Lutherie Demystified Ep.14 | Techniques: Making and Measuring Double Top Soundboards

[@willstutely]

I’ll echo the comment sentiment common to your videos… your channel is a breath of fresh air. No gimmicks. No stupid thumbnails. No clickbait titles. Super informative and presented in a manner that elevates the viewer rather than appeals to the lowest common denominator. As someone who is researching prior to building his first classical guitar your channel is invaluable. Thanks!

[@GarrettLeeLuthier]

Thanks for the super encouraging comment. I'm so happy you find the information useful. There's an article on my website that I wrote for people who are starting to build. This might be of interest to you.

[@willstutely]

I will definitely check it out. I’ve been watching lots of different channels, I’ve got Bogdanovich’s book, and I’ve got a set of plans for the 1937 Hauser as reference. I’m also leaning heavily towards using wood I have easy access to in my general woodworking. I have some douglas fir that I’m strongly considering for the top that I have confidence is at least 400-500 years old, and my consideration of it is influenced by the Pragmatic Luthier here on youtube. Although I might try to make one first with a spruce top to work out kinks in the process and not screw up that special wood m. Thanks again!

[@seanhallahan14]

This is FABULOUS! Thank you so much. Best & cheers, Sean

[@josetarragonatyvallejoslut2]

Thanks for sharing such a valuable knowledge in such a generous and rational way! I must say all your videos are amazing, but this chapter and chapter 13 are pure gold, for sure they will help me cutting down the developing time in my guitars. I´ve already built the deflection rig and i have been measuring densities for a long time. Thanks again, you are a true master and teacher: Best wishes form Argentina!

[@GarrettLeeLuthier]

Thank you, Jose. I'm glad you fine these videos of help.

[@alessandromartinez4305]

This is the best video i found about double tops, and so far, the best lutherie channel, you explain everything so clearly, new sub!

[@kevinhill6734]

Thank you so much for sharing this. Really a great watch!!!

[@jwilt1225]

Fascinating how management of the flexibility of the top replaces much of the sound profile adjustment that has been the historical domain of bracing. The new "secret sauce," as it were. Also, inasmuch as I will likely NEVER replace my beloved GL cedar core #65 (2017) it is comforting to learn that the double top construction even lends an element of durability! I'll certainly never attempt to build a guitar, but I LOVE understanding "how the watch is built!" Thank you, Gary!

[@GarrettLeeLuthier]

Thanks, Jeff. I think throughout history, soundboard optimization and bracing have always worked hand in hand. Bracing tends to get the most attention, especially by players, because it's a feature that can be readily seen.

[@philltadman]

Even though I’m a player and not a luthier. I find these videos terrifically interesting. Thanks for sharing

[@gusti77]

Thank you for sharing so much information! This is incredibly generous of you.

[@GarrettLeeLuthier]

It's my pleasure. I'm only repaying those who showed great generosity towards me by paying it forward.

[@bohemiangroove9751]

This is by far by new favorite channel! Thanks for sharing your techniques and truly demystifying the art of lutherie!

[@Andrzej-m9k]

Dziękuję.

[@PaulMcEvoyGuitars]

wow that was excellent. no secrets. Thanks so much!

[@GarrettLeeLuthier]

You are very welcome, Paul!

[@jesusmagdalena625]

Excellent video, thanks for sharing such an interesting analysis.

[@GarrettLeeLuthier]

Thanks for watching. I'm glad you find it interesting.

[@marcusburnett22]

This is incredible work

[@theluthier1957]

Thank you so much for the information.

[@DSteinman]

Thanks for sharing! Do you know if any steel string guitar makers have experimented with double tops?

[@GarrettLeeLuthier]

Alan Dunwell was one of the first steel string builders to adopt double tops, maybe going back 25 years. Today, there are some extremely fine examples of double top steel stringed guitars, such those by Kevin Muiderman.

[@davidlang6550]

Great video!!

[@danalain4126]

I wonder if DT guitars opens up with playing time like traditional guitars?

[@GarrettLeeLuthier]

Yes. The improvement over time has a very similar profile compared to solid tops.

[@theluthier1957]

Hi Garrett , thank you for the inside of making doble tops , Question what tipi of vacuum do you use ., thank you for you reply.

[@GarrettLeeLuthier]

It's a Gast MOA-V113-AE. There are often used ones listed on eBay for a reasonable price. My used one has been running well for about 15 years.

[@seanman22001]

Where does one get the balsa?

[@GarrettLeeLuthier]

Try specialty balsa companies that supply model airplane builders.

[@davidlang6550]

Have you measured the Q of the top fundamental for the solid vs double top?

[@GarrettLeeLuthier]

No.

[@jorgesavelli]

What’s the density for honeycomb?

[@GarrettLeeLuthier]

The raw balsa is approximately 8 lb/cubic ft = 0.13 g/cm3. Once the holes are cut, it becomes about 0.05 g/cm3. For comparison, when I use Nomex, I use the variety that is 1.8 lb/ft3 = 0.029 g/cm3. The gluing surface areas are different, and Nomex will carry less glue than balsa with holes.

[@davidlang6550]

Is your balsa core a specific type ie end grain, flat or quarter sawn?

[@GarrettLeeLuthier]

End-grain of density of approximately 0.10 g/cu. cm.

[@dantahoua]

How does double tops would work for steel strings guitar? I'm really curious. 😊

[@GarrettLeeLuthier]

There are several string builders that use double tops with very good results. The stiffness of the sandwich needs to be adjusted accordingly to withstand the increased string tension. I have used it for a Puerto Rican cuatro, which is a 10 string steel string instrument and the result was extremely good.

[@Dhammawitt]

Have you experimented with different PU glues? Which have you found the best?

[@GarrettLeeLuthier]

Gorilla glue works well if you can get your layup in the bag in under 20 minutes. Loctite UR30 can be used if you need up to 30 minutes. Both have worked well for me for Nomex and balsa.

[@karelenhenkie666]

May i ask where you bought the vacuumbag sealer strip? Ive been using a stickey compound but that is pretty finicky and needs to be replaced often.

[@GarrettLeeLuthier]

Veneersupplies.com sells them. Also refer to JoeWoodworker.com for other ideas of closures you can make.

[@seanman22001]

and how do you get holes in it? Does it come in a sheet? Shall I google guitar shape balsa/w holes?

[@GarrettLeeLuthier]

The holes are machined by CNC using a pattern of my design. The balsa is purchased from a specialty balsa company that is often used by model airplane builders.

[@billgreen4592]

Hi and thanks for the very informative video! I make double top steel string acoustics. I have been using nomex successfully, but I'm always looking for other methods. Particularly with LMI out of business, the idea of balsa sounds like a good choice, as I have a CNC and the extra machining is not a problem.. What drove you to move to Balsa, and have you found it to be a cost saving decision? Any thoughts that you might offer would be very helpful. You mentioned that you are using polyurethane glue for the sandwich, I have been using system 3 epoxy. Frankly, I'm not a fan of epoxy and looking for an alternative. What brand of glue are you using? Again, thank for the video and any advice you could offer.

[@GarrettLeeLuthier]

The use of balsa was an exploration into sonic differences and the ability to use CNC to strategically position solid areas, such as borders at the periphery and areas under the bridge and rosette without having to rout pockets for the Nomex. In recent years, one significant truth I discovered is that regardless of Nomex or balsa, a "natural" sound can be achieved by either material or mixtures of the two. What determines the sound quality is to achieve the right resonances that are the fingerprints to the sound you are after. The idea of a synthetic material giving a synthetic sound vs. a natural material giving a natural sound is false, as I have proven to myself in many guitars. They can give similar voices to the point that I can use the different cores interchangeably or in mixtures. Light, end-grain balsa more expensive than Nomex. You can buy Nomex from ACP Composite Products in Livermore, CA. Gorilla glue works well if you can get your layup in the bag in under 20 minutes. Loctite UR30 can be used if you need up to 30 minutes. Both have worked well for me for Nomex and balsa.

[@short6691]

Protective cardboard? Is this to keep from glueing the sandwich to the board? To avoid imprinting scoring marks on the show face?

[@GarrettLeeLuthier]

The cardboard keeps the veneer protected and the curves smooth.

[@BlaisPianoGuitars]

Hmm. We have an Vin. 1856 grand piano with a corrugated SB = bizarre.

[@davidlang6550]

Have you measured monopole mobility with your solid and double tops to support this theory?

[@GarrettLeeLuthier]

No.

[@crandallwoodworking2988]

I'm still learning about guitar building(haven't built one yet), so I'm curious what a carbon fiber core would produce? Or if it's even a viable option for a core. Would it be too stiff, since you would have to use epoxy? Could it be thin enough and/or resonant enough? Has anyone ever used carbon fiber?

[@GarrettLeeLuthier]

You're inclination is correct--carbon fiber with epoxy would be too stiff. The cores actually need to be very flexible for the design to work.

[@GavinChenTW]

👍👍👍

[@danalain4126]

You buy the balsa already holed out because You don’t have a CNC to make the balsa pattern with. There has to be a better design than symmetrical holes which makes no sense. Having a CNC would allow you to make the balsa layer with your own design which, I think, would enhance sound response.

[@GarrettLeeLuthier]

The core is cut with a CNC using a pattern of my design. The balsa is purchased in raw form from the specialty balsa supplier. Different builders have different opinions about the amount of flexibilty needed in the X and Y axes. A uniform distribution of holes simply allows me to achieve the ratio of stiffness that I'm after. This is similar to the uniformity you have with Nomex. It's still possible to achieve additional directionality by spatial alteration of the core thickness, if that's what you want.

[@danalain4126]

@@GarrettLeeLuthier So the symmetrical holes assimilates the uniformity of Nomex- now I understand. Thank you for the explanation . Also, thank you for your answer on the question of “do DT guitars open up ?”. MERRY CHRISTMAS and HAPPY NEW YEAR!!!

[@PaulMcEvoyGuitars]

Thanks again for this video. Can you tell me what the balsa material you're using for the core is and where you get it? Are the holes all the way through and if not, why not?

[@GarrettLeeLuthier]

The core is end-grain balsa of "light" classification (6-10 lbs/cu. ft.) purchased from specializedbalsa.com. I machine the holes part way through in order to maintain some integrity in the sheet for ease of handling. You can certainly machine them all the way through if you want.

[@PaulMcEvoyGuitars]

@@GarrettLeeLuthier thanks so much. How thick do you start with? I'm going to try this on a retop as an experiment. I really appreciate the time you put in this video.