Thread: WIP Box Guitar.

In regards to sound hole location....the size of the hole will affect the Helmholtz frequency of the box more than location of the hole. The Helmholtz frequency along with the main top frequency are two important contributors to the sound of the instrument.

3mm ply will vibrate but nowhere as well as a solid top of similar thickness. Top thickness will influence both the volume of the instrument and the way it behaves at different frequencies (commonly referred to as vibrational "modes").

At 5mm thick I doubt your sides will need any bracing.

Watching.

Got some more done. All roughed out, some glued and ready for sanding. Im at a standstill till the components arrive from Hong Kong so probebly a month or so.

piccies of the template for holes, progress so far and neck under the strings inside the box.

The jack chair has never looked so in place with a photo

cheers

Not F holes, Seahorse holes.

Originally Posted by Cliff Rogers

Not F holes, Seahorse holes.

Sometimes I get the impression that Cliff sees things from a different perspective.

I like the ffs. There is a bit of short grain but you'll get away with it because it's ply. Having some space between the neck and the top looks a good idea as well. You will need the smallest bit of support under the bridge because string tension will be pushing in.

I have decided to fret so have chiselled out neck to run flush with the box, this was an after thought so has left a 3mm gap where the neck joins the top of the box, I'll hide that with neck support like on a traditional guitar and add the support under the bridge. The bottom of the neck has been left under the top so a 3mm offset from square.

the ffs so to speak (fender?) weren't supposed to be ffs they were just something easy to do for holes with a file. I was thinking of using stainless wire behind them to give that 1950's radio look, I would assume this would effect vibration though?

cheers.

Originally Posted by kiwigeo

In regards to sound hole location....the size of the hole will affect the Helmholtz frequency of the box more than location of the hole. The Helmholtz frequency along with the main top frequency are two important contributors to the sound of the instrument.

3mm ply will vibrate but nowhere as well as a solid top of similar thickness. Top thickness will influence both the volume of the instrument and the way it behaves at different frequencies (commonly referred to as vibrational "modes").

At 5mm thick I doubt your sides will need any bracing.

Solid tops may give twice the volume of a plywood one, mate, but have you any data showing this?
I understand the difference is a deal smaller, say 20% or less. it depends on the specs. of the woods, too of course. It may be true when comparing say Engelmann spruce AAA grade, quartersawn, with common 3mm plywood. Let's remember too that plywoods don't crack like the solid wood tops.
I agree, 5 mm hardwood sides would be plenty strong enough.

Originally Posted by HARPER

Solid tops may give twice the volume of a plywood one, mate, but have you any data showing this?

A couple of comments:

1. I wasnt just referring to the volume of a solid top being greater than a plywood top. I'm also talking about the way the top vibrates at different frequencies (modes).
2. One doesn't need screeds of tap test and Chladni test results to to tell one that solid wood makes a better sounding top than plywood. Ive done a fair bit of tap and Chladni testing on the tops (and backs) of the the acoustics I build. Admittedly I've never built a plywood topped guitar and subjected it to similar testing but Ive never felt a great need to......a simple qualitative tap test on a piece of plywood tells me it's not going to make as good a top as a solid piece of average grade spruce. I would bet my left nut that if I subjected a plywood topped guitar to tap and Chladni testing I'd see the Helmholtz and main top frequencies but the numerous other modes that I see on my solid topped acoustics would be lacking.

Originally Posted by HARPER

Let's remember too that plywoods don't crack like the solid wood tops.

All the cracks repairs I've had to deal with in solid wood tops have been due to either 1. the instrument being exposed to extreme swings in humidity or 2. the instrument being badly built (eg poor quality top wood, poorly glued centre seam etc).

The risk of cracking can be reduced by running reinforcing patches along the underside of the centre seam and controlling the humidity in the workshop where the instrument is being built. My shop stays at 40-45% humidity, the idea being that the instrument will generally be going to an environment that's either of similar or higher humidity. At a higher humidity the wood is going to swell which rarely generates cracks.