Official Luthiers Forum!

That's great Chris. That's the sort of effort that produces results. Let us know how it works out for you. I wouldn't be surprised that, as a fingerpicker, you will be pleased.

Hey Claw - hope you don't mind that I resurrected this thread AND a big, warm welcome to the OLF to ya too my friend!

In your post above that I am quoting there is actually a lot of agreement between you and I in what you said. Guitars are a stew, nice way of putting it as well, and it's very possible to put a bag of parts together and have a GREAT sounding instrument!

For some of us though we are wanting to push the envelope so-to-speak and have more control over our resulting tone. That's when things such as bridge weight get more important. Mind you I have never been a grain line counter but now that you brought it up there is still time.... But.... I am keen to weigh every single component part of my own guitars including estimating finish weight.... Wrapped too tight - you bet!

Last summer one of our clients (we have a busy repair shop, Martin authorized, Taylor too) brought us a 30's Martin that is not an all that valuable instrument, maybe $5K in current condition, and not all that rare either. But it's his and as such priceless to our friend and client. Somewhere back in time some Yahoo repair person replaced the original BRW bridge with an ebony one. The current steward of the instrument had only known his ax in the time that he has had it with the ebony bridge.

This was his idea mind you and we only enabled his dysfunction as we love to do at times but he was wondering about replacing the non-stock ebony bridge with a BRW bridge that we would craft from scratch. I was all for it. My business partner was not all that keen that it would make any difference. At the end of the day the client's wishes prevailed and we ripped off the rasta imposta ebony bridge (carefully removed it...) and replaced it with a BRW bridge that was 5 grams less in weight.

What resulted was the guitar was a VERY different instrument. Open, lots of sustain, and seemingly better definition as well. I heard it but I'm nuts.... and the client heard it big time too and was thrilled. Anyway happy camper, end of story, everyone got to where they had hoped to be. Next.

Moving back to the thread Al and Trevor (just occurred to me that if I got their names confused we might have Al Gore.... no offense intended... besides you can claim that you invented the Internet and get massages from.... well I won't go there...) Al and Trevor have done the math and heavy lifting applying physics to what we do.

Something that they can do far better than folks who assemble a bag of parts is approach or achieve to some degree "repeatability" with their creations. Being able to manipulate the response of a guitar is huge AND likely a life long study with some surprises I suspect along the way.

When one is a builder and selling their wares repeatability is HUGE and very desirable.

OTOH as you say guitars are stew I'm also keen to agree with this idea and also offer that in my experience it's pretty difficult to make a bad stew in respect to guitars. All or most of them are going to sound fine and even great I suspect at times too. But the ability to predict the outcomes and target specific models for specific playing styles won't be there to the degree that it is for the guys who do the math.

That's my take on things and it's not a matter of agreeing to disagree with me because I actually agree with much of what you said. In your model guitars are much more likely to be individuals just like we human bags of mostly water (on a Star Trek kick, sorry). And there is something to be said for guitars that are individuals as well in that some are going to be exceptional individuals more than likely.

Again welcome aboard.

Trevor and Al these are some of the very best posts ever IMHO on the OLF that you guys made - Thank You![/quote]


I agree, this is a good discussion, and thanks for the greetings! It's always an

I'm trying a light bridge on my current classical. Attached is a pic of Walnut/carbon laminate per Trevor Gore,
Mike

Although bridge weight is important to the sound of the instrument, I think the stiffness of the bridge also has a large affect. In some sense pyramid bridges could be thought of as the "scalloped" version of the "bridge brace". I have heard that adjusting the wings' stiffness on classical guitar bridges is one way to fine tune their response.

Yes, on classicals at least, the bridge is the stiffest brace on the active part of the soundboard. The reason for the two layers of carbon fabric in the bridge I posted is to engineer the typical bridge stiffness back in that was lost by using a low density wood like walnut
Mike

Ah, but with a low density wood you can just leave it thicker. Also, it's not always true that higher density equals higher stiffness along the grain. That's pretty much true for softwoods, but far from true for hardwoods. Many rosewood samples I've checked are no stiffer along the grain than some of the denser pieces of spruce, and walnut is not all that much less stiff than, say, IRW in most cases, even if it's a good bit less dense. With lower density and nearly the same Young's modulus along the grain, a walnut bridge could well end up having a higher stiffness to weight ratio than a rosewood one of the same size. Again, the only way to know any of this for sure is to measure.

The wings on a Classical bridge add stiffness particularly to the 'cross dipole' and 'cross tripole' modes of vibration. The dipole doesn't produce as much sound as you might think, due to the more or less equal areas in opposite phase on the two sides of the top, but it does affect the pattern of radiation from the guitar, and may have other influences on the sound. The tripole is a good sound producer, often up around 500 Hz (say, C on the high E up over the box). This is probably the main thing people are working on when they shave the bridge wings.

Alan,
Trevor cites research (if I understand him correctly) that finds shorter bridge wings produce better (more?) sound. Thus, the bridge design from his book that I used is about an inch shorter than the normal classical. Have your investigations led you in this direction? I'm a retired engineer, and find that your and Trevor's posts and writings are based more on objective findings than many others. I'm not denigrating the more intuitive luthiers as that has produced most of the early advances, but with my background, I naturally gravitate towards the measurement based research,
Mike

I don't have much in the way of recent direct measurements on that. In the past I've done modifications on 'test mules' and so on looking into that aspect, but didn't have the wherewithal to make some of the acoustic measurements I would now. It certainly makes sense that shorter bridge wings would allow the top to vibrate more freely; you're reducing both the stiffness and the mass. 'More' sound should be pretty much a given. Better is one of the longest 6-letter words out there: just what do you mean by 'better'?

A good example of that would be some of the differences between Classical and Flamenco guitars. Flamencos typically omit the outer two fan braces, as well as making the top thinner. They get away with it structurally by keeping the bridge torque down by having the strings close to the top. The 'main top' resonance on Flamencos that I've looked at tends to be lower in pitch than on Classicals, but not a lot lower. The resonance that shows the largest change is the 'cross dipole', which is very much lower due to the lower stiffness outside of the bridge wings associated with the lack of the outer fan. Shortening the bridge wings, or thinning them, would also move you in that direction. The low cross dipole pitch seems to contribute to the characteristic sound of a Flamenco, possibly by enhancing the way it 'cuts' through a noisy room. There are, of course, other things that they do that tend to move it in the same direction, so it's hard to say which variable in the most important. IMO that's the real key to getting the sound you want: figure out a number of things that tend in the right direction, and do some of all of them, rather than trying to get it all from one big change. At any rate, Flamenco and Classical guitars have evolved in different directions, and what's considered a 'good' sound in one might not fly in the other.