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I got a home organ in my living room, and I get a lot of bass resonance. I'm looking for easiest ways how to get rid of these. The room is 350x590cm and 260cm high, the organ stands in the corner, about 8cm from each wall.

Experimentally, the most noticable resonance seems to be vertical and in the range low G--low B on 16' ranks.

I would of course prefer something effective that can be hid behind the organ, if possible, but I understand that this can be difficult. Second reasonable option is arranging some (book)shelves above the organ, if this helped, but I have no idea how effective this could be.

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    What frequency range (in Hz) is low G to low B? A bookshelf or a thin wall ornament isn't going to absorb much bass frequency; but a strategically placed wardrobe or cupboard full of blankets or towels might. Look up "bass traps", and how they are placed in home studios (in the corners mostly). – Your Uncle Bob Sep 20 at 21:03
  • @YourUncleBob That would be 42Hz (704cm) to 62Hz (560cm). Thanks for bass traps tip, but the thing is, I don't want my living room spoiled by these things all around the place, obviously :) – yo' Sep 23 at 15:31
  • Those low frequencies will be very tough to do anything about, especially if it has to fit in visually in a living room. There's a reason why bass traps are so big, and that's because you need a lot of mass to absorb low frequency energy. You may have to look at removing some of the low end at the source, by adding some sort of equalisation or filtering or using smaller speakers. – Your Uncle Bob Sep 23 at 15:47
  • @YourUncleBob I realize this is a tough job. Fortunately the volume of specific "pipes" (specific keys in a specific register) can be modified, so this is an option. Still, I would prefer to do as much as possible to kill the resonance. I consider trying to dump the polystyrene parcel fillers behind the organ as the mass that can be put there is actually quite large; however, I have no idea how efficient that would be. – yo' Sep 23 at 15:55
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    Polystyrene will be much too lightweight for bass frequencies. You're probably better off using (closed) bags of sand. Even then, the location of the traps is crucial; putting them in the wrong spot may lead to them having no effect at all. You'll have to experiment with objects that are both heavy and slightly malleable, like sand, rubber, vinyl, dense rockwool... A large plant pot may work (the earth in the pot, not the plant itself). Rigid objects or lightweight heat insulation materials won't work. – Your Uncle Bob Sep 23 at 22:23
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Your basic problem is that you have a sound source in one corner of what looks like a box-shaped room. That in itself will boost the sound output at low frequencies, by reflecting the sound coming from the back of the instrument into the room.

If the organ amplifier has some type of "tone control" or "equalizer," simply reducing the bass response may fix the problem. The picture looks like a Johannus organ, so you probably already have a separate amplifier and speaker channel for the pedals. You may be able to adjust the balance between the divisions, or route the pedal to an external speaker somewhere else in the room which avoids the resonance problems. In a fairly small room the bass sound will be almost completely non-directional, so the speaker could be positioned anywhere to minimize problems with the room acoustics.

The walls and floor are effectively forming a "corner cube" reflector which will return sound waves approaching from any angle back in the exact opposite direction. That is very desirable property of a corner cube if you are putting a radar reflector on a small boat for example, but not if you want good room acoustics.

Assuming the other walls are similar to the one in the picture (i.e. flat and reflecting sound well) you are probably creating a standing wave as the sound is reflected back and forth between the parallel walls.

The most effective solution would be relocate the organ somewhere in the middle of the room, but that might not be practical. If you can turn it through an angle of say 30 degrees from the wall while keeping it in the corner, that might help. You may have to move the yellow seat slightly out of the way, but not by much.

Another line of attack is to damp out the reflections. Covering the opposite wall with something that absorbs sound, like a decorative curtain, will help. A cheap way to experiment with that idea is to "borrow" a duvet from your bedroom and see how much effect it has held up against the wall. An open door is also a good way to avoid reflected sound by removing it from the room completely, if the layout of the house is suitable.

Breaking up the reflective surface with bookshelves or something similar will also help, but they will be most effective on the opposite wall, not behind the organ. The idea is not so much that the books and shelves will absorb the sound, but that the irregular surface of different sized books(or any other objects that you might want to display on shelves) will disrupt the standing wave between the two parallel walls.

If you are in a house, a really radical solution (which has been built, and does work!) would be to move the pedal speaker out of the room completely, and install a speaker in the roof space above stair well, using the whole ceiling as an "infinite baffle". This doesn't involve designing a speaker cabinet - you literally just have a speaker with the cone facing downwards and the back open into the roof space, with a lightweight dust shield protecting the back of the speaker from dirt falling onto it. If there is a removable panel in the ceiling to allow access into the roof space, that can be used to mount the speaker cone without any structural alterations to the building.

The speaker will then be operating into an air column about 16 feet long from the top of the stair well to ground level, which is of course the same length as the longest open organ pipe of 16' pitch. A surprisingly low power amplifier (only a few watts) will be enough to produce a very smooth bass response through the entire house, if the other residents apart from the organist don't have any objections!

  • Hello and thanks. Just couple things: Note that there is no "pedal speaker" for the organ, the built-in speakers (placed below the manuals, close to the organist's knees) deliver way enough power to make the organ loud. Also note that this is an appartment house, so there is nothing like roofs and stuff. The idea with bookshelves on the opposite wall is interesting; there is one just now, but I plan an upgrade, so I hope it will help. Relocating the organ is really the least thing I'd like to do. Well, I'll try couple things and see what works, and I'll return here to report :) Thanks again! – yo' Sep 23 at 15:36

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