posted
So you want an advanced topic, eh?? I'll try...
Anyone experiment with extreme cabinet damping or isolation? I'm planning on using sand-loaded walls in the enclosure on my new system as well as an acoustic foam lining. Additonally, all construction will be with Noisekiller yellow.
I've been perusing some European sites for homeaudio and those guys go off! Some of the cabinet reinforcing arrays would make B&W jealous, and sand loading seems common. Comments on extreme bracing?
Also, what about isolation. I teter on 2 camps. One camp says bolt the cabinet in securely so it grabs the car hard on low transients. The other camp stems from home audio and spiking cabinets to make them sound tighter. I was thinking of a spike set up, possibly with tensioned aircraft cable to keep it from moving in an accident.
I also entertained an idea of a 'liquid isolated' enclosure that would rest on a 'bag' filled with oil or other suitable fluid to decouple it from the chassis.. Again, restraints would be necessary.
------------------
And that's the bottom line, cuz: LORD DUKK SAYS SO!
The Big Show The Dukk says: Know your bass: PORT your damn box!! Have HoleSaw, Will Travel!
posted
Dr. Floyd E. Toole (National Research Council) tried sand, didn't work effectively, the sand eventually setteled, and became solid, transmitting vibrations to the cabinet walls. Hand carted (fluffed) sheeps wool remains as best choice, but in a pinch...yellow or Dakron (tm) will do. Take the B&W Matrix design as an example of cabinet bracing, and their 300 series Prism System, and youv'e got some engineering feat in cabinetry that would have very interesting results I would think. As for spiking, I would suggest welding lag bolts to the chassis/frame and mounting the cabinet on four points to the car.
------------------ E.C. Wuz here
[This message has been edited by Eli47 (edited 12-22-1999).]
Posts: 1057 | From: Vancouver, British Columbia, Canada 'eh | Registered: May 1999
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posted
I'm with the bolt to the chassis group. I think spiking subs in a home environment works wonderfully, however, just isn't practical in a car. Eli's suggestion of the lag bolts is a good idea, however, your pretty much securing it to the car that way. I know of a guy who did some experiments with lining the walls with plaster of paris and then acoustic foam on top of that, the walls all got about 1.5" of the plaster, and then the foam over the top. He claimed it helped quite a bit, however, I was never able to detect a big difference in SQ between his Oz 250L's in that box, and my box which was 3/4" oak plywood and simple bracing... By the way, both were bolted to the car. I did notice some differences in lower register tightness, however.
------------------ STILL waiting to hear a GOOD pair of HLCD's!!
If it dont fit, force it... if it breaks, it needed to be replaced anyway...
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They question i have above box damping is what is some of the ways you all have sandwiched sheets of MDF together? and what was the strongest and most Damping for the time and money involved. Also what are some of the best thincknesses and with it being how think do you need to limit the inside bracing?
Posts: 804 | From: olathe, ks | Registered: Jun 1999
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posted
What about silcone mixed with sand,or just silcone between the wood? I know it would be really messy to do but might work rather well.
Posts: 7865 | From: Charlotte,NC USA | Registered: May 1999
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That sounds like a good idea Winslow (sand and silicon). I have never bolted my enclosures down. I just bolted the seat belts to them. hehe. so I take it that bolting them down helps on the transients. My problem is the gas tanks are right below the wall. question- has anyone ever built a midbass enclosure out of 3/16 aluminum? I plan on useing it and then coating the inside with rubber or that spray undercoating and cotton. and then maybe glueing carpet to the outside with a rubber glue. I,m woried about that aluminum colouring the sound.
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Posts: 1259 | From: Fullerton. CA ,USA | Registered: Oct 1999
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posted
I like the idea of making the cabinet one with the car. Seems to help (as mentioned) in the lower register (which I am quite partial to) but at the same time seems to introduce more pronounced rattles in the vehicle. As far as damping, I generally use, glue on all enclosure joints (as you normally would), silicone around the edges, and generally over brace things so I hear absoulutely no hollow sound when you tap on any surface of the box. Braces are placed in a completely random pattern. I usually calculate a number of extra internal braces (same dimensions as the end caps for easy calculation) into the box and cut them up to randomly shaped pieces for wherever they are needed. Then I spray rubberized undercoating (the rough surface on the rocker panels of some cars) which leaves the surface rough and completely sealed (unless, of course, it's ported). As far as stuffing, I leave that up to my ears. Some sound better stuffed (usually dacron, or pillow stuffing), some sound better with nothing.
Posts: 490 | From: Fort Frances, Ontario, Canada | Registered: May 1999
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posted
the VERY BEST way to damp the cabinet is to use sheets of double stick adhisive provided with RC recievers. The sheets area 1/2" gell that doesnt compress and is designed to reduce vibration, sandwich that between two sheets of 3/4" hdf and you have one solid box. It may not be the chwapest way to do it, but who cares about money anyway
Posts: 335 | From: utah | Registered: Sep 1999
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posted
The most cost effective way to effectively reduce/eliminate cabinet resonance is, to use diffrent thicknesses of material, preferably particle board (K3-or MDF). The idea being that each thickness or type of material will have it's own resonant frequency, using different material for the front/side baffle will not allow the cabinet to resonate. Try it it works. As for silicone, it's popular, but not as good as glue, or putty. Since silicone is an oil base, the wood will absorb the oil, and the silicone will shrink in time, and lose it's grip. The Sand idea was prefected into the Prism concept by B&W, the idea being an uneven surface for internal diffraction. Spray glueing the internal walls and then lightly dusting them with sand will achieve results as well. but hardly discernable I would think. The best remains to round off all internal corners and edges, brace the sub woofer if it's not die cast, and brace the walls of the cabinet.
------------------ E.C. Wuz here
Posts: 1057 | From: Vancouver, British Columbia, Canada 'eh | Registered: May 1999
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posted
I agree that cabinet damping is a requirement, unless one wants that really 'woody' sound, in which case try building the cabinet using panels which have equal length and width, heck, just build a cube, but use only silicone rubber, no glue , and try to get a uniform 1/8 inch or so thickness on all joints. This should allow all box panels to resonate at the same frequency.If you do some homework, you should be able to get the frequency to correspond with the woofer's resonant peak, thus ensuring a high spl at that point. Note that this box can have no covering, except stain or paint. And it will have to be mounted using only the corners for support. Of course, it will need to be raised up from the floor as well. I can't vouch for it's performance, but I find it interesting that the box itself can be used thusly. Anybody done any work on this ? I'm not talking about the first box you or I ever built, as they might have responded with some extra enthusiasm unintentially due to poor construction, thin materials, etc. Seriously though, cabinet resonance is generally to be avoided.One factor I have been experimenting with, at least in my head, is pretensioning the sides via a slight bending of the sides. The resultant cabinet would then be slightly ovoid. The pretensioning would tend to raise the resonant frequency of the sides,making further damping easier to do, as well as strengthening the structure. I am assuming here that the glue used is up to the task of holding the thing together, and that the constructor is able and willing to make four of the six sides with slightly curved edges.You must be awfully good with a jigsaw or be able to cobble up a jig to make these cuts on a tablesaw.Any comments? I'll just go and lose myself in a dark corner now and contemplate why I spent years learning how to make straight cuts! Posts: 7 | From: Chilliwack | Registered: Nov 1999
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posted
On the subject of bracing, it is important to do this, and to do it in a manner that will dampen as much vibration as possible, not create higher frequencies out of lower ones. Avoid putting a brace in the center of a panel, as that will divide the panel into equal sized smaller areas, that will then resonate in unison. Measure the points to affix the bracing to via some formula, such as 0.7 to 1. So if the length of a side is 10 inches, pick a point about 7 inches from one edge to glue a brace to. You will be putting braces at 90 degrees so glue them together where they cross. If we think in terms of one brace side to side, one top to bottom, and one end to end, the last end will be not a panel but the magnet. Chances are this brace won't be able to center on the magnet, but that's ok. Just make sure to affix it solidly to the magnet. It won't be easy to get a length for this last brace, since the vagaries of mounting the speaker will get in the way, but it can be done. The resultant box will be as anti-resonant as reasonably possible, and very sturdy. Now add further damping, stuffing, covering, whatever. Because this bracing is either in tension or compression, it need not have much meat to it,since it won't stretch or compress much. Just have enough area at the ends to form a solid glue joint.Keeping the actual volume of the bracing down will help keep the size of the box down. Posts: 7 | From: Chilliwack | Registered: Nov 1999
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If you made the box, then mounted it inside another enclosure by means of pieces of mdf coated with high-pressure rubber, the rubber under tension might allow some damping yet still a stiff hold on the inner box...
ShadowStar
Posts: 2578 | From: Somewhere In the Northeast | Registered: May 1999
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posted
Would a foam fiberglass and wood enclosure need much damping? I was thinking of making a wood box, lining it with the blue house foam insulation, then covering the inside with fiberglass. This is very similar to simple aircraft construction. It is also very lightweight. Since there is mainly air in the foam, it shouldn't transmit too much to the wood. Thinking of 1/4 ply with 1/2 to 3/4 of foam, and then lined with enough glass to seal it well and keep the foam from compressing.
------------------ Overcoming by out-thinking
"Forget about subsonic, I'm trying for supersonic, and I don't mean a high note."
posted
Make sure the pieces are glued TIGHT! I'd hate to hear the squeak of styrofoam on styrofoam at 30Hz. Kinda like fingernails on a chalk board! Actually, as I think about it, I worked on an electric organ at a local church and the woofer was constructed out of styrofoam! It was an odd shape, not quite circular, cast frame, but I didn't see the back of it. Neat!
------------------ inno73@hotmail.com
[This message has been edited by Inno (edited 01-05-2000).]
Posts: 490 | From: Fort Frances, Ontario, Canada | Registered: May 1999
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posted
when I was at Dynamic Control, makers of Dynamat. They took two pieces of 1/2" MDF and put Dynaply in between and then made a sub box outta this to do a A/B comparison and there was a noticable difference between the box with just 1" MDF and the treated box
------------------ spydermann
Don't get caught in the WEB Gimmie some bass baby keep you RF and others, MTX for me Is that me in the top 10 now?? Do you smell what the BASS is cooking...
Posts: 6799 | From: cincinnati, oh, USA | Registered: Jun 1999
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posted
The styrofoam is actually a good idea. Alot of experimental aircraft are built the same way. Make sure you work your fiberglass layup on both sides. On just one side you still get flex. Both sides done and you can stand on it. Very sturdy. 3-4 layers of cloth per side squeegee'd just right will give you a nice light box.
posted
What about sandwhiching some of tha CAE(Cascade Audio Engineering) material between two sheets of 1/2 inch MDF. I know you can do this with some other materials, but they have some good looking stuff. They call them V-Block materials, it looks like they have a type of wood, gel, and other stuff. I can't think of a more solid enclosure design.
Posts: 48 | From: willimantic,CT,US | Registered: Sep 1999
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BTW I'm not a big fan of bracing.. As the box becomes infinitely stiff, the rear wave of the speaker has only one exit- Through the woofer cone.. you must damp that energy out, with fiberglass insulation or something similar.
If i can find the page where the guy named Art Ludwig did numerous tests on the matter, I'll hook you up with the addres..
ShadowStar
Posts: 2578 | From: Somewhere In the Northeast | Registered: May 1999
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posted
BIGBLUE DC makes of Dynamat already did something like you described
------------------ spydermann
Don't get caught in the WEB Gimmie some bass baby keep you RF and others, MTX for me Is that me in the top 10 now?? Do you smell what the BASS is cooking...
Posts: 6799 | From: cincinnati, oh, USA | Registered: Jun 1999
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