Interesting read I found on Lossy Cabinet designs by Harbeth - diyAudio
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Old 8th November 2012, 09:06 PM   #1
ORNJ is offline ORNJ  United States
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Default Interesting read I found on Lossy Cabinet designs by Harbeth

BBC-style thin-wall cabinets. Why so special?

I have always found the lossy design to be interesting and decided to do some digging today as I haven't had much going on at work.

This thread is very interesting and I thought I would share it here.

It talks about how you can "tune" a thinner walled lossy box but not the standard thick walled boxes.
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Old 8th November 2012, 10:00 PM   #2
VaNarn is offline VaNarn  Australia
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Thanks to Martin Rubinstein for providing readable copies, another reference for thin walled cabinets can be found in the Full Range Forum " Rex Baldocks' Paraline Speakers " Post#24. The Leak Sandwich speaker system designed by D.A. Barlow is possibly the first commercial speaker to utilise 3/8" plywood construction with the addition of bitumen loaded felt pads.
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Old 8th November 2012, 10:13 PM   #3
ORNJ is offline ORNJ  United States
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Hey thanks for that, I just emailed my self that webpage for a later read.
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Old 9th November 2012, 02:36 AM   #4
system7 is offline system7  United Kingdom
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Good article. Since we are ENTHUSIASTS, ORNJ, I'll tell you what I know on this plywood cabinet idea, before you are led astray by the pointless waffle on cabinets that abounds here at diyaudio. Frankly, the advice here on cabinets is CONFUSED to say the least. I had to figure it out for myself in the end. I like to share, because we gotta be getting on with things really. No time to waste.

Troels Gravesen is of the opinion that a good solid braced MDF cabinet is as good as a hard birch plywood/beech battened one. He uses both, although it should be noted that MDF and chipboard are both little better than thick cardboard acoustically.

Click the image to open in full size.

Spendor and Harbeth both advocate rigid, light and strong 12mm plywood cabinets, preferably in 0.618:1:1.618 golden ratio. Beech Battening is to help construction mainly, and panels can be removable. Doesn't matter much whether it's reflex or closed box. The damping idea is to stick something rubbery (like carpet underlay) on the smaller sides and top and bottom, but strangely, not the front and back. You can mix MDF and ply, the more rigid ply is used on back and front. Add a little bit of fluff behind the woofer to limit box resonances, but no need to overdo it.

If you use a narrow front baffle and a deep box, the big resonant sidepanels can be braced with the same material as in this Dayton example. That's it really. Usual images enclosed to clarify. Not rocket science. Sorted, I'd say.
Attached Images
File Type: jpg BBC_LS3_5A_Cabinet.JPG (24.6 KB, 1397 views)
File Type: jpg Falcon_Acoustics_BBC_LS3-5A_Kit.JPG (60.9 KB, 1369 views)
File Type: jpg BBC_Ls3-5A_Cabinet.JPG (73.0 KB, 1354 views)
File Type: jpg Harbeth_HL_P3_Outer.JPG (40.6 KB, 1343 views)
File Type: jpg Harbeth_Small_Monitor.JPG (67.0 KB, 402 views)
File Type: jpg Regupol_Acoustic_Floor_Underlay.JPG (70.5 KB, 411 views)
File Type: jpg Floor_Underlay_Loudspeaker.jpg (96.2 KB, 244 views)
File Type: jpg Dayton_Audio_TW-0.25BK.JPG (14.7 KB, 322 views)
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Well, there it is! Best regards from Steve in Portsmouth, UK.
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Old 9th November 2012, 01:09 PM   #5
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Very interesting stuff here guys.

Here's my thread about improving the cabs on some plastic PA speakers. Thinking of some sort of damping like deflex and or damping paint, with one large brace side to side.

Plastic speaker cabinets - improving internal bracing & damping

I'm also doing a pair of 15" subs in 1/2" ply cabs, which will see internal damping paint. They have large braces:

Ultra compact ported 15" Dayton Ref HO
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Old 9th November 2012, 05:55 PM   #6
ORNJ is offline ORNJ  United States
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Well I thought that if a driver had a Qes that was less than 1 that Lossy cabinets have no use. However, I am starting to think otherwise based on what I have read because a soundwave from any driver is going to be the exact same length no matter what driver makes it and what the T/S parameters are.

So I would really like to see some experiments of a single mid or mid/bass drivers in heavily braced cab and a lossy cab of the same internal deminsions and see how they compare.
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Old 9th November 2012, 06:18 PM   #7
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The only lossy cabinets I'm aware of, are, except mines , the Pearl evo
6moons audio reviews: PearlEvo Ballerina 301-8"
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Old 9th November 2012, 06:20 PM   #8
tinitus is offline tinitus  Europe
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I prefer this 'method'
this one was a small closed box for 15"
but basicly you can do it on all inner surfaces
if there is room enough
Attached Images
File Type: jpg IMG_5927.JPG (94.9 KB, 504 views)
File Type: jpg IMG_5985.JPG (141.5 KB, 412 views)
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Old 9th November 2012, 07:41 PM   #9
ORNJ is offline ORNJ  United States
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Quote:
Originally Posted by system7 View Post
Good article. Since we are ENTHUSIASTS, ORNJ, I'll tell you what I know on this plywood cabinet idea, before you are led astray by the pointless waffle on cabinets that abounds here at diyaudio. Frankly, the advice here on cabinets is CONFUSED to say the least. I had to figure it out for myself in the end. I like to share, because we gotta be getting on with things really. No time to waste.

Troels Gravesen is of the opinion that a good solid braced MDF cabinet is as good as a hard birch plywood/beech battened one. He uses both, although it should be noted that MDF and chipboard are both little better than thick cardboard acoustically.

Click the image to open in full size.

Spendor and Harbeth both advocate rigid, light and strong 12mm plywood cabinets, preferably in 0.618:1:1.618 golden ratio. Beech Battening is to help construction mainly, and panels can be removable. Doesn't matter much whether it's reflex or closed box. The damping idea is to stick something rubbery (like carpet underlay) on the smaller sides and top and bottom, but strangely, not the front and back. You can mix MDF and ply, the more rigid ply is used on back and front. Add a little bit of fluff behind the woofer to limit box resonances, but no need to overdo it.

If you use a narrow front baffle and a deep box, the big resonant sidepanels can be braced with the same material as in this Dayton example. That's it really. Usual images enclosed to clarify. Not rocket science. Sorted, I'd say.
That guy has a TON of build logs!

I like that he has also done some Garrard and Lenco restorations as well. I wish I could get ahold of a Lenco but they are hard to find in the States.
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Old 10th November 2012, 12:03 AM   #10
system7 is offline system7  United Kingdom
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It's very enjoyable to read the musings of someone like Alan Shaw of Harbeth. Let's have a look inside a BBC based similar small Spendor Cabinet:

Click the image to open in full size.

Looks about right. Let's not kid ourselves that birch ply is floppy stuff. It's actually as tough and rigid as you like. Bentwood chairs made of it are incredibly strong for such thin stuff. The idea is to reduce energy storage by keeping things light. An idea that Joachim Gerhard goes along with. I was incredibly impressed with the side damping I applied to a decent little Mordaunt Short closed box cabinet. It gave an openess to the sound that a heap of wadding kills stone dead. Gives you reflex open sound in closed box.

I also was given some cheap IKEA kitchen cabinet door closer dampers (2!), which work very well as loudspeaker corner mounts. We assume you have taken care of any harshness on the drivers here with suitable crossover design, because a heap of wadding ain't gonna help.

I always like Tinitus' ideas on cabinets too. He's tackling cabinet and box resonance in one fell swoop. It's a good idea to affix wadding to something solid. Turns energy into heat.
Attached Images
File Type: jpg Spendor_Cabinet.JPG (38.4 KB, 117 views)
File Type: jpg Mordaunt_Short_MS15_Parts.JPG (40.9 KB, 200 views)
File Type: jpg Floor_Underlay_Loudspeaker.jpg (96.2 KB, 205 views)
File Type: jpg Mordaunt_Short_MS15_Wadding_and_Damping.jpg (88.2 KB, 164 views)
File Type: jpg IKEA_Kitchen_Cabinet_Door_Dampers.jpg (62.9 KB, 249 views)
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Well, there it is! Best regards from Steve in Portsmouth, UK.
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