# 5: Acoustics¶

## Example number 5.1, Page number 97¶

In [4]:
#importing modules
import math
from __future__ import division

#Variable declaration
T1=1.5;     #R time for empty hall(s)
T2=1;       #R time with curtain cloth(s)
A=20;       #area of absorber(sq.m)
V=10*8*6;   #volume of hall(cu.m)

#Calculation
a=((0.161*V)/(2*A))*((1/T2)-(1/T1));   #absorption coefficient

#Result
print "absorption coefficient is",round(a,2),"Sabines"
print "answer given in the book varies due to rounding off errors"

absorption coefficient is 0.64 Sabines
answer given in the book varies due to rounding off errors


## Example number 5.2, Page number 97¶

In [8]:
#importing modules
import math
from __future__ import division

#Variable declaration
V=20*15*10;    #volume of hall(cu.m)
T1=3.5;        #reverberation time(s)
l=20;
b=15;
h=10;      #dimensions of hall
am=0.5;     #absorption coefficient
T2=2.5;    #reverberation time after cloth use(s)

#Calculation
A=(0.161*V)/T1;
S=2*((l*b)+(b*h)+(h*l));    #surface area(sq.m)
sigma_a=A/S;   #average absorption coefficient of hall(o.w.u)
S1=(((0.161*V)/(am-sigma_a))*((1/T2)-(1/T1)));     #area of wall covered by curtain cloth(sq.m)

#Result
print "average absorption coefficient of hall is",round(sigma_a,3),"o.w.u"
print "area of wall covered by curtain cloth is",round(S1,3),"sq.m"
print "answer for area covered S1 varies due to rounding off errors"

average absorption coefficient of hall is 0.106 o.w.u
area of wall covered by curtain cloth is 140.156 sq.m
answer for area covered S1 varies due to rounding off errors


## Example number 5.3, Page number 98¶

In [12]:
#importing modules
import math
from __future__ import division

#Variable declaration
V=1450;    #volume of hall(cu.m)
A1=112*0.03;   #absorption due to plastered wall
A2=130*0.06;   #absorption due to wooden floor
A3=170*0.04;   #absorption due to plastered ceiling
A4=20*0.06;    #absorption due to wooden door
A5=100*1;      #absorption due to cushioned chairs

#Calculation
sigma_as=A1+A2+A3+A4+A5;   #total absorption in empty hall
T1=(0.161*V)/sigma_as;     #reverberation time case-1(s)
T2=(0.161*V)/(sigma_as+(60*4.7));   #persons=60,A=4.7 case-2
T3=(0.161*V)/(sigma_as+(100*4.7));  #seat cushioned=100 case-3

#Result
print "reverberation time for case-1 is",round(T1,3),"sec"
print "reverberation time for case-2 is",round(T2,3),"sec"
print "reverberation time for case-3 is",round(T3,3),"sec"
print "answer for T3 given in the book is wrong"

reverberation time for case-1 is 1.959 sec
reverberation time for case-2 is 0.582 sec
reverberation time for case-3 is 0.396 sec
answer for T3 given in the book is wrong