Veneering Speaker Boxes

      Wood veneer on an MDF box makes for a tricky veneering problem. May 13, 2005

Question
I am working on designs for some high end speakers for low volume production. These are not rectangular boxes, but other shapes with few parallel sides. I am using a combination of veneer and laminate to cover them (such as metal laminate on the front and veneer elsewhere). I decided to give PSA backed veneer a try. It is an appealing idea, but it didn't work very well. The PSA backed veneer I put on the long sides and back looked good, but after a couple of days has become wavy in places. I followed the directions very carefully, sealed the substrate surface with shellac, cleaned it and applied plenty of pressure with a scraper. This experience makes me want to use some other method.

Another option I have considered is designing the boxes so that I can use pre-veneered sheet goods and cover the exposed edges with laminate or miter joints. I think this would be less expensive and faster, but it is somewhat limiting and less forgiving in joinery. What is your idea on the best way to cover speaker type shapes? I can get a vacuum press if that is what I need, but it sounds like it would be slow and not necessarily easy for these odd shapes. Other options: using laminate or phenolic backed veneers with contact cement, FSA, yellow glue and an iron, finding someone else to do it and not worrying about how. I am in Seattle.

Forum Responses
(Veneer Forum)
From contributor J:
If you didn't like the results with PSA veneer, contact cement and ironing are going to be disappointing as well. It sounds like you know what high-end means: something that's built to last, and these methods are not for long-lifespan projects. Of your other options, getting someone who can veneer with appropriate adhesives and also do clean joinery sounds like the way to go.



From the original questioner:
While having someone else do it for us is the goal for the future, right now we don't have the volume to justify it. The designs tend to change rather frequently as to be almost custom jobs. I can build the cabinets with sufficient accuracy, the problem is getting the veneer to really bond to the boxes so that it will look perfect and last. Speakers are not abused as much as normal cabinets, but still, they had better last. We can do flat panels in-house and find a way to do parts of assembled speakers with a vacuum bag system, if that is what it will take. I don't mind spending some time and money to get it worked out, I just am trying to find the right direction to take my efforts.


From contributor E:
Before you give up on your first choice (resulting in wavy veneer), contact the veneer supplier and have him come by and see if he can determine what the problem is. It might be something simple.


From contributor B:
I've made various styles of prototype speakers for a couple small speaker designers. In theory, you could veneer a completed enclosure in a vac bag by using an air bladder to equalize the pressure inside the enclosure while it's in the bag so it doesn't implode, but practically speaking, it's not going to be fun or worth the trouble.

I don't know how higher-volume, higher-end manufacturers do it, but what has worked well for me is to veneer an entire panel blank first. Each blank is laid out so that I can cut an entire speaker enclosure out of it, orienting the pieces so that I can get a continuous grain match on the sides and top, or front, back and top (not both, of course). It requires careful layout and machining of whatever joinery you plan to use, because if you mess up and cut any piece too small, you may have wasted the entire panel if a particular grain match is required.

I also machine all the holes and rabbets for the drivers, port tube and binding posts after I machine whatever joinery I need, but before assembly.

I use Unibond 800 glue exclusively for all my veneer work, though I imagine any one that gives you a rigid glue line will give similar results. All my veneering is done in a vac bag. I use either paper-backed or wood-backed veneers.

As you might already know, one of the gospels of veneering is to balance your panels with a backing veneer on the opposite side of the panel. Otherwise, when you pull the panel out of the vac bag, it's already warped. I don't do this on the enclosures I build, because once they are pulled together with clamps and glued with tight joinery, the panels are as flat as they need to be, though it might not be a bad idea with large enclosures.

I either use mitered joinery (difficult on other than square or rectangular shape enclosures) or a solid wood corner insert on all edges (time consuming to shape it quickly to the thin veneered surface).



From the original questioner:
Thanks for sharing your experience with speakers. The flat panel approach is definitely an option, but it would sure be nice to be able to veneer a finished speaker. There must be a way to do it without using dubious methods like contact cement. Looking around and asking on speaker discussion boards, it sounds like most people (mostly diy'ers) use contact cement). I found at least a couple of folks who used vacuum bags on finished speakers without them imploding. Some speaker manufacturers use special build presses (hydraulic) to apply veneer to non-square boxes. I would like to get into raw veneer, but will FSV and paper backed veneers provide a lasting bond without a press?


From contributor B:
I suppose you could use press-type clamps, which are available through many woodworkers' supply houses. These are used in conjunction with some type of caul to more evenly spread the clamp's pressure across the surface. Nothing will spread the clamping force as evenly as a hot press or a vac bag, but it's better than nothing. You'd probably want to press only one side at a time using this method, though I've never tried it.

I suppose a finished enclosure with good internal bracing would stand up to lower levels of vacuum (say under 10" HG - though I've never personally tried it. You would have to wait and cut your openings afterwards). Practically speaking, you would probably only want to veneer opposing sides (side facing up and side facing down), so it would take three bagging sessions.

Regardless what you read elsewhere, forget contact cement and veneer. It works well on a solid laminate to solid substrate bond, but remember, wood veneer is real wood and real wood moves; your MDF substrate does not. If your glue line is not rigid, it may pull apart at the seams or bubble, especially when left in the sun or exposed to wide changes in temperature and humidity. Heavy applications of solvent based finishes such as lacquer can potentially penetrate through veneer and soften the contact cement, causing it to loosen.

Since you plan on having production done by another shop, you might want to touch base with one first, to see how they would handle the production pieces so that you don't have to design the construction twice, if it's different from your method.



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