Official Luthiers Forum!

Does anyone here use double tops like this?

http://www.classicalguitars.ca/doubletops.htm

Check out the latest American Lutherie for an article on double tops by Randy Reynolds, which shows how to make one (or at least his version of one.)

I'm a little sketchy still on the glue-up. People early on were advocating polyurethanes (Gorilla Glue), but seem to be coming around to epoxy now. Would the tendency of urethanes to foam and fill the voids in the nomex sheet give different characteristics than the epoxy?

At any rate, it doesn't look like something that you try on a whim some Saturday afternoon.

Jim

_________________
Jim Kirby
kirby@udel.edu

Hey Jim,

Yeah I figured I'd save this one for a Sunday afternoon whim.

I did find this discussion about gluing double tops in the archives though.

http://www.luthiersforum.com/forum/forum_posts.asp?TID=5843& KW=double+top#forumTop

Sweet! I found this tutorial.

http://dunwellguitar.com/DoubleTop/DoubleTop.htm

I also do double tops like this.

_________________
Jim Watts
http://jameswattsguitars.com

Jim,

Can you tell me where I can get the Nomex stuff from?

Thanks!

Graham

LMI sells it. I also use epoxy. Randy and Fritz both were very free with their information when I built my first one a few years back. I,m doing steel strings like this, haven't done a classical like this yet.
Randys' article in the latest GAL is great BTW.Jim_W39105.0355555556

_________________
Jim Watts
http://jameswattsguitars.com

[QUOTE=Graham Steward] Jim,

Can you tell me where I can get the Nomex stuff from?

Thanks!

Graham[/QUOTE]

LMI carries it now. It may be cheaper at places that market composites directly?

_________________
Jim Kirby
kirby@udel.edu

Regarding Alen Dunwell's tutorial - For the case where a cavity is routed out for the nomex to sit in, why do the cavity in the outside face wood rather than the inside face wood? If something is going to go wrong in re-thicknessing the nomex-wood glueup, I think I'd rather tear up the inside face, which is presumably a cosmetic second compared to the outside.

This may be an academic question, since it seems easier to just do the three layers. If done the way it's described in Randy Reynolds article, without a perimeter rim in the middle layer, you can get a number of the middle layer sections out of a single top set.

_________________
Jim Kirby
kirby@udel.edu

Jim, you are right in that it doesn't matter which skin you rout out. It just happened that I did it that way when I was taking that series of photos. In a more recent one I did just as you said. I also tend to leave the face skin a bit thicker these days, about 0.050" so I have more meat to sand in case of dings. You can also do a bit of perimeter sanding too if you want but I find these tops don't need that. 3-M makes some sheet films used to protect things like stainless steel products that I slap on the face side to protect it till I am ready to finish.

I find that it takes less time and material to do the rout method. I can blast the cavity in about 5 minutes or less and I don't have to mess with either using a third full center piece from which I then cut out the hard parts from, or fiddling around and fiting with offcut pieces from some other skin. Note that Randy doesn't bother with the perimeter hard parts anymore. His comment is that "you just have to trust the glue". In which case it probably is easier with the three layer method. Just different strokes. I've been in contact with a builder from Britian who is doing some experiments with wood lattice structures inside skins instead of Nomex. Lots of cat skins we can try here.

Alan D.
dunwell39105.3753819444

Alan - Thanks. This really seems to be a growing industry. So, when are we going to start seeing vendors offering ultra-thin top sets?

_________________
Jim Kirby
kirby@udel.edu

I suspect you won't see that for a while. However, if you have resaw.... Actually, I'm guessing folks like Orcas Island Tonewoods or some of our sponsors would be glad to run you off a billett's worth of thin tops. When I resaw my own I run them at about 0.090" if I expect to end up with 0.060". You want to leave a bit of extra to allow for blade wiggle

I'm building double backs now too, most recent in Am. Black Walnut. I'm checking with some of the veneer suppliers who provide sawn veneers, 0.040" might be available. The sawn veneers can be had in quarter-sawn as opposed to the usual turned veneers that are just knife cut in a sheet off the lathe turned log.

Alan D.

Lutz wafers!

_________________
Jim Kirby
kirby@udel.edu

Any recommendations on where I can purchase topwood billets?

I'm confused about something, according to the article in GAL double tops have little sustain. It would seem that they would be very good for flamenco guitars but bad for classicals. Correct me if I'm wrong (my wife says I usually am ) didn't Segovia say that one of the most important qualities a classical guitar should have was sustain?

I'll never tey to discourage anyone from building with double tops if they are convinced that it improves the sound or sustain but to me, it takes away all the magic of building with the single top.

I recently heard Jason Vieaux play his new Gernot Wagner double top live and to my ear, that was a phenomenal guitar (and player) capable of producing sweetness, power, articulation, richness, and yes, sustain. I have also heard David Russell and Manuel Barrueco play their Matthias Dammann double tops live and don't notice a lack of sustain.

I believe the issue of sustain that Ed is referring to in the Brian Burns article on pg. 13 in AL 88 (that accompanies Randy Reynold's article) is based on Burns' theoretical speculation that a lighter soundboard should result in "higher volume, faster attack, and shorter sustain". His output vs. frequency analyis did not directly measure sustain, so experimentally, the jury is still out.

[QUOTE=EBarajas] I'm confused about something, according to the article in GAL double tops have little sustain. It would seem that they would be very good for flamenco guitars but bad for classicals.[/QUOTE] I don't recall the quote or context, but I have played several classical double tops, as well as heard many in concert. Rest assured that these guitars do not lack for sustain.

I'm glad to hear that there doesn't seem to be a loss of sustain. I always wanted to try to build a double top but I was discouraged when I read the article in GAL.

If a good hard setting glue is used, the internal damping of the laminated top should not necessarily be worse than a single piece top, IMO.

Question for those of you building with double tops. Do you normally glue up the top flat, or in a dished mold? I'd think that if the final configuration of the top is to be a 25' or so radius, you'd want to glue up the laminate structure in a dish. TIA

_________________
Gene

Politicians and diapers must be changed often, and for the same reason- Mark Twain

I too was thinking that a top's sustain and volume would be at odds with each other. The only thing I can think of is indeed that they are at odds; however, both are perhaps superior due to the structure or air mass in a double top. Why that is - less dampening? less conversion of string energy to heat? - I cannot say.

[QUOTE=lex_luthier] I too was thinking that a top's sustain and volume would be at odds with each other. The only thing I can think of is indeed that they are at odds; however, both are perhaps superior due to the structure or air mass in a double top. Why that is - less dampening? less conversion of string energy to heat? - I cannot say.
[/QUOTE] You have to consider what is constant, and what is variable in the equations. In this case, string energy is constant. So, if you take a standard spruce top, and rebrace it or thin it so it is louder, that energy for the loudness has to come from somewhere, so the sustain is less. The strings output all of their energy at a higher level, but more quickly.

A double top is lighter for the same stiffness, so you are getting the extra volume that way. The top uses the energy from the strings more efficiently than the corresponding solid top, so you still have plenty of sustain.

[QUOTE=gozierdt]

Question for those of you building with double tops. Do you normally glue up the top flat, or in a dished mold? I'd think that if the final configuration of the top is to be a 25' or so radius, you'd want to glue up the laminate structure in a dish. TIA [/QUOTE]

I have been building the top/plate on a flat piece of plexiglass, then bacing in a hollow form just like I would with a regular solid top. I plan to try gluing up the last skin in the hollow form on a bozouki top that I will be doing next just to see if it will hold its shape.

On the sustain/volume issue, what I have been seeing is that there is a LOT of sustain with these. The other observation is that the projection, not necessarily the volume, is greater out front. Folks in the back row hear it just as clearly as the folks in the front. However, the preceived volume in the playing position seems less to the person playing. I now build them only with a sound port and that in no way reduces the reach out front but makes it wonderful for the player as well.

As always, your mileage may vary, not sold in states that don't allow free speech, do not lean on a window screen in an upper floor while playing, and beware of rampant matress tags.

Alna D.

How would a double top compare with a latticed braced guitar such as courtnall's plan not the plywood superstructure of smallman? I believe Dave Schramm now favors latticed braced guitars over double tops.

I've been off a business trip most of the week and wanted to catch up on this thread as a builder of double tops as well as standard tops.
I can't figure out where the notion of a lack of sustain comes from. My experience is very similar to Alan's. These guitars have tons of sustain. But I could easily see if you try to build too light how you'd sacrifice the sustain, but quicken the response time. The last one I did also had a sound port and it worked out incredibly well.
These instruments still sound like guitars with subtle differences as Alan pointed out. You can really build a nice contemporary fingerstyle guitar with this type of construction, as you can a standard top as well.

_________________
Jim Watts
http://jameswattsguitars.com