Audio-filter: Where should I put my new Subwoofer?

March 9, 2010 3:49 PM

Audio-filter: Where should I put my new Subwoofer?

I recently purchased a KRK 10s and I was wondering where I should place it in my room to get the most out of the sub. I have read a few things online about subwoofers but they all seem to pertain to home theater setup. I am an amateur DJ and I am setting this up in my rectangular bedroom that measures 20' by 15'. My desk (where I will be mixing and where my monitors are already set up) is on one of the shorter walls. I am running into problems when I place the sub directly under the desk (actually just a fold out table) because I can't hear the bass when sitting at the desk. when I move the sub over to the corner to my right I can hear it a little bit, but the place where I can hear the most bass is still the center of the room. I really want to be getting the loudest response from the bass when I am sitting, that way i don't have to crank it to hear it, disturbing the neighbors and such. How can get rid of this pocket of no bass, right where I need it!?

posted by alextprice to technology (8 answers total)

Jeez - I just had two neighbors get subs who thankfully were totally cool with working with us due to all the noise we were getting. I'd go up and listen at the door (50ft long loft style apartments) and there was no bass at *all*, whereas in our apartment it was louder than the vacuum and dishwasher combined.

Guitar World carries pads that decouple the bass from the floor so the bass doesn't just travel down but out towards you. Also consider having it at waist level for the same reason. Don't put it up against the wall as that'll have the same effect.

It can greatly depend on how the sub is designed too. Some are huge speakers pointing down in a box with a hole on a side, so the brunt is pointed down, not out that hole. Hopefully some audio folks will pop in and explain this better. I'm hoping my neighbor's aren't just placating me!
posted by jwells at 4:01 PM on March 9, 2010

The guy at Axiom speakers has a video where he does the "subwoofer crawl". He positions the sub where he would normally sit and then crawls around the room until he find the spot where he hears it the best. Then the sub goes into that spot. Supposedly they're two nodes of the same standing wave pattern (or something like that).
posted by bonobothegreat at 4:36 PM on March 9, 2010 [2 favorites]

Does the subwoofer need to be on a solid surface to function properly? If not, I would suspend it from the ceiling. You should be able to put it somewhere a little closer to your head space and balance it with your existing monitors.
posted by snsranch at 4:39 PM on March 9, 2010

He positions the sub where he would normally sit and then crawls around the room until he find the spot where he hears it the best.

I've heard of this technique too.
posted by ROU_Xenophobe at 5:53 PM on March 9, 2010

Googling "subwoofer placement" brings up a bunch of results.
posted by ludwig_van at 6:40 PM on March 9, 2010

Your room is too small for serious bass waves to propagate, without folding back on themselves, creating nulls and peaks. The approximate physical length of a sound wave is given by the formula: wavelength (in feet) = 1130 (speed of sound in air, at sea level, standard air pressure, in feet/second) / frequency. So, a 20 Hz organ pipe fundamental is going to have a wavelength = 56.5 feet, and an approximately 70Hz C2 mid-bass note, from a bass guitar, is going to have a wavelength of about 16.14 feet. See this chart for fundamental frequencies of musical tones created by various instruments and human voices.

You can try to fabricate and strategically place/install some bass traps, at the worst nodes where waves fold for any given sub-woofer & speaker placement. You can install very steep crossover networks, electronic equalizers, or bandpass filters in line to the amplifiers that drive your speakers and your sub-woofer, to make sure that notes being sent to your speakers, aren't also being sent to your sub-woofer, thus creating more energy in the room for bass notes, at more physical points of origin, than they should have. And, yes, as has been suggested above, it's good to physically decouple large bass drivers from architectural elements of your structure, to avoid sending all the mechanical energy your sub-woofer is generating directly into the structure. The bass traps will suck up a lot of the acoustic energy the sub-woofer generates, and, theoretically, leave you with a room that is much "drier" even into the "presence" frequency range (2000 - 4000 Hz). So, you'll be able to turn down your overall sound pressure levels a bit, while achieving a flatter, "truer" frequency response.

But, don't kid yourself that you can ever shoehorn 50+ foot long sound waves into a 20' X 15' room, no matter how extensively treated, with anything like an accurate sonic result. Whatever you do, you'll just be making compensations that you like better than some other treatments that you like less. This is something a lot of car audio enthusiasts never "get," either, and they are really dealing with an extreme form of your problems, generally. But the physics of sound waves in air are invariant, so, if you want to enjoy bass, you need a big room, for a start, into which you can generate the full length waves, before damping them, or otherwise trying to control their reflections and foldings against walls and other architectural surfaces. Say, something like a roughly 100' D X 75' W X 50' H space, with no parallel walls - like, say, a movie theater or a concert hall, is generally built.

Good luck.
posted by paulsc at 11:41 PM on March 9, 2010 [2 favorites]

Have you tried flipping the phase?
posted by jade east at 12:38 AM on March 10, 2010

Thanks Paulsc! that was very informative, also those of you who said to crawl around with the sub placed where I was going to sit were right! This method worked very well. In the end I isolated the sub by putting some foam pads that I bought at Guitar center under the sub and then placed the sub to the right of the table, facing the shorter end of the table. This gives me the best response. sadly I won't be able to build any bass traps, but maybe I will when I settle down a bit, (i'm in college now) thanks so much again everyone.
posted by alextprice at 2:48 PM on March 10, 2010