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Discussion in 'Home Theater Projects' started by Shawn Keeler, Jul 29, 2003.
Does anyone have any pics of some bass traps they have built?
Here are some that I made.
My traps are errrrr... Big, but they do work, I promise you that.
Your traps are some of the first DIY bass traps I've seen that weren't following the general Jon Risch design, such as what Chris built. I had thought that the way the Risch design worked was to use the pressure gradient between the air outside the trap and the air in the hollow center to suck in the high pressure of the standing wave. Your traps seems to work without the hollow center. Does the foam alone provide enough internal air to relieve the external pressure? And would someone get the same effect just stuffing a trap with fiberglass alone, seeing as how someone can't afford to buy a huge bunch of acoustic foam blocks?
Typically in a large room there is not sufficient differential of air pressure to suck out anything, unless you are pushing the air around with a lot of big subwoofers.
The solid foam wedges are more effective in absorbing sound waves.
The thicker the foam the lower in frequency its effectiveness.
Most companies that make foam dampening panels or wedges rate the effectiveness as a percentage at a given frequency.
The traps I made were 16" thick wedges facing out in 4 directions.
It was effective down very low.
Sonically, it tightened up the bass response a lot. Took out room boom. Improved imaging too.
The difference before and after was easily measured too using and RTA with pink noise.
How thick or what type of bass traps will be best for you depends on your room response and where or at what frequency needs attenuation.
John Risch's design might be more effect when used with smaller speakers to help attenuate the range that a small speaker is playing while effecting little the really low frequencies that may be week to begin with.
John's design is really cheap to build too.
Thanks Danny. I checked the websites linked from your page but couldn't find any prices for the foam. I'll have to look for the absorption ratings when I look again, but your saying that the foam is more effective at the lower frequencies than fiberglass alone? Jon has a 'quick and dirty' design that is basically just stacking rolls of fiberglass, which would (I guess) be equivalent to stuffing a wire tube full of compressed rolls and finishing it off with a fabric cover.
Thanks for the information.
Looking at various designs has left me with a question. I notice in bass traps all the materials are lightweight which makes sense. Most of the DIY panels I see are built with pegboard or even plywood sheets and 2x4s. Why would anyone want to use such heavy reflective material to build a sound absorbing/diffusing panel? I built mine with 1x4s, chicken wire, insulation, batting and burlap. They're ~4'x7' and weigh ~15 lbs each. Is there something I'm misunderstanding about the physics behind these things?
The panel traps only affect certain freqs. So if you don't want to deaden the room too much in the midrange, the panels designed to absorb low bass are a better alternative. Fiberglass absorbs higher freqs as well as lower, and it takes a lot more fiberglass to absorb low freqs than 4". It sounds like you have more like reflection control (higher freqs) than bass absorption.
So an equal volume of foam will do better than fiberglass for a low frequency bass trap? Is there anything special about the sculpted acoustic foam, or would any high density closed-cell foam work as well to fill a bass trap?