Considerations for hardwood cabs

[deaconschwaz]

So I recently got into a discussion on another forum with some folks debating making a guitar cabinet out of solid hardwood. There was someone asking if it had been done before and a lot of people responding that it wasn't a good idea. I felt like there was a lot of specious information being thrown into it to justify their positions, with kernels of truth here and there. I'm interested in a couple things that were brought up and figured this would be a good place to ask since Boogie actually makes hardwood shells for combo's, and there are likely some folks around here who have them.

First off, one argument that someone was making is that plywood is stiffer than solid wood, something I know is not true but surely you could find harder plywoods and softer hardwoods to have this argument work. But for our purposes I'm going to use Koa as an example of hardwood and baltic birch ply as the plywood, which is nearly the stiffest plywood you can get. The reason this was brought up was that people were saying that the inferred flexibility of hardwood would make the cabinet flex and therefore cause problems with volume and resonance apparently. Firstly, plywood, even baltic birch is not stiffer than most hardwoods and certainly not stiffer than koa. Plywood is stronger in a couple ways, but stiffness is not one. Hardwood is stiffer when flexed across the grain than plywood, but it really doesn't fare well when flexed parallel to the grain. This is one of the main reasons why plywood is found in things like skateboard decks and hockey sticks, but as far as guitar amp cases I don't think it's an important consideration because this force is not being applied here.

Another consideration for the superiority of plywood is the uniformity of material dimensionally as a new material and over time. Plywood doesn't change as much as hardwood with respect to environmental influence, temperature and humidity. Hardwood becomes acclimatized to it's environment even after it's been cured in the initial drying processes either kiln or air dried. Rapid changes in humidity can have drastic effects on hardwood, especially after it is joined to other pieces since the expansion forces may oppose each other and magnify problems like cracking and checking. This could be an argument for plywood over hardwood as a material of choice for cab construction. I do think though that this is only a consideration if proper care isn't given to the amp cabinets in storage, transportation and exposure. I would think that taking such an amp out to the local bar or club for a gig isn't going to have a drastic effect on such and amp, while going from a home in the SW to one in the south in summer could have a huge effect. This could probably be mitigated somewhat by using a road case for all of the time the amp isn't in use, and dehumidifying materials. For these reasons though I'd give the nod to plywood as being more user friendly.

Lastly, and this is the one I'm really interested in, someone brought up the idea that if you're going to make an amplifier case from hardwood, you should also "tune" the case. In the discussion I had talked about how hardwood, being a contiguous material could propagate vibrations and even amplify them, whereas plywood because it is made up of opposing layers would suppress such vibrations. So I'm wondering, does anyone know if Boogie tunes their combo cases? I'm trying to imagine how exactly you'd do that, not from a practical standpoint so much, but how you'd tune something to inhibit vibrations across the entire spectrum of guitar notes, not to mention additional wave formations brought on by the use of effect pedals and feedback.

I'm curious because of how adamant some were that cases should never be built of hardwood, yet some of the most beautiful amps I've ever seen are made of hardwood, as well as by one of the most revered names in the business. If it was really such a fussy thing, or so difficult, would Boogie be doing it? Also, has anyone here had Boogie replace their original cab with a hardwood? I'm interested in finding out what's involved. Do you have to send the amp to them to do it, or can you order the shell and have a local boogie tech do it? Is tuning the shell really part of the process? I nearly replaced the shell on my Mark IIc+ a few years back and decided to just keep it stock, but I hadn't considered much of any of these factors back then.

 

[stokes]

Whether or not a hardwood cab sounds better than plywood is very subjective.The first argument against hardwood being too flexible is exactly what you would want from a hardwood/solid wood cab,I say "solid wood" because the early Fenders were made with solid pine,not a hardwood,but many think it sounds great.What makes an accoustic guitar sound good?The vibrating or flexing of the wood.As to "tuning",I've never heard of anyone doing it,but doesnt mean there wasnt some consideration when considering the thickness of the wood used.But I'm pretty sure the early Fenders chose pine because it was the cheapest to source,the fact that it sounds good today is more an effect of it aging.As far as ordering a cab,no need to send it anywhere,just order the cab and fit the speaker and chassis.Before you decide to get a hardwood cab do a search for memeber called "gts" he makes some killer cabs,I beleieve a number of members here have gotten cabs made by him and I've nothing but raves.

 

[RR]

As a weekend woodworker I've build both baltic plywood and some hardward wood enclosures.

Stokes above pretty much sums up about solid wood.

Emery Sounds prefer using 1/2" mahogany claiming there's some resonance they like.

Did you check out member's Geeze builds? Nice!

If you play hi-gain you probably not going to hear much difference and would actually prefer plywood build enclosures.

As far as ports, optimum interior volume size, that really depends. Parts Express sells drivers for hi-fi, sound reinforcement and guitar use (Celestion, Eminence, ...) and they include parameters what are the best volume, duct size and duct depth to get the most out of the drive.

I remember one manufacture that sells and over-sized 2x12" that's well ported and could compete against 4x12"

When it comes down to it, its trial and error that determine which you like best.