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Old 17th November 2003, 12:26 PM   #1
Pan is offline Pan  Sweden
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Default Active bass absorbers

Is what I am going to build this winter amongst other things..

How important is it to have a "proper Q" of the closed box/woofer combination? Guess not so important but maybe its better anyway to shoot for a damped Q?

I will start out with a 12" tube or so, from floor to ceiling more or less. Or rather, Ill use two pieces of 1 meter stacked on eachother. The tubes will be sealed midways and one woofer will be mounted on each side of the tubes... meaning there will be four woofers in the corner. One close to floor, one close to ceiling and two facing eachother in the middle about 1.2 meters above floor. Heigth to ceiling is standard 2.4 meter.

This mean I will have two tubes of 70 liters volume, each volume of 70 liter will be parted into two volumes of 35 liters by the means of a MDF circle in the middle. So, what drivers to use in a 35 liter volume...

I have a bunch of SS 25W8565-01 laying around but maybe a lower Q and VAS driver would be better. Peerless XLS 10" has low Q, VAS and Fs and also have double the displacement.

Yes, this is meant to be a serious atempt to correct the anomalies in the room response.

Any recommendations on mic capsules? Also I was thinking on using one 50W LM3886 chip for each woofer.

If the project turns out to be successfull (sp?) Ill consider using one or two more of these creations in other corners of the room.

Comments and suggestions are very much welcome, thank you!

/Peter
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Old 17th November 2003, 12:49 PM   #2
Pan is offline Pan  Sweden
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Hmm, the limitaions in BW of the ABA is set by?

Inductance and upper extension of the driver unit of choise?

If Im thinking right it should be possible to use it deeper down in frequency the lower the box resonance is?

To put it another way, what is the relationship in lower useable range and box resonance? I have a room mode about 30 Hz which would be nice to damp seriously without using EQ if possible.

I use 8 RPG bass traps in the corners now and they are really good but I want it to be better yet.

/Peter
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Old 17th November 2003, 07:52 PM   #3
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I think you're probably on the right track, particularly if you
are looking to replicate the Shadow but on a larger scale.

The tubes were stuffed in the original, which damps out
resonance, so the Q gets lowered, and in addition the feedback
system removes much of what is left. It's not an issue.

The bandwidth limiting and the setting are mostly functions
of the stability of the system in its intended location.

I suggest you make such adjustments while measuring the
amplitude and phase response of the active loop. You can
do this by stimulating the input electronically.
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Old 18th November 2003, 10:34 PM   #4
Pan is offline Pan  Sweden
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Thanks. I get back with a couple of hundreds questions when I have the basic stuff built .

Might as well ask if theres anyone that have built these things here on the board... anyone?

/Peter
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