| Author | Subject: balsa wood in speaker enclosures |
| Stewart Schooley | Posted At 13:52:40 09/13/99
I've posted this question on another site and didn't get any rsponses, but I think it is a good question and would like to have some input from experienced enclosure builders. The newest model Corvette has balsa wood sandwiched between two layer of plastic for floor boards. The reduced noise and vibration has made this the quietest Corvette ever made. Why wouldn't a 1/4 inch ormore thick strip of balsa between every joint in an enclosure be worth trying? Comments are welcome. |
| Israel |
Re: balsa wood in speaker enclosures (Currently 0 replies)
Posted At 08:50:26 09/14/99 Stewart, What do you mean by, "between every joint?" Balsa wood is too soft for use as a joint in an enclosure. I haven't studied up too much on the new Corvettes, but it seems that the lowered noise floor is because of several factors. The plastic floor boards will not resonate the same as sheet metal. This resonance (sheet metal) transfers alot of unwanted sound into the vehicle. That's why mass loading is popular in the auto audio world (Dynamat, etc.). It helps dampen any resonance of sheet metal surfaces. This is what makes the car quiter going down the road; less road noise is being resonated into the cabin. Plastic has a different resonant frequency than sheet metal which is good. What is not good about platic is that it's not as rigid as the sheet metal. The plastic will bend and flex so it takes a fairly thick layer of plastic to stand up to the same stresses as the sheet metal. To remedy this, the balsa wood is sandwiched between two layers of plastic. The balsa wood acts as structural support between the layers. Balsa wood by itself is not very rigid. The plastic by itself isn't either. Now laminate the two and you get a much more rigid structure. It's interesting that this method is being used in new cars. This laminating has been around for quite some time in the composite aircraft community. The difference being that composite aircraft use styrofoam sandwiched between layers of fiberglass. It makes for a light weight, very durable structure. In fact its many times more durable than its sheet metal / aluminum counterparts. Israel |
| Stewart Schooley |
Re: balsa wood in speaker enclosures (Currently 0 replies)
Posted At 19:02:59 09/14/99 By " between every joint" I mean evey corner and top and bottom. since I will be using 3/4 inch plywood for this enclosure I will put a 1/4 inch thick by 3/4 inch wide strip of balsa between every "joint" before screwing them together. I believe this would reduce any vibration that might b generated there. Do you remember the Lexus commercial that showed the firewall construction in the car? |
| Stewart Schooley |
Re: balsa wood in speaker enclosures (Currently 1 replies)
Posted At 19:36:14 09/14/99 By " between every joint" I mean evey corner and top and bottom. since I will be using 3/4 inch plywood for this enclosure I will put a 1/4 inch thick by 3/4 inch wide strip of balsa between every "joint" before screwing them together. I believe this would reduce any vibration that might b generated there. Do you remember the Lexus commercial that showed the firewall construction in the car? The Lexus had two pieces of metal sandwiching a sound absorbing material. the quietness of this was demonstrated by tapping on this with drumsticks as opposed to tapping on plain metal. The sound absorbing material had nothing to do with the structural rigidity of the car, but was there to keep engine compartment noises from entering the passenger cabin. Similarly, the balsa in the Corvette cannot add structural rigidity, but is only there to reduce sound transmission into the cabin. Evidently Chevorlet thinks balsa is superior for this. Yes I know, being GM , maybe they do it because it is cheaper. The car magazine I read only identified the plastic used as a composite plastic. The real question is, Will the balsa wood strips along with internal bracing-again using the strips-and balsa as an additional lining material give me less vibrations and less resonance? By the way, this enclosure is for my 42 year old Goodmans Axiom 22 speaker. I am not into just vintage here, but into nostalgia. I'm 68 and want a mono setup to play all my old mono LPs. Using my old Heathkit tube amp of course. |
| Rick Slazenger |
Re: balsa wood in speaker enclosures (Currently 0 replies)
Posted At 07:37:38 09/15/99 Not to be picky, but... Dynamat really isn't mass loading. In fact, mass loading in a car is BAD. Not in audio terms, but in the fact that you're loading the car down with mass. Dynamat is better compared to semi-viscous damping. The softer material absorbs the sound and resonances, rather than "sandbagging" them with mass. Okay, absorb isn't exactly right. Converts the sound to heat, instead of re-radiating as resonant sound. But you get the idea. The balsa/plastic sandwich probably operates in that fasion. That, and the different layers have different resonant characteristics cancelling each other's resonances out. Unlike undamped metal, which would have a single annoying resonance. |
| Calvin |
Re: balsa wood in speaker enclosures (Currently 0 replies)
Posted At 10:05:55 09/15/99 Balsa in the corvette is for panels not joints. I think that balsa in the joints would lower the rigidity unless there are screws. Screws would then negate the effect of the balsa. I never make a box from material that I could make a musical insturment from i.e. plywood. I get good results with MDF that is braced extensively internally and then laminated with thick high pressure laminate (Formica being one example). Braces should be side to side and maybe top to side and not centered on any dimensions. To duplicate the corvette. Build an inner box and outer box from 5/8" mdf and pack the void between them with portland cement. Use WonderBond to glue it together, wood glue isn't compatable with cement. This is all guilding the lilly if your listening level isn't very loud. Just a well braced MDF box is enough. Keep the exterior surface area small as possible. |
| Israel |
Re: balsa wood in speaker enclosures (Currently 0 replies)
Posted At 17:08:35 09/15/99 Hi Stewart, Sorry to get off on a tangent like I did. I'm sure Balsa wood was chosen for it's resonant characteristics(or lack thereof) to be used in the plastic lamination. Doing such does indeed provide more structural regidity to a panel, but I realize that wasn't your intended question. To use a strip of balsa wood between every joint could compromise your structural integrity. You should have no problems with an enclosure at the joints. This is generally not your source of panel resonance because you should secure the panels with nails, screws, glue, or all of the above. Just be sure all your panels fit properly so that they can be properly secured. I agree with Calvin above. Use MDF(Medium Density Fiberboard) and properly brace the enclosure. The more surface area you have to a panel, the better it needs to be braced. This is where your resonance comes from. Israel |
| Rick Slazenger |
Re: balsa wood in speaker enclosures (Currently 1 replies)
Posted At 22:33:51 09/15/99 I think maybe I'll answer your question, this time, without so much non-essential info: No, that probably won't work the way you want. If you use the balsa, it will likely compromise the structural integrity of the box. Unless you screw it together tight enough to compress the balsa. But that would do away with whatever damping characteristics it may have had. And now the non-essential additional info: What you can do is make a damping "sandwich" of each panel. 3/4" MDF on the outside, balsa in the middle, and more 3/4" MDF of 3/4" void free cabinet grade plywood on the inside. Then cross-brace the interior with either more MDF or pylwood. Yes Virginia, you can make speakers with plywood. But only GOOD plywood. But you can't make musical instruments out of it (i.e. cheap Asian made electric guitars SUCK because they're made with plywood, instead of rich, resonant, natural... WOOD). Here endeth the lesson (rant). |
| Calvin |
Re: balsa wood in speaker enclosures (Currently 0 replies)
Posted At 10:58:33 09/16/99 Rick, Sorry, my fault. If you take a piece of ply, say 4x8", and play it with a mallet, it makes a note like a xylophone, where MDF isn't too good at it. Ply is fine, especially good for humid or high strength areas like cars and stage equipment. And 10-4 on the GOOD plywood. |
| Israel |
Re: balsa wood in speaker enclosures (Currently 0 replies)
Posted At 12:37:40 09/17/99 Well, I guess I wasn't too clear on my posts. It seems that there was some confusion in my Dynamat analogy. I didn't mean that the balsa in the plastic/balsa lamination defeated panel resonance in the same manner as Dynamat or any other mass loading material. At least not by the means of adding mass to the panel to lower its resonance. I wasn't sure exactly where Stewart was coming from with his question, what exactly he was asking, or how much knowledge he had on panel resonance. I decided to take a very broad and basic approach at explaining a little about how road noise, etc. made it into a vehicle. This was just an attempt to help explain something Stewart may not have been familiar with while I was waiting for him to clarify what he meant by using the balsa between every joint. I simply stated that road noise enters the cabin by panel resonance(of course not the only way), and that mass loading was popular in the car audio community because it helped reduce this resonance that was being transfered to the cabin. Not everyone knows this, and because I don't know Stewart, I figured it wouldn't hurt to relay the information. I then started off with the different accoustical characteristics of plastic, then lost it from there. Lack of sleep + early morning = incoherent post. I probably should've went into more accoustical theories of the lamination and its insulating properties similar (not exactly) to that of a double leaf partition. Or maybe even state the fact(or theory) that the resonance was damped because the first layer of plastic resonates at a different frequency than the balsa wood. Since they are directly coupled and the balsa does not resonate as efficiently at the frequency being applied by the first layer of plastic, less energy is transfered to the second layer of plastic, then into the cabin. Know what happens to the rest of the energy? Heat. hmmmm. interesting. I just hit on something rather interesting. (no, I'm not talking about the cute receptionist) The accoustical energy that isn't being transfered to the second layer of plastic is being dissipated as heat. That sounds alot like what Dynamat and others do, doesn't it? Basic physics tells you that energy is neither created nor destroyed. You also learn that work produces heat. When the accoustical waves create vibrations in any material, the waves are doing work. Where there's work, there's heat. Of course depending on the material, you will get different amounts of heat being created and different amounts of energy being transfered. -- hang on, I'm going somewhere with this -- So why not just glue some balsa to a single layer of plastic and use it as a floorboard? Structural regidity. The plasic by itself, unless thick enough, will not support the weight of the seats, much less the passengers. Don't forget about the torque the floorboard must withstand as the vehicle is traveling down the road. A thin layer of balsa wood glued to the top of the plastic doesn't offer much more support. To support the weight and torque, you need something rigid. Being lightweight is also a plus, especially for a high performance vehicle like the Corvette. In comes the plastic/balsa lamination. I don't know what the engineers had in mind at the time, but I would suspect that they were looking for a strong material that could be used in place of the sheet metal floorpans to make the car lighter. Call me crazy, but I think the sound deadening characteristics of the lamination were a secondary consideration at best. I mean, come on! This is America's sports car! Which would sell more sports cars? A: quicker slalom times,quicker 0-60 times,etc. OR B: A quieter ride. Of course this is all relative to the buyer, but I would guess that the engineers, and probably the marketing department, think that 'A' will sell more new Corvettes. If you want a quieter ride, buy a luxury car, not a sports car! :-) Oops. Maybe I got a little off topic again. I appologize. I hope I at least cleared up some of the things I was writing about in my previous posts. At least now you know from where I was coming. Does this post make sense? Who knows. Deadline is here and I still haven't had sleep. Israel |
| Stewart Schooley |
Re: balsa wood in speaker enclosures (Currently 0 replies)
Posted At 15:56:58 09/17/99 This discussion has been more than I hoped for. I've read every word and learned a lot. Heres how I'm going to build the cabinet, based somewhat on materials I already have available: I am not going to use balsa strips between the joints. I will make a laminate of 3/4 inch MDF, 1/4 inch balsa and 1/8 inch untempered Masonite. It will be braced internally, vertically and horizontally. I will use foam backed carpet to line it and lots of the batting my wife uses in her quilt making. I'm not going to do anything to the outside because this will be used in my studio and doesn't have to look pretty. Thnk you all, sincerely Stewart Schooley |
| Israel |
Re: balsa wood in speaker enclosures (Currently 0 replies)
Posted At 16:43:40 09/17/99 Stewart, It sounds like you've got it. I appologize for any confusion I may have caused, and I appologize for the direction this thread has taken. Good luck with your enclosure. Israel |
| Wes Keller |
Re: balsa wood in speaker enclosures (Currently 0 replies)
Posted At 01:57:56 09/18/99 The vast majority of the new Corvette's low idle dB is because of a much stiffer chassis(something like 150%) which, as we all now, lowers the ambient resonances. It also gets the GM SPONG O' QUIET treatment. I have forgotten the name of the substance, but it is similar to silicone. It is injected at every crack, joint, fitting, etc that it can be in this fine american automobile. POW - no rattles, less reosnance, less noise. Now, stop it with the balsa wood and start filling your listening room with wall to wall silicon caulking. Enjoy, WYK |
| ray |
Re: balsa wood in speaker enclosures (Currently 0 replies)
Posted At 22:28:44 09/20/99 nice discussion,lost me on the balsa wood. |
| Frank |
Re: balsa wood in speaker enclosures (Currently 0 replies)
Posted At 17:25:48 10/22/99 I don't know much about balsa wood in speaker enclosures, but the newer Kenworth trucks have a floor made of a composite 'sandwich'. A thick layer of fiberglass then 2.5 inches of balsa then another layer of fiberglass, this is for a smoother quieter ride. |
| JP |
Re: balsa wood in speaker enclosures (Currently 0 replies)
Posted At 00:10:10 04/14/2000 Your bals wood idea seems ok, but there is a much better way to accomplish vibration reduction of box joints. Just put a thin layer of caulking on each of your joints. Not only will it reduce noise and vibration, but it will also make an airtight box free of leaks. |
| pedro claver |
Re: balsa wood in speaker enclosures (Currently 0 replies)
Posted At 12:29:59 03/14/2001 excuses for a mail.. i sell balsa wood here in colombia.. do you have address of company interesting in this product?? many thanks pedro claver colombia |
| pedro claver orozco |
balsa wood for sell (Currently 0 replies)
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