What effects sound?

[ProfessorO]

True. However, "affects" is the verb and "effects" is the noun. Easy to get mixed up. Being a recording engineer, I see "effects" in terms of a reverb or delay anywhere I read it. The English language is fun.

Yes. And “effect” can even also be a verb: to effect a change.

[Stopstop]

From a layman's perspective it seems obvious that different bracing would change the sound of the an instrument. Also I feel like there is a bit of marketing that surrounds this question suggesting the same, so it is interesting to learn that it is not the case. Thanks for the educational discussion.

[j. condino]

"EffectceffA"

My new almost palindromic band name.

[PT66]

I think my new band name should be “Can of Worms”. Looks like I opened one. Or maybe two.

[Jim Garber]

No, Dave… as much as I like your band name I think this is an exceptionally apt discussion especially now that we got the grammar out of the way. I, too, was under the impression that bracing affected tone quite a bit but Peter Coombe’s statement is exemplary.

[Richard500]

The physics of a membrane moving air - pretty much the top of a mandolin, must involve not only stiffness to mass, but also how the thing is damped. One could have a very stiff top that also dissipates energy inside; I think plywood is one example, so that motion goes into heat rather than air movement. How the membrane is connected to the rim, and the degree of compliance there also determines where the energy is going. This is part of a basic description, ignoring the actual modes of vibration of a thin plate, and all of the acoustics of the instrument interior. That is, think of the top as the cone of a loudspeaker, where mostly it’s acting like a transformer of mechanical energy in a small area (the bridge) to a large area with a certain impedance to air.
The recognizable ‘mandolin’ sound is the sum of this, plus the acoustics of a ported box, mechanical interactions between strings and string pairs through the bridge, and very likely details of the strings themselves.
I haven’t read any of the technical literature on the subject, but I’m pretty sure that things with plucked strings can be engineered for desired qualities: in the evolution of these, a primary goal was obviously loudness in a defined frequency band, and that’s largely a matter of making a a motion-to-air transducer that’s efficient. The rest are byproducts of the basic design. We must like some of those byproducts.

[Dave Cohen]

Daniel Haines' Nov., 2000 CASJ paper included damping coefficients both parallel and perpendicular. I haven't found that damping varies within species as much as does the perpendicular modulus. I've noticed that some of the very low-density pieces of redwood and western red cedar (ca less than 0.30 g/cm3) had especially high damping, although there were even a few of those samples that have had normal damping coefficients. Given that, I have usually chosen not to make things any more complicated than necessary when posting. It's complicated enough just trying to get people to measure the elastic moduli, which along with density seem to have the greatest impact on what to do with a given plate.

[PT66]

Maybe I could get more from my instruments if I did all these scientific things but usually I tap the braced top with my knuckle and shave the bracing until I hear a clear sound that isn’t a thud. It has worked for me so far.

[Dave Cohen]

To each their own. Seems a bit self-contradictory though, in that you start by asking "What effects sound?", and now say in essence that you don't need anything more complicated than tapping your plates with your knuckles or fingers.

To me, your description of your tapping observations requires some clarification. Having built over 100 instruments, I also tap my plates in addition to doing the "scientific things". The difference between "a clear tone" and "a thud". has to do not with free plate motions, but rather with damping. When you tap your plate and hear a "thud", that means you are somehow damping its motions, likely by holding the plate at an antinode for its free-plate motions (an antinode is any location on the plate that is not on a nodal line). With any plate, in any condition, if you experiment with the location at which you hold the plate, you will eventually find what you are calling "a clear tone". At that point, you are holding the plate at the location of a nodal line, and that is just as valid for a 1" thick board as it is for a 1/8" thick flat plate or for a fully carved arched plate. you will also find that as you change the dimensions of the plate by removing material, the location(s) of the nodal lines may move slightly. So what should happen is that as you start tapping at the beginning of the process, you will hear a higher-pitched "clear tone", and as you remove material, the "clear tone" will drop in pitch as material is removed and consequently stiffness is reduced. As you remove material, mass is also removed, which in general raises frequencies. But in wood, stiffness wins, so you will always see the pitch of your tap tones drop as you remove material. Finally, if you really can't find a holding location on the plate that results in a clear tap tone,, you likely have a piece of wood with relatively high damping, so you will never hear a clear tone with that particular plate.

[PT66]

When building instruments in a vacuum (no other instrument builders to collaborate with in real time) you go by what feels right. My original post was about two instruments that I felt should sound quite different based on wood choice and bracing pattern but didn’t. I did use the same method of “tap turning” the tops. Based solely on 60 years and over 200 instruments of experience. When I started building there were no schools, no Guild of American Luthiers, and very few books on the subject. I respect all the scientific research on the subject. I just don’t have the patience or equipment to do that kind of analysis.

[Dave Cohen]

I can't help you with the patience. But if, as I have pointed out several times recently, you read the articles in American Lutherie by Jim Blylie, particularly in AL#128, he solves the equipment problem. He shows you how to make a very simple apparatus for measuring elastic modulo. Can be made from just about anything - scraps of plywood, or mdf, or osb, or ???,,,,, And his measuring implement is a ruler. I improved on that only slightly by using an ordinary dial indicator (ca $50).

[PT66]

It just happens that I have that issue. I will reread it.

[PT66]

You might want to look up this issue. An interesting article about a tenor lap steel.

[peter.coombe]

Just to illustrate what Dave Cohan has said about tapping free plates, read my article I wrote way back in 2004 on free plate modes of mandolins. There is a diagram of the lowest 4 modes and it is explained where you hold the plates and where to tap to hear the modes (or "tap tones"). Basically you hold on the node and tap on the antinode, but because the patterns are different for each modal frequency, you need to hold and tap at different places for each mode. Gets very confusing if you can't see the nodal patterns, but once you see the patterns it is obvious. This is all very interesting stuff, but as Graham Caldersmith once told me, the difficult part is the interpretation.

http://petercoombe.com/publications/jaamim7.html

[Bob Schmidt]

Thanks for the references. My AL subscription started at 129 so I will have to see if I can get the back issue. I am reading the article in Peter's link and am finding it quite informative. This will help in the 2 flat top OM's I am currently building since I am about ready to start the tops.
This is a very interesting thread, thanks for posting.

[PT66]

Bob, I can send you some old issues of AL if you pay the postage. I don’t have every issue but probably about 50 or so.

[Bob Schmidt]

Dave,
That would be great. I have every one from 129 up to the present.
I will PM you with the address and you can let me know how to cover the shipping.

[Mandoplumb]

Never made an instrument, done minor repair ( very minor) and set up quite a few mandolins. But I have played one for about 60 years. So with that qualifications my answer to the question “What affects sound” is EVERYTHING!!! From wood to bracing to strings to picks to shape of case to color of shirt you are wearing!!

[HoGo]

So with that qualifications my answer to the question “What affects sound” is EVERYTHING!!! From wood to bracing to strings to picks to shape of case to color of shirt you are wearing!!

And don't forget your yesterday's lunch!

[Bill McCall]

Let me take a moment to adjust my hearing aids.

I’m so glad we all have perfect hearing.

[Mark Gunter]

Never made an instrument, done minor repair ( very minor) and set up quite a few mandolins. But I have played one for about 60 years. So with that qualifications my answer to the question “What affects sound” is EVERYTHING!!! From wood to bracing to strings to picks to shape of case to color of shirt you are wearing!!

lol, had I responded to this thread, that is what I would have written. Pretty much EVERYTHING including sunspots affects sound (and thank you for using the correct spelling).

[PT66]

I suppose you are right. Everything affects the sound of an instrument. But not to the extent that some people think it does. There have been “behind the curtain tests” that have proven that two guitar built identical in every way except for the wood can not be told apart. I guess my original point was that all these factors do not have as great an influence on the sound as some people say they do.

[Mark Gunter]

Can’t tell two guitars apart in a blind test, okay, but test them in a church first, then in the subway or on the street and see if the sound is affected. Also, you have people, with human error in hearing and recollection, trying to distinguish between guitars in your test. Maybe could say that many, many things affect the sound more than the things you originally assumed. Dunno. But interesting I suppose.

[TX2AK]

I’ve not built a mandolin, but have made a few banjos and upright basses. I fall in the “everything” camp. I have a lot more experience with banjos, so that’s my frame of reference. A super-pro banjo player once told me that he played a slightly bent neck on his favorite banjo, because despite trying over and over, he had never been able to find one on that banjo that sounded better. There’s a lot going on with a banjo - resonator, head, tone ring, rim, bridge, strings, etc., before the neck comes into play; and he was positive. He even said he and a top luthier had performed tests, and he could hear differences and identify that neck on a variety of banjo pots. For a trained ear, it has to be the case that everything affects the sound. How that could not apply to a mandolin or fiddle with far fewer parts, is beyond me. It can’t just be the top and bracing that affect sound. That’s like saying the head on a banjo dictates it’s sound - maybe head and tone ring - and that is decidedly not the case.

On the other hand, there’s the story about the man who walked up to J.D. Crowe and asked to play his banjo because it sounded so amazing. The man played it and shrugged, “hmmm, sounds just like mine.” The player has to be the #1 factor, and ability to hear subtle differences is key as well. I’ve had the opportunity to play a Collings MF, Pava F5, Gibson F5G, and a Paganoni side by side (all inartfully, I’m sure), asking about perceived differences in sound, and the 3 listeners (one musician and 2 fans of music) all said, “they sound like mandolins.” Maybe some of that is going on with the instruments you made?