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E-Lo Roberts
05-20-2009, 08:41 AM
Is this the first-ever Double Top ukulele? Could be, but that wasn’t the point of the build.

First, what constitutes a double top? The general idea is to make the soundboard (and back) into a composite sandwich that uses standard tone woods and an aerospace composite called Nomex®, (a honeycomb structured material made by Dupont). So you got a wood/Nomex/wood sandwich for the soundboard.

Over the last ten years Double Top classical instruments have been built with apparent & surprising tonal results. The benefits include: clarity of the individual notes, much more sustain, better balance, and an improved projection in front of the instrument. In addition, it is noted that even small-bodied instruments can fill a room with ease.

Small-bodied instruments? hummm?? So I set out to challenge myself (and the tonal ukulele gods) to see if I could harness any of the above attributes. The results were hit and miss for my first DT build, but none-the-less promising and continues to spark my curiosity for future builds.

Special thanks to acoustic guitar luthier Alan Dunwell for the numerous emails that helped walk me thru the Double Top building process. To find out more about the process of Double Top building you can check out Alan’s website: http://www.dunwellguitar.com/DoubleTop/DoubleTop.htm (http://www.dunwellguitar.com/DoubleTop/DoubleTop.htm)

Here are some specs on the completed Double Top tenor.

African Kiaat “Double” Top (Kiaat/Nomex/Kiaat sandwich)
Kiaat also used for back and sides.
Rosette and soundhole; wood banding.
Tortoise binding; top and back.
Cocobolo/wood banding butt joint & back center strip.
One piece Mahogany bolt-on neck with carbon fiber struss rod.
17” scale joined to the body at the 14th fret.
19 frets total.
Rosewood fretboard with paua abalone/wood banding markers.
Koa peghead overlay with paua abalone "E" logo.
Gotoh Peg Tuners Gold/white.
Rosewood bridge with wood banding tie bar.
Bone nut and saddle.
Top finished in Nitro lacquer.
Back, side, neck finished in Tru-Oil .

deach
05-20-2009, 08:50 AM
Looks awesome! I want to hear it!

Mobben
05-20-2009, 09:47 AM
That top looks very nice.. I would love to hear a sound sample..

kailua
05-20-2009, 10:16 AM
Beautiful! Can't wait to hear it. Not being a guitar guy, I never heard of a double top. Learn something new here all the time.

Dominator
05-20-2009, 10:24 AM
Looks sweeet E-lo. Looking forward to some sounds clips of all these ukes.

Jimmy
05-20-2009, 10:54 AM
Purty. I love the wood and the finish. I'd love to hear it, that double top sounds really fascinating.

seeso
05-20-2009, 01:52 PM
Wow, she's gorgeous. I love that back strip.

gp-ak
05-20-2009, 02:58 PM
That looks really cool!! I'd love to hear what I sounds like!

Pete Howlett
05-20-2009, 03:27 PM
I really appreciate reading about stuff like this and admire anyone who wants to innovate. Well done for exploring this!

However I have to ask - 'What's the point?' If it is curiosity then great. If it is to improve the sound then I am not so sure. There always appears to be an element of gimmickry in stuff like this especially with small instruments where the margin for improvement in sound architecture is minimal. Lastly in this age of modern technology, a pickup and sound module will model any sound you want...

pithaya9
05-20-2009, 05:04 PM
Thats a really nice looking uke E-Lo.

E-Lo Roberts
05-21-2009, 05:52 AM
I really appreciate reading about stuff like this and admire anyone who wants to innovate. Well done for exploring this!

However I have to ask - 'What's the point?' If it is curiosity then great. If it is to improve the sound then I am not so sure. There always appears to be an element of gimmickry in stuff like this especially with small instruments where the margin for improvement in sound architecture is minimal. Lastly in this age of modern technology, a pickup and sound module will model any sound you want...

Pete, thanks for the view and comments on my first DT build. I was awaiting your feed back and had anticipated your purist view points towards this particular build. I consider you to be one of my mentors when it comes to taking a slab of wood and creating something from nothing. In this case a ukulele. You are one of the best at it, therefore, my response is delivered with the upmost respect for you in this area. So here goes...

"...what's the point?" you ask. Well, to me, it's all about uke tone, visual appeal, economics and the "what if?" factor. Why did the Applause instrument co. even try to create a guitar with a plastic, oval back when solid wood backs sounded perfectly fine already? Why do customers continue to snap them up? I'm thinking people dig the way they sound. And who boldly bucked traditional acoustic guitar buildings methods by adopting to bolt a neck to a body and then sell and market them as a highend instrument? Taylor did...successfully.

So I'm thinking "what if" I could build a DoubleTop uke that might yield tones equal to that of a great solid koa top using veneers of unexplored tone woods not normally associated with uke building. Like say, some beautiful African Kiaat used to make traditional native instruments like the small hand-held Kalimba. Or some curly maple veneers that might produce a warm and balanced tone without the additional weight and brightness of a solid maple top. If I could create a lightweight, satisfing, tonal soundboard that is not so dependant on the actual top wood itself, then this could possible open up a whole new list of woods to be used for soundboards. Additional, a DoubleTop AAAAA curly koa top could yield 3 or 4 soundboard as oppossed to one traditional solid top.

Of course, nothing can or will replace a good solid koa top uke, but if (or when) the supply runs out, alternative methods for creating great tone should be explored and welcomed not looked at as "gimmickry". It wasn't but 50 years ago, we thought we would never run out of fossil fuels. Now we are scramming around the globe looking for an alternative....thanks pete...e.lo....

Pete Howlett
05-21-2009, 07:19 AM
Sorry mate - just an old stick in the mud :eek: Ignore me... I don't use graphite either so I am a true ludite tho I my have to use it on my 15 fret to the body uklectics :music:

If you really want to go for projection try a double back. Remember to port the back of the instrument otherwise the trapped air will create weird overtones. A chap called Peter Sensier made double backed guitars in London in the 60's and 70's so he could project above his singing partner in one of the first 'world music' duos Dorita y Pepe.

E-Lo Roberts
05-21-2009, 08:16 AM
Sorry mate - just an old stick in the mud :eek: Ignore me... I don't use graphite either so I am a true ludite tho I my have to use it on my 15 fret to the body uklectics :music:

If you really want to go for projection try a double back. Remember to port the back of the instrument otherwise the trapped air will create weird overtones. A chap called Peter Sensier made double backed guitars in London in the 60's and 70's so he could project above his singing partner in one of the first 'world music' duos Dorita y Pepe.

Yes, I'm with you on the double backed projection thought. Perhaps I could google Peter Sensier and see his method. I don't believe the back port is being used with the current classical DT guitar build. Also, Nomex was not marketed until 67' so I'm thinking Peter probably used an alternative approach to his double backed guitar. Nomex is really the cornerstone to the current double top acoustic guitar builts. Thanks for the feedback and acknowleging my work in the ukulele luthier forum. e.lo....

Moore Bettah Ukuleles
05-21-2009, 08:35 AM
Kudos to you for exploring alternative methods E-lo. Remember there will always be innovators and traditionalists. We can learn from both and both are to be respected. Can you share with us you final thicknesses for each of the layers and the final top thickness? Did you brace any lighter? How does the top flex in comparison to a solid top?
BTW, Looking good as always.

Pete Howlett
05-21-2009, 03:50 PM
You'd be hard pressed to find any information about Peter except in my college dissertation which isn't cited anywhere and is buried in the attic. He was a true artisan and had a great collection of South American instruments - I saw my first armadillo shell charrango in his collection and a guitar like instrument that had a back that simulated the shell of a turtle!

His double back method was to build a standard classical guitar with square kerfed lining around the back rim about 1" deep. He'd drop onto the top of this a thin spruce top and in the back, cut two discrete sound holes. These guitars were incredibly loud. You can see some Neapolitan style mandolins with double backs and the ports are a series of fine holes close to the rim. If you have a double back yo must allow for the enclosed air space to freely vibrate which means letting out that air some how.

If you are really into experimenting you might want to try Balsa Wood - you can get this in very 'hard' grades. The guitar maker Paul Fisher won a Churchill Scholarship and did a lot of research with the money into alternative tonewoods, particularly substitutes for Brazilian Rosewood.

E-Lo Roberts
05-22-2009, 06:21 AM
Kudos to you for exploring alternative methods E-lo. Remember there will always be innovators and traditionalists. We can learn from both and both are to be respected. Can you share with us you final thicknesses for each of the layers and the final top thickness? Did you brace any lighter? How does the top flex in comparison to a solid top?
BTW, Looking good as always.

Chuck, glad to share some of my double top specs with you. However, this first DT on the Kiaat tenor is simply a prototype. These specs will be altered and tested further to create better movement and balance to the soundboard to my future DT builds. Currently I am working to tweak and apply the present knowledge available about classical guitar DT building to the much smaller ukulele soundboard. Ultimately, I would like to present a competitive soundboard alternative that offers exceptional tone and visual presentation that currently can only be found in our present solid top construction methods. Thanks for supporting my alternative building quest…e.lo...

Here is a run down on the steps and specs of the African Kiaat Double Top.

1. The top and bottom (Kiaat) pieces started out around 0.110 “ in thickness and both were glued up (booked matched) up in the usual way.

2. These were then cut and profiled just as regular tops.

3. I then thinned the top and bottom pieces in my drum sander; the top piece to around 0.090” and the bottom piece to 0.030”.

4. The top piece then needed to be routed out to 0.060" (the same thickness of the Nomex®.) The area to be routed followed Dunwell’s template specs.

5. So now I have a top (0.090”) piece with a routed out area (0.060”) where the Nomex is to go.

6. (Without going into a bunch of detail), I then glued the Nomex into the routed out template area of the top.

7. Next the top (with the now installed Nomex) is run through the drum sander to level the Nomex with the top.

8. At this point I glue the top (now around 0.085”) to the 0.030” bottom piece.

9. After drying, again through the drum sander to level it up.

10. The soundboard was then completed in the usual method. (i.e. install the rosette inlay and cutting out the sound hole) Note: To visually hide the two layers (sandwich look), I bound the sound hole much the same way you do on your ukuleles.

11. The final soundboard thickness came out to around 0.110” thick, with a weigh factor closer to that of a 0.080” soundboard.

I used a standard fan bracing method without altering the thickness of the bracing in anyway. This was simply because I was in denial that the strength of the top would not withstand the pull of the strings once completed. However, due to the Nomex honeycomb structure, I have found that the top is very strong indeed. Therefore, I have the option to really thin down (or completely remove) the bracing to allow for more top movement and a better-balanced tone as needed. How far I can push this tone vs. strength envelope is yet to be seen, but I am looking forward to future DT builds to find out...

E-Lo Roberts
05-22-2009, 06:24 AM
His double back method was to build a standard classical guitar with square kerfed lining around the back rim about 1" deep. He'd drop onto the top of this a thin spruce top and in the back, cut two discrete sound holes. These guitars were incredibly loud. You can see some Neapolitan style mandolins with double backs and the ports are a series of fine holes close to the rim. If you have a double back yo must allow for the enclosed air space to freely vibrate which means letting out that air some how.

Pete, great info. Yes I looked around for Peter on the web but found nothing on his guitar work. Thanks for keeping my "what if?" brain waves ticking...e.lo...

Lori
05-22-2009, 06:45 AM
I think this is a really exciting development. This method might also make it possible to mix tone woods for the soundboard. What would happen if one layer was spruce, and the other koa? Would it make a difference which one is on the inside and which one on the outside? I guess a lot of trial and error is the only way to find out. Keep up the good work. You may be on to something good! Love to hear a sound sample!

–Lori

E-Lo Roberts
05-22-2009, 07:22 AM
I think this is a really exciting development. This method might also make it possible to mix tone woods for the soundboard. What would happen if one layer was spruce, and the other koa? Would it make a difference which one is on the inside and which one on the outside? I guess a lot of trial and error is the only way to find out. Keep up the good work. You may be on to something good! Love to hear a sound sample!

–Lori

Lori, thanks for your encouraging words and interest in my work. And you are correct with the mix and match concept. It has already been address on the classical guitar front and does play a part in the tonal structure of the final DT. And added benefit to this build approach is that only the top layer need be visually appealing. For example, a lower grade koa with surface flaws could be used for the bottom layer to save costs which will yield the similar tonal properties as it's curly top layer counter part ...e.lo...

Moore Bettah Ukuleles
05-22-2009, 07:26 AM
Whoa, that's a lot of work. I have a couple of concerns. These are simply out of curiosity and by no means are meant to diminish your efforts.
First, when gluing the Nomex into the routed area and then gluing the final layer of the sandwich on, how are you keeping glue from filling all the voids in the Nomex and turning it into a solid substrate?
The final top thickness seems rather thick at .110". Are you getting any resilience or deflection in the top? My concern is that the bridge will not be able to drive a top that is too stiff. But it should certainly cut down any lateral flexing. Bracing or even a bridge patch seems redundant.
And finally, stepping into the devil's advocate role now, is it necessary or even noticeable on such a tiny instrument? How does it sound when compared to a similar solid top build of yours? There are probably way too many variables to be able to do a fair comparison..........
Again, I dig this kind of experimentation and I am constantly playing with different ideas, primarily to keep things exciting for myself. Keep it up.

E-Lo Roberts
05-22-2009, 07:44 AM
Chuck, great questions and concerns! I've got a gig tonight and a family outing this weekend, so I won't be able to address this post respectfully probably until Monday or Tuesday...thanks...e.lo...

Kekani
05-22-2009, 07:47 AM
The final soundboard thickness came out to around 0.110” thick, with a weigh factor closer to that of a 0.080” soundboard. .

Holy smokes, that is a thick top. Even with a strength ratio of .080, I gotta agree with Chuck on this one. Maybe Steel Strings? I would imagine with the structure of Nomex and a DT, the ability to go thinner is there, possibly down to .050 or something like that - then that top would really move (Kasha who?).

Question: Why do the whole routing thing, instead of just a sandwich? If you really needed an edge for a glue joint, you could make a "frame" around the soundboard, and sandwich that as well - at least you know your .060 section stays .060. If not, binding would cover the edge anyway (like the soundhole). I don't mean to question your methods, just trying to get your advice as I'm questioning mine.

In any case, very interesting. Mind if I ask what type of Nomex, and where you get it from? I'm thinking a .030/.010/.020 (Spruce/Nomex/Spruce) sandwich, just for the fun of it - I'll throw it on one of MGM's thinlines, and do the back the same way.

Interesting stuff. - Aaron

Moore Bettah Ukuleles
05-22-2009, 07:50 AM
Good. A while back one of the Guild of American Luthiers (GAL) publications had a great article about this. I'll see if I can dig it up in the time being. Have a good weekend.

E-Lo Roberts
05-22-2009, 07:59 AM
Holy smokes, that is a thick top. Even with a strength ratio of .080, I gotta agree with Chuck on this one. Maybe Steel Strings? I would imagine with the structure of Nomex and a DT, the ability to go thinner is there, possibly down to .050 or something like that - then that top would really move (Kasha who?).

Question: Why do the whole routing thing, instead of just a sandwich? If you really needed an edge for a glue joint, you could make a "frame" around the soundboard, and sandwich that as well - at least you know your .060 section stays .060. If not, binding would cover the edge anyway (like the soundhole). I don't mean to question your methods, just trying to get your advice as I'm questioning mine.

In any case, very interesting. Mind if I ask what type of Nomex, and where you get it from? I'm thinking a .030/.010/.020 (Spruce/Nomex/Spruce) sandwich, just for the fun of it - I'll throw it on one of MGM's thinlines, and do the back the same way.

Interesting stuff. - Aaron

Aaron, the frame is also another method of this approach already being used. I chose the routing method as used by Dunwell. His was my guide through this process. Yes, the Nomex will allow for a thinner sandwich. The 0.060" is the thinness Nomex avaliable. However, once glued in place you could drum sand it down to whatever. Don't know if you would reap any benefits if it got too thin though. You can purchase it at http://www.lmii.com/CartTwo/Results.asp?searchtext=nomex

Like I pointed out, this was a prototype top to see if it would fly. Found out, it flies very well and the tone and projection (even with the bracing and thickness) is comparable to that of other solid top ukuleles I have built. So there is plenty of room to improve on the ability of the bridge to drive the top via brace sizing or removal and the thickness of the overall DTop.
P.S. Keep in mind that most of the thickness is filled with air. Also you need a solid wood structure surrounding the soundhole and bridge area, as well as, a small foundation around the outside profile of the top for support...elo..

E-Lo Roberts
05-26-2009, 11:09 AM
Good. A while back one of the Guild of American Luthiers (GAL) publications had a great article about this. I'll see if I can dig it up in the time being. Have a good weekend.


Chuck, here are some replies to your questions...

Q1: When gluing the Nomex into the routed area and then gluing the final layer of the sandwich on, how are you keeping glue from filling all the voids in the Nomex and turning it into a solid substrate?


I used an epoxy glue that I rolled out on wax paper on a flat surface, spread very thin. The cutout Nomex® is then laid into the epoxy for about 30 seconds so that only the honeycomb area’s are coated with glue. You want to keep the open (honeycomb) spaces free of glue throughout the total top gluing process. The Nomex® is then placed into the routed out Kiaat top piece. A piece of ½” glass is then placed on top of the combo. Note: the Nomex® is slightly higher than the router area to allow full pressure from the glass to press down on it. This needs to dry overnight. Once dries, the combo goes through the drum sander to bring the Nomex® thickness even with the top piece. To glue the bottom piece to the combo piece, you need to again roll out epoxy and laid the combo (top & Nomex®) piece into the epoxy for 30 seconds. Pry off the combo from the glue and place it on top of the bottom piece. Pressure is again applied over night to combine the top and bottom.

Q2: The final top thickness seems rather thick at .110". Are you getting any resilience or deflection in the top?

The top does seem thick as opposed to the final 0.066” solid tops that I have been making. However, a lot of this is trapped air chambers in the honeycomb spaces. Visually speaking this thickness is mostly unnoticeable to the eye from the soundhole. It looks quite nice with the banding of the hole. As for resilience or deflection in the top, I haven’t done my own tested for this. Therefore, I can only give you Dunwell’s test results on his Double Tops. He states, “The mode shapes for a given model of guitar are the same but where they occur and how clean they are is not. What I notice with the double tops is that the modes are very clean and narrow and the frequency at which they happen is very narrow, plus-minus only a few Hertz , and they are very strong, almost violent. Which all says that the plates are much more uniform than a similar solid plate. This is understandable since the Nomex has kind of homogenized out the wood variances.”

Q3: Is it necessary or even noticeable on such a tiny instrument?

This is what I am trying to find out. Only building such instruments will answer this question. I am only one uke into it so it’s way to soon to tell.

Q4: How does it sound when compared to a similar solid top build of yours?

Well, I never used Kiaat for a top before so I can't compare the results directly. Addition this was simply a prototype which allowed me to learn the process of a DT build on a ukulele scale.
But if I were pressed for an overview of the Kiaat’s tonal performance, I would have to say that string tone/volume are well balanced and that the volume level is similar to my other solid tops. The overall tonal spectrum (though clear and pleasant in nature) lies more so in the mid-range area. That is, it doesn’t have an ultra bright or boomy tone to it. Which is good in a way. But I am looking for more projection, more complex highs and a bit more bottom end.
Considering that I used an unlikely tone wood for the top, the results are were quite favorable. But these concerns are premature at this point due to it being my first DT build. It’s a bit like asking why the Wright Bros. first Kitty Hawk flight only lasted 120 feet.
To better address the tonal characteristics on my next DT build, I will changing out the wood; thin the overall thickness more; and remove/change the bracing pattern. I will also begin to set up and run some Chladni mode patterns on each top before I glue it to the body to get a visual on how these small tops will vibrate in comparision to the same solid top before I rout out and modify it into a DT.

I hope I have answered your questions in a clear manner. Thanks..e.lo..

Moore Bettah Ukuleles
05-26-2009, 03:56 PM
I respectfully remain skeptical. Nonetheless I am excited for you for trying this. Good luck.

Bradford
05-27-2009, 01:29 PM
For everyones info, the American Lutherie article is in vol. 93, spring 2008. It is an article on Robert Ruck and has a good description on how he does composite tops. He resisted the idea for quite a while, but when the top players started demanding them, he went along. He uses three laminations of wood, instead of Nomex. I suspect that some of the appeal of this method is that the top does not need a long time to mature, as does a spruce top. That is why western red cedar tops have become popular with classical guitars.

Brad

kerneltime
09-16-2018, 04:05 AM
What an interesting thread!! Wonder if anyone has tried or has any updates or newer opinions. Learnt something new about the world of tops.. thanks to this thread.

Beau Hannam Ukuleles
09-20-2018, 05:16 AM
From my experience on double tops, or more specifically me watching others make classical guitars with double tops and asking them and listening myself to the results, all the work that goes into a double top doesn't yield better results.

It's similar to Kasha bracing- why glue on and carve 21 braces when it doesn't sound better than 3 fan braces??????

Also, a 1mm (.040") top wood skin is (and the same on the inside) is cutting it to fine for sand throughs straight into the nomex etc- one tiny scratch or dent and it's all over.

Having said all that, I know it's fun and exciting and very interesting to do such experiments and you should be applauded for exploring this and having a curious mind.

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