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Many times we've discussed that when the natural frequency of the top and back are near each other, they will couple and and give a nice bass boost across a broader frequency range. It's always been said to leave the top requency at least a semi-tone higher than the back frequency. What is the reasoning behind the top frequency being higher? Is it just the fact that you want the back stiff for structural reasons? Anyone know how the tone would change if the back were slightly lower than the top?

I ask because I thinned the back bracing on my 000 slightly more than intended on my first build (good learning experience). The back is tuned to an F3 and the top is tuned to a G#3 (whole step apart +/- a few cents). Anyhow, it sounds good just like it is.......but it makes me wonder if I'm missing out on something by having a back more "loose" than the top (maybe the top would move more if the back were stiffer giving better/more sound???). I could change it easily I think by stiffening the 3rd back brace counting down from the neck. With that said, this guitar sounds great!.......good sustain, very loud (100 deg X brace angle), good bass, strong treble with nice harmonics, and responds well to a light touch so even finger picks nice.

Another interesting fact about this guitar, I have the Analyzer Lite software on my IPhone. If I damp the strings and tap the top with my finger, it shows peaks at F3 (for the back) and G#3 (for the top). What's odd is the back frequency is louder......coming in at 104.5db compared to the top at 101.8db (for the G#3 frequency). I wouldn't have thought the back would be louder than the top.....ehen taping the top! If I dampen the back with my belly while tapping the F3 drops away so I know it's the back creating this peak.

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Formerly known as Adaboy.......

I don't think having the top resonance be higher than the back resonance is a golden rule. If I remember correctly, Al Currath aims for similar top resonances in both the top and back because after a few months of being played the resonance of the top drops about a half step to allow for a close pairing without wolf tones.

I think it has less to do with which plate is higher than the other than it does with the relationship between the two. But I'm a relative newbie, so . . .

Aaron

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Aaron Craig

From what I've learned from reading Al's comments, the top should be about a semi-tone lower than the back.
As Aaron stated, the top resonance tends to drop with time, and you don't want the two
resonances to end up on top of each other. That can lead to wolf notes.

Here's a thread from late last year where Al discusses the topic in some depth.

http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=30474&p=407664#p407664

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Gene

Politicians and diapers must be changed often, and for the same reason- Mark Twain

Bump.

Hoping to get a little more feedback on this topic. Thanks!

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Formerly known as Adaboy.......

I believe there's literally hundreds of ways to approach this, many which work. For me, I'm looking to make the top and back either be the same, or the top slightly lower than the back, without the bridge. Installing the bridge will lower the top some, as will string tension, and time. My favorite "tuner" is my ear, but I've recently starting logging the actual frequencies for future reference.

That's just the way I do it. I'm not an expert, and I don't play one on TV.



Edit/Added. You say you like that way the guitar you're talking about sounds. That's great. For my ears, a really loose back can sound really good to the player, but not project as well. If you haven't, have someone else play it while you listen from across the room. It may still sound great. If so that's good. I'd also pay attention to how it sounds, and possibly check the frequencies in a few months, just for future reference.

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I didn't mean to say it, but I meant what I said.
http://www.brackettinstruments.com/

Thanks for that response Woody. I have listned to soemone else play the guitar......but I was always sitting right in front of them. I'll see how it does from across the room.

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Formerly known as Adaboy.......

a couple of months ago Galloup showed me audacity on his laptop. he picked up several guitars and tapped the top and back. they were all different. one was one of his. another was a collings dread. i was most interested in what he had to say about mine. i had the back a whole step higher than the top, and he said that it was what Martin (the other one) did, so I was happy about that, even though it was an accident. I really wish I had a video of that quick demonstration. It seems like a blur now, too much info for me to digest in such a quick passage of time.

Galloup has done quite a bit of research on this and I think I am firmly in his corner on the topic (for now).

I think the bottom line is that you can get different results doing different things and it is much like anything else. there is almost no "better" or even "correct."

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"...you have to get over your strict adherence to your largely imagined notion of absolute perfection..."

There is something to be said about that.
All data that I have read on Cremona violins stated that both Stradivari and Guarneri Del Gesus violins have the back one full step higher than
the top.
The fact that Maple is harder than Spruce has a lot to do with this.
But it surely is not accidental.
Ronald