Imagine this situation: Three rooms in a row, each one connected by a door to the next one. Room 1 has something that makes a loud noise, e.g. a washing machine. I’m standing in room 3 listening. In one situation, the door between rooms 1 and 2 is closed, while the door between 2 and 3 is open. The other situation it’s the other way round.
Does it make a difference which door is open for the volume of the sound I’m hearing? Why (not)?
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In any real life situation, there are going to be too many variables to say. In a “vacuum” where the rooms are perfectly constructed and symmetrical and ideal, it shouldn’t matter.
“Vacuum” as in an unrealistic setting for a scientific hypothetical, not literally a vacuum.
In real life, you have tons of things affecting the acoustics. The biggest thing would probably end up being whether one door sealed better than the other. But besides that, you have the shape of the rooms, the furnishing, the flooring, even what the walls are made of, the location of the source of the noise, etc.
I would imagine that it doesn’t matter which door is open or closed, you would hear it at the same volume. Think about how sound works. It travels though medium, in this case the air and a door, and the further away from its source you get the quieter it becomes. Regardless of either scenario, the sound wave is traveling the same distance, and traveling though the save amount of material (some air and 1 door). So I see no reason why it shouldn’t be the same volume in both scenarios.
Like the other comment says, there are too many variables. But if we assume the doors and rooms are identical I think closing the first door would reduce the volume more.
You have direct sound and reflected sound. Direct comes directly from the sound source to your ears, in this case through whatever door is open and through the gap under whatever door is closed.
Reflected is what has bounced off the walls and floor and ceiling before it reaches your ears. That’s what reverberations and echoes are. And when you hear music from a different room it sounds muffled and more bassy because the higher frequencies bounce more and the lower frequencies travel through walls better. Some of that reflected sound will also travel through the open door and under the closed door, but not before it has bounced and lost some energy.
If you closed the first door, the nearest one to the sound source, almost all of the sound would bounce off the walls and floor and ceiling in the first room. That would make it lose energy farther away from your ears than if the first door was open. There would be less of both direct and reflected sound in the middle room, which means less sound to travel through the walls of that room and into your ears. So it would be quieter.
If you closed the second door, the one farthest away from the sound source, more of the direct sound would enter the middle room through the open first door, more of that would be turned into reflected sound in the middle room, and more of it would come through the walls into the third room. So it would be louder.
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