High frequencies

You can ask questions here about Trevor and Gerard's exciting new book on Luthiery.

Moderators: kiwigeo, Jeremy D

Post Reply
blackalex1952
Blackwood
Posts: 776
Joined: Tue Aug 27, 2013 6:36 pm
Location: North East Victoria

High frequencies

Post by blackalex1952 » Fri Jan 24, 2020 7:38 pm

I have made a guitar using an Italian Alpine spruce soundboard. Previously, I have used my stack of Sitka for my steel string guitars. I may be guilty of changing too many variables simultaneously! The guitar is an L-OO design with forward shifted bracing and two finger braces, instead of one as per the original Gibson idea. One of my friends dropped by for a truss rod adjustment on Gibsons version of an L-OO. I noticed that the single finger brace on the Gibson version was very peaked with lots of scalloping either side of the peak in the brace .The comparison with the guitar I have made is that my instrument has a nice mellow tone, but lacks that zingy stringy sound the Gibson had- the breathiness, shimmer or chime for want of better words. I recorded my guitar today and used a parametric equaliser to experiment on the texture of this guitar and I figure from that test that the guitar sounds more "zingy" with a boost a boost at around 8K. Visual analyser, when I use it, only seems to want to go as far as around the 2k mark and is relatively useless for these higher frequencies. Unless I'm not using it properly. I have the books, and table 3.2-6 talks about these frequencies. The top is very lightly braced and not scalloped, but tapered. So! How do I get that characteristic that I'm looking for, and how can I help it along in a finished guitar. I have been told by a couple of luthiers who's guitars I like the sound of, that they leave a lot more wood in the braces than I do, trading the weight, therefore the inertia of the top, for tone. Would the Alpine spruce account for the tone I'm getting, where that high frequency response in the 8k region is damped somehow? I used adirondack bracing, imagining that it would allow a lighter brace carve. The cross dipoles and tripoles are obviously being affected by the extra finger braces, but of course those frequencies are much lower than the 8k region. I admit that I'm still learning, and my output of instruments is low for reasons of my health. All help appreciated!
Cheers! Ross
"Everything I say on the topic is based solely upon inexperience and assumption!"

User avatar
kiwigeo
Admin
Posts: 10582
Joined: Sat Sep 29, 2007 5:57 pm
Location: Adelaide, Sth Australia

Re: High frequencies

Post by kiwigeo » Tue Jan 28, 2020 8:45 pm

I was always lead to believe that anything above 1K really isn't worth worrying about. Happy to be proved wrong. Trevor??
Martin

User avatar
Trevor Gore
Blackwood
Posts: 1605
Joined: Mon Jun 20, 2011 8:11 pm

Re: High frequencies

Post by Trevor Gore » Thu Jan 30, 2020 10:18 am

kiwigeo wrote:
Tue Jan 28, 2020 8:45 pm
I was always lead to believe that anything above 1K really isn't worth worrying about. Happy to be proved wrong. Trevor??
It's certainly difficult to target specific modes of vibration up beyond 1k Hz, so it's down to doing things that support high frequencies generally, like keeping monopole mobility high and overall moving mass low.

After that, it's set-up details and that most slippery of properties, material damping, which is hard to measure in any meaningful way. What we need is a measurement of the vibration absorption properties of materials across the audible range and preferably be able to measure it in a comparable way that is independent of the material's shape and size. Materials like Tusq, for example, seem to be lower damping than bone in my experience (though others have different experiences).

I had a phone call from Ross and we talked though a lot of options specific to his build. He appears to be doing most things right and has had great results on his Martin based builds, so it remains a bit of a mystery why this Gibson style project is different.

We developed a list of ideas for Ross to try and he will report back if he finds something that works.

blackalex1952
Blackwood
Posts: 776
Joined: Tue Aug 27, 2013 6:36 pm
Location: North East Victoria

Re: High frequencies

Post by blackalex1952 » Thu Aug 13, 2020 1:33 pm

Trevor, that was a great phone conversation! Very informative for a start. Thank you for your generosity! I haven't called you back to report as I have been unwell. I was initially spooked by a Gibson, which retails for around $6000. I couldn't understand the taps I was getting on VA but suffice to say, they certainly seemed incorrect. Being overbuilt, it had a lot of sustain, which would be expected. The Gibson returned to me for further repair as a music shop "luthier" had replaced the original bone saddle with a thinner Tusq saddle which was rolling forward because it wasn't wide enough, causing intonation issues and also "grabbing" in the saddle slot on the top and bottom contact points along with poor transmission of sound on the bottom E string via the piezo pickup. I don't know how these guys get and keep their jobs!
So the Gibson returned and I had by then got my L00 strung up having achieved more finessing of the braces. For my build, I had intended to create a good player with a lightish action suitable for both a beginner or a good muso to enjoy. I wanted more in the bottom end with a rich bass, so I had forward shifted the braces in my design. I modified brace angle from the original L00 design as well, the forward shift caused that. The consequence, which I'd planned for, was a larger area of the soundboard lower bout available for bass, and a different bass bar configuration, along with slightly less bridge contact with the lower X braces, but not enough to have to move the bridge forward as well. I used a scrap of Brasillian Rosewood for the bridge plate and a 25g pyramid bridge. My guitar had resonances in pretty good places, and ate the Gibson for breakfast when compared! Mine was a a lot more bassy but not tubby, still a nice tight picking sound, so the overbuild on the Gibson probably accounted for a little more in the high frequencies? Mine still had a more pleasing balance to my ear, but it just wasn't what I'd describe as really "Zingy"or perhaps "Silky" in the highs. But it did pack a punch when picked up the neck and was a lot louder. I've not got to where I have heard a good player attack it whilst listening from a distance.
I think that it's absurd that a Gibson of such poor quality can achieve such a high price, but that's branding and marketing for ya! The Gibson is X braced, and they seem to have achieved a quiet ladder braced sound with more attention to looks than tone. The original that it was a copy of was probably ladder braced anyway and thrown together in the Kalamazoo factory. Cheers! Ross
"Everything I say on the topic is based solely upon inexperience and assumption!"

User avatar
Trevor Gore
Blackwood
Posts: 1605
Joined: Mon Jun 20, 2011 8:11 pm

Re: High frequencies

Post by Trevor Gore » Sat Aug 15, 2020 10:13 am

blackalex1952 wrote:
Thu Aug 13, 2020 1:33 pm
Trevor, that was a great phone conversation! Very informative for a start. Thank you for your generosity!
No worries, Ross!
blackalex1952 wrote:
Thu Aug 13, 2020 1:33 pm
My guitar had resonances in pretty good places, and ate the Gibson for breakfast when compared! Mine was a a lot more bassy but not tubby, still a nice tight picking sound, so the overbuild on the Gibson probably accounted for a little more in the high frequencies? Mine still had a more pleasing balance to my ear, but it just wasn't what I'd describe as really "Zingy"or perhaps "Silky" in the highs.
Remember that tone as we hear it is the balance of the amplitudes of the frequencies that are there. So more bass can come across much the same as less highs and a volume shift. I think I mentioned it when we spoke, that to get those "airy" highs you need to conserve all those high string partials without producing dissonance. So it helps to think about the guitar as a differential filter (as you have found) using the ideas in Section 3.2 et seq.

Post Reply

Who is online

Users browsing this forum: No registered users and 37 guests