Official Luthiers Forum!

Hi Folks,

The first guitar I built was a nylon string classical that used the bracing pattern in Bogdanovich’s DVD with an Italian Red Spruce top and EIR back and sides. I love the sound of the guitar. I would describe it as bright and balanced.

I’m about to start on my second guitar. I want my second guitar to sound “darker”, perhaps more Spanish, but I don’t want dull thumpy trebles.

So I’d like your thoughts on how to proceed

1. Use the Bogdanovich bracing pattern with a cedar top and EIR b/s – I’m hoping this bracing pattern might retain the beautiful trebles and the cedar would give it a darker sound.

2. Use a Torres bracing pattern with a spruce top.

3. Something else?

Thanks,
Steven

Below are photos of the bracing I used on the first guitar:

Steven,
I would recommend that you try to pinpoint exactly how far you want to change the sound from your first. Do you want to 1) keep more or less the same voice and make it less bright, or 2) do you really want the next one to sound like a Madrid-style cedar guitar? Note that I'm reading cedar into the word "Spanish", although that could also mean Granada- or Romanillos-inspired with a spruce top and a completely different sound aesthetic. If 1), I would consider keeping your current system and reducing the doming. If you were at say, 25 foot radius, reduce it to 28 foot. That will increase the richness/warmth of the voice and reduce the brightness, and for the most part retain much of the other characteristics you enjoy. The benefit of doing this is that you have all the experience you already gained from your first guitar in terms of materials, bracing, etc. The downside is that you will have to retrofit your work board. If 2), then go for cedar, but realize that cedar doesn't automatically mean darker. To me, the operative words for cedar are glassy, hollow, fast response, less body and tonal color than spruce. For your own learning, keep the same system, change the top wood to cedar and adjust its thickness to account for any change in stiffness. In the end you will have gained much more useful information on how to shape the sound than if you throw the baby out with the bath water. Good luck and happy building.

The overall tonality of a guitar (dark vs. bright) is largely governed by the balance of stiffness to mass in the top and, in particular, how that balance affects the resonant frequencies of the two lowest modes of vibration, usually called the main air resonance and the main top resonance. If you want brighter, you need more stiffness/less mass (which has the effect of raising the resonant frequency of the previously mentioned modes) and if you want darker you need less stiffness/more mass which lowers those resonant frequencies. To improve the guitar's sensitivity to high frequency signals, the soundboard should be made lighter. To increase the guitar's sensitivity to low frequency signals, the soundboard should be made less stiff (more flexible).

Looking at what you have in guitar 1, there seems to me to be plenty of wood in the braces, making for a stiffer guitar which will have relatively high resonant frequencies and therefore a brighter sound. I would guess that the main top resonance is well above 200Hz. To get the darker sound you're after, pitching around 190Hz will serve you better. You can trial this by adding mass to the bridge area of the guitar using poster putty (add a good dollop) which will certainly darken the sound, but also kill the trebles somewhat, too, due to the reasons above. You may also get a rather muddy sound due to the lack of trebles, but listen through that and it will give you an impression of what darker will sound like if you stick with the basic layout and brace geometry you have.

What you will need to do on guitar 2 is to get down to the lower resonant frequency that you preferred using the poster putty test, but achieve it by removing stiffness rather than by adding mass. That will give you improved bass response (darker) with little loss of the trebles. There is a lot of scope for this, looking at the size of the bracing. Just reduce all the lower bout brace heights. For comparison, will will see pictures of braced guitars similar to yours, but missing the closing bars and the diagonal brace at the waist and these will have ample structural integrity.

There are many other ways to alter the mass/stiffness ratio and distribution in a guitar (e.g. make the top panel thinner) as well as messing with the coupling between components (e.g. make the box deeper/shallower). That's the fun of it.

_________________
Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

Trevor, great answer. I assume the same is true on SS?

_________________
Joe Beaver
Maker of Sawdust

Yes.

The few paragraphs above form the basis of "tone tweaking" for want of a better expression. Obviously, there's a lot more to it, but those are the basic principles.

_________________
Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

Great posts Gary and Trevor.
Posts like these are the reason I joined this forum- good question from an ameteur, invaluable advise from the pros.

_________________
We are all in the gutter but some of us are looking at guitars.

Wow, thanks a lot Trevor and Gary. You've given me a lot to digest and pointed me in a certain direction.

Now I have to find out what a "Madrid-style cedar" guitar and a "Granada- or Romanillos-inspired" guitar sounds like to determine what I want. I just know that I've ran across guitars that sound darker and that's what I'd like for the next guitar.

The simple answer is that if you want the guitar to sound more "Spanish" then you should build Spanish. Its hard to go wrong with a Torres plan. Try to go as authentic as possible.

Pick up the CD "The Sound of Spain" by Granary Guitars.

_________________
Expectation is the source of all misery; comparison the thief of joy.
http://redrivercanoe.ca/