- #1
APUGYael
- 41
- 1
Hey all,
I am doing some work to brush up my acoustics and one of the problems I came across this goes like this (translated, so sorry for potential grammar mistakes although I'll do my best to avoid them):
A singer exhales 0.1 Litre Air per second. The 'overpressure' (pressure difference, so not absolute pressure) of his lungs is 1257 Pa. On 1 meter from his mouth the soundpressurelevel is 70 dB. We assume a point source (so Q=1).
- Caculate the mechanical output power of the person.
- Calculate the acoustic output power of the person.
- Calculate the acoustic effeciency.
So, I know how to do the last 2 parts:
L_p = L_w - 10*log(Q/(4*pi*r^2)) is the equation I'll use for this problem.
r = 1, Q = 1, so: L_p = L_w - 11dB
Which means
L_w = 70 dB + 11 dB = 81 dB
L_w = 10*log(W/W_0) --> W = (10^-12)*(10^8.1) = 0.1259 mWatt
This is the acoustic ouput power. The answer sheet says this is correct.
The effeciency would simply be: (acoustic power/mechanic power)*100%.
But this is where I am stuck. How do I calculate the mechanic power with the given values?
Thanks for reading!
I am doing some work to brush up my acoustics and one of the problems I came across this goes like this (translated, so sorry for potential grammar mistakes although I'll do my best to avoid them):
A singer exhales 0.1 Litre Air per second. The 'overpressure' (pressure difference, so not absolute pressure) of his lungs is 1257 Pa. On 1 meter from his mouth the soundpressurelevel is 70 dB. We assume a point source (so Q=1).
- Caculate the mechanical output power of the person.
- Calculate the acoustic output power of the person.
- Calculate the acoustic effeciency.
So, I know how to do the last 2 parts:
L_p = L_w - 10*log(Q/(4*pi*r^2)) is the equation I'll use for this problem.
r = 1, Q = 1, so: L_p = L_w - 11dB
Which means
L_w = 70 dB + 11 dB = 81 dB
L_w = 10*log(W/W_0) --> W = (10^-12)*(10^8.1) = 0.1259 mWatt
This is the acoustic ouput power. The answer sheet says this is correct.
The effeciency would simply be: (acoustic power/mechanic power)*100%.
But this is where I am stuck. How do I calculate the mechanic power with the given values?
Thanks for reading!