# Sound wave propagation through a wall

My question are actually two, but are somehow related.

1) Does a sound wave always (no matter what frequency) needs of the interaction (set in motion particles) with the element the wave is transmitted through?

2) Is the sound that gets transmitted to the other side of the wall only a result of the vibration transmitted through the wall, or also a combination with the sound that is radiated by the wall at its resonant frequencies after having been excited by the impinging sound wave?

This could be thought of in terms of the impulse response of the wall.

If the impulse response was non oscillatory (say, a decaying exponential) then the sound on the other side would be a low pass filtered version of the impinging wave--whether it is an impulse or something else.

Otherwise the wave on the other side could include the resonant frequencies--which would be summed together with the low pass filtered impinging frequencies (assuming the impinging wave contains the some of the resonant frequencies ).

1) Does a sound wave always (no matter what frequency) needs of the interaction (set in motion particles) with the element the wave is transmitted through?

Yes--in all cases this would depend on vibrating particles since sound is a mechanical wave.

2) Is the sound that gets transmitted to the other side of the wall only a result of the vibration transmitted through the wall, or also a combination with the sound that is radiated by the wall at its resonant frequencies after having been excited by the impinging sound wave?

(As you say) It is a combination of the sound that is radiated by the wall with the wall's resonant frequencies after having been excited by the impinging sound wave? So the sound on the far side of the wall would consist of the frequency components of impinging sound wave with their amplitudes modified by the frequency response of the wall including any resonant frequencies.

• Sorry I dont really understand what you mean with "non oscillatory impulse response" – sdiabr Oct 13 '19 at 18:03
• I mean a decaying exponential type response where the impulse response goes high and then relatively slowly declines back to zero without crossing zero and becoming negative (no undershoot). – user45664 Oct 13 '19 at 18:18
• So your answer to my question nº2, would be that what we would hear in the adjacent room would be a combination of the transmitted wave and the radiated wave? – sdiabr Oct 13 '19 at 18:48
• Yes--or you could say: "the filtered incident wave". This would be a more typical description. – user45664 Oct 13 '19 at 18:53
• Okey, thanks. I didn´t give you the "correct answer" though because I was hoping for a bit more detailed answer, going deeper into the physical phenomena. – sdiabr Oct 15 '19 at 13:01