It gets the job done...
And much simpler than your matrix. Witch I'm not at all convinced works. I haven't seen any measurements of this method. Can you provide them?
Look at speaker measurements on Stereophile. I'm sure there's more than one example on there that uses that method. The BBC approach was for their specific model speaker. I wouldn't want to create a floor standing speaker that way.
Hi system7,
i really cannot follow that, being an experienced "BR-stuffer" so to say ...
There may be "critical zones" to be left free from stuffing material - e.g. around the inner port - but away from those a BR-cabinet can be filled rather "tightly" without having Qb too low.
You surely need come "helpers" like nets, hooks and spacers to keep the material in place. So "stuffing" BR cabinets may be a bit more elaborate and "tricky" and may also call for different materials here and there. But it is no problem at all to cut down standing waves at their velocity maxima in BR cabinets in a similar way you do it in closed boxes.
Kind Regards
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I'm not entirely convinced that building a speaker cabinet with effective constrained layer damping is exactly a trivial exercise either.
The BBC method would be pretty straightforward to utilise although there is always the question of what bitumastic damping material one should use. QTA Systems, Falcon & Wilmslow all offer options and car ICE suppliers should be able to help. Perhaps damp proof membrane would also work?
There is an interesting discussion of constrained layer damping (CLD) HERE.
@ wesayso:
- How is anyone going to figure out how the panels are moving from those measurements? The impedance curve only gives very subtle hints.
- A floor stander would be easier, because (at least some of) the resonances are lower in frequency.
@ surv1v0r:
- Very interesting link!
- I have 4mm bitumen that works great. Got it from a car customizing shop.
You can use both sides of the wood to put damping material on it.
Would be great if someone did some tests on panel damping with all mentioned methods and see what works best.
- How is anyone going to figure out how the panels are moving from those measurements? The impedance curve only gives very subtle hints.
- A floor stander would be easier, because (at least some of) the resonances are lower in frequency.
@ surv1v0r:
- Very interesting link!
- I have 4mm bitumen that works great. Got it from a car customizing shop.
You can use both sides of the wood to put damping material on it.
Would be great if someone did some tests on panel damping with all mentioned methods and see what works best.
For every speaker they measure they provide tests what the cabinet is doing. Never seen that?
I wouldn't want a floorstander that goes "flob flob" 😀.
I wouldn't want a floorstander that goes "flob flob" 😀.
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CLD damping sounds interesting, but that's a lot of work for something like a pensil or any other larger cabinet. Still, it might be interesting to experiment on a smaller bookshelf or stand mount.
Let's say you were working with two sheets of 1/4" plywood, what kind of material would you typically sandwich between the two outside layers of ply (for a 1/2" - 3/4" wall)?
Let's say you were working with two sheets of 1/4" plywood, what kind of material would you typically sandwich between the two outside layers of ply (for a 1/2" - 3/4" wall)?
A heavy rubber like Mass Loaded Vinyl would probably help glued together with a neoprene based glue. It would work even better with 2 different materials. One ply layer and the other material could be either something more rigid or something less stiff than the ply.
I used mass loaded vinyl between 2 layers of aluminium as a baffle construction. I also believe in decoupling driver and baffle.
Here are a couple of examples: http://www.zelfbouwaudio.nl/index.php?option=com_content&task=view&id=18&Itemid=2
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Building a cabinet is obviously a VERY COMPLEX BUSINESS! 😀
It's amazing that they work at all, to listen to this debate. What the BBC found was that if you get colouration below a certain level, it is inaudible. That's it. End of story.
http://www.diyaudio.com/forums/multi-way/223174-interesting-read-i-found-lossy-cabinet-designs-harbeth.html#post3234256
I probably sound like I'm picking holes here, but wesayso's bass brace looks like genius. Except it isn't. It's awful. It's gonna sound like a plunky xylophone at a certain exciting frequency. It's just putting a wooden batten on the front panel. What you do with the BBC approach is build a light rigid box. Then add a thick layer of rubbery damping material glued to the side and top and bottom sidepanels. Every time the vibration travels round the box, it gets damped. As good as it gets.
Overly heavy and braced and rigid front panels just excite bass chassis resonance. The whole thing is counter-intuitive. But you know when you've got it right. 😎
It's amazing that they work at all, to listen to this debate. What the BBC found was that if you get colouration below a certain level, it is inaudible. That's it. End of story.
http://www.diyaudio.com/forums/multi-way/223174-interesting-read-i-found-lossy-cabinet-designs-harbeth.html#post3234256
I probably sound like I'm picking holes here, but wesayso's bass brace looks like genius. Except it isn't. It's awful. It's gonna sound like a plunky xylophone at a certain exciting frequency. It's just putting a wooden batten on the front panel. What you do with the BBC approach is build a light rigid box. Then add a thick layer of rubbery damping material glued to the side and top and bottom sidepanels. Every time the vibration travels round the box, it gets damped. As good as it gets.
Overly heavy and braced and rigid front panels just excite bass chassis resonance. The whole thing is counter-intuitive. But you know when you've got it right. 😎
The BBC design uses a frame with usually removable front and back panels. The design to a fair extent decouples the panels from each other and prevents vibration travelling around the box in the manner of a simpler more conventional construction. The chap from Harbeth described it as like putting a crack in a bell but he has does have some speakers to sell you that are constructed in this manner.
I don't know if I believe the cracked bell theory.
But for sure, what happens with old glued cabinets, is the PVA wood glue cracks and works loose. You will see this on old Celestion speakers.
So a certain amount of battening (or beech fillets as the BBC called them) round the edges is a good thing IMO. Screwed or glued, I don't know.
But for sure, what happens with old glued cabinets, is the PVA wood glue cracks and works loose. You will see this on old Celestion speakers.
So a certain amount of battening (or beech fillets as the BBC called them) round the edges is a good thing IMO. Screwed or glued, I don't know.
Hi from the last posts it seems that only BBC and Harbeth have found the way
Personally i prefer the B&W Matrix design with extensive bracing
I liked the 801 a lot ... maybe the drivers were debatable, but not the cabinet.
Regards, gino
Personally i prefer the B&W Matrix design with extensive bracing
I liked the 801 a lot ... maybe the drivers were debatable, but not the cabinet.
Regards, gino
Did the BBC LS3/5a have a removable back panel, I was under the impression that it was fixed?
The setup shown in the picture from wesayso's link is not a brace as such. It is a test enclosure constructed from mdf/concrete with on which you can mount a test panel. The results shown give waterfall plots for the transmission of sound by various panel materials.
The brace across the driver was used in some of the tests to see the effect on panel resonance of bracing the centre of the test panel
Lol, as was said earlier, that link provided some samples of CLD damping with tests. That brace has nothing to do with the subject on hand.
Steen Duelund wrote in his paper about the approach of Bowers & Wilkins matrix brace, but suggested to make the brace a damper by using the right glue.
The test I linked showed that sandwiches of different materials worked best to lower resonances and ringing. Surprisingly bracing also worked well in that test. At least when there was also some glass fibre damping involved.
The BBC paper was just that, aimed at that particular speaker and not the end all for all other type of speakers. But due to it's good documentation it gets cited over and over while there are many more working solutions.
Low frequencies: stiffness is your friend. Mid and higher frequencies: damping is your friend 🙂.
Hi i think that the real challenge is lowest frequency vibrations control, clearly.
Mid and high freq vibrations are very low in energy and just some good damping sheetd can work nicely.
I am sure the way is a rigid cabinet and even a "brace as such" improves things, because increases the overall cabinet stiffness.
Just look at the best sub out there ... they have unbelievably rigid cabinets.
The Krell sub, maybe one of the best in the world, has a thick and extremely rigid metal cabinet and it is said to have one of the best bass around.
Of course a speaker like the ls3/5a has no bass to speak of so the cabinet can be almost everything.
Even a rubber ring between the woofer and the cabinet is a bad thing ... it dissipates energy. A waste of energy.
Regards, gino
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I believe some have removable backs and some do not. As far as the mechanical construction is concerned I suspect it makes little difference because a "fixed" rear panel still sits inside the side and top panels and is attached to the frame. It is still essentially "cracked".
The extensive bracing approach that some people here are eschewing is two fold. First, it adds stiffness. This reduces large panel resonances and turns them into small panel resonances. Indeed, these panel resonances would occur at higher frequencies. Secondly, it adds a large amount of mass. No one yet has mentioned mass in lieu of damping. When you create a system which consists simultaneously of high mass and high stiffness, you would in fact get a similar resonant frequency as one with low mass and low stiffness.
The difference which everyone is neglecting is the amount of force or energy required to excite the highly massive system/speaker. The drivers in a massive, extensively braced speaker are less likely to be able to excite the high panel resonances due to its stiffness because of the cabinet's inherent mass. The addition of damping material is then to remove the low level excitations that are created internally. Damping material does not get used to stop outward cabinet vibration. The difference between damping and mass loading needs to be stated clearly. They are not the same thing. If said mass loading materials have good internal damping, then so be it.
For you car guys, it's like this. Dynamat is a mass loading material, not a damping material. It stops panel vibrations in this way. It does have damping, yes, but that's not the point. Mass is king. Those who have used Dynamat will also note that road noise, particularly rain, is largely unaffected if your car is built properly. That is when you employ damping material. For normal driving use, damping wins because there is nothing in the car to really excite the large panels so you need to absorb the gunk transmitted via the outside. For car audio enthusiasts, mass wins because the noise is then from the panel itself. For the best, you use both, much like high end loudspeaker companies do.
The difference which everyone is neglecting is the amount of force or energy required to excite the highly massive system/speaker. The drivers in a massive, extensively braced speaker are less likely to be able to excite the high panel resonances due to its stiffness because of the cabinet's inherent mass. The addition of damping material is then to remove the low level excitations that are created internally. Damping material does not get used to stop outward cabinet vibration. The difference between damping and mass loading needs to be stated clearly. They are not the same thing. If said mass loading materials have good internal damping, then so be it.
For you car guys, it's like this. Dynamat is a mass loading material, not a damping material. It stops panel vibrations in this way. It does have damping, yes, but that's not the point. Mass is king. Those who have used Dynamat will also note that road noise, particularly rain, is largely unaffected if your car is built properly. That is when you employ damping material. For normal driving use, damping wins because there is nothing in the car to really excite the large panels so you need to absorb the gunk transmitted via the outside. For car audio enthusiasts, mass wins because the noise is then from the panel itself. For the best, you use both, much like high end loudspeaker companies do.
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