"Void free" or "no core gaps" plywood - diyAudio
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Old 13th March 2007, 06:32 AM   #1
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Default "Void free" or "no core gaps" plywood

(a few situations, a couple of solo and a sort of ‘group’ project)

How much of an advantage for reduced resonances in speaker boxes, is the lack of gaps in 19 mm (3/4 inch) plywood, for

100 w subs with panel sizes up to 600 * 400 mm (24 * 16”)
25 w satellites (> 100 Hz) up to only 300 * 225 (12 * 9”)
50 w mostly full range speakers of an in-between size

Or can leadlining/ heavy lining like used in car sound insulation/ roof felt lining

and/ or appropriate bracing provide the same benefit?

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Old 13th March 2007, 07:11 AM   #2
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The risk you run with voids is loose material in the void which buzzes.
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Old 13th March 2007, 08:01 AM   #3
fred76 is offline fred76  Philippines
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Hi,

I'm with John here experience-wise... Use void-less as much as possible. I think the extra lining would only be icing on the cake, for tweaking etc.

FWIW, I found this interesting source of quality ply for more ambitious projects etal:

http://www.internationalpaper.com/PD...lyBrochure.pdf
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Old 13th March 2007, 12:18 PM   #4
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Even for little 25 w satellites (only handling > 100 Hz) up to only 300 * 225 (12 * 9”)?

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Old 13th March 2007, 03:27 PM   #5
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Rick,

The odds are in your favor. I've built a lot of different speakers, seldom with void free, and only once had a buzzing problem. That box ended up having to be scrapped though. Be alert for voids when cutting your panels, and either cut another or inject some glue in the void. Give the cabs a good test before doing the finish work and listen for buzzing in the panels.
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Old 13th March 2007, 10:28 PM   #6
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Hi John

Have you changed your view somewhat?
From some risk “The risk you run with voids is . . “
To low risk “built a lot of different speakers, seldom with void free, and only once had a buzzing problem . . “

Initially I thought void free a likely benefit for subs handling eg 50+ watts down to 30 Hz ~ high energy level; but not lower watts at 2 kHz.

On further thought, buzzing sounds like a higher Hz, based on the thickness of the ply where the voids are.

Any other views?

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Old 14th March 2007, 01:09 PM   #7
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Default Plys v plys

Hi

For subs . .
i've read here, that eg lining the walls of a centre channel with carpet can eliminate boominess, and make eg vocals easier to understand – but the same carpet with a sub, gave little improvement.
. . SL recommends unlined 19 mm birch ply, and I’m using the same Peerless drivers he recommends . . .


But for naturalness, from over time enjoying Spendors, Missions & Rogers for mids & treble (hence satellites too) I lean to the BBC school. Light (not thick), strong and stiff, well damped . .


I’ve just found a supplier with a range of specialty plywoods (haven’t checked costs, but separate mid-tweeter boxes won’t be large, so won’t matter much). They have

- “Acousti-ply” Marine or exterior grade, combined with a heavy, mass-loaded core material to provide excellent acoustic dampening properties

- Birch Ply

- “Cortech” Balsa-cored plywood - very high stiffness to weight; from end grain balsa, very high compressive strength, bonded between sheets of light Gaboon plywood.

- Gaboon Very light weight plywood

- Hoop Pine Plantation - multilam (crossband laminates) construction

- African Mahogany – multilam

To achieve most natural mids, any suggestions between these?
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