Sound between two rooms - closing which door affects the sound most?

[NEWBIE1212]

Imagine you have two identical rooms opposite each other with some space in between. (Ie two rooms across from the passage or two rooms leading off of another room). Sound is being emitted from one room only. Would closing the door in the room where the sound is being emitted from or would closing the door of the other room (listening room) result in less sound being heard?

My logic is that closing the door of the listening room would have a greater effect than closing the door of the sound emitting room.

 

[berkeman]

Welcome to PF.

My logic is that closing the door of the listening room would have a greater effect than closing the door of the sound emitting room.

Why do you say that? (you may be right, but why?)

 

[tech99]

Welcome to PF.

Why do you say that? (you may be right, but why?)

It cannot be any different, because if you interchange the source and receiver you must always have the same overall loss. In radio engineering this is known as the Rayleigh-Carson Reciprocity Theorem.

 

[olivermsun]

For the idealized problem, reciprocity should answer the question. It might be fun to think about whether there exist any real-world conditions under which reciprocity might break down in across the two rooms.

 

[Keith_McClary]

I think you need to be more precise about where in the rooms the emitter and listener are located.

If the sound is high frequency so that the ray approximation is valid, and the walls are sound absorbing, I don't think reciprocity applies.

 

[hutchphd]

Would the answer be in question if we were talking about light?? Why should there be a difference? I think you shut the door to your room. More good places for dissipation that way.

 

[tech99]

I suggest reference to the Rayleigh Reciprocity Theorem. In practice, if the ambient noise differs at the two locations then we will notice a difference in audibility, but the received sound power will be the same.

 

[danielhaish]

Assuming the door is blocking the sound in a mount relative to it volume. For example x% or yDB if so the first door would be more important because it will reduce part of higher number . That why we usually put the amplifier in the beginning of the circle for not increasing the noise

 

[tech99]

Let us assume a sound power of 1W, a first door attenuation of 10dB and a second door attenuation of 20dB. The sound power in the second room is then 0 - 10 - 20 = -30 dBW. If we reverse the situation the sound power reaching room 1 is also 0 -20 - 10 = -30dBW. However, if there is a noise source of -30dBW in room 2, then it will be seen that communication is only possible in the direction Room 2 to Room 1. So I agree that any amplifier should in this case go at the sending end , but notice that it might have to deliver a lot of power.