Two Speakers & Intensity/Frequency

[lc99]

Homework Statement

b) What is the distance from speaker B to the microphone at point P?
c) What are the first 2 frequencies at which the microphone at point P would detect sound waves of maximum intensity? Give answers to 2 significant figures.
d)What are the first 2 frequencies at which the microphone at point P would detect no sound? Give answers to 2 significant figures.
e) Describe in words what would be different if the speakers were emitting sound at different intensities.

Homework Equations

The Attempt at a Solution

a) sqrt(17)
b)sqrt(20)
c) sqrt(20) - sqrt(17) = 0.349 m --> 0.349m = nlambda --> lambda = .349/1 and 0.349/2
lambda = 0.349 and lambda = 0.174
f1 = 344/0.349 =986 Hz
f2 = 344/0.174= 1977 Hz

d) 0.349 = (n+ 1/2)lambda
lambda = 0.349/1.5 and 0.349/2.5
=0.233 and 0.1396
f1 = 344/0.233 = 1476 Hz
f2=344 / 0.1396 =2464
(destructive)e) the loudness would changeI'm pretty sure I've done something wrong, but I am not sure where. The frequencies are clearly too high.

 

[haruspex]

c looks right, but it does say 2 sig figs.
For d, are you sure you have chosen the lowest two values of n?
There is a flaw in question d. Because of the different distances there will be some sound. It should ask for least sound.

 

[lc99]

c looks right, but it does say 2 sig figs.
For d, are you sure you have chosen the lowest two values of n?
There is a flaw in question d. Because of the different distances there will be some sound. It should ask for least sound.

Ahh, n=0 and n=1 would work. I thought n=0 would make the whole thing 0 like in part c.

 

[haruspex]

Ahh, n=0 and n=1 would work. I thought n=0 would make the whole thing 0 like in part c.

Right.

For e, maybe you could say a bit more, but the flaw in question d bothers me. I.e. if d had correctly asked for least sound then in e you could point out that with the right emitted intensities there would be no sound at the microphone.

 

[DrClaude]

a) sqrt(17)
b)sqrt(20)

Is speaker A really closer to the microphone than speaker B?

 

[lc99]

Is speaker A really closer to the microphone than speaker B?

A is closer

 

[DrClaude]

A is closer

Really? I guess I need to get my eyes checked...

 

[lc99]

Really? I guess I need to get my eyes checked...

nope