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Consider a situation where I am listening to loud music in a room. If I move into another room and close the door (so music is now played in another room behind the closed doors), I will hear the bass component of the music much better than other components.

I would like to know why the bass voice is more audible (can be better heard through the closed door from another room) than other components in the music ?

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A simple model of a door as a linear time-invariant filter through which the acoustic waves are passing is a first-order explanation. The door is a low-pass filter (better yet, a bandpass filter with low resonant a.k.a. center frequency) which attenuates the higher frequencies far more than it attenuates the low frequencies. So the bass tones are heard more than the altos and sopranos. –  Dilip Sarwate Nov 16 '12 at 12:42
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@DilipSarwate You should make that an answer. –  Jim Clay Nov 16 '12 at 14:31
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@JimClay Thanks for the suggestion but I don't know enough about acoustics, audio, auditory processing and hearing, etc. to feel comfortable offering it as an answer. There are people on this forum who possess far more knowledge in these areas than I do, and one or more of them will likely offer up a more sensible answer than my back-of-the-envelope idea within a day or two. –  Dilip Sarwate Nov 16 '12 at 15:19
    
A room with a closed door is essentially a speaker enclosure with a frequency response. My guess it that if you measured the frequency responses of the door and walls as loudspeaker membranes or transducers, they would be pretty low. A sub-woofer of a sort. The rest of the internal spectral energy gets absorbed or reflected around inside the closed room. –  hotpaw2 Nov 16 '12 at 16:55

3 Answers 3

The sound wave is a pressure wave in the air, a mechanical vibration. If you have two rooms separated by a wall or door, there is little or no air passage through which the sound can propagate.

Instead, the wall itself have to absorb and re-emit the mechanical vibration on the other side. Since doors and walls are massive objects, they are resonating on lower frequencies.

The high frequency sound cannot pass through the doors since it is able to make only small particles vibrating (or just surface of the door), hence the wave is not completely absorbed and rather reflected back.

The bass sound wavelenghts are about feet long (the range is quite large depending how you define "bass"), which roughly matches the size of such large objects like walls and doors.

Of course, waves with even larger wavelengths are unable to make objects of this size resonate and hence doors behave like a band-pass filter (as Dilip Sarwate noted).

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That's a basic property of room acoustics. In essence the wall is a mass (ignoring resonant structures for now). Transmission through walls works as follows: sound energy hits the wall -> wall starts to vibrate -> wall radiates sound into the adjacent room. The wall simply follows Newton's second law of motion: F = m*a, force = mass times acceleration. For a given velocity the acceleration is proportional to the frequency, i.e. the walls moves half as much when the frequency doubles. In other words it takes a lot less force to shake a heavy object slowly than to shake it fast. In practice the transmission drops roughly by 4dB per frequency doubling.

This is quantified here:

http://www.engineeringtoolbox.com/sound-transmission-massive-walls-d_1409.html

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Something about low-freq can circumvent the objects and high-freq can only reflect and vanish? Microwaves works better in direct visage. Open spaces are better for high-freq and closed spaces are better to low. Observe: Country people, supose to leave in unobstrusive opened spaces, generally have high-freq voices (Willie Nelson) to be listen far in the hill. Otherwhise, city people must be listen in the near room so they have louder voices(Ezio Pinza);

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Waves with low frequencies are diffracted stronger and can propagate "around the corner". But diffraction doesn't make them escape from a closed room. So this effect is not the reason for bass sounds beeing heard through a closed door. –  Deve Nov 22 '12 at 12:14

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