That, i would say, is a BAD idea. BBC philosophy has one pushing the box wall resonances down in frequency.
In a subwoofer it is really easy to completely eliminate potential box wall resonances by pushing the potential resonances well above the bandwidth of the speaker. BBX moves it right into the bandwidth and almost guarantees your box will resonate.
A push-push subwoofer built of quality well-braced 15mm plywood does a quite sufficient job. Push-push active reaction force cancelation dramatically reducing boxwall-load.
dave
Perhaps 100 Hz up (what the research paper shows) but with a sub you are dropping the resonances down right into the bandwidth of the sub… not good. The BBC method in a sub will not work well.
I see GM beat me to the puch with the reasoning.
dave
Dave, You got me wrong , I can see it wasn't clear. This whole BBC part relates to the 2 way speaker, I'm not crazy to build a sub with panel resonances below 25 or 20 Hz 🙂 I planned to use double the wall thickness of the 2 way speaker (so 14-16 mm plywood) and brace it, subs are pretty straightforward.
My problem is with the 2 way speaker, which will have to handle some 130 Hz+ notes (bass reflex port will take over below and fill the gap to sunwoofer xo at around 80 Hz). In theory going thinner (7 mm instead of 8 mm used in commercial thin-panel 2 ways) should give me more chance to push the resonance below speaker's passband but I have seen no reasearch or instructions as to how thin I can go, just general rules of thumb. I do plan to use a lot of damping (8mm alubutyl) so perhaps this will dominate over panel thickness with regard to total sound signature.
My problem is with the 2 way speaker, which will have to handle some 130 Hz+ notes (bass reflex port will take over below and fill the gap to sunwoofer xo at around 80 Hz). In theory going thinner (7 mm instead of 8 mm used in commercial thin-panel 2 ways) should give me more chance to push the resonance below speaker's passband but I have seen no reasearch or instructions as to how thin I can go, just general rules of thumb. I do plan to use a lot of damping (8mm alubutyl) so perhaps this will dominate over panel thickness with regard to total sound signature.
Yes, cork must be good. But not only a single layer of cork, mix it with rubber like its been done with the turntable mats. And because it won't be complex enough, put a layer of rockwool in between, too. And a layer of bitumen on the inside. Above a layer of rubber again. And last, but not least, a wool layer of damping on the inside, combined with a scottish kilt layer, double woofen.
Get an idea why this is all bollocks, and never someone else than BBC has done it?
The concept is the usual way of dampening and controlling something totally. Why not use concrete for a speaker cabinet? Even that Ive seen. Not with the BBC, but its there. You only just digg deep enough and you'll find it.
Get an idea why this is all bollocks, and never someone else than BBC has done it?
The concept is the usual way of dampening and controlling something totally. Why not use concrete for a speaker cabinet? Even that Ive seen. Not with the BBC, but its there. You only just digg deep enough and you'll find it.
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Harpeth, Spendor and Stirling. And people are still copying the BBC Ls35a. How thick can you get mass loaded vinyl? 1/2" and you wouldn't need a frame ( possibly ).
For subwoofers You don't want damping, You want stiffness, to push panel resonances above sub's lowpass filter. That way they are not excited.
What You propose is a constrained layer damping, a different but also effective approach, though from what I've read on the subject not easy to achieve. You need two layers of significantly different stiffness and a lossy layer in between. Thats why You have a layer of aluminium on alubutyl mats.
...and just to add a few more to the list of companies that build or have built loudspeakers with damped thin-wall construction, you can count: Falcon, Rodgers, KEF, Graham Audio, Goodmans...
To provide some historical fact rather than opinion, the BBC R&D department did not in fact produce very many of their own designs at all, prototypes aside. They did not have production facilities -that is not what their job was. Production of BBC designs was in fact primarily handled by external companies who applied for a license, and could achieve the specified tolerances. Many of those companies (and others who did not, or have not produce[d] any of the BBC's own designs) went on to manufacture and retail products of their own, using the same or similar basic approaches. This is not open for debate or argument: as noted it is simply a matter of historical fact. So I'm afraid any claims to the contrary are incorrect.
To provide some historical fact rather than opinion, the BBC R&D department did not in fact produce very many of their own designs at all, prototypes aside. They did not have production facilities -that is not what their job was. Production of BBC designs was in fact primarily handled by external companies who applied for a license, and could achieve the specified tolerances. Many of those companies (and others who did not, or have not produce[d] any of the BBC's own designs) went on to manufacture and retail products of their own, using the same or similar basic approaches. This is not open for debate or argument: as noted it is simply a matter of historical fact. So I'm afraid any claims to the contrary are incorrect.
Re mass-loaded vinyl, you can get it up to about 1/4in - 8mm thicknesses, although 2mm - 4mm tend to be more commonly available. Depends on what density you want too of course.
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Obviously, there are tens of thousands companies who have produced speakers in the long history of speaker designs. You'll find everything, from concrete cabinets to any exotic materials. Its very easy to build a speaker, thats the reason why so many companies do it.
And there were hundreds of companies that produce and have produced musical instruments. But only a fraction of them made it to the top. All others are middle class or way below.
There are hundreds of companies that produce cars, but only one Rolls Royce.
Life is way too short to re-assemble ill fated speaker designs, that nobody seem glorious, expect five companies.
I'm not wasting time on those, just doing the best whats possible.
And on those famous designs, nobody did it that way.
Thats enough of an argument that the whole thing is a bad idea. Even when it was developed by BBC. But who are they in the world of speaker designs? Problem is, most people have no clue what was developed in audio history and what makes a good design count.
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Yeah, Harbeth and KEF and the others mentioned produce really awful speakers, totally "middle class or below" 🙂 Complete waste of time, obviously!
Though there seem to be many people who fall for those designs, must be marketing prowess surely.
Though there seem to be many people who fall for those designs, must be marketing prowess surely.
Why would one go for deliberatly thin cabinet walls and then stiffen it up with bracing and damp the vibration with damping material??
The only reason I could see is to save some weight in mobile applications or maybe in a communist economy where labour is cheaper than materials. If extra bracing and damping doesn't come cheaper than thicker walls we are left with weight savings for mobile applications.
Or weight savings to make the ship transport in the container from China to somewhere else cheaper.
You obviously only listen to wax rolls and 78 rpm mono records with a cactus needle I presume?
Schmitz, You have already stated Your opinion as to why thin wall + damping approach would not make an outstanding design, and what is more You know from experience. What is, then, the approach of Your choice? How would be build a 2 way speaker to cover the range above 100hz? I know that going two way is a compromise in itself but lets stay on that and see what are the most successful box design approaches, if not thin wall + damping.
Speakers have conflicting design goals; they should be both stiff and heavy to give something to anchor the drivers to, but also none resonant. Perhaps a Remlab sandwich baffle on an epoxy/granite or epoxy/slate box.
I'll be honest and say I don't know, I can only presume heaver the better. I think Eclipse used something like 7kg ( this is a guess, it's a long time since I read the review ) mounted on the back of the ( 5" I think ) driver.
