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Who has experience with building an "X" braced guitar ("traditional" top bracing) and combining that with Trevor Gore's design for mass loading the sides together with his radially braced back that can be adjusted (some back bracing reduced/removed)?

If so, did you find it effective in adjusting the frequency of the top and back?

Also, if you have only done an "X" braced with just one of these (just mass loading or just adjustable back bracing), what were your results?

Thank you!

You don't need to use the asterisk pattern to get a live, adjustable freq back. It's about the overall mass/stiffness. Every guitar I build has adjustable bracing, and every back gets adjusted to be precisely where I want it. I use tall thin 3&4 back braces, not wide squat Martin style ones. The asterisk pattern does yield a more clear monopole however. With a standard ladder brace, there is sometimes confusion and overlap and sudden shifts between dominant freqs.

In the way the top has a clear, unconfused monopole, due to the mass of the bridge in the center, the asterisk pattern yields a more clear monopole.

You can easily adjust the freq of the back with either pattern by changing the height of the braces once the true numbers are measurable after the guitar is strung up and working as a system. It is extremely effective.

I have never used his mass loaded sides, since, with a traditional x-brace (no CF cap), you can simply adjust the top freq very precisely by changing the brace height, once again, after the true numbers can be known by measuring the strung up guitar working as a system.

Trevor needs to mass load his sides because with the CF caps on his falcate design, he can't reduce brace height to adjust the freq.

I have done one guitar with double sides, and it was starkly different than my usual tone. It sounded like it was being run through a compressor. It was richer, and thicker, and took less effort to make 'go', but it was overall quieter with reduced headroom. Fortunately it went to a fella with a light touch and sounded bloody great when he played it, moreso than my ham fisted bashing.

So I feel that using mass loaded sides is actually counterproductive to a traditional build, and if you want to create the 'modern' style, may as well go all in and do the whole falcate system. But that's just me... And that's based off of only one guitar, so inappropriate sample size for hard conclusions...

I'm in the middle of building a guitar right now, and it is the first time that I am installing the two side braces (recommended by Gore/Gilet) with T nuts for accepting mass blocks later on. The guitar otherwise has a traditional, all-wood X braced top and the regular four back braces. We'll see how much help the mass blocks are when I go to adjust the resonant frequencies after stringing it up. At worst, they are just larger than normal side braces, and therefore worth the experiment to me.

Let us know...

I used both mass loading and radial bracing on an X braced SJ which I built several years ago.
Yes, they were effective in adjusting the frequency of both the top and the back.
I have done 4/5 radially braced backs on X braced guitars, and you can adjust the back frequency with this, but this will of course effect the other frequencies.
Never done mass loading only.

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Trevor points out that as well as trimming frequencies the mass loading of the sides can also move the node line of the main top frequency towards the edge, thus increasing the area of top radiating sound and hence loudness.

Dave

That is a good point, Dave.

This is covered, I believe, on page 2-29 and page 2-30 of the Design book. There are 3 photos of what I am nearly sure is the same guitar on these 2 pages.

I think there is a typo in Figure 2.3-13. I believe the stated 189.3 HZ non-mass loaded should be 179.3 HZ since the same guitar is stated as 179.3 HZ non-mass loaded at the bottom of page 2-29. If 189.3 HZ is correct, then the spread (to 168.2 Hz) after mass loading of 21.1 Hz appears to be too large. 11.1 Hz would seem (from 179.3) to be more reasonable. Has anyone ever verified this with Trevor? (I tired, but no answer from him.)

The stated spread for the mass-loaded test of the same guitar in Fig. 2.3-17 is 179.3 - 172.8 = 6.5 Hz which seems reasonable.

Don as you say it is not a big deal to install them and one can then work out how useful it is.

As Ed says let us know.

Dave

Will do. Don’t expect it soon, however. I’m pretty tied up at my day job for the next few weeks/months. Slow going in the guitar workshop right now.

Hi all - i've built a few X braced guitars and used side mass loading to adjust the top resonance as described by Trevor in his books. My experience is that if your sides are laminated, the frequency is a little less sensitive to the added mass. (you need more mass for an equivalent drop in frequency) If you build with normal sides, it was pretty spot on to what Trevor has in his design book. YMMV.

Cheers - Rob

Apologies for not responding Ed H., but I don't recall this question before, from anyone, but thanks for letting me know.

It took me a while to sort out, raking through hundreds of archived files, but I think I've got the answer.

Figure 2.3-13 and the captions are correct. The mass of the mould is very close to 5kg which explains the large frequency drop, even though the mould is not fully coupled to the sides of the guitar. I discovered in an archived, early draft of that chapter the numbers at the bottom of page 2-29 are written as "the top resonant frequency dropping from 189.3 Hz to 172.8 Hz." It looks like I spotted that typo, but erroneously changed 189.3 to 179.3 instead of the 172.8 to 182.8. Likely a middle of the night brain fade! So the correct numbers for the bottom of page 2-29 are 189.3 Hz and 182.8Hz.

I checked that against the Visual Analyser files for that guitar and the T(1,1)2 frequencies all correlate accordingly.



Double sides are not quite the same as mass loaded sides. They add more stiffness than mass, rather than just mass. If the extra mass of double sides is enough to move the T(1,1)2 node line outboard like mass loading does, the effect is to reduce the area of the "horse shoe" of top outside the node line that vibrates in antiphase to the rest of the top in the T(1,1)2 mode. That "horse shoe" can act as a "monitor" for the player and the guitar will sound quieter to the player (compressed?) as that radiating area is reduced. However, the guitar will sound louder to an audience. With X-braced tops, the cross dipole is quite suppressed, which is just part of the deal with X-bracing, so not much monitor effect is evident from that mode. Falcate braced guitars, on the other hand, have a more active cross dipole, so the player hears that as a monitor, whilst the audience gets the benefit of the extra sound radiated out front because of the reduced "horse shoe" radiation due to the mass loaded sides. So with falcate bracing and mass loading, I hear Ed B's "richer, and thicker, and took less effort to make 'go'" but I don't hear compression; I hear louder, as does an audience.

That's probably as clear as mud if you haven't messed with this style of building, but if you give it a go it will all become a lot clearer.

Returning to Ed H's original question, does mass loading change the T(1,1)2 frequency on X-braced guitars, the answer is "Yes". This effect seems to be the same independent of bracing style (X, fan, falcate and lattice (sparse and dense)) and the guitar size (00, 000, classical and all my "modern" shapes).

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

http://www.goreguitars.com.au

Is mass loading really only for CF laminated braced guitars though? I always like to leave a little room for adjustment on the top, and I mean a little, I basically err on the side of taller. But after deflection testing and by comparing notes from previous guitars I get it pretty close. So if I wanted to adjust the body resonance it would mostly be from the back or I thought, mass loading, which I have never done.

Using bridge mass to your advantage can also be used to place resonant frequencies where you want them.
I'm sure you know that jf, but just adding that, for others who may not.

JF, at least in the designs in the book Trevor does not use CF for the x brace or fan braced models so I think the answer to your question is in Trevor's post

Cheers Dave M

Trevor,

You are welcome.

I had PM'ed you a few weeks ago to see which of the numbers was a typo. So its in your inbox. Anyway, thanks for digging through your data to determine the correct numbers.

.

OK, Ed, I've found it and responded to your other points there.

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

http://www.goreguitars.com.au