Bwaslo: That's an interesting option. I suppose it could be combined with mine as well. In retrospect, it might be worth building a properly braced cabinet, and also use the techniques discussed in this thread to further improve it. It seems that is what KEF did, as traditional methods appear to be lacking I effectiveness. When I embarked on refreshing the Tangent 500s, I considered a full cladding of the cabinet with another layer of 3/4 plywood, and internal bracing. It seemed like far too much effort and work. That was a large part of the impetus for my bracing method.
That's a shock absorberIf you're after damping (rather than bracing/stiffening), another option is to use two boards in parallel planes with damping material between. The shear force should transfer energy to more damping material that way*.
*(idea stolen from Earl Geddes)
I like it What sort of damping material would be used between the sheets? Wouldn't it need to be well attached to both sheets? Unless the sheets don't need to be under tension with respect to the cabinet sides? Couldn't you attach a sheet to the interior of each panel, have them overlap in the middle, and use some sort of caulking between the sheets? Or make up the entire brace assembly and then push it in, perhaps squeezing the sides slightly?
When I put the braces into the Tangents I attempted to do a mirror image of braces in the two cabs. The rectangles of plywood were different sizes but in matching pairs. The sponge was cut and applied unevenly to the plywood. Once installed, even if the stick is centred in the middle of each the opposing boards, the boards vary in distance from the cabinet panel. I suppose you could use an even layer of foam, center the stick, and have it be level and apply even pressure all across the plywood. I didn't do it that way. I thought it made more sense to have the foam push unevenly against the cabinet sides. With the existing set of plywood rectangles with foam glued on to them, and the sticks, there are many different ways you can treat a speaker by swapping foam covered plywood pieces around to place them in different parts of the interior panels. In practice, I used longer pieces on the side panels, I did the first of the pair with four sticks and eight panels, on the second I used four sticks and six panels. The longer side panels used two sticks per panel. In some respects, having the two speakers be entirely different may be a good thing. I went for symmetry, but ended up with an approximation of it.
Subjectively, the speakers sound better with the braces. Again, I compare it with a pair of Heresy II speakers as my reference. I still prefer the Heresy II to the Tangents, but I use the Tangents sometimes for more bass heavy music. Before the braces, I hardly ever bothered with the Tangents. They sound better than before. To be honest, it's very difficult to remember specifically what it was that I didnt like about the Tangents. I like them now.
Subjectively, the speakers sound better with the braces. Again, I compare it with a pair of Heresy II speakers as my reference. I still prefer the Heresy II to the Tangents, but I use the Tangents sometimes for more bass heavy music. Before the braces, I hardly ever bothered with the Tangents. They sound better than before. To be honest, it's very difficult to remember specifically what it was that I didnt like about the Tangents. I like them now.
'damping bacing' with shear damping material has been reinvented several times, long enough ago that that any current patent would be invalidated by 'piror art'
Patent US7270215 - Loudspeaker enclosure with damping material laminated within internal ... - Google Patents is recent but notice the fee staus is marked 'lapsed' so the patent isn't enforcable
Patent US7270215 - Loudspeaker enclosure with damping material laminated within internal ... - Google Patents is recent but notice the fee staus is marked 'lapsed' so the patent isn't enforcable
I think Geddes uses some sort of adhesive made for CLD (Constrained Layer Damping). I think Melamine Glue works for that purpose.
Titebond Melamine Glue, 16 Ounces - Cyanoacrylate Adhesives - Amazon.com
Titebond Melamine Glue, 16 Ounces - Cyanoacrylate Adhesives - Amazon.com
I had a look at the patent. Very interesting. When I first thought up my damping brace, the inspiration was actually what happened when I firmly pressed my hand, palm down, on a vibrating cabinet panel. The vibration stops. The sponge on ply is like a big hand, that never gets tired, pressing on the cabinet. I don't think my method increases the rigidity of the cabinet much. The patent would appear to increase the rigidity of the cabinet more, but not in a way that transmits vibration from one panel to another like a regular wooden brace.
This idea is what I have been doing for years except that my "stick" is damped along its length such that vibrations along the stick shear the adhesive layer thus providing a strong damping. My cross-brace goes in two directions and takes eight pieces to construct and has to be molded in a form. It's a very complex part.
I tried melamine glue and it was not so good. I use a two part polyurethane with a filler. That stuff is exceedingly well damped.
No, but I have been doing it for a long time so it might be considered "prior art". I'm not really in the patent business anymore so I don't know the details.
Earl. Yours is an elegant solution. Mine is not elegant in the least, but it is easy to experiment with. It's also something you can easily put into an existing speaker that has issues with panel vibration. There are a lot of commercial speakers with poor cabinets. If I was building from scratch I would definitely consider using something like your design. It would appear to take up minimal cabinet volume as well. With respect to patents, I do this diy audio thing strictly as a hobby. I have never made a cent on it, and likely never will. It has in fact only ever cost me money, as my dear wife often reminds me.
Earl - I guess I'm too lazy / incompetent in my forum search skills, but unless it gives away any trade-craft, this should be an easy answer for you - are you saying your cross bracing members are overlapping struts joined with a moderately elastomeric adhesive - such as Sikabond, etc, -or need it be more rigid than that? I've long employed a different approach -bracing panels rigidly connecting at least three panels and nesting to the driver motor assembly, and while there may not be that many new builds in future, I'd be curious to try something like that.
I cross brace to four panels with overlapping struts bonded with my poly mixture. The panels are front to back and side to side. The two crossing cross braces are connected together in the center. This creates a fixed point in the center through which the struts actuate (force/shear) against. This creates maximum shear in the viscous layers.
I would not want to connect anything to a woofer magnet as they need to be replaceable (although none have ever actually failed.)
I would not want to connect anything to a woofer magnet as they need to be replaceable (although none have ever actually failed.)
Not sure that I understand why you would cradle the magnet. The main problem vibration mode is longitudinal along the speakers axis. A cradle won't do much but help support the magnets weight, which really isn't a problem. A wedge would work between the magnet back and the back panel, but then that seals the vent hole AND couple the motors vibration to the back panel, the biggest radiation offender.
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