Anyone using tuners for tap tuning?

[scamp]

I want to be a semi tone different on the top and back. I just use my ear .

Higher on the back than the soundboard, or vice versa?

And, now that I have a thicknessing sander, I can control the soundboard thickness much better than before. It seems that some luthiers base their decisions on thicknessing from the stiffness of the soundboard, which they measure by deflection. Is there a guide that tells me how I can rig up something to test that deflection? And what would that deflection be? (I'm guessing that it's proportional to the width of a soundboard, but the actual values are a mystery to me.)

If you are interested in defection measurement testing then you might want to check out this video by Ben Wilborn

https://www.youtube.com/watch?v=m5Epr3U0rDw

He measures deflection of the top and back panels before bracing to help determine thickness, since the stiffness of the wood varies. He also measures the deflection of the top and back of the braced guitar as he thins the sides to get what he is looking for. I am trying to do the same with my build ( see "Wilborn Guitar Attempt " in the " Blog Your Project" section of this site). Unfortunately, the deflection measurement is not standardized. Different people use different methods so it is difficult to compare numbers. I more or less copied Ben's setup so I could use some of his numbers but in the long run defection testing is probably only useful if you make a lot of guitars and keep records of deflection for each guitar build using the same setup.

As far as tap tones, it seems you really need to have the top and back braced and held down (in a jig or the real guitar sides ) to fine tune the braces properly. In a book by Trevor Gore ( Contemporary Acoustic Guitar Design and Build ) he recommends that the top resonate about 110 to 140 Hz ( about between A and C ). The back he recommends be higher by at lease 4 semi tones. He claims that otherwise it interferes too much with the top resonance.

Hope this helps.

[phavriluk]

I'm curious If the 'tuner test' can be applied to a finished and strung-up guitar, I.e., if I tap the top with the tuner on the headstock, would the tuner give me a valid reading?

This may not do that very guitar any good, but seeing as I'm the one who made it, and I've kept notes, I could use the information gleaned to help design future instruments.

Thanks!

[scamp]

I find that it’s easier and better to use a spectrum analyzer. You can download one for free on your iPhone. I use something called sonic tools on my phone. If you tap test the finished guitar you will get the full spectrum of the guitar including the Helmholtz resonance, the top resonances and the back resonances.

Just an FYI. I find the ones on my phone a bit hard to use sometimes. I prefer to use my PC. You can get a free program on your PC called REW. ( https://www.roomeqwizard.com/ ). Works really well.

Here is an example of the spectrum from taping the bridge of a Martin D28.

Martin D28 Top Coupled Spectrum.jpg

The peak at 100 is the Helmholtz resonance ( determined by air volume in guitar body and size of sound hole)
The peak at 180 is the monopole ( primary) top resonance
The peak at about 220 is the back resonance
and the others are resonances from various modes of the top ( cross dipole, long dipole, etc)

Hope this helps.