Small room bass management problem

I've been searching around on the web trying to find a decent place to get some good acoustics advice, and I came across this forum. Here's hoping that despite this being my first post, someone will be kind enough to help me. :) We've recently redesigned the back room and have moved the stereo / home theatre out there. It's a small room (haven't got the exact measurements on hand, but it's roughly 8 feet (w) x 15 feet (l) x 14 feet (h). It's pretty tight - the couch is sitting about three feet away from the wall in the rear with the surrounds on stands pointing towards the roof in the back. The TV and amp are sitting on an entertainment unit that's roughly the same width as the room. It's floorboards with a carpet covering about 2/3 of the room. The front speakers are floor-standing and are placed half-way out from the entertainment unit so I could get enough room to toe them in. After being toed in, they're standing about three feet away from the rear wall and the rear corner is less than a centimetre from the skirting. Nothing can really move - everything "fits", and without resorting to buying new furniture, I can't really move the speakers anywhere. In a nutshell, here's the problem - I've used RoomEQ with a radioshack SPL meter to measure the frequency response of the room. I've (apparently) taken into account the distortion from my soundcard and the inherent distortion of the SPL meter. I realise it's not the ideal measurement tool, but given that I'm not going for studio quality (only as near as I can get), it's probably "good enough". The room response (not surprisingly, from what I've since read) shows horrendous bass response. I've got a major null point at around 80hz - from memory, it's something around -20db to -25db. It also peaks just before and after - the response is roughly 10db higher than it should be. I've got the curves if anyone wants to see them, I just don't have them on this computer. The upper end is overly bright, but that's likely due to the french doors we had installed (lots of glass). That I can deal with - we're having insulated curtains installed soon, and I'm pretty comfortable with trying to dampen the room. Otherwise, the response is mostly pretty flat - it's definitely not studio quality, but it's pretty good. I can work with it, anyway. So, my major priority is trying to solve the bass problem. I don't mind building something - I'm pretty comfortable with woodwork, and I'm not scared about getting into anything harder. Here's my major constraints: * I need a solution that's reasonably cheap - I can spend up to a few hundred AUD total, but the cheaper the better. * It needs to be "spouse friendly" - I need to able to either hide it or turn it into a room feature. Panels look like they may work, but I don't know the dimensions of what I'd need or where I'd need to place it to know whether I could fit them or not. * I'd rather not mount it into any fixed structure (roof or wall) - while I could, I'd strongly prefer not to. I could compromise on the wall if necessary. Any ideas? If anyone can point me to the basics for a reasonably frequency targeted bass trap (80hz +- about 20hz) with the general principles behind the design, it'd be a big help. Full instructions or better ideas would be even better. Any and all suggestions are appreciated. :) Thanks in advance ... Edit: One other thing - corner mounting would be extremely difficult. Because everything's so tight, something that creates a triangle between the left / right walls and the rear wall would eat up too much space. We'd need to move the couch out to the point where's it's blocking the french doors.

Aloha evan, Here's a good place to read up on some acoustics principles, how/why they happen, and how to treat them, as well as a set of plans for various absorbers and where to put them. (Click on acoustics, absorbers tabs on left, and any tabs that show up on at the top of the pages) http://www.saecollege.de/reference_material/index.html DIY wall units: http://www.johnlsayers.com/HR/index1.htm Hope these help, Aloha 8)

That SAE link is awesome - thanks! One question I've got about corner absorbers vs. rear wall absorbers for those with experience in this area. The rear wall is split in the middle by a very small (2 foot tall by half a foot wide) window at roughly eye height. Forgetting about the cost for a second, it'd be far easier for me to build a pair of rear wall absorbers that cover the entire wall than it would be for me to build a pair of corner absorbers. I've got enough room to probably fit something about a foot deep if I had to (preferably less, but I may be able to fit something that deep in). I believe (and I could be wrong) that a corner absorber would need greater depth than that, hence my interest in rear wall absorbers. Has anyone been able to get equivalent performance at low frequencies by using rear wall absorbers rather than corner absorbers? Also, I've got some spare wool roofing insulation left-over - does anyone know what kind of frequency absorbtion properties it's likely to have? Or where I could find more information about it? Rockwool / fibreglass insluation I've seen, but wool I haven't. It's rated R3.5, if that's any help. :)

Welcome to RSD too!

I believe (and I could be wrong) that a corner absorber would need greater depth than that, hence my interest in rear wall absorbers

Corner absorbers use the reflection from the adjoining walls of a corner (a celing is another wall in this message) to effectively double the effective amount of absorption at low frequencies. A wall or corner absorber uses the same depth for low end absorption. Good luck! Andre

Can you post the actual dimensions from the center of the woofer cone of each speaker to rear AND side walls? There's a good chance your speakers are in TWO nulls, both of which are close to 80 hZ... Steve

Yeah that does sound like really bad bass response. It's pretty kick ass that you're trying to make your home entertainment listening experience better by using bass traps. A lot of people might that that's a little extreme, but I just think it's cool as hell. After I treat my studio I may have to try to convince my wife to let me do that to our living room. :)

knightfly wrote:

Can you post the actual dimensions from the center of the woofer cone of each speaker to rear AND side walls? There's a good chance your speakers are in TWO nulls, both of which are close to 80 hZ... Steve

Each speaker is 20cm (7.8 inches) from the side wall, 195cm (76.7 inches) from each other, 90cm (35.4 inches) from the front wall, and 320cm (126 inches) from the back wall. The exact room dimensions are 240cm (94.5 inches) by 410cm (161.4 inches). It's 270cm (106.3 inches) high. Sorry for not replying sooner - yesterday was a public holiday in Australia, and I decided to use it to build some broadband absorbers (based on one of the threads here). I used two strips per absorber of leftover wool roofing insulation (rated R3.5 for heat insulation) packed into a 35 cm deep plywood case I built. I built them out of ply so they'd be easy to hang and move. I'll take some photos when I get a chance and post them. They've already made a massive difference - eyeballing it, I've had a roughly 6db drop across the board from 200hz to 7000hz. That puts it pretty flat (+- somewhere roughly between 3db and 5db). The high frequencies are better, but are still too loud relative - that glass sure is a pain. Now I've got a personal reason to hurry up and get curtains ... 'Course, the best measure is that my wife's eyes bugged out when she heard the difference. I took them away and she immediately said she didn't like the sound of it. So, despite having these two massive padded boxes hanging on the wall, she doesn't actually want them out of the room anymore! She no longer thinks I'm mad. Well, not totally, anyway. :) The bass still exhibits the same problems - I've got a big dip at around 30hz, a peak at around 50hz, and a big dip at around 90hz. I've bought wood and silicon to make either a Helmhozlt panel absorber or a straight panel absorber, but I probably won't get to it this weekend (have to change all the powerpoints in the house). If moving the speakers could help, I'm all ears (pun intended).