composite vs. conventional tonewoods

[barry k]

If this was covered in another thread somwhere, i apologize. I havent yet had the opportunity to see in person , or even hear one of the composite instruments. They look great, and really like the idea of using composites, I worked in the aircraft industry for 35 years where composites were used a lot . For the people that have them , or played them , tonewise what are the sound characteristics vs. conventional tone woods? I was wondering if anyone had built instruments out of conventional wood and then lined the instrument with a composite material. If they did, what were the results. If it hasnt been done, what would you imagine the results would be? I have used composite cloth for the last 12 years for repair work, (super for upright basses), and have been happy with that process. Never have totally lined the interior of a mandolin. The people that manufacture the cloth material , claim it is tonally inert when saturated with the calayst and cured , do you agree??

[dunwell]

Howdy BarryK, can you please expand a bit on what you mean by "composite" tonewoods. From your post I assume you are not talking about double-top type composites but things like making double sides with graphite cloth or similar, right?

Alan D.

[MikeEdgerton]

Other than discussing the Peter Mix instruments and one other builder that I can't recall at this point, there really hasn't been a discussion about mixing the materials that I'm aware of.

[Tony Sz]

The only composite in mando building that I'm aware of, (outside of Peter Mix's work) is in the area of tone bars. I know Grady Jones uses a wood, graphite combo in his tone bars, (which are curved, not straight, by the way)

[barry k]

Yes Alan, i was wondering about standard tonewoods lined with composite cloth ??, but inside the whole mandolin

[man dough nollij]

I saw a piece somewhere about the construction of guitars. The way I remember it, the guy was making guitars specifically for flamenco. The tops were made of two paper-thin layers of wood, making a sandwich with a thin layer of Nomex honeycomb in between. Can't imagine the advantage of that, but it was certainly high-tech.

I've seen pictures of bowlbacks here on the Cafe that were lined with cloth or newspaper. Probably not a big strengthener, but it surely affected the sound.

I'm a pretty noobie player and certainly not an acoustic engineer, but intuitively I wouldn't think that a composite layer on the inside would be a good thing. I imagine an acoustic instrument as a somewhat flexible box that can move and resonate in many different ways. I'm guessing that a totally rigid box would not produce good tone. Applying carbon fiber, fiberglass, or some other composite lining to an instrument would kill the tone, in my ignorant opinion. :whistling:

[Rick Turner]

There's no such thing as tonally inert unless you're talking lead or foam rubber or some other material that simply absorbs vibration. Even all-carbon fiber instruments have characteristic resonances.

I've been working with carbon fiber composites in instrument building since 1976, and I now do like to combine wood with CF in primarily structural elements of the instruments. In necks I find the addition of CF stiffening bars tends to even out string response. As a topping for guitar back braces, it helps make the backs very rigid and tends to make the instruments project really well. I also use CF tubes as flying buttresses to support the neck block inside my guitars. I'm now using CF to line my reverse kerfed lining for the guitar tops, and on one guitar I made the top binding out of CF as well. That's one stiff rim!

For a look at all of that, check the Summer 2008 issue of Fretboard Journal. There are a number of photos of the interior of one of my guitars.

[artboy]

Have a look at http://www.danielbrauchli.com/ he has some interesting sonic ideas about mandolin and guitar construction.

[Dan Voight]

I think there is great potential in the area of incorporating these materials into traditionally assembled instruments as we know them. Personally, I love the sound of some of the carbon fiber Cellos. The Mix mandos sound nice also. I plan on doing some experimentation down the road simply because of the strength to weight ration that carbon fiber has.

I second the fact that Grady Jones uses laminated "nodal" tone bars. Those suckers sure come out strong. I apprenticed with him for about a year.

[dunwell]

I saw a piece somewhere about the construction of guitars. The way I remember it, the guy was making guitars specifically for flamenco. The tops were made of two paper-thin layers of wood, making a sandwich with a thin layer of Nomex honeycomb in between. Can't imagine the advantage of that, but it was certainly high-tech.
.......

What you are describing is double top construction that I was referencing earlier. Take a look at http://dunwellguitar.com and the link on the left for Double Tops for more info.

Alan D.

[man dough nollij]

Hey Alan,

Yep, that's the exact site I was thinking of. That is some of the most intricate and scary workmanship I think I've ever seen. By scary I mean that I can see myself destroying 147 tops before I ever got one right. Thanks for posting that!

Lee

[Rick Turner]

The quality that CF has is not strength, it's stiffness. Different engineering issue.

[EffimoFunk]

These guys were at NAMM this year and I thought this was interesting.

http://www.flaxwood.com

Basically, they take spruce and create a "mash" material that can be injection molded. They take this and make some interesting thinline guitars. My initial guess would be the same could be applied to a mandolin (at least with some pieces).

The guitar played well and had a feel of a graphite guitar. Pretty nice all in all. It is definitely an interesting idea so I thought I would share it.

[barry k]

Rick, are you truly saying that CF is not strong?, Im glad I didnt know that when I was in Iraq with my CF helmet and bullet proof/ flak vest.THEY said it would protect me. I have worked on modern fighter aircraft with their control surfaces ( ailerons, flaps rudder and elevators) made of total CF, with the manufacturer choosing that material for strength to weight ratio. Manufacturers are also making propellers out of CF, now that blows my mind!!, incredible forces at work there, and the props hold up!. To me , I think that CF material is one of the top ten inventions of the last 30 years, well that, and Velcro of course, how else would I keep my sneakers on?

[Bernie Daniel]

barryk:Rick, are you truly saying that CF is not strong?, Im glad I didnt know that when I was in Iraq with my CF helmet and bullet proof/ flak vest.THEY said it would protect me.

Barry I certainly agree with you that CF is strong -- on a weight basis it is cF fiber stronger than steel wire. Reason? Because it is so light that the steel wire matching its weight would not have much tensile strength. So CF is very hard, very light, and very "strong".

It is also very brittle -- due to the fact Rick mentioned that it is so inflexible. It breaks before in bends. And of course CF materials are excellent at providing protection from projectiles.

But it is curious to me that it makes for a great instrument sounding board -- I think of all the years I watched Formula 1 and Indy race cars with their very light and very strong CF body parts that nonetheless shattered into thousands of tire-puncturing shards of CF on an impact from a crash.

It did not occur to me that this would make a good material for a mandolin top as well! :)

Thanks for serving in the military and I am glad you are back safe and sound.

[Rick Turner]

You guys are confusing tensile strength with tensile modulus...stiffness; in real and engineering terms they are different qualities. Stiffness comes from fibers that tend not to elongate much under stress until they just snap. Strength is a measure of ultimate yield point. Yes, CF is strong, but Kevlar is stronger (but less stiff) and would have made up more of your bullet proof stuff. These are subtle but very important issues when dealing with the why and how of designing structures, instruments, helmets, or whatever.

The engineering factor here is Young's Modulus...the number that will predict how stiff a structural member will be based on the resistance to stretch of the material. Young's Modulus is also one of the numbers that tells you why spruce is such a good top wood...it has an excellent stiffness to weight ratio.

[first string]

What you are describing is double top construction that I was referencing earlier. Take a look at http://dunwellguitar.com and the link on the left for Double Tops for more info.

Alan D.

I've become very intrigued by double top guitars. The ones I've heard were all extremely loud, but had a more natural sound than some of the Smallman style CF/Lattice guitars, though I guess it's a similar concept in a lot of ways. I couldn't tell you what accounts for the difference. It could be because double tops usually have standard (albeit substantially lighter) bracing in addition to the NOMEX reinforcement. Or it could be the second skin of standard tonewood. Who knows. Even so, some double tops sound a little "cold" too...especially when strummed. Of course these techniques are just starting to gain traction in the steel string world anyway. On a mando I think they might make for a somewhat brittle tone. It's just speculation, but I would expect a lot of power, but also some serious harshness. When it comes to OMs or bouzoukis on the other hand, I think there is a lot of potential there.

Now laminating the tonebars with CF is something that has intrigued me for a while. Don't Phoenix mandolins use a scheme along those lines?

[Bernie Daniel]

Rick Turner: You guys are confusing tensile strength with tensile modulus...stiffness

I don’t think I am confused. But I do think I agree with you.

Tensile strength is just the measure of the force required for a material to break under "separation" stress – I used wire as an example. Tensile strength is just a number and it’s larger for carbon fiber than steel.

Elastic modulus on the other hand is related to the force required to deform or bend that object. The term “modulus” refers to the fact that the more deformation you want to cause the more force will be required and it is not linear often -- so the relationship is described by a function.

I think that the elastic modulus is merely the slope of the function describing force need to overcome resistance as the deformation increases.

Tensile modulus is the same as elastic modulus and Young’s modulus is one of several formulas for computing elastic modulus?

Back the topic of composite tops my uninformed opinion would to take Rick's point that the elastic modulus is what is important for this topic of instrument soundboards. Hence I am not confused?

Now how does the elastic modulus of the composites and spruce compare? :)

[johnwalser]

I recently purchased a "Little Martin" guitar ( 23" scale with a very small body ) for travel and it is a composite body of wood pulp and plastic, from what I understand. It doesn't sound s good as my Takamine full size koa wood, but I have played many solid top guitars that this puppy will blow the doors off. It is the perfect travel guitar in my mind for tone, playability and the puppy even stays in tune. I'm not sure if this type of material could be used on a mandolin because of tonal considerations and higher pitch requirements. The few Mix carbon fibers I've played were quite good, but still not a match to solid spruce.
John

[Rick Turner]

I'm going to say it again, stiffness and strength are different qualities which can be but are not always directly related. I'm not saying that carbon fiber is not strong, but it is the resistance to elongation which is it's main important property to us. Under increasing load, it will barely stretch until it reaches it's elastic limit and then it just pops unlike other materials that deform, stretch, and then let go. This is where Kevlar (aramid fiber) is superior and is why it is used in bullet proof vests and helmets, sometimes along with carbon fiber. Each is chosen for it's particular qualities.



http://pslc.ws/mactest/mech.htm

[first string]

I'm going to say it again, stiffness and strength are different qualities which can be but are not always directly related. I'm not saying that carbon fiber is not strong, but it is the resistance to elongation which is it's main important property to us. Under increasing load, it will barely stretch until it reaches it's elastic limit and then it just pops unlike other materials that deform, stretch, and then let go. This is where Kevlar (aramid fiber) is superior and is why it is used in bullet proof vests and helmets, sometimes along with carbon fiber. Each is chosen for it's particular qualities.



http://pslc.ws/mactest/mech.htm

I wonder if this is perhaps why I prefer the the double tops which rely on NOMEX for reinforcement (which I believe is Kevlar based) and not the CF lattice style. I've always read that stiffness is to be desired as long as long as it doesn't come at the cost of increased weight...But perhaps there is such a thing as too stiff. Thoughts?

[Rick Turner]

The stiffness can be controlled and designed in, just like with wood, but you've got less weight to deal with. The double tops and lattice bracing so far seems best used on nylon string guitars where getting smooth and quick treble response is a real issue. Steel string instruments, mandolins and guitars, are quite different in what we seek tonally. Yes, you can make a lighter weight top, but if you don't balance that with making the edges more flexible or by working the monopole response more, you may wind up with an instrument that sounds too trebly and lacks warmth. I'm finding that to get the sound I want in instruments, blending the new materials with the old gets me where I need to go.

[first string]

That's interesting. The steel string double tops I've heard all had booming bass. Really powerful treble too, but the volume and sustain of the bass is what I noticed. What bothered me about the worst of them was that they sounded kind of metallic when strummed. That said, the best ones really seemed like they extended the sonic pallet, so to speak. I'm seriously considering one in fact.

I haven't heard of as many people using the CF lattice on steel strings, and based on the one I have heard, I can understand why. Sounded like a banjo. Even on classical guitars, I'm far from sold. I don't know enough about that genre to really judge, and John Williams sounds good to me (though he really seems to get a lot of classical guitarists incensed), but a number of other players who use Smallmans and the like, sound...well, a little like Earl Scruggs.

[dunwell]

I've become very intrigued by double top guitars. ......... On a mando I think they might make for a somewhat brittle tone. It's just speculation, but I would expect a lot of power, but also some serious harshness. When it comes to OMs or bouzoukis on the other hand, I think there is a lot of potential there.


Interesting on that take. For OM and smaller bodies, take another look at my web pages and the Serenade model. With mandos I think that the tone can be controled, I'm suspecting that you need to be careful not to have too tall an arch to the top, less than a normal Loar, to let the bass side come through with a nice woody mix. A lot of the DT guitars you may have heard were probably over-braced and that makes them pretty dry sounding. It is a common error with DT's when folks first start building them. For making a real mando it is a technical issue that I'm trying to figure out, how the heck to get the skins to form an archtop design. I'm working on it. So in the mean time I built a flat top pin bridge bouzouki, just finished it in January. Dang thing is so loud I have top stand across the room to play it, but still has a good tonal range. For any of you Colorado folks, I'll have it down to the Mid-Winter Bluegrass Festival in Denver on the 20-22, table in the Vendors room.

I just got some info up on that today that I was going to go over more before I posted here, but what the hay. If you go back to my web sit at
http://dunwellguitar.com
and click on the Luthier Links, part way down the page in the mandolin sections is a blurb on building a bouzouki. This is all very fresh and probably has typos, missing links and such despite my having gone over it a zillion times. If anyone finds errors please pop me an email offline from the group to
alan at dunwellguitar dot com

Sorry, this got a bit more spammy than I intended.
TIA,
Alan D.

[man dough nollij]

For making a real mando it is a technical issue that I'm trying to figure out, how the heck to get the skins to form an archtop design.

Here's a thought: carve the desired contour into a blank of, say, 1/4" thickness or thicker. Carve the mirror image of it into a supporting fixture with a CNC mill, so that the top blank fits down onto it perfectly. Then mill it out to 0.06" or whatever with the mill. I can't imagine any manual way to work wood that thin without tearing it up. It's amazing that you can do it on flat pieces. :disbelief:

[Bernie Daniel]

Rick Turner: I'm going to say it again, stiffness and strength are different qualities which can be but are not always directly related.

Ok, and I agree -- I don't think anyone was taking issue with that? :)


Rick Turner: The stiffness can be controlled and designed in, just like with wood, but you've got less weight to deal with. The double tops and lattice bracing so far seems best used on nylon string guitars where getting smooth and quick treble response is a real issue. Steel string instruments, mandolins and guitars, are quite different in what we seek tonally.

Please clarify. I don't follow -- regardless of what material the string is made of the idea is the vibration of the string sends energy through the bridge to the move the top board -- yes?

So, what aspect of this leads you to suggest that the desired results will be different "tonally". It seems to me the only difference between a nylon guitar and a steel string one might be quantitative (i.e., in term of string energy generated) not qualitative as you seem to imply? If I understand your point.

Getting a good treble response is not limited to nylon string guitars IMO.

Many mandolins are lacking on one end of the scale or the other -- lacking tonal balance across the four courses.

If fact, and I have no data here -- but my impression is that with Gibson mandolins you often have relatively stronger bottom end and a weaker reponse on the trebles courses -- and again just my opinion -- I think Collings mandolins are the exact opposite. Webers tend to be more balanced.

At least that is what I hear.


Taking it a step further. Those who have played the Mix carbon fiber mandolin seem to think it works quite well indeed. I have never played thus have no opinon on it.

[Rick Turner]

re. Nylon vs. Steel...there's the need for a top to control frequency response, and too much treble from a steel string guitar gets into fingernails on a blackboard territory pretty quickly. The harmonic content of the different types of strings is very different.

Working with these "new" materials is interesting because you do have such amazing control over the independent variables of structure and tone. I think there's a lot of potential with CF and other composites. One engineer I worked with back in the early 1980s described CF as "wood that we can design from scratch."

Just be careful re. throwing the baby out with the bath water and praising the emperor's new clothes, to throw in couple of cliches. What I found with the all CF necks was that many player felt the sound was too cold...and that's one of the reasons I now combine CF with wood...to try to get the best from each.

[Bernie Daniel]

Rick Turner: Working with these "new" materials is interesting because you do have such amazing control over the independent variables of structure and tone. I think there's a lot of potential with CF and other composites. One engineer I worked with back in the early 1980s described CF as "wood that we can design from scratch."

Yes, that is a pretty interesting thought. What about the composite woods? The constuction industry is building homes from composite woods these days -- do you think these have any potential as tone woods? Not for carving but as molded pieces?

[first string]

Interesting on that take. For OM and smaller bodies, take another look at my web pages and the Serenade model. With mandos I think that the tone can be controled, I'm suspecting that you need to be careful not to have too tall an arch to the top, less than a normal Loar, to let the bass side come through with a nice woody mix. A lot of the DT guitars you may have heard were probably over-braced and that makes them pretty dry sounding. It is a common error with DT's when folks first start building them. For making a real mando it is a technical issue that I'm trying to figure out, how the heck to get the skins to form an archtop design. I'm working on it. So in the mean time I built a flat top pin bridge bouzouki, just finished it in January. Dang thing is so loud I have top stand across the room to play it, but still has a good tonal range. For any of you Colorado folks, I'll have it down to the Mid-Winter Bluegrass Festival in Denver on the 20-22, table in the Vendors room.

I just got some info up on that today that I was going to go over more before I posted here, but what the hay. If you go back to my web sit at
http://dunwellguitar.com
and click on the Luthier Links, part way down the page in the mandolin sections is a blurb on building a bouzouki. This is all very fresh and probably has typos, missing links and such despite my having gone over it a zillion times. If anyone finds errors please pop me an email offline from the group to
alan at dunwellguitar dot com

Sorry, this got a bit more spammy than I intended.
TIA,
Alan D.

Very interesting. I would love to hear a sound clip of that, being that I don't think I'll be making it out to Colorado any time soon. :(

A double top bouzouki is very much something that I would consider when the funds allow...Though I was thinking more of a guitar bodied one. Now that would be one powerful instrument!

[dunwell]

Here's a thought: carve the desired contour into a blank of, say, 1/4" thickness or thicker. Carve the mirror image of it into a supporting fixture with a CNC mill, so that the top blank fits down onto it perfectly. Then mill it out to 0.06" or whatever with the mill. I can't imagine any manual way to work wood that thin without tearing it up. It's amazing that you can do it on flat pieces. :disbelief:

Well, you are on the right track. I intend to use a concave form that it is the outside face profile and press the skin into that. The problem that comes up with the two forms of hard stuff is that the wood likes to stick to both and it tears, cracks, gets wrinkles, etc. I made a simple two piece mold, not even working with the 3-D contours yet, and got lots of issues. Further, it would be nice to work a heat blanket in there somehow. This is all leading me into some sort of inflatable bladder type press like used to be used for making Hexcel skis. Yow! Now I'm dating myself.

Alan D.

[dunwell]

Very interesting. I would love to hear a sound clip of that, being that I don't think I'll be making it out to Colorado any time soon. :(

A double top bouzouki is very much something that I would consider when the funds allow...Though I was thinking more of a guitar bodied one. Now that would be one powerful instrument!

Right you are. I am aiming at more of an archtop DT Bouzouki next with a tailpiece and floating bridge, but it would be dead easy to just do an OM with a bouzouki neck running the a 25.4" long scale length, ore even a 24.9". My DT Serenade model quite powerful and I currently have a DT OM set up as a lap dobro in blues tuning. Again, it is kind of hard to play with all that aimed right at your head :)) you develop a light touch in a hurry!