14: Acoustics of Buildings and Acoustic Quieting

Example number 14.1, Page number 399

In [1]:
#importing modules
import math
from __future__ import division

#Variable declaration    
V=7500;      #volume(m**3)
T=1.5;       #time(sec)

#Calculations
aS=0.165*V/T;     #total absorption in hall(OWU)

#Result
print "total absorption in hall is",aS,"OWU"

total absorption in hall is 825.0 OWU

Example number 14.2, Page number 399

In [2]:
#importing modules
import math
from __future__ import division

#Variable declaration    
V=1500;      #volume(m**3)
A1=112;      #area of plastered walls(m**2)
A2=130;      #area of wooden floor(m**2)
A3=170;      #area of plastered ceiling(m**2)
A4=20;       #area of wooden door(m**2)
n=100;     #number of cushioned chairs
A5=120;    #area of audience(m**2)
C1=0.03;    #coefficient of absorption in plastered walls
C2=0.06;    #coefficient of absorption in wooden floor
C3=0.04;    #coefficient of absorption in plastered ceiling
C4=0.06;    #coefficient of absorption in wooden door
C5=1.0;     #coefficient of absorption in cushioned chairs
C6=4.7;     #coefficient of absorption in audience

#Calculations
a1=A1*C1;    #absorption due to plastered walls
a2=A2*C2;    #absorption due to wooden floor
a3=A3*C3;    #absorption due to plastered ceiling
a4=A4*C4;    #absorption due to wooden door
a5=n*C5;     #absorption due to cushioned chairs
a6=A5*C6;    #absorption due to audience 
aS=a1+a2+a3+a4+a5;       #total absorption in hall
T1=0.165*V/aS;       #reverberation time when hall is empty(sec)
T2=0.165*V/(aS+a6);    #reverberation time with full capacity of audience(sec)
T3=0.165*V/((n*C6)+aS);    #reverberation time with audience in cushioned chairs(sec)

#Result
print "reverberation time when hall is empty is",round(T1,2),"sec"
print "reverberation time with full capacity of audience is",round(T2,3),"sec"
print "reverberation time with audience in cushioned chairs is",round(T3,2),"sec"

reverberation time when hall is empty is 2.08 sec
reverberation time with full capacity of audience is 0.362 sec
reverberation time with audience in cushioned chairs is 0.42 sec

Example number 14.3, Page number 401

In [3]:
#importing modules
import math
from __future__ import division

#Variable declaration    
V=1200;      #volume(m**3)
a1=220;      #area of wall(m**2)
a2=120;      #area of floor(m**2)
a3=120;      #area of ceiling(m**2)
C1=0.03;    #coefficient of absorption in wall
C2=0.80;    #coefficient of absorption in floor
C3=0.06;    #coefficient of absorption in ceiling

#Calculations
A1=a1*C1;    #absorption due to plastered walls
A2=a2*C2;    #absorption due to wooden floor
A3=a3*C3;    #absorption due to plastered ceiling
aS=a1+a2+a3;       #total absorption in hall
abar=(A1+A2+A3)/aS;    #average sound absorption coefficient
AS=abar*aS;       #total absorption of room(metric sabines)
T=0.165*V/AS;       #reverberation time(sec)

#Result
print "average sound absorption coefficient is",round(abar,2)
print "reverberation time is",round(T,1),"sec"

average sound absorption coefficient is 0.24
reverberation time is 1.8 sec

Example number 14.4, Page number 401

In [5]:
#importing modules
import math
from __future__ import division

#Variable declaration    
I0=10**-12;      #standard intensity level(watt/m**2)
A=1.4;     #area(m**2)
il=60;     #intensity level(decibels)

#Calculations
x=10**(il/10);
I=x*10**-12;      #intensity level(watt/m**2)
Ap=I*A;      #acoustic power(watt)

#Result
print "acoustic power is",Ap,"watt"
print "answer in the book is wrong"

acoustic power is 1.4e-06 watt
answer in the book is wrong