Official Luthiers Forum!

On my current build (my 7th) I was a bit concerned about the resonance of the soundbox when tapping it, prior to routing binding channels and gluing the binding - frankly it sounded like a bag of rocks. I was as careful with the fit of the top and back to the sides as I know how to be, and used radius dishes to sand the sides to the proper radius (and taper and glue the braces to both side and back).

When I routed the bindings, and glued the ebony bindings in place, BEHOLD, a musical instrument! The soundbox now has a nice, deep ringing quality, like some of my previous guitars. In another post I'll probably ask for some advice on the specific frequencies of the resonance, but anyway, it's a much, much more responsive, clear and musical sound with bindings, than before the channels were routed.

What's going on here? Totall typical, opr evidence of something suboptimal in my fit on the top and back? Thanks!

I've noticed this in all my builds (only 4!)
I was told on my course to expect it, and have seen it suggested that binding and purfling on heavily decorated models may contribute to a slightly better sound than simpler B & P schemes.

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

I had the same thing happen on my last one. I was ready to give up on this hobby after hearing it. Once the binding was on it actually had a nice voice. We'll see once I string it up.

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Wisdom is justified by her children

What you guys may be noticing is that when the box is closed and you have any leaks such as you routed for your linings and exposed kerfs but have not yet installed the linings or any other leaks the integrity of the box in terms of being air tight is not there - yet. So when you tap it may sound like that bag of rocks. Install the bindings and eliminate any previous gaps/leaks and the box comes alive.

Somogyi will tell you that a guitar is an air pump. If it's leaky it can't pump much air eh....

Sound like what you are noticing?

Hesh,
I can't say about the others, and the "air pump" reason you indicate makes perfect sense if there were gaps.
For me I was talking the sound after fitting back and sides, routed flush and sides sanded, but before routing the ledges.
Then comparing it to what I get after fitting bindings & purfling. I do find the volume increases.

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

It seems to loosen the top, and to some extent the back, where they're glued to the sides and linings. I've compared resonant frequencies before and after routing, and the routing causes a drop. After routing, the plates are sitting an a narrower edge, perhaps allowing them to move more freely? I've also found that gluing the binding & purfling on tightens it back up, but not all the way.

Pat

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formerly known around here as burbank
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http://www.patfosterguitars.com

All -

Thanks for your responses. Glad to hear that I'm not alone.... One would have thought that I'd have noticed this on the previous builds, but I'm learning something new on every one -




Hesh, this makes a lot of sense. I expected that the "pump" would not function well, and would be leaky after routing the binding ledge. What I was a bit concerned about is that even PRIOR TO routing for the bindings, the box was not at all responsive. I guess there must have been some leaks in the glue joint between top and sides, and top and back.

(I was also concerned that an experiment in laminated braces had gone horribly wrong. I do think that these braces have caused the top to be a bit tighter than with plain spruce braces, but I think I can thin the top a bit on the edges, to increase the responsiveness.)

Anyway, the good news is that once the bindings are glued, it's tight, and rings well.

Hesh,
What about a big leak called a sound port? How does that fit into your view? I do not notice a difference in tap tone of the body when comparing before and after binding. Maybe reverse kerfing seals better????

Perhaps many small leaks would have more of an effect than one big one - sound port.

I don't know!

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"An adventure is only an inconvenience rightly considered. An inconvenience is an adventure wrongly considered." G. K. Chesterton.

Steve the OP or anyone else for that matter didn't introduce a sound port to the questions here so I didn't address it. But you are more than welcome to....

My point is that a leaky box sounds differently than a sealed box with only the sound hole being open. Haven't you ever attached the plates and had a nice resounding tap to the box. Then when you route for bindings and expose some open kerfs in the linings that resounding tap goes away. Install the bindings and presto the resonate box is back. That is what I am referring to.

IIRC in another thread some years back where OLFers were discussing if bindings have any sonic value someone perhaps Al pondered if there is indeed any sonic impact, and he was not saying that he thought that there was but just pondering the question that perhaps there is a "hinge" effect from bindings.

Anyway sound ports are over my head and out of my experience so you guys will just have to figure that one out for the rest of us. But if I was stupid enough to consider it anyway, and I am....., I would consider the sound port to simply be just like the sound hole and when properly calculated sized in conjunction with the sound hole for a targeted response. Add leaks that are large enough to a guitar with a sound port and sound hole and I'll bet it goes dead too just like the OP's original example.

Oh Al?