trapezoid acoustic lap steel guitar - questions

[Manos Tourpalis]

Hi everybody.
I am a new member, I recently introduced myself here:

https://www.acousticguitarforum.com/...d.php?t=510594

and opened this thread according to the moderator’s suggestion.

as an introduction, I started making instruments (mostly bouzoukis and a few guitars recently) just a few years ago. A friend asked me to build a simple acoustic lap steel guitar (similar to DL lap steel guitars).
I have so many questions on this that I decided that I would need some help, so here I am.

This will be a “just the basics” construction, a trapeze box with a headstock and a fixed bridge. Unfortunately, I have limited experience on guitars and only of “Greek folk” guitar (~ 24.75” scale, steel strings, ladder bracing, joint at 12th ). Absolutely none on lap steels – or any other type of guitar, actually.
I can understand essential principles on static behavior and acoustics though, and I do have some experience on other instruments (Greek bouzouki family – similar to Italian mandolins).
However, this one has got me troubled, due to these certain characteristics:

- narrow shape that limits down the soundboard width (and I imagine its response: comparing to any other guitar, the lower bout is just not there) in combination with the heavy strings and
- Higher saddle /steep break angle that tends to twist the bridge. I imagine that this would need some kind of extra bracing / reinforcement at the bridge area.

I think the “key” here is the bracing pattern. I haven’t found any plans or pictures depicting the bracing of the particular construction (I found for Weissenborns type but that is another chapter), so I searched the net for similar shapes. Dulcimers and backpackers are the closest I found – but both the backpacker and the dulcimer have much lower string load.

I understand that most dulcimers are quite different constructions. Nevertheless, there are some instruments with “conventional” soundboard and bridge function. Here are some brace patterns that I spotted on this search. All instruments appear with 60 cm (~ 23.5”) scale.



The only similar shape on a guitar that I have found is this Greenfield guitar (I don’t remember where I found the link to this site, quite possibly right here on AGF)
http://www.notecannons.com/



Does anyone have any clue on this one’s braces?

I would appreciate any suggestion(s) you might have on possible bracing patterns. I have made some more plans and extra thoughts that I would be happy to discuss with anyone interested in this topic.

Thank you in advance
Manos

[mirwa]

You have put some work into that.

The soundboards on these instruments are so small, not a lot of bracing is required.

When I am experimenting with bracing, that is when I built my own guitars and taught other people, I would make the instrument with a false back.

On the neck and tail block you glue a one inch by one inch block

You maker a false back out of mdf or scrap wood and screw it into the one inch blocks, Then simply use binding tape on the sides.

String the instrument up and measure bridge rotation, dependant on how much you get or the ideal sound you are after, your unscrew the false back and replace a brace or thin a brace until you get the desired bridge rotation.

Once happy, steam the blocks of and fit a back

Its a very simple process, sounds complicated but really really basic

Steve

[Manos Tourpalis]

Thanks Steve!

This seems to be a clever solution (that I haven’t thought of: I usually make Spanish heel joints and I think that the back must be well fixed, otherwise everything will twist). Anyway, I have already finished the body with the back fixed. I am prepared to make two or more soundboards with different patterns, though. I could take off the back, too. I see the whole thing as an experiment.

But I have not reached that phase yet. I think that you described more likely a “method to correct a problem / enhance the voicing” - rather to locate the initial bracing. I am trying to figure out the pros and cons of the various patterns above.

The only thing I know for this guitar : the more sustain, the better.

Let me put once more the patterns – adding the “Laiki guitar” typical bracing and an explanatory legend – and after that a sketch of the “influences” - tryouts on the bracing.

BP = Backpacker, D = Dulcimer, GFG = Greek Folk Guitar





The ladder brace (GFG – type) comes natural to me. Given the narrow soundboard, this was what I had in mind in the first place. Maybe with a couple of longitudinal short braces under the bridge – like the gypsy guitars – to deal with the heavier gauges’ load. Bouzoukis (that is the other instrument I make) have even simpler pattern, and baglamas usually has just one brace. This width is similar to a large baglama’s width – but the load is significantly lighter (50 kgs ~ 110 lbs on a three course bouzouki, maybe less than 20 kgs on a baglamas).

On the other hand, both the Backpackers and at least one Dulcimer, apart from X-bracing, also endorse longitudinal braces –parallel and close to the sides.

I don’t know the function of these braces, though. I have never heard - or lay hands - on an instrument with this pattern. The only thing that comes to my mind is the fan bracing of classical guitars, but I don’t think that this is the case – these braces extend far upwards.
These are my sketches so far – the legends for the origins of each one.



My consideration for the bracing has to do with the balance : the braces should not limit the part of the soundboard that would contribute the most to the sound production and - at the same time - adequately support the bridge.

On bouzoukis and guitars (GFG) I know – up to a point - how to deal with the “responsive” area (mostly the lower bout - and the relatively area to a bouzouki). On this soundboard, I am puzzled trying to figure out which particular area should be left clear – or with lighter bracing – to resonate.

The load is also a consideration. I used the calculating machines on D’ Addario and McDonaldstrings.com.
For a “standard” D’addario EJ18 (.014 - .059) and a “lap steel” John Pierce set (.015 - .060). Tuned to open D and open G (scale ~ 23.5”) the load is correspondingly 73-74 Kgs (~ 161 – 163 lbs). It is quite similar to a standard EJ16 (.012-.053 = 73 kgs) that I use on my guitars – but there I have the space to design the pattern.

On this narrow and “boutless” soundboard, I am afraid that I will “choke” its response, trying to support the bridge.

Any thoughts would be helpful and appreciated. Thanks once more.

[mirwa]

The only thing I can add is, sustain comes from the neck / fretboard /headstock / tuners, not the body.

The thinner you make a neck or the more pliable it becomes through wood selection or in conjunction with the mass of the tuners, allows us to increase or decrease sustain.

Steve