OB bass with bass trap

[oon_the_kid]

Originally Posted by john k...

Damping the rear wave of a dipole to produce asymmetry between front and rear will make the woofer behave more like a monopole. While it will tend to increase bass response it will also increase room mode excitation making the response potentially more irregular.

Here is a link to a discussion of woofer ype and rear wall reflections.

Hi John K,

That was quite informative. So putting on something at the back will make it a bit more like a monopole speaker. How would one execute such a procedure. I was looking at the 5" wedge acoustic foam as something that would absorb bass well. Would that be a good technique? Or do you have a better idea.

Say a u-frame with the 5" wedge acoustic foam?

Oon

[mondogenerator]

to the best of my knowledge, a 5 inch thickness will only absorb frequencies above the quarter wavelength of the frequency that corresponds to that distance. Its about 679 hz if ive done the math right.

[pop4richard]

These show absorbtion to 125Hz

Bass Traps - Foam Bass Treatment For Studio Performance

[mondogenerator]

yes they do, but im not stating any level of attenuation either. The method i used, perhaps not entirely correctly, is what ive seen referred to in architectural noise reduction, and attenuation is also dependant on the absorbent Sabine rating. Also those traps are more than 6 inches deep at their greatest point, so they would perform slightly better.

Perhaps i shouldve said that absorption begins to become 'useful' at frequencies where the thickness is greater than the quarter wave. Once we get to whole wavelengths it is much more effective. Of course the value in traps like those could lie in the diffusion of the serrated shape. They may well work to high bass region, im not saying i know it all. However, i wouldve thought that attenuation BELOW 125hz wouldve been the goal.

BUT, i have used similar traps and of much larger size, with little improvement.

[mondogenerator]

from rough calcs- to get to 125hz the trap would be 26 inches (0.7metre) thick

[oon_the_kid]

Hi mondo,

When you say you have use those traps. Do you refer to damping the rear wave of an open baffle. Or just using them as a bass trap?

I am interested to know if anybody has sucessfully applied this technique..

Oon


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[mondogenerator]

I mean generally, i have used similar types merely as bass traps in a recording room, but as TVRgeek said earlier, they really need to be big, and probably floor to ceiling. It would be fun to try with a couple of metre cubes of foam and a knife though!

[oon_the_kid]

I am hopping by putting it at the source before the sound spreads it would be significantly more effective. I would agree that if you wanted to reduce nodes in the room you will need to fill up the wall. But in my case, you can view it as lining up the insides of a sealed speaker cabinet with bass trap. That is how i intend to use it.
Has anybody ever tried using 5 inch wedge as cabinet stuffing.

Melon head, u have seem to have tried everything under the sun. Tried this before in your audio nirvana 15inch cabinet before?

Oon