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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.

room

  • So, ...what's your question? – leftaroundabout Feb 8 '15 at 3:39
  • How could I solve it?... I've added a drawing – whitenoisedb Feb 8 '15 at 3:40
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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? – whitenoisedb Feb 8 '15 at 3:49
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    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. – leftaroundabout Feb 8 '15 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? – whitenoisedb Feb 8 '15 at 4:09
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    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 ;) – Tetsujin Feb 8 '15 at 8:47
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    @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. – leftaroundabout Feb 8 '15 at 13:21
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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?

Need more info for a better response.

  • Thanks for replying. That stunned hum appears when i'm playing or listening to music, through the speakers, and D2 note (~146hz) come in place. Synths produce more ideal waves, so when using them, this issue is very noticiable, even at medium volume levels. – whitenoisedb Feb 9 '15 at 4:52
  • MrAnnex, why do you think this is a Power/ground issue? If the hum would be 50 or 60 Hz I'd agree that this would be the first thing to look at. Right now your second suggestion sounds much better, it's an acoustic issue. @redraw: Do some research on 'standing waves' and room acoustics in general. There are great forums out there, example: hometheatershack.com/forums/… – Arnoud Traa Feb 9 '15 at 10:30
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    A small point; resonance will only happen if something drives that resonance. If you don't put 146 in or any of its lower harmonics, you won't drive any resonance and you shouldn't hear it. If you can hear that when the speakers are on and you have put nothing through them, then it is a power/interference etc problem. Also, ground loops don't always sound like 50-60Hz due to the fact that mains power is never that pure, and differences between loops can result in phasing and other noise intrusions at very different frequencies. I've had ground loop that hit 1kHz before. – David Boshton Feb 9 '15 at 15:18
  • Again, as stated in my first comment. If you're not playing anything, then it's not a musical issue but since it's been clarified that it's only during playback then it must be a standing wave issue. Thanks @David for adding that :) I hope you straighten out the issue. Have you tried any acoustic treatment or moving your desk? Give it a go if not. See if you have any issue after a change. Best. – MrAnnex Feb 9 '15 at 17:35
  • My thinking is that the problem can be decoupled from any devices that may be inadvertently gating by putting a high passed signal through the system. If you high pass at 500Hz, and still hear it, it's unlikely to be a resonance issue. – David Boshton Feb 9 '15 at 19:59

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