Amplification of sound in a pipe

[tom10122]

How loud would a 105 db speaker be in a 3 inch metal pipe?

 

[rootone]

I suppose that depending on what material the pipe is made from and it's length, there will be certain frequencies which resonate the pipe and so these would sound louder.
It's unlikely that you would get some clean 'amplification' across the whole audio spectrum, there could be some frequencies which are 'damped' as well,again depending on the material used.

 

[davenn]

How loud would a 105 db speaker be in a 3 inch metal pipe?

105 dB at the sound source and less as the distance from the source increases ...
the longer the pipe the more losses there will be as the pipe absorbs some of the sound

why would you think it would be amplified ?
you need an active system with an additional power source to amplify something

 

[sophiecentaur]

Not an easy question, as it stands. The answer would depend upon the details of the speaker, the frequency and the length and position of the pipe. "105dB" refers to the sound energy flux at the place it's measured and not to what the speaker cone (or whatever else is vibrating) is doing. A simple loudspeaker drive unit (the magnet / coil / cone) doesn't couple sound energy into the air very well and you need to match the acoustic impedance for it to be much use. A length of pipe can achieve this, if it's chosen to be the right length. If you swept the frequency from low to high, you could expect a set of peaks and troughs in the response as you pass through the frequencies at which the pipe resonates.