Suggestions for minimizing acoustic resonances in large sealed box ?

Paul W · 6th February 2008, 01:14 PM

Looking for a wide variety of suggestions for minimizing acoustic resonances and reflections inside a very large sealed enclosure. Not panel resonances, but standing waves and reflections.

Need a fairly broadband solution, or a combination of solutions, to be effective from bass to 1k.

Ideas?

PigletsDad · 6th February 2008, 01:26 PM

Matrix construction, which also helps with panel resonances.

Put internal dividers in two (or three if you are very clever) directions. These have holes in to allow some air flow, but break up the plane waves.

BlueWizard · 6th February 2008, 05:13 PM

Well, the most obvious is to line the inside of the cabinet (sides and back) with fiberglass, polyester, or acoustical foam insulation. Some prefer to line the walls, other prefer to loosely fill the cabinet.

The other is to not have flat parallel surfaces. The cabinets could be built with curved sides or in a shape similar to a pentagon (more like pentagon-ish).

You can get some construction ideas for both curved sides and multi-sided geometic shapes from this discussion-

Bendable plywood-mdf combination-
Bendable plywood-mdf combination.

Of course to keep the cabinet itself from vibrating or resonating, you need adequate bracing.

Just a thought.

Steve/bluewizard

sreten · 7th February 2008, 09:43 AM

Hi,

For sealed lining the box (needs to be good acoustic foam) does not
make much sense (it does for vented boxes). Stuffed in the way to
go with anything sensible - BAF (polyester pillow fill) usually.

/sreten.

Hezz · 7th February 2008, 11:50 PM

My understanding of the old methods for the best sounding closed boxed systems were to use a combination of acoustic foam on the sides of the walls and a near complete filling of polyester batting and fiberglass cut in 1-2 inch size squares. The stuffing density is important and need experimentation for best sound.

Some also drilled a couple of small holes 2-3 mm in diameter to make the enclosure slightly lossy and aperiodic. This can improve the sound a lot.

Of course, adding the matrix bracing and baffling inside will also help and it's best to use a combination of all methods and balance as necessary. As has been stated the wall lining is probably less important than the inner volume stuffing. For midrange you will want more stuffing. For bass driver you want somewhat less so you don't over damp the bass response.

noodle_snacks · 8th February 2008, 01:05 AM

Build the box so it doesn't have the same dimensions in any direction (so standing waves are all on different frequencies). Any bracing "matrix" or otherwise should also be built with lots of entropy in placement (but the same for each pair).

Hennie · 8th February 2008, 06:27 AM

Theorize, select the best concepts and then experiment. Connect your measurement microphone to the internal volume of the box and you will see the effect of cavity resonances. You will have to measure a number of points inside the box. This may help you to select the bst concept and to optimize it.

JimT · 8th February 2008, 02:56 PM

Use the Golden Ratio for dimensions.

Brett · 8th February 2008, 04:04 PM

What about a tapered 'tube' a la the B&W Nautilus (the snail shaped one) though it need not look like a snail.

6th February 2008, 01:14 PM	#1
Paul W diyAudio Member Join Date: Oct 2003 Location: North Georgia	Suggestions for minimizing acoustic resonances in large sealed box ? Looking for a wide variety of suggestions for minimizing acoustic resonances and reflections inside a very large sealed enclosure. Not panel resonances, but standing waves and reflections. Need a fairly broadband solution, or a combination of solutions, to be effective from bass to 1k. Ideas?

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6th February 2008, 01:26 PM	#2
PigletsDad diyAudio Member Join Date: Jul 2007 Location: South Worcestershire	Matrix construction, which also helps with panel resonances. Put internal dividers in two (or three if you are very clever) directions. These have holes in to allow some air flow, but break up the plane waves.

6th February 2008, 05:13 PM	#3
BlueWizard diyAudio Member Join Date: Jun 2007	Well, the most obvious is to line the inside of the cabinet (sides and back) with fiberglass, polyester, or acoustical foam insulation. Some prefer to line the walls, other prefer to loosely fill the cabinet. The other is to not have flat parallel surfaces. The cabinets could be built with curved sides or in a shape similar to a pentagon (more like pentagon-ish). You can get some construction ideas for both curved sides and multi-sided geometic shapes from this discussion- Bendable plywood-mdf combination- Bendable plywood-mdf combination. Of course to keep the cabinet itself from vibrating or resonating, you need adequate bracing. Just a thought. Steve/bluewizard

7th February 2008, 09:43 AM	#4
sreten diyAudio Member Join Date: Nov 2003 Location: Brighton UK	Hi, For sealed lining the box (needs to be good acoustic foam) does not make much sense (it does for vented boxes). Stuffed in the way to go with anything sensible - BAF (polyester pillow fill) usually. /sreten.

7th February 2008, 11:50 PM	#5
Hezz diyAudio Member Join Date: Dec 2002 Location: Utah	My understanding of the old methods for the best sounding closed boxed systems were to use a combination of acoustic foam on the sides of the walls and a near complete filling of polyester batting and fiberglass cut in 1-2 inch size squares. The stuffing density is important and need experimentation for best sound. Some also drilled a couple of small holes 2-3 mm in diameter to make the enclosure slightly lossy and aperiodic. This can improve the sound a lot. Of course, adding the matrix bracing and baffling inside will also help and it's best to use a combination of all methods and balance as necessary. As has been stated the wall lining is probably less important than the inner volume stuffing. For midrange you will want more stuffing. For bass driver you want somewhat less so you don't over damp the bass response.

8th February 2008, 01:05 AM	#6
noodle_snacks diyAudio Member Join Date: Mar 2004 Location: Hobart, Tasmania	Build the box so it doesn't have the same dimensions in any direction (so standing waves are all on different frequencies). Any bracing "matrix" or otherwise should also be built with lots of entropy in placement (but the same for each pair).

8th February 2008, 06:27 AM	#7
Hennie diyAudio Member Join Date: Nov 2004 Location: Pretoria	Theorize, select the best concepts and then experiment. Connect your measurement microphone to the internal volume of the box and you will see the effect of cavity resonances. You will have to measure a number of points inside the box. This may help you to select the bst concept and to optimize it.

8th February 2008, 02:56 PM	#8
JimT diyAudio Member Join Date: Oct 2004 Location: Waterloo	Use the Golden Ratio for dimensions.

8th February 2008, 04:04 PM	#9
Brett diyAudio Member Join Date: Jan 2002	What about a tapered 'tube' a la the B&W Nautilus (the snail shaped one) though it need not look like a snail.

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