5 string acoustic bass bass guitar

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Alan Carruth
Posts: 1070
Joined: Sun Jan 15, 2012 1:11 pm

Re: 5 string acoustic bass bass guitar

Post by Alan Carruth »

A Smith/Manzer wedge is actually quite effective, and much easier to do. It may require a deeper case, though.

Added depth doesn't seem to actually lower the 'main air' resonant pitch to speak of. A long time back Fred Dickens made a classical guitar that was 6" deep, checked it out, and then started cutting it down in 1/2" increments, replacing the same back ever time, until he could not go any further. At that point I think the sides were 2" deep. The 'air' pitch rose by 7%; just over a semitone.

There are a couple of different ways to explain this; the one I prefer is that making the box shallower gives a greater pressure change inside for a given a mount of top motion. This strengthens the coupling between the top and the air in the 'bass reflex' action. The coupling serves to push the two resonances apart in pitch; the top moves up and the back moves down. Reducing the box depth does raise the 'real' Helmholtz frequency, but the stringer coupling pushes it back down again, so it ends up not changing much.

Sadly, I never got to see or hear that guitar, and when Fred told me about it he didn't talk about other aspects of the sound that might have changed. The deeper box gives a broader 'main air' resonance, in my experience, which tends to produce a 'rounder' or 'fuller' sound in the low range, all else equal. In the couple of cases where I have cut down the body depth, the shallower box also has a stronger air resonance, which may or may not sound 'louder', especially to the player and close up in front of the guitar. This all gets complicated, especially when you start trying to relate the objective changes to perceptions of tone. At some point it would be useful to duplicate Fred's experiment, but if I do I won't use Brazilian rosewood, the way he did.....

JW Stapleton
Posts: 19
Joined: Thu Jan 02, 2020 9:32 pm

Re: 5 string acoustic bass bass guitar

Post by JW Stapleton »

This is a interesting design, I am to far along to try this now, but if I build another one for myself I would seriously consider this design- if nothing else it would make a better fit against my big belly!😂

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