Official Luthiers Forum!

Hi guys. I have been thinking alot about thickness graduation on the
sound board and hoe this effects tone. Can you guys share any info on
this, opinions, history of it, measurments, anything you have to shed light
on this topic.
thank you
avilaguitars

bump

Admittedly I know very little about this but something that may be helpful to you is what Taylor Guitars does.  Taylor mills a thinned ledge around the perimeter of at least the lower bout, not sure if this extends around the upper bout.  This thinned area of the top is IMHO is not so much to impact tone as it is to permit greater flexibility of the top, around the perimeter permitting the top to move more.  This would in my view have more impact on volume.

Many builders here, myself included, do something toward a similar end and that is to simply thin the top, once on the rim, around the edges of the lower bout.  We are looking for a very slight amount of flexibility in the top when we take our thumbs and press with moderate pressure in the bridge area.

I learned this from my pal Lance K. and it seems to indeed open up the guitar a bit.

Hopefully someone will post a link to the info on what Taylor does and why to help you out.

Have a look HERE you want to follow the "Factory Friday" link and I think it is video 7 on the second page.

Cheers

Kim

I would reccomend getting a Hacklinger Gauge
http://www.stewmac.com/shop/Tools/Measuring_tools/Hacklinger _Thickness_Gauge.html

I disagree with hesh on this one, thinning the edge of the soundboard is all about tone and not volume.
stiffer is louder, more flex = more tone,
too much flex = mud puddle top.

the hacklinger gauge is a great tool which allows you measure the top, back, and side thicknesses of any already built instrument. I measure every guitar i get my hands on and make a note of the top back and side thicknesses.

also I think it`s important to remember that you thin the edges of a top when you sand your bindings flush. the gauge can tell you exactly how much you lost during that proccess and will help you get a handle on whats happening there.

Matt

Thanks, Matt...I think you're the first to ever tout the use of this gauge on the OLF. I like objective data. Over time and lots of measurements it can really shed some light on choosing a direction. How accurate would you estimate the Hacklinger measurements are compared to those of a digital caliper for example. I realize the kinds of measurements you describe can't be made with a caliper but am interested in knowing how accurately and repeatably the Hacklinger measures.

Any other info you can shed on your collection of measurements would be appreciated.

TIA

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JJ
Napa, CA
http://www.DonohueGuitars.com

The Hacklinger thickness gauge is one tool I've been
wanting, But they are pricey ..Stew-Mac sells them for $ 385.00 !
Any other sources out there for this cool tool?

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Anderson Guitars
Clearwater,Fl. 33755

I had to trade my Taylor fret buck for mine!
but it was definitly worth the trade.

JJ, it is an extremely accurate precision tool.
the coolest thing about it, is how the magnet travels around over the bracing revealing more than just the thicknesses, but locations of the bracing, bridge patch, etc.
it`s really fun to use.

Matt

Matt my friend thanks for setting me straight on this.  I buy your explanation completely and just learned something - Thanks!

Dave, ive seen it in two other places for more than 400.  I sure want one too!

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Build log

Thinning the edge is about tone & volume!
They actually go together in this area!

Mike

_________________
Mike Collins

To really open a can of worms we can discuss how stiff the top & braces are as a unit-then how the braces are tapered to the linings-the intended use for the guitar
(flat-picking,fingerpicking;etc.-classical?)
So many variables !!!!!

Mike

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Mike Collins

Mike, what can you share about this issue on classicals.  Both the plate edge and the thickness of the outer fan braces and "V" closing braces. 

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Build log

The hacklinger (sp*) gauge is an important tool in my shop for measuring the graduation and thickness of fine vintage guitars that pass through my repair shop, for reproducing that graduation and checking that my new reproductions consistenly follow the graduation set by the vintage guitars. I only wish they made a imperial one!

I tried this on one guitar and was pleased with both the volume and tone of the guitar. It was a WRC top and not spruce. I purposly left the center of the top thicker than normal (~.140) and then thinned the outer edges of the lower bout to around .050. I wouldnt try this with spruce, but the wrc was so stiff it worked for me on that one. The guitar has loads of volume and the tone aint bad either.

I will mention that I progressively sanded the top from the bridge area to the outer edges of the lower bout and not just a ring around the edge of the lower bout. The upper bout remained at .140

I do something similar with my spruce tops, but not as drastic on the thicknesses. I have found that if you get too carried away and sand the top too thin, it will telegraph the braces through the finished top when you string it up. With spruce, think of sanding from .110 down to about .095 on the very edge of the lower bout ring. Any thinner and you are asking for big problems.

_________________
Reguards,

Ken H

Dave White posted awhile ago about a tool he conjured up to measure thickness. Maybe he'll pipe up.

_________________
now known around here as Pat Foster
_________________
http://www.patfosterguitars.com

What I've found, so far:

Thinning behind the bridge tends to give a 'fuller' or more 'bassy' sound. Note that you can go pretty thin at the tailblock without compromising structural integrity.

Thinning in the 'wings', from the bridge ends out to the edges, but leaving the tailblock area thicker, tends to give a 'brighter' or 'more forward' sound.

One student of guitar acoustics (Bernard Richardson, who teaches Physics at the U of Wales in Cardiff), feels that thinning in the center would do more to increase output than thinning at the edges. This would most likely give a more 'bassy' and 'punchy' sound, similar to scalloping braces, and for the same reason. I have not tried this as yet, but see no reason to doubt it.

I feel that the critical area for stress on the top is between the bridge and soundhole, and usually leave my tops thick there.

The Taylor 'channel' should have a similar effect to thinning all around the perimiter: a bit more output without effecting the balance too much. It's a surrogate for tapering the graduation when that is hard to do owing to tooling costs. I have to wonder if that groove is not also a stress riser, and whether we'll see cracks in the lower bout edges from it over time.

The purfling rabbett also loosens the edge up a bit, and a wide purfling or narrow liners can act like thinning the edges to some degree.

Aside from these generalities, thinning the top in different areas lowers the pitches of the various top modes differently, and alters the relationships between them, and between the 'wood' and 'air' resonant modes. If, by thinning someplace, you move a 'wood' mode pitch to where it couples strongly with an air mode the sound of the guitar can change quite noticably, and it ways that are hard to predict from general rules. What works in this way for one person, or on one guitar, might not for somebody else or another instrument. That's one reason there seem to be so many exceptions to any set of 'general' rules.

Tony, I would be very leery of basing reproductions on thickness measurements unless your top material exactly matches the stiffness and density of the original tops. This is the great trap that so many Strad copyists got caught up in. It's the wood plus the graduation (and bracing), not one independent from the other(s) that makes the tone and volume.