Tap tone on the closed box

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Tap tone on the closed box

Postby Bryan Bear » Wed Dec 11, 2019 4:16 pm

The thread about tap tone going away when the binding channels were cut got me thinking about what "tap tone" really means and how you use it to predict the outcome.

I'm going to guess that we all have a different idea of what tap tone is and what we are looking for. That could be a thread in and of itself. Clay S. raised the question of how telling a good tap tone really is (especially for the back). Alan Carruth said “I think a well defined top tap tone is probably a good thing. Maybe not so necessary on the back. . .”. I have heard many people say that a wood had no tap tone and made a great guitar anyway.

This got me thinking about the box I just closed up last night. I took it out of the clamps this morning and noticed that it didn’t really have much tap tone at all (more like a thud) when I tapped the top as it sat on its back. When I lifted it up so the back was free, it had a nice tap tone. The back also had a nice tone though different from the top. This was exactly the same experience I had with the last two guitars I made and both of those came out quite nice.

I guess at this point, I’m not really asking a question as much as just starting a conversation and not hijacking the other thread.
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Re: Tap tone on the closed box

Postby Brian Evans » Thu Dec 12, 2019 10:04 am

I like tap tones. I do archtops, and they need a live box, particularly the back, to generate tone and volume. My expectation is that I will build what amounts to a drum, leave out anything that muffles the drum, and I will have a great tap tone. I actually call it a drum tone. As long as it is robust I'm pleased. As important and so far completely out of my control is what I call the open air resonance, the lowest tone that I can sing into the guitar and cause a strong response resonance. It often causes a dead note at the same tone when playing, so I like to get it as low as possible and as far out of the way as possible. Putting the sound hole in the upper bout yielded a low F resonant tone, almost out of the playing range of the instrument, and essentially no dead notes to speak of.
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Re: Tap tone on the closed box

Postby Dave Meyrick » Thu Dec 12, 2019 1:37 pm

Bryan I would think your experience would suggest that you are building with what Trevor G calls a 'live back'. Thus when the box is on the bench the back is deadened so you are not getting that interaction between the top, back and the insides.

Possibly...

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Re: Tap tone on the closed box

Postby Bryan Bear » Thu Dec 12, 2019 3:47 pm

Dave, that is my assumption as well. I don't really have any exposure to non-live backed instruments so I don't know that they tend to sound like when tapped. I would have expected them to sound nicer than what I seem to get. Mine mostly just thud.
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Re: Tap tone on the closed box

Postby Alan Carruth » Fri Dec 13, 2019 5:51 pm

The 'tap tone' that you perceive is generally the 'main air' half of the 'bass reflex couple'. The air and the top (and the back as well, usually) work together to alter the 'natural' pitches that each would make in isolation. Generally on flat top and classical guitars these end up about an octave apart, somewhere near G n the low E string, and the open G pitch. On arch tops they're generally higher in pitch by a whole tone or even more.

When your ear gets a couple of tones that are reasonably close to an octave apart it tends to lump them together, and assigns all of the energy to the lower pitched one, as if it were the fundamental of a complex tone. This is the normal situation in nature, so it's not an unreasonable assumption, but in this case it's wrong, and it keeps you from hearing the 'top' tone. To do that you have to eliminate the 'air' resonance. You do this by blocking the sound hole as much as you can, preferably without actually touching the top. You can reach in between the strings with your fingers to pinch the UTB between them and your thumb. That damps the strings and blocks the sound hole, allowing you to hear the 'top' tap tone as a separate pitch. Of course, without the 'air' tone to perturb it, it's at a somewhat different (usually lower) pitch than it would be with the hole open, but at least you can get a decent idea of where it is. While you're at it you can also check out the 'real' back tap tones as well.
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Re: Tap tone on the closed box

Postby Matt Atkinson » Fri Dec 13, 2019 8:18 pm

For what it’s worth my top rings at Ab when I tap it. Dunno what that means but it’s certainly better than what it sounded like when the binding channels were cut! Probably a good thing that it’s not tapping at one of the open string pitches.
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