# Room Frequency Hum

In my apartment I always had the same problem with D2 at ~146Hz. It feels like a deep hum. The distance between speakers and wall is about 2.38 meters, so

f = v / L
L = v / f ---> L = 343[m/s] / 146 [1/s] = ~2.38[m]


means something like the lenght of the wave (L) is equal to the distance between my speakers and the wall. I guess this is called intrinsic vibration modes.

Is there a way to mitigate this phenomenon?

EDIT: Here's an audio. If I playback that audio file through the speakers the hum effect doubles its intensity ! D2 note isn't even distinguished.

• So, ...what's your question? Commented Feb 8, 2015 at 3:39
• How could I solve it?... I've added a drawing Commented Feb 8, 2015 at 3:40

This probably has little to do with the distance from the speakers to the wall, and everything with the distance of the opposing walls themselves. Parallel walls always have a problem with standing waves; diffusors are the solution to this.

• Good point, but do you think this has nothing to do with that math coincidence? Commented Feb 8, 2015 at 3:49
• Those values you were using are't as well-defined as your figures suggest: a room resonance always happens over a whole small range of frequencies. So the near-equality still holds when you put in the distance between the walls, or perhaps the room height. Both are much more relevant for issues like yours, than the distance between speakers and any walls. That is relevant for comb-filtering problems, but not for resonances. Commented Feb 8, 2015 at 3:56
• Well, you must be right because sound waves bounces between walls rather than between the wall and speakers. Does diffusors work at certain frequencies? Should I cover my walls and roof with them, or should I try a few ones at certain places? Commented Feb 8, 2015 at 4:09
• Sometimes you can just get lucky & move a set of bookshelves to the offending wall. Bass-trap that looks like furniture. You don't want to spend a couple of grand on generic diffusers only to discover it's the floor that resonates ;) Commented Feb 8, 2015 at 8:47
• @redraw: diffusors aren't tuned to a specific frequency; they improve the whole spectrum, but indeed you need to cover most of the critical areas with them to get good results (i.e. probably also the ceiling), not just one spot. Which means that a bookshelf alone probably won't quite do the trick, though it's still a good idea to try something like that first, as Tetsujin says. Commented Feb 8, 2015 at 13:21

It could be that you need either a power conditioner, or perhaps ground lifts on something. There's not enough info on the situation you're in when you hear this. I do see that you're dealing with parallel walls, this is an issue right away. Standing waves are not good for a mix room. If that's what you're doing?

Bass traps could be useful, diffusers sure but that may be a shot in the dark. I take it that this hum is just always going when your gear is on? Or when you're recording? Or playback? Or strange to ask, but the building?