced effects were obtained4 ,the  
sounding board should  be of special    
design to fit the conditions under which
 it is to be used4    ,modeling ,new    
,auditoriums after ,old ,ones with ,good
 ,acoustics4--,another  suggestion often
 made is for architects to model        
auditoriums after  those already built  
that have good acoustical properties4   
,it does not  follow that halls so      
modeled will be successful1 since the   
materials  used in construction are not 
the same year after year4 ,for instance1
  a few years ago it was the usual      
custom to put lime plaster on wooden    
lath2 now it is frequently the practice 
to put gypsum plaster on metal  lath1   
which forms an entirely different kind  
of a surface4 ,this latter  arrangement 
makes hard1 non-porous walls which      
absorb but little sound1  and thus      
aggravate the reverberation4 ,further1 a
 new hall usually is  changed somewhat  

in form from the old one1 to suit the   
ideas of the  architect1 and it is very 
likely that the changes will affect the 
acoustics4      ,d4 ,,the ,,effect ,,of 
,,the ,,ventilation ,,system ,,on ,,the 
,,acoustics4    ,at first thought it    
might seem that the ventilation system  
in a room  would affect the acoustical  
properties4 ,the air is the medium that 
transmits the sound4 ,it has been shown 
that the wind has an action  in changing
 the direction of propagation of        
sound4#ac ,sound is also  reflected and 
refracted at the boundary of gases that 
differ in density  and temperature4#ad  
,it is found1 however1 that the effect  
of the  usual ventilation currents on   
the acoustics in an auditorium is small4
  ,the temperature difference between   
the heated current and the air in  the  
room is not great enough to affect the  
sound appreciably1 and the  motion of   
the current is too slow and over too    
short a distance to  change the action  
of the sound to any marked extent4#ae   

,under special circumstances1 the       
heating and ventilating systems may     
prove disadvantageous4#af ,a hot stove  
or a current of hot air in the  center  
of the room will seriously disturb the  
action of sound4 ,any  irregularity in  
the air currents so that sheets of cold 
and heated air  fluctuate about the room
 will also modify the regular action of 
the  sound and produce confusion4 ,the  
object to be striven for is to keep  the
 air in the room as homogeneous and     
steady as possible4 ,hot stoves1        
radiators1 and currents of heated air   
should be kept near the walls and  out  
of the center of the room4 ,it is of    
some small advantage to have  the       
ventilation current go in the same      
direction that the sound is to  go1     
since a wind tends to carry the sound   
with it4          ,,iv4 ,,the           
,,investigation ,,in ,,the ,,auditorium 
,,at ,,the ,,university ,,of ,,illinois4
      ,a4 ,,preliminary ,,work4    ,as  
already stated1 a chaos of sound was set

 up when an observer in  the ,auditorium
 spoke or shouted or clapped his hands4 
,both echoes and  reverberations were   
present and could be heard in all parts 
of the  room1 though the echoes seemed  
to be strongest on the stage and in  the
 balcony4 ,the prospects for bettering  
the acoustics were not very             
encouraging4 ,luckily1 the cure for the 
reverberation was fairly simple1  since 
,sabine's method gave a definite        
procedure that could be applied  to this
 case4 ,the cure for the echo1 however1 
was yet to be found4 ,it  was first     
necessary to find out which walls set up
 the defect4    ,the attempt to locate  
echoes by generating a sound and        
listening with  the ear met with only   
partial success4 ,the ear is sensitive  
enough but  becomes confused when many  
echoes are present1 coming apparently   
from  every direction1 so that the      
evidence thus obtained is not altogether
  conclusive4 ,it became apparent that  
the successful solution lay in  fixing  

the attention on the sound going in a   
particular direction and  finding out   
where it went after reflection2 then    
tracing out the path  in another        
particular direction1 and so on until   
the evidence obtained  gave some hint of
 the general action of the sound4       
,illustration3 ,,fig4 #d4 ,,watch ,,as  
,,source ,,of ,,sound1 ,,backed ,,by ,a 
,,concave  ,,reflector4    ,the first   
step in the application of this         
principle was to use a  faint sound     
which could not be heard at any great   
distance unless  reinforced in some way4
 ,the ticks of a watch were directed1 by
 means  of a reflector 7,fig4 #d7 to    
certain walls suspected of giving       
echoes4  ,using the relation that the   
angle of incidence equals the angle of  
reflection1 the reflected sound was     
readily located1 and the watch  ticks   
heard distinctly after they had traveled
 a total distance as  great as #gj to   
#hj feet from the source4    ,in a later
 experiment1 a metronome was used which 

gave a louder  sound4 ,it was enclosed  
in a sound-proof structure 7,fig4 #e7   
with only  one opening1 so that the     
sound could be directed by means of a   
horn4  ,this method was suggested by the
 work of ,gustav ,lyon in the ,hall of  
the ,trocadero at ,paris1#ag where a    
somewhat similar arrangement was  used4 
,the method was successful and verified 
the observations taken  previously4     
,illustration3 ,,fig4 #e4 ,,metronome   
,,as ,,source ,,of ,,sound4             
,illustration3 ,,fig4 #f4 ,,arc-,,light 
,,as ,,source ,,of ,,sound4    ,though  
the results obtained with the watch and 
metronome seemed  conclusive1 yet the   
observer was not always confident of the
 results4 ,a  further method was sought1
 and a more satisfactory one found by   
using  an alternating current arc-light 
at the focus of a parabolic reflector   
7,fig4 #f74 ,in addition to the light1  
the arc gave forth a hissing sound1     
which was of short wave length and      
therefore experienced but little        

diffraction4 ,the bundle of light rays  
was1 therefore1 accompanied by  a bundle
 of sound1 both coming from the same    
source and subject to  the same law of  
reflection4 ,the path of the sound was  
easily found by  noting the position of 
the spot of light on the wall4 ,the     
reflected  sound was located by applying
 the relation that the angles of        
incidence  and reflection are equal4    
,the arc-light sound was intense and    
gave the  observer confidence in results
 that was lacking in the other methods4 
,to trace successive reflections1 small 
mirrors were fastened to the  reflecting
 walls so that the path of the reflected
 sound was indicated  by the reflected  
light4 ,a 8diagnosis0 of the acoustical 
troubles of the  ,auditorium was then   
made by this method4    ,it should be   
noted here that the arc-light sound is  
not the same as the  sounds of music or 
speech1 these latter ones being of lower
 pitch and  of longer wave length4 ,it  
was1 therefore1 a matter of doubt       

whether the  results obtained would hold
 also for the case of speech or music4  
,tests  made by observers stationed in  
the ,auditorium when musical numbers    
and speeches were rendered1 however1    
verified the general conclusions        
obtained with the arc-light4    ,it     
should be pointed out in this connection
 that there is an objection  to applying
 the 8ray0 method of geometrical optics 
to the case of  sound4 ,it is much more 
difficult to get a ray of sound than it 
is to  get a ray of light4#ah ,this is  
due to the difference in the wave       
lengths in the two cases4 ,it appears   
that the waves are diffracted1  or      
spread out1 in proportion to their      
length1 the longer waves being  spread  
out to a greater extent4 ,the short     
waves of light from the sun1  for       
instance1 as they come through a window 
mark out a sharp pattern  on the floor1 
which shows that the waves proceed in   
straight lines  with but little         
diffraction or spreading4 ,far different

 is it with  the longer waves of sound4 
,if the window is open1 we are able to  
hear  practically all the sounds from   
outdoors1 even that of a wagon around   
the corner1 although we may be at the   
other end of the room away from  the    
window4 ,the longer sound waves spread  
out and bend at right angles  around    
corners1 so that it is almost impossible
 to get a sound shadow  with them4      
,furthermore1 in the matter of          
reflection1 it appears that  the area of
 the reflecting wall must be comparable 
with the length of  the waves being     
reflected4 ,in the case of light1 the   
waves are very  minute1 hence a mirror  
can be very small and yet be able to set
 up a  reflection2 but sound waves are  
of greater length1 the average wave     
length of speech 7#de cm47 being about  
#gjj #jjj times longer than the  wave   
length of yellow light 74#jjjjf cm471   
hence the reflecting surface  must be   
correspondingly larger4 ,an illustration
 will perhaps make  this clearer4       

,suppose a post one foot square projects
 through a water  surface4 ,the small   
ripples on the water will be reflected  
easily from  the post1 but the large    
water waves pass by almost as if the    
post were  not there4 ,the reflecting   
surface must have an area comparable    
with  the size of the wave if it is to  
cause an effective reflection4 ,relief  
work in auditoriums1 if of small        
dimensions1 will affect only the high   
pitched sounds1 i4 e41 those of short   
wave length1 while the low  pitched     
sounds of long wave length are reflected
 much the same as from  a rather rough  
wall4 ,it is also shown that the area of
 the reflecting  surface is dependent on
 its distance from the source of sound  
and from  the observer2 the greater     
these distances are the larger must be  
the  reflecting surface4#ai    ,these   
considerations all show that the        
reflection of sound is a  complicated   
matter4 ,the dimensions of a wall to    
reflect sound1 or of  relief work to    

scatter it1 are determined by the wave  
length and by  the various other factors
 mentioned4 ,it should be said with     
caution  that a 8ray0 of sound is       
reflected in a definite way from a small
 bit  of relief work4 ,we must deal with
 bundles of sound1 not too sharply      
bounded1 and have them strike surfaces  
of considerable area in order to        
produce reflections with any            
completeness4    ,illustration3 ,,fig4  
#g4 ,,longitudinal ,,section ,,showing  
,,the ,,chief  ,,concentrations ,,of    
,,sound1 ,,the ,,diffraction ,,effects  
,,being ,,disregarded4      ,b4         
,,details ,,of ,,the ,,acoustical       
,,survey ,,in ,,the ,,auditorium4       
,the general effect of the walls of the 
,auditorium on the sound may be         
anticipated by considering analogous    
cases in geometrical optics1 but  with  
the restrictions on 8rays0 described in 
the preceding paragraph4  ,the sound    
does not actually confine itself to the 
sharp boundaries  shown4 ,the diagrams  

are intended to indicate the main effect
 of the  sound in the region so bounded4
 ,fig4 #g gives such an idea for the    
concentration of sound in the           
longitudinal section of the ,auditorium4
    ,the plan followed in the           
experimental work was to anticipate the 
path  of the sound as indicated in ,fig4
 #g1 then to verify the results with    
the arc-light reflector4 ,figs4 #h and  
#i show the effect of the rear  wall in 
the balcony in forming echoes on the    
stage4 ,the speaker was  particularly   
unfortunate1 being afflicted with no    
less than ten echoes4    ,illustration3 
,,fig4 #h4 ,,longitudinal ,,section     
,,showing ,,how ,,sound ,,is  ,,returned
 ,,to ,,the ,,stage ,,to ,,form ,,an    
,,echo4    ,illustration3 ,,fig4 #i4    
,,longitudinal ,,section ,,showing      
,,formation ,,of ,,echo  ,,on ,,the     
,,stage4    ,the hard1 smooth1 circular 
wall bounding the main floor under the  
balcony gave echoes as shown in ,fig4   
#aj1 the sound going also in the        

reverse direction of the arrows4        
,illustration3 ,,fig4 #aj4 ,,plan ,,of  
,,auditorium ,,showing ,,action ,,of    
,,rear ,,wall  ,,on ,,the ,,sound4      
,illustration3 ,,fig4 #aa4 ,,plan ,,of  
,,auditorium ,,showing ,,concentration  
,,of  ,,sound ,,by ,,the ,,rear ,,wall4 
,illustration3 ,,fig4 #ab4 ,,this       
,,figure ,,taken ,,with ,,fig4 #i       
,,shows ,,how ,,an ,,echo  ,,is ,,set   
,,up ,,on ,,the ,,stage4    ,a more     
comprehensive idea of the action of this
 wall is shown in ,fig4  #aa4 ,this     
reflected sound was small in amount and 
therefore not a  serious disadvantage4  
,the cases cited were fairly easy to    
determine since the bundles of  sound   
considered were confined closely to     
either a vertical or a  horizontal plane
 for which the plans of the building    
gave some idea of  the probable path of 
the sound4 ,for other planes1 the paths 
followed  could be anticipated by       
analogy from the results already found4 
,fig4 #ab  shows in perspective the     

development of the result expressed in  
,fig4 #i4    ,a square bundle of sound  
starts from the stage and strikes the   
spherical surface of the dome4 ,after   
reflection1 it is brought to a  point   
focus1 as shown1 and spreads out until  
it strikes the vertical  cylindrical    
wall in the rear of the balcony4 ,this  
wall reflects it to a  line focus1 after
 which it proceeds to the stage4        
,auditors on all parts  of the stage    
complained of hearing echoes4           
,referring to ,fig4 #g1 it is seen that 
the arch over the stage reflects  sound 
back to the stage4 ,fig4 #ac shows in   
perspective the focusing  action of this
 overhead arch4 ,fig4 #ad shows the     
effect of the second  arch4 ,some of    
this sound is reflected to the stage and
 to the seats in  front of the stage2   
other portions1 striking more nearly    
horizontally1  are reflected to the side
 balconies4 ,the echoes are not strong  
except  for high pitched notes with     
short wave lengths1 since the width of  

the  arch is small4    ,illustration3   
,,fig4 #ac4 ,,perspective ,,of ,,stage  
,,showing ,,focusing ,,action ,,of      
,,arch ,,on ,,sound4    ,illustration3  
,,fig4 #ad4 ,,perspective ,,of ,,stage  
,,showing ,,focusing ,,action ,,of      
,,second ,,arch4    ,illustration3      
,,fig4 #ae4 ,,transverse ,,section      
,,showing ,,how ,,most ,,pronounced     
,,echoes ,,are ,,set ,,up ,,by ,,the    
,,two ,,concave ,,surfaces4    ,passing 
now to the transverse section1 ,fig4    
#ae1 we find the most  pronounced echoes
 in the ,auditorium4 ,if an observer    
generates a sound  in the middle of the 
room directly under the center of the   
skylight1  distinct echoes are set up4  
,a bundle of sound passes to the concave
  surface which converges the sound to a
 focus1 after which it spreads  out     
again to the other concave surface and  
is again converged to a  focus nearly at
 the starting point4 ,the distance      
traveled is about  #bbe feet1 taking    
about  second1 so that the conditions   

are right for  setting up a strong echo4
 ,this echo is duplicated by the sound  
which  goes in the reverse of the path  
just described4 ,another echo1 somewhat 
less strong1 is formed by the sound that
 goes to the dome overhead  and which is
 reflected almost straight back1 since  
the observer is  nearly at the center of
 the sphere of which the dome is a part4
 ,these  echoes repeat themselves1 for  
the sound does not stop on reaching the 
starting point but is reflected from the
 floor and repeats the action  just     
described4 ,as many as ten distinct     
echoes have been generated by a  single 
impulse of sound4    ,illustration3     
,,fig4 #af4 ,,action ,,of ,,sound ,,in  
,,causing ,,echo ,,on ,,the ,,stage4    
,the echo shown in ,fig4 #ae is repeated
 in a somewhat modified form for  a     
sound generated on the stage by a       
speaker4 ,fig4 #af shows the path  taken
 by the sound4 ,this echo is duplicated 
by the sound that goes in  the reverse  
direction of the arrows1 so the speaker 

is greeted from  both sides4 ,fig4 #ag  
is a perspective showing the path4 ,the 
sound does  not confine itself closely  
to a geometrical pattern1 as shown in   
the  picture1 but spreads out by        
diffraction4 ,the main effect is shown  
by  the figure4    ,illustration3 ,,fig4
 #ag4 ,,perspective ,,showing ,,how ,,an
 ,,echo ,,is ,,formed ,,on  ,,the       
,,stage ,,by ,,two ,,reflections4       
,,diffraction ,,effects ,,are ,,not     
,,considered ,,in  ,,this ,,drawing4    
,thus far only the echoes that reached  
the stage have been described4  ,other  
echoes were found in other parts of the 
hall1 and it seemed that  few places    
were free from them4 ,the side walls in 
the balcony1 for  instance1 were        
instrumental in causing strong echoes in
 the rear of the  balcony4 ,fig4 #ah    
shows in perspective the action of one  
of these walls4  ,these two surfaces    
were similar in shape and symmetrically 
placed4 ,each  was the upper portion of 
a concave surface with its center of    

curvature  in the center of the building
 under the dome4 ,the general effect of 
the left hand wall was to concentrate   
the sound falling on it in the  right   
hand seats in the balcony4 ,some of the 
sound struck the opposite  wall and was 
reflected to the stage1 as shown in     
,fig4 #ag4 ,auditors who  sought the    
furthermost rear seats in the balcony to
 escape echoes were  thus caught by this
 unexpected action of the sound4 ,the   
right hand wall  acted in a similar way 
to send the sound to the upper left     
balcony4    ,illustration3 ,,fig4 #ah4  
,,perspective ,,showing ,,sound         
,,reflected ,,from  ,,concave ,,wall    
,,in ,,balcony4 ,,diffraction ,,not     
,,considered4    ,the dome surface      
concentrates most of its sound near the 
front of the  central portion of the    
balcony and the ground floor in front of
 the  balcony in the form of a caustic  
cone4 ,figs4 #g1 #i and #aa give some   
conception of how a concentration of    
sound is caused by this spherical       

surface4 ,the echo in the front portion 
of the balcony was especially  distinct4
 ,on one occasion1 in this place1 the   
author was able to hear  the speaker    
more clearly from the echo than by      
listening to the direct  sound4         
,minor echoes were set up by the        
horizontal arch surfaces in the         
balcony4 ,the sound from the stage was  
concentrated by reflection  from these  
surfaces and then passed to a second    
reflection from the  concave surfaces   
back of them4 ,auditors in the side     
balcony were thus  disagreeably startled
 by having sound come from overhead from
 the rear4      ,c4 ,,conclusion ,,drawn
 ,,from ,,the ,,acoustical ,,survey4    
,the results of the survey show that    
curved walls are largely  responsible   
for the formation of echoes because they
 concentrate the  reflected sound4 ,it  
seems desirable1 therefore1 to emphasize
 the danger  of using such walls unless 
their action is annulled by absorbing   
materials or relief work4 ,large halls  

with curved walls are almost sure  to   
have acoustical defects4      ,d4       
,,methods ,,employed ,,to ,,improve     
,,the ,,acoustics4    ,reflecting       
,boards4--,the provisional cure was     
brought about gradually  by trying      
different devices suggested by the      
diagnosis4 ,in one set  of experiments  
sounding boards of various shapes and   
sizes were  used4 ,a flat board about   
five feet square placed at an incline   
over  the position of the speaker       
produced little effect4 ,a larger canvas
  surface1 about #ab by #bj feet1 was   
not much better4 ,a parabolic           
reflector1 however1 gave a pronounced   
effect4 ,this reflector was  mounted    
over a pulpit at one end of the stage   
and served to intercept  much of the    
sound that otherwise would have gone to 
the dome and  produced echoes4 ,the path
 of the reflected sound was parallel to 
the  axis of the paraboloid of which the
 reflector was a quarter section4       
,there was no difficulty in tracing out 

the reflected sound4 ,auditors in  the  
path of the reflected rays reported an  
echo1 but auditors in other  parts of   
the ,auditorium were remarkably free    
from the usual troubles4  ,the device   
was not used permanently1 since many    
speakers objected to  the raised        
platform4 ,moreover1 it was not a       
complete cure1 since it was  not suited 
for band concerts and other events1     
where the entire stage  was used4       
,another reflector similar in shape to  
the one just described  is shown in     
,figs4 #ba and #bb4    ,illustration3   
,,fig4 #ai4 ,,reflecting ,,board ,,in   
,,process ,,of ,,construction4          
,illustration3 ,,fig4 #bj4 ,,finished   
,,reflector4 ,,hard ,,plaster ,,on      
,,wire ,,lath4    ,sabine's             
,method4--,the time of reverberation was
 determined by  ,sabine's method4 ,an   
organ pipe making approximately #ebf    
vibrations a  second was blown for about
 three seconds and then stopped4 ,an    
auditor  listened to the decreasing     

sound1 and when it died out made a      
record  electrically on a chronograph   
drum4 ,the time of reverberation was    
found  to be #e4ij seconds1 this being  
the mean of #ai sets of measurements1   
each of about #bj observations4 ,the    
reverberation was found also by         
calculation from ,sabine's equation 7see
 ,section ,,iii71 taking the  volume of 
the ,auditorium as #aa1hjj cubic meters 
and calculating the  absorbing power of 
all the surfaces in the room4 ,this     
calculation gave  #f4d seconds4 ,the    
agreement between the two results is as 
close as could  be expected1 since      
neither the intensity of the sound nor  
the pitch  used by the author was the   
same as those used by ,professor        
,sabine1 and  both of these factors     
affect the time of reverberation4       
,illustration3 ,,fig4 #ba4 ,,parabolic  
,,reflector ,,showing ,,its ,,action    
,,on  ,,sound4    ,illustration3 ,,fig4 
#bb4 ,,photograph ,,of ,,parabolic      
,,reflector4    ,several years later the

 time of reverberation was again        
determined  after certain changes had   
been made4 ,a thick carpet had been     
placed  on the stage1 heavy velour      
curtains #ah by #cb feet in area hung on
 the  wall at the rear of the stage1 a  
large canvas painting #djj square feet  
in area was installed1 and the glass    
removed from the skylight in the        
ceiling4 ,the time of reverberation was 
reduced to #d4h seconds4 ,with an       
audience present this value was reduced 
still more1 and when the hall  was      
crowded at commencement time the        
reverberation was not troublesome4      
,method of ,eliminating                 
,echoes4--,although the time of         
reverberation  was reduced to be fairly 
satisfactory1 as just explained1 the    
echoes  still persisted1 and were very  
annoying4 ,attempts were made to reduce 
individual echoes by hanging cotton     
flannel on the walls at critical        
points4 ,thus the shaded areas in ,fig4 
#ag were covered and also the  entire   

rear wall in the balcony4 ,pronounced   
echoes still remained1 and  it was      
evident that some drastic action was    
necessary to alleviate this  condition4 
,four large canvases1 shown in ,figs4   
#bc and #bd1 were then  hung in the dome
 in position suggested by the results of
 the diagnosis4  ,a very decided        
improvement followed4 ,for the first    
time the echoes were  reduced to a      
marked degree and speakers on the stage 
could talk without  the usual annoyance4
 ,this arrangement eliminated the echoes
 not only on  the stage1 but generally  
all over the house4 ,a number of minor  
echoes  were still left1 but the        
conditions were much improved1          
especially when  a large audience was   
present to reduce the reverberation4    
,proposed ,final ,cure4--,the state of  
affairs just described is the  condition
 at the time of writing4 ,two           
propositions were considered in         
planning the final cure4 ,one           
proposition involved a complete         

remodeling  of the interior of the      
,auditorium4 ,plans of an interior were 
drawn  in accordance with the results of
 the experimental work that would       
probably give satisfactory acoustics4   
,this proposition was not carried  out  
because of the expense and because it   
was thought desirable to  attempt a cure
 without changing the shape of the room4
 ,the latter  plan is the one now being 
followed4 ,it is proposed to replace the
  present unsightly curtains with       
materials which will conform to the     
architectural features of the           
,auditorium and which will have a       
pleasing  color scheme4 ,at the same    
time1 it will be necessary to hold to   
the  features which have improved the   
acoustics4    ,illustration3 ,,fig4 #bc4
 ,,photograph ,,of ,,two ,,of ,,the     
,,canvas ,,curtains ,,in ,,the  ,,dome  
,,of ,,the ,,auditorium4 ,,note ,,also  
,,the ,,absorbing ,,materials ,,under   
,,the  ,,arches4    ,illustration3      
,,fig4 #bd4 ,,photograph ,,of ,,dome    

,,of ,,auditorium ,,showing ,,the       
,,canvases ,,installed ,,to ,,eliminate 
,,echoes4          ,v4 ,,bibliography   
,,of ,,publications ,,on ,,acoustics    
,,of ,,auditoriums4      ,auerbach1 ,f4 
8,akustik40 ,winkelmann's ,handbuch der 
,physik1 ,vol4 ,,ii1  #aiji4 ,an        
encyclopdia of acoustics1 the following 
topics applying  to the subject in hand3
 8,akustik der ,gebude10 pp4 #ehj-ehd1  
with  references4 8,nachhall und ,echo10
 pp4 #efe-efi1 with references4         
,blackall1 ,c4 ,h4 8,acoustics of       
,audience ,halls10 ,engineering ,record1
  ,vol4 #de1 pp4 #eda-edb1 #aijb4 ,a    
paper recording the opinions of the     
author with many references to          
acoustical properties of particular     
audience halls4    ,cornelison1 ,r4 ,w4 
8,the ,acoustical ,properties of ,rooms 
,particularly as  ,affected by ,wall    
,coverings10 #aije4 ,a pamphlet         
describing the merits of  8,fabrikona0  
burlap as a sound absorber4 ,h4 ,b4     
,wiggin's ,sons ,company1  ,bloomfield1 

,n4 ,j4    ,eichhorn1 ,a4 8,die ,akustik
 ,grosser ,rame nach ,altgriechischer   
,theorie40 ,ernst and ,korn1            
,publishers1 ,berlin1 #ahhh4 ,a         
discussion of  ,greek buildings and     
acoustics1 with applications to modern  
conditions4    ,eichhorn1 ,a4 8,der     
,akustische ,masstab fr die             
,projectbearbeitung  ,grosser ,innen    
,rame40 ,published by ,schuster and     
,bufleb1 ,berlin1 #ahii4 ,a             
continuation of the previous work4      
,exner1 ,s4 8,uber die ,akustik von     
,hrslen und ein ,instrument1  sie zu    
bestimmen40 ,zeitschrift des            
,osterreichischen ,ingenieur und        
,architekten-,vereines1 ,vol4 ,,lvii1 p4
 #ada1 ,march1 #aije4 ,indicates his    
opinion of good acoustical properties in
 a hall4 ,gives experimental            
determination of reverberation4         
,fournier1 ,lucien4 8,the ,suppression  
of ,echoes40 ,la ,nature 7,paris71      
,april #bd1 #aiji4 ,english translation 
given in 8,the ,literary ,digest10 ,new 

,york1 ,may #bi1 #aiji1 p4 #ibd4 ,an    
account of the experiments of ,gustav   
,lyon in investigating the echoes in    
,trocadero ,hall in ,paris4             
,franklin1 ,w4 ,s4 8,derivation of      
,equation of ,decaying ,sound in a ,room
  and ,definition of ,open ,window      
,equivalent of ,absorbing ,power40      
,physical  ,review1 ,vol4 #af1 pp4      
#cgb-cgd1 #aijc4 ,a theoretical         
development of the  formula found       
experimentally by ,sabine4    ,haege4   
8,bemerkungen ber ,akustik40            
,zeitschrift fr ,baumesen1 ,vol4 ,,ix1  
pp4 #ehb-eid1 #ahei4    ,henry1 ,joseph4
 8,acoustics ,applied to ,public        
,buildings10 ,smithsonian  ,report1     
#ahef1 p4 #bba4    ,hoyt1 ,j4 ,t4 ,n4   
8,the ,acoustics of the ,hill ,memorial 
,hall10 ,american  ,architect1 ,vol4    
,,civ1 pp4 #ej-ec1 ,august #f1 #aiac4   
,discusses the design of  the hall and  
indicates how it fulfills his ideas of  
good acoustics4    ,hutton1 ,w4 ,r4     
8,architectural ,acoustics2 ,hall of    

,representatives1  ,u4 ,s4 ,capitol1    
#ahec40 ,engineering ,record1 ,vol4 #db1
 p4 #cgg1 #aijj4 ,a  discussion of the  
cure of the faulty acoustics in the ,u4 
,s4 ,hall of  ,representatives4         
,jacques1 ,w4 ,w4 8,effect of the       
,motion of the ,air ,within an          
,auditorium  ,upon ,its ,acoustical     
,qualities40 ,philosophical ,magazine   
7#e71 ,vol4 #g1  p4 ,,iii1 #ahgi4 ,a    
record of experiments in the ,baltimore 
,academy of  ,music showing that the    
ventilating current had a marked action 
on the  acoustics4    ,jager1 ,s4 8,zur 
,theorie des ,nachhals10                
,sitzungsberichten der ,kaiserl4        
,akademie der ,wissenschaften in ,wien4 
,matem4-naturw4 ,klasse2 ,bd4 ,,cxx1    
,abt4 ,ha1 ,mai1 #aiaa4 ,an important   
paper giving a theoretical development  
of ,sabine's formula showing the factors
 that enter into the constants4         
,considers also the case of the         
reflection of sound from a thin wall and
  also the case when it encounters a    

porous material such as a curtain4      
,lamb1 ,horace4 8,the ,dynamical ,theory
 of ,sound40 ,published by ,edward      
,arnold1 ,london1 #aiaj4 ,a more        
elementary treatment than ,rayleigh's   
8,theory of ,sound40    ,marage4        
8,qualites acoustiques de certaines     
sailes pour la voix  parle40 ,comptes   
,rendus1 ,vol4 #adb1 p4 #hgh1 #aijf4 ,an
 investigation of  the acoustical       
properties of six halls in ,paris4      
,norton1 ,c4 ,l4 8,soundproof           
,partitions40 ,insurance ,engineering1  
,vol4  #d1 p4 #ahj1 #aijb4 ,an account  
of experimental tests of the soundproof 
qualities of materials that are also    
fireproof4    ,orth1 ,a4 8,die ,akustik 
,grosser ,rame mit ,speciallem ,bezug   
auf  ,kirchen40 ,zeitschrift fr         
,bauwesen4 ,also reprint by ,ernst and  
,korn1  ,berlin1 #ahgb4 ,assumes that   
sound waves behave like light waves4    
,discusses1 with detailed drawings1 the 
paths of sound in the ,zion  ,church in 
,berlin and the ,nicolai ,church in     

,potsdam4 ,also gives his  opinion of   
the effect of surfaces and materials on 
sound4    ,rayleigh1 ,lord4 8,theory of 
,sound40 ,two volumes1 ,macmillan1      
#ahif4  ,the unsurpassed classic in the 
subject of acoustics4 ,references to    
architectural acoustics as follows3     
8,whispering ,galleries10 ,vol4 ,,ii1   
#bhg4 8,passage of ,sound ,through      
,fabrics10 ,vol4 ,,ii1 p4 #caa4         
8,resonance in  ,buildings10 ,vol4 ,,ii1
  #beb4    ,sabine1 ,wallace ,c4        
8,architectural ,acoustics40            
,engineering ,record1  #aijj1 ,vol4 #a1 
pp4 #cdi1 #cgf1 #djj1 #dbf1 #dej1 #dgg1 
#ejc4 ,published also  in book form and 
in ,american ,architect1 ,vol4 #fh1     
#aijj1 pp4 #c1 #ai1 #ce1  #dc1 #ei1 #ge1
 #hc4 ,an important series of articles  
giving the relation  between the time of
 reverberation in a room1 the volume of 
the room1  and absorbing materials      
present4 ,gives table of absorbing      
powers  of substances1 so that an       
architect can calculate in advance of   

construction what the time of           
reverberation will be4    ,sabine1 ,w4  
,c4 8,architectural ,acoustics10 ,proc4 
of the ,amer4 ,acad4  of ,arts and      
,sciences1 ,vol4 ,,xlii1 ,no4 #b1 ,june1
 #aijf4 ,a continuation of  the previous
 work1 showing the accuracy of musical  
taste in regard to  architectural       
acoustics and also the variation in     
reverberation with  variation in pitch4 
,sabine1 ,w4 ,c4 8,architectural        
,acoustics10 ,engineering ,record1 ,vol4
 #fa1  pp4 #ggi-gha1 ,june #ah1 #aiaj4  
,discusses the case of flow of air in a 
room  and its effect on the acoustics4  
,concludes that the usual ventilation   
system in a hall has very little effect4
    ,sabine1 ,w4 ,c4 8,architectural    
,acoustics3 ,the ,correction of         
,acoustical  ,difficulties40 ,the       
,architectural ,quarterly of ,harvard   
,university1  ,march1 #aiab1 pp4 #c-bc4 
,an account of the cures of the         
acoustical  difficulties of a number of 
audience rooms1 also a description of   

further experiments on the absorbing    
power of different materials4           
,sabine1 ,w4 ,c4 8,theater ,acoustics40 
,american ,architect1 ,vol4 ,,civ1 pp4  
#beg-bgi1 ,december #ca1 #aiac4         
,describes theater with model acoustics4
  ,discusses behavior of sound in a room
 and shows photographs of sound  waves  
in miniature rooms4    ,sabine1 ,w4 ,c4 
8,architectural ,acoustics4 ,building   
,material and  ,musical ,pitch40 ,the   
,brickbuilder1 ,vol4 #bc1 pp4 #a-f1     
,january1 #aiad4 ,a  continuation of    
previous work1 describing absorbing     
powers of different  materials4         
,sharpe1 ,h4 ,j4 8,reflection of ,sound 
at a ,paraboloid40 ,camb4 ,phil4 ,soc4  
,proc41 ,vol4 #ae1 pp4 #aij-aig1 #aiji4 
,stewart1 ,g4 ,w4 8,architectural       
,acoustics40 ,sibley ,journal of        
,engineering1 ,may1 #aijc4 ,published by
 ,cornell ,university1 ,ithaca1 ,n4 ,y4 
,an account of an investigation leading 
to the cure of the acoustics of  ,sibley
 ,auditorium4    ,sturmhfel1 ,a4        

8,akustik des ,baumeisters40 ,published 
by ,schuster  and ,bufleb1 ,berlin1     
#ahid4 ,an #hg-page pamphlet on the     
acoustics of  rooms4 ,discusses effects 
of relief work in rooms on sound4       
,account of  experimental work4         
,references to auditoriums4    ,tallant1
 ,hugh4 8,hints on ,architectural       
,acoustics40 ,the ,brickbuilder1  ,vol4 
#ai1 #aiaj1 pp4 #aaa1 #aee1 #aii1 #bdc1 
#bfe4 ,a series of articles  giving an  
exposition of the principles of the     
subject with practical  applications4   
,tallant1 ,hugh4 8,acoustical ,design in
 the ,hill ,memorial ,auditorium1       
,university of ,michigan40 ,the         
,brickbuilder1 ,vol4 ,,xxii1 p4 #afi1   
,august1  #aiac4 ,see also plates #aac1 
#aad1 #aae4 ,a discussion of the        
acoustical  results obtained in this    
auditorium1 a special feature being the 
action  of a huge parabolic reflecting  
wall surface over the stage4            
,tallant1 ,hugh4 8,architectural        
,acoustics4 ,the ,effect of a ,speaker's

  ,voice in ,different ,directions40    
,the ,brickbuilder1 ,vol4 #bb1 p4 #bbe1 
,october1 #aiac4    ,taylor1 ,h4 ,o4 8,a
 ,direct ,method of ,finding the ,value 
of ,materials as  ,sound ,absorbers40   
,physical ,review1 ,vol4 #b 7#b71 p4    
#bgj1 ,october1 #aiac4    ,tufts1 ,f4   
,l4 8,transmission of ,sound ,through   
,porous ,materials40 ,amer4  ,journal of
 ,science1 ,vol4 ,,ii1 p4 #ceg1 #aija4  
,experimental work leading to  the      
conclusion that sound is transmitted    
through porous materials in  the same   
proportion that a current of air is4    
,watson1 ,f4 ,r4 8,echoes in an         
,auditorium40 ,physical ,review1 ,vol4  
#cb1  p4 #bca1 #aiaa4 ,an abstract      
giving an account of the experiments in 
the  auditorium at the ,university of   
,illinois4    ,watson1 ,f4 ,r4          
8,inefficiency of ,wires as a ,means of 
,curing ,defective  ,acoustics of       
,auditoriums40 ,science1 ,vol4 #ce1 p4  
#hcc1 #aiab4    ,watson1 ,f4 ,r4 8,the  
,use of ,sounding ,boards in an         

,auditorium40 ,physical  ,review1 ,vol4 
#a 7#b71 p4 #bda1 #aiac4 ,also a more   
complete article in ,the  ,brickbuilder1
 ,june1 #aiac4    ,watson1 ,f4 ,r4 8,air
 ,currents and the ,acoustics of        
,auditoriums40  ,engineering ,record1   
,vol4 #fg1 p4 #bfe1 #aiac4 ,a detailed  
account giving  theory and experimental 
work1 with application to ventilating   
systems  in auditoriums4    ,watson1 ,f4
 ,r4 8,acoustical ,effect of            
,fireproofed ,cotton-,flannel ,sound    
,absorbers40 ,engineering ,news1 ,vol4  
#ga1 p4 #bfa1 ,january #bi1 #aiad4      
,results of experiments showing that    
cotton-flannel has practically the  same
 absorbing power after fireproofing as  
before4    ,weisbach1 ,f4 8,versuche ber
 ,schalldurchlassigkeit1                
,schallreflexion  und                   
,schallabsorbtion40 ,annalen der        
,physik1 ,vol4 #cc1 p4 #gfc1 #aiaj4     
,williams1 ,w4 ,m4 8,echo in ,albert    
,hall40 ,nature1 ,vol4 #c1 p4 #dfi1     
#ahgj-ga4 ,observations on the shape of 

,albert ,hall in ,london and the  echoes
 set up4    ,editorial ,notice4 8,the   
,dresden ,laboratory for ,architectural 
,acoustics40 ,american ,architect1 ,vol4
 #ajb1 p4 #acg1 ,october #af1 #aiab4    
,states that a laboratory of applied    
acoustics is authorized in the  ,dresden
 7,germany7 ,technische ,hochschule1 and
 that expert advice will  be furnished  
architects and others regarding problems
 of acoustics of  auditoriums4          
,,the ,,university ,,of ,,illinois      
,,the ,,state ,,university    ,urbana   
,,edmund ,j4 ,,james1 ,ph4 ,d41 ,,ll4   
,d41 ,president      ,the ,university   
includes the following departments3     
,the ,graduate ,school      ,the        
,college of ,liberal ,arts and ,sciences
 7,ancient and ,modern      ,languages  
and ,literatures2 ,history1 ,economics  
and ,accountancy1      ,political       
,science1 ,sociology2 ,philosophy1      
,psychology1 ,education2                
,mathematics2 ,astronomy2 ,geology2     
,physics2 ,chemistry2 ,botany1          

,zoology1 ,entomology2 ,physiology2 ,art
 and ,design2 ,ceramics7      ,the      
,college of ,engineering 7,architecture2
 ,architectural1 ,civil1                
,electrical1 ,mechanical1 ,mining1      
,municipal and ,sanitary1 and ,railway  
,engineering7      ,the ,college of     
,agriculture 7,agronomy2 ,animal        
,husbandry2 ,dairy      ,husbandry2     
,horticulture and ,landscape ,gardening2
 ,veterinary      ,science2             
,agricultural ,extension2 ,teachers'    
,course2 ,household      ,science7      
,the ,college of ,law 7,three years'    
course7      ,the ,school of ,education 
,the ,courses in ,business 7,general    
,business2 ,banking2 ,accountancy2      
,railway ,administration2 ,insurance7   
,the ,course in ,journalism      ,the   
,courses in ,chemistry and ,chemical    
,engineering      ,the ,courses in      
,ceramics and ,ceramic ,engineering     
,the ,school of ,railway ,engineering   
and ,administration      ,the ,school of
 ,music 7four years' course7      ,the  

,school of ,library ,science 7two years'
 course7      ,the ,college of ,medicine
 7in ,chicago7      ,the ,college of    
,dentistry 7in ,chicago7      ,the      
,school of ,pharmacy 7in ,chicago2 ,ph4 
,g4 and ,ph4 ,c4 courses7      ,the     
,summer ,session 7eight weeks7          
,experiment ,stations3 ,u4 ,s4          
,agricultural ,experiment ,station2     
,engineering ,experiment ,station2      
,state ,laboratory of ,natural          
,history2 ,state ,entomologist's        
,office2 ,biological ,experiment        
,station      on ,illinois ,river2      
,state ,water ,survey2 ,state           
,geological ,survey2      ,mine ,rescue 
,station        ,the library collections
 contain 7,may #a1 #aiad71 #bie1jjj     
volumes1        including the library of
 the ,state ,laboratory of ,natural     
,history1        the ,quine ,medical    
,library and the library of the ,school 
of        ,pharmacy4    ,for catalogs   
and information address                 
,,the ,,registrar                       

,urbana1 ,illinois          ,,footnotes 
#a 8,theory of ,sound10 ,vol4 ,,ii1 p4  
#caf4      #b 8,theory of ,sound10 ,vol4
 ,,ii1  #cea4      #c 8,dynamical       
,theory of ,sound10 p4 #aif4      #d    
8,theory of ,sound10 p4 #ccc4      #e   
8,architectural ,acoustics40 ,a series  
of articles in the        ,engineering  
,record1 #aijj2 also the ,american      
,architect1 #aijj4      #f              
8,architectural ,acoustics10 ,proc4 of  
,amer4 ,acad4 of ,arts and              
,sciences4 ,vol4 #db1 pp4 #di-hd1 #aijf4
      #g ,g4 ,w4 ,stewart4              
8,architectural ,acoustics10 ,sibley    
,journal of        ,engineering1 ,may1  
#aijc4 ,published by ,cornell           
,university1 ,ithaca1        ,n4 ,y4    
#h 8,qualits acoustiques de certaines   
salles pour la voix parle40             
,comptes ,rendus1 #adb1 #hgh1 #aijf4    
#i ,w4 ,s4 ,franklin4 8,derivation of   
,equation of ,decaying ,sound in        
a ,room and ,definition of ,open ,window
 ,equivalent of ,absorbing              

,power40 ,physical ,review1 ,vol4 #af1  
pp4 #cgb-cgd1 #aijc4     #aj ,g4 ,jger4 
8,zur ,theorie des ,nachhalls40         
,sitzungsberichte der                   
,kaiserliche ,akad4 der ,wissenschaften 
in ,wien1 ,math-naturw4        ,klasse2 
,bd4 ,,cxx4 ,abt4 #aa a4 ,mai1 #aiaa4   
#aa ,science1 ,vol4 #ce1 p4 #hcc1 #aiab4
     #ab ,arch4 ,quarterly of ,harvard  
,university1 ,march1 #aiab4     #ac     
,osborne ,reynolds4 ,proc4 of ,royal    
,soc41 ,vol4 ,,xxii1 p4 #eca1 #ahgd4    
#ad ,joseph ,henry1 8,report of the     
,lighthouse ,board of the ,united       
,states for the year #ahgd40            
,j4 ,tyndall1 ,phil4 ,trans41 #ahgd4    
#ae ,sabine1 ,engineering ,record1 ,vol4
 #fa1 p4 #ggi1 #aiaj4 ,watson1          
,engineering ,record1 ,vol4 #fg1 p4     
#bfe1 #aiac4     #af ,sabine and        
,watson4 ,ibid4     #ag ,la ,nature     
7,paris71 ,april #bd1 #aiji4     #ah    
,rayleigh 8,theory of ,sound10 ,vol4    
,,ii1  #bhc4     #ai ,rayleigh1 ibid1   
#bhc4          ,transcriber's ,notes    

,punctuation1 hyphenation1 and spelling 
of ,english words were made  consistent 
when a predominant preference was found 
in the original  book2 otherwise they   
were not changed4 ,the spellings of     
non-,english  words were not changed4   
,simple typographical errors were       
corrected2 unbalanced quotation  marks  
were remedied when the change was       
obvious1 and otherwise left  unbalanced4
    ,illustrations in this e,book have  
been positioned between paragraphs  and 
outside quotations4 ,in versions of this
 e,book that support  hyperlinks1 the   
page references in the ,list of         
,illustrations lead to  the             
corresponding illustrations4            
,footnotes have been sequentially       
numbered and placed together at the  end
 of the book4