Lutherie Demystified Ep.13 | Techniques: Thinning and Measuring Soundboard Plates

[@customgtrs]

Do you have the measurement for steel string tops?

[@GarrettLeeLuthier]

When I was building small jumbo steel string guitars (about 10 years ago), my target deflection was 0.110 inch in the with-grain direction and 0.180 in the cross-grain. This is for the same weights described in the above video, and with the plate similarly supported 1 cm from the edges and at the widest point of the upper bout. (Of course, the plate is a different size compared to a classical). As an example, for a Euro spruce top with density of 0.42 g/cu. cm, the final plate thickness in the upper bout and in the center of the lower bout would be 2.55 mm. In the lower bout, the thickness would taper to 2.30 mm at the edges. The bracing was a typical X braced pattern. This creates a very balanced, rich and articulate sounding guitar.

[@robertgodreau6516]

What an absolutely fantastic , clear and articulate presentation. Thank you!!!

[@GarrettLeeLuthier]

My pleasure, Robert.

[@mflazar]

This approach is in some ways similar to what Greg Byers taugt me 22 years ago. The difference was that Byers dealt primarily with resonance targets rather than compliance (stiffness) however, he did measure stiffness in a way similar to what is done here. What I found after 22 years and well over 100 guitars was this: If I thicknessed my tops to achieve the same target resonance and the measured the resulting stiffness they were not always the same. So , with this approach, stiffness is the target and with the approach I use, it is fundamental resonance. There are top resonance targets throughout construction ie; at the initial stage as shown here, after the top is braced, after it is attached to the sides, and the back is glued on and after the bridge is on. All this having been said, I think this approach is both valid and well organized and executed and shouold be very helpful to beginning luthiers.

[@GarrettLeeLuthier]

Thank you, Michael. What you point out is true. Resonance targets are the most direct markers to final sound outcome, ahead of flexibility. As you point out and as I showed in Episode 14, for consistency of sound, it's important to get the resonances similar for different soundboards because the plate properties can be different. An extreme example is what I demonstrate at the end of Ep. 14 for a solid top vs. double top. Greg's teaching is profound, and fortunately is available for all to read in American Lutherie Vol. 134.

[@KBorham]

@@GarrettLeeLuthier thank you for the reference (American Lutherie Vol. 134).

[@LucaBenders]

Thank you for this priceless contets. We all owe you a lote Garrett

[@GarrettLeeLuthier]

I'm glad this video is of help.

[@MrMombip]

Great series. Nice precise approach, clear explanations. Thank you.

[@FiddleSticks800]

These videos are gold. As an engineer getting into guitar making you scratch that itch for solid rational. Thank you.

[@clementgerardin2896]

As a begginer luthier in France, I would like to thank you very much for those clean and methodic advices. At last a practical approch, untainted by belief or myth about luthery. Your serie is absolutely great.

[@hascesar]

thank you Master, you have just opened my eyes! many thanks.

[@glennlopez6772]

Most impressive and informative presentation! Thanks for the video!

[@JoelSundkvist]

Thank you Garrett for sharing your luthrie wisdom in such a pedagogical way. I will right away start measuring the deflection and keep track of my upcoming builds. Grateful wishes from Sweden! Joel

[@garylee6266]

Joel, it's my pleasure. I wish you good progress in your building.

[@saschanowak2964]

Dear Garrett, excellent video! You are very gererous to share your experience. Very inspiring, the information as well as the attitude. Thanks a lot and cordial greetings. Sascha

[@raulcroquevielle8387]

Hello Garrett this is the most illuminating piece of information I ever had received… thank you so much. At this point I have been working in the dark on this most important issue in building guitars. Now I have e the chance to start again 😅 with some objective references to step on

[@GarrettLeeLuthier]

Not exactly starting again for you. If you've already built tops, you no doubt have at least some feel for those flexibilities. Think of the deflection numbers just adding to the awareness and knowledge base that is already in you.

[@davidhole8175]

Hi Garrett, this is a fantastic informative video and thanks for sharing your approach, insights and equipment design. A wonderful series that will be very useful for myself and many others I'm sure.

[@garylee6266]

David, I'm glad to hear the video will be helpful. Happy building.

[@amhackdpt]

This is exactly what i needed. Just ordered a dial indicator. Thank you so much. So much more helpful than other information i have received that basically just says you have to learn to listen to the tapping and just trial and error.

[@GarrettLeeLuthier]

I'm happy you find the techniques useful. If you put them together with complementary practices like tapping and flexing with your hands, you'll have a very rich set of skills.

[@chrisb3k1]

You are the man. Fascinating stuff.

[@GarrettLeeLuthier]

Chris, thanks a million for the encouragement.

[@waltersguitars3336]

Great information I’ve been building Guitars for years ! I never measure anything I just go by feel, but I appreciate you going about all this time to make the video to tell everyone. I believe it’s a very intuitive and intimate relationship between the Luthier and the wood. feeling and understanding how bracing works and correlation with the top thickness and flexibility ,, guitar building is just one of those things you have to do yourself to fully understand how to make it sound great ❤ thanks so much

[@fusion-music]

This episode took me back to the 70s in training as a potter. Note taking was essential to learn and replicate. To see where you are making good judgements and where you need to alter things next time. This is wonderful. Many thanks.

[@GarrettLeeLuthier]

You are very welcome. I'm glad you're a note taker too.

[@jiri_markalous]

Thank you, Garrett, for sharing your valuable information with us.

[@GarrettLeeLuthier]

You are very welcome!

[@tomallen8527]

Garrett, thank you for sharing this. I will definitely incorporate what I’ve learned here on my next acoustic guitar.

[@murraykilpatrick3029]

I'm personally very interested in the nodes and anti nodes. Where the occur and varied thickness and placing of the braces in accordance with them. A friend built a contra bass marimba in my workshop. The shaping of the bars, corresponded with the nodes and anti nodes. Obviously the carving and shaping affected the fundamental note. But it also greatly affected the resonance of the bar.

[@classicalguitar715]

Hi Gary. This is very helpful and takes the guesswork out of thinning the tops...thanks.

[@GarrettLeeLuthier]

My pleasure. I hope these ideas will save you a lot of time and energy.

[@dukhovich]

Hi Garrett, I have watched all your videos and admire your approach and sharing your experiences. Thanks a lot🙏

[@garylee6266]

Thank you very much for watching and your encouragement.

[@jesusmagdalena625]

Brilliant.!! Thank you!

[@GarrettLeeLuthier]

My pleasure! I hope the videos help you.

[@andreashaselhoff2445]

First time I heared about this. Very interesting! Thank you very much.

[@lush462]

Really interesting and useful information! Thanks

[@GarrettLeeLuthier]

Great! I'm happy to hear you will be able to make use of the concepts.

[@titidadgad3784]

Thanks a lot for your videos. They are fascinating. Greetings from France.

[@GarrettLeeLuthier]

Thank you for watching the series. I'm glad you are enjoying the videos and I hope it stimulates your curiosity about how guitars work.

[@titidadgad3784]

I am an acoustician and also a guitarist and I really like this pragmatic approach to the instrument. A guitar is certainly a work of art but also and definitely a vibration machine. I think science can greatly help musicality. Thank you for sharing this valuable know-how.

[@dennisboyce813]

Excellent, thank you.

[@GarrettLeeLuthier]

You are very welcome!

[@davidduca8421]

Good video thanks .I'm also finding the back can help influence overall flexibility.

[@bobdechenne]

Thanks very much for this comprehensive and insightful video. Starting my first and second guitars and this finally gives me some clear direction for one of the most crucial aspect of guitar building. Thanks for the steel string mini-jumbo numbers. If you ever build other steel string guitars I would be interested in those numbers. Thanks again!

[@KBorham]

Thank you for the clear, concise presentation. I'm building dreadnaught steel string guitars. It's interesting that the most precise mechanical discussions, on top resonance and response (physics are the same for both), are presented by Spanish style guitar makers. It leaves many steel string dreadnaught details on stiffness targets, and methods to measure them, left to the student (me, in this case). I'm not sure I have enough years left to develop my own data set : ). Thanks again for sharing your details and methods.

[@smurphy50]

Excellent video series. Loving your approach with the objective scientific applications as well as the personalized insights. I’m wondering if you have experience with live back applications of your thinning approach? Do you experiment in that realm or use the more traditional rigid?

[@GarrettLeeLuthier]

My backs are "tuned" relative to the top resonance so that they will weakly couple. When you play, you can feel them somewhat move, but rigid enough that they allow ample forward projection.

[@Andrzej-m9k]

Dziękuję.

[@montekristo8252]

Thank you so much Garrett for this video series. I'm planning on making a couple of classical guitars soon and will definitely be using your method for determining stiffness. Question: will there be videos about the design of “lattice” bracing? I look forward to new videos and woud like to thank you for sharing your knowledge!

[@garylee6266]

Fantastic. I hope these ideas will help you progress with greater confidence. I don't make lattice braced guitars, so I won't be making such a video. There are several on KZbin, including those by David Schramm

[@markgrimm3564]

wow thanks so mush for sharing your knowledge much respect for you as i'm really into the acusticial science of the guitar and sound transfor

[@GarrettLeeLuthier]

Mark, thank you very much for the encouragement. It's my pleasure.

[@MrChatmoon]

Excellent

[@ΓρηγορηςΜαυρακης]

Hello and thank you for the video!! Finally what resonance has this top after the last sanding??

[@thomaskeithlutheir]

Great video. You inspired me to make an exact replica of the jig dimensioned to suit the size of top I use. I have thinned my spruce top to the same finally thickness shown at the conclusion of you video. But I cannot hit the target flexibility suggested. I think it maybe because my rosette is about 2mm thick which is creating extra stiffness in my top that I cannot compensate by thinning the lower bout to 1.9mm. Any helpful comments would be appreciated.

[@GarrettLeeLuthier]

The rosette could be adding stiffness, but unless you know the stiffness or density of the material you are starting with, you cannot compare the final thicknesses. I suspect your material happens to be a stiffer board compared to the one I was using. [Episodes 7 and 9 talk about the correlation between density and with-grain stiffness, and in this video, the density was 0.40 g/cm3]. As I mentioned, the final thickness is not important, but the final flexibility is. Try to trust the process and what is the more important parameter which is stiffness, not thickness. Remember that some Torres guitars have extraordinarily thin tops, less than 1.9 mm thick.

[@jonahguitarguy]

Great information Gary. Very practical and straight forward procedure. Can I assume the same procedure but with different target numbers would work for steel string?

[@GarrettLeeLuthier]

I'm glad to hear it. These concepts would work on just about any stringed instrument.

[@GarrettLeeLuthier]

I just checked my notebook and I did run deflection analysis for my steel string guitars, which were small jumbo models. My target deflection was 0.110 inch in the with-grain direction and 0.180 in the cross-grain. This is for the same weights described in the above video, and with the plate similarly supported 1 cm from the edges and at the widest point of the upper bout. (Of course, the plate is a different size compared to a classical). As an example, for a Euro spruce top with density of 0.42 g/cu. cm, the final plate thickness in the upper bout and in the center of the lower bout would be 2.55 mm. In the lower bout, the thickness would taper to 2.30 mm at the edges. The bracing was a typical X braced pattern. This creates a very balanced, rich and articulate sounding guitar.

[@henricussagittarius1]

Thank you, Garrett, these are very helpful explanations. One question about the weights: did I understand it right that the dumbbell weight has 1000g? (and not two american pounds?)

[@GarrettLeeLuthier]

The dumbbell weight is 2 American pounds = 907 g.

[@Daniel22147]

Thanks!

[@GarrettLeeLuthier]

It's my pleasure! Thanks for watching.

[@JoseOchoa-dw9vk]

Excellent video. Can your measuring method be used on the raw rectangular sound boards as part of a selection process?

[@GarrettLeeLuthier]

Jose, absolutely yes, so long as your boards are of uniform dimension.

[@maxbishop8224]

Hi Garrett, Where do you place the island of thickest top material with regard to the bridge? Thanks so much for sharing your kmowledge. Best wishes, Max Bishop

[@GarrettLeeLuthier]

Max, if you look at the contour map at minute 33:40 in the video, the tie block-edge of the bridge will sit in line with the widest part of the lower bout, so most of the thickest part of the soundboard lies in front of the saddle.

[@PaulMcEvoyGuitars]

Hi Gary I think I see an error in your diagram at this point: kzbin.info/www/bejne/raC0ZIJvqLCpeM0 those dimensions say 87mm and 87mm taking you from the of the guitar bottom to middle of the top bout, but the total length is 488, it doesn't add up. Seems like maybe 200 and 200 would be right?

[@GarrettLeeLuthier]

Good catch, Paul! The distances in question should be 187 and 187 mm. I will make and edit. Thank you!

[@yiwutcmmedicalenlightenmen922]

insightful. thankyou. I felt some lack of clarity about the weights used - mixing imperial and metric measures. Having a weight with two points of contact vs other at a single point. the point about the pre-load concept wasn't entirely clear to me - was that intended to help the table meet the deflection measurement instrument?

[@red58impala]

Check out the video at 15:18 where he mentions his reasoning for preloading the top. If his reason is more complicated than what he mentioned in the video, hopefully he'll respond.

[@ryanbreslin5981]

great video, thank you for sharing your methods. Can i ask, do your guitars have a consistent body resonance? if so, can you asses at this stage, what resonance this guitar will end up at?

[@GarrettLeeLuthier]

Yes, consistent top and air resonances are the ultimate goal, because those relate the strongest to the final sound. Getting the plate stiffness consistent is a big step toward this end. Every manipulation will manifest itself in the final structure. The sooner you start controlling the important variables in each guitar's construction, the better able you are to steer to your target at the end. These physical markers gained in deflection analysis have been correlated to resonance in my completed guitars. For example, the air resonances in my double top guitars always lie between 85-87 Hz, and in Episode 14, I show how to make a double top sandwich and measure its deflection.

[@wimesser2621]

Hi Garrett, this is a fantastic informative video, one question, the 2 pound weight is that U.S. pounds so 0,9Kg ?

[@GarrettLeeLuthier]

That is correct. I'm very glad you find the video helpful.

[@AuditoryStorytelling]

I have a question. If you get the top the exact thickness you want, once you put the whole box together, you will likely do some more sanding to get it ready for finishing, won't you? And if so, will that finish sanding mess up the top thickness you tuned it to?

[@GarrettLeeLuthier]

Think of it this way: the target numbers chosen in a sense have all the subsequent steps factored into the calibration. Keep in mind that the targets are only based on correlation to good sounding guitars at the end, and as you'll see later, some resonant frequencies of the air and top once the box is closed. That's why it's important to do all your procedures as consistently as possible. This is the true meaning of control--control of intent and the control of process that adds up to the control of structure and therefore sound. Even when levelling the bindings and purflings, I remove very little material off the soundboard. This becomes especially important when working with the outer veneer of a double top. I do very little final sanding before finishing because it's essentially already at finish-ready smoothness before thining the inside face.

[@tomjacobsen1943]

In your stiffness testing do you find cedar ends up slightly thicker than spruce to achieve similar results? Thank you

[@GarrettLeeLuthier]

In general, yes because of the average lower stiffness of cedar compared to spruce. Each board has different inherent stiffness, but without measuring a board's density or stiffness, the conventional wisdom is that cedar soundboards should be about 15% thicker. You can see how this could be a dangerous generalization to follow.

[@hereasafanofallsorts5164]

Hi Garret Thanks for the great videos and information - I'm just wondering - Would the desired deflection numbers be vastly different in a steel string OM sized guitar and if so is there any good source of data on desirable deflection numbers for different types of guitar ? I realise its very specialist and subjective but baseball park numbers would be really useful for the beginning Guitar builder.

[@GarrettLeeLuthier]

Definitely stiffer (lower deflection) for a steel string instrument. When I was building small jumbo steel string guitars, my target deflection was 0.110 inch in the with-grain direction and 0.180 in the cross-grain. This is for the same weights described in the above video, and with the plate similarly supported 1 cm from the edges and at the widest point of the upper bout. (Of course, the plate is a different size compared to a classical). As an example, for a Euro spruce top with density of 0.42 g/cu. cm, the final plate thickness in the upper bout and in the center of the lower bout would be 2.55 mm. In the lower bout, the thickness would taper to 2.30 mm at the edges. The bracing was a typical X braced pattern. This creates a very balanced, rich and articulate sounding guitar.

[@hereasafanofallsorts5164]

Hi Garrett - Thanks so much for that - these are trade secrets and I very much appreciate you sharing - I wouldnt know where to start with this. Thicknessing a top to get the best tone is a complete dark art to us uninitiated so to have some sort of reference and methodology shown here is 24 carat Gold - I hate to rabbit on and perhaps you have a video on this but how are you getting such specific top thicknesses ? - I'm reliant on a dum sander and calipers and maybe feathering the sides a bit but anything more specific would be crazy difficult - do you do it with a hand plane ?@@GarrettLeeLuthier

[@GarrettLeeLuthier]

You can hand sand with a sanding block or use a palm sander as shown when you near the desired flexibility. The key is that the thickness number is not important, but rather, that you achieve the right flexibility. The thickness that I show is just the measurement at the end of the process to give you an idea of what the thickness looks like.

[@hereasafanofallsorts5164]

@GarrettLeeLuthier OK - Thanks so much for your replies. That is all very helpful

[@ruisousa4835]

Hi Garrett, thanks a lot for this invaluable information. Question : what would be the target deflection numbers for a steel string guitar like an OM or Dreadnought, do you have any experience with these kind of instruments using your method ? Thanks again.

[@GarrettLeeLuthier]

I'm really glad this info will help you. I'm sorry that I don't have deflection numbers for steel string guitars because at the time I was building small jumbos, I didn't apply the technique to them or my classicals. I sure wish I had, if nothing else but to give it to you and keep for my own records. I hope someone will be open enough to share theirs with you.

[@GarrettLeeLuthier]

I just checked my notebook and I did run deflection analysis for my steel string guitars, which were small jumbo models. My target deflection was 0.110 inch in the with-grain direction and 0.180 in the cross-grain. This is for the same weights described in the above video, and with the plate similarly supported 1 cm from the edges and at the widest point of the upper bout. (Of course, the plate is a different size compared to a classical). As an example, for a Euro spruce top with density of 0.42 g/cu. cm, the final plate thickness in the upper bout and in the center of the lower bout would be 2.55 mm. In the lower bout, the thickness would taper to 2.30 mm at the edges. The bracing was a typical X braced pattern. This creates a very balanced, rich and articulate sounding guitar.

[@PaulMcEvoyGuitars]

@@GarrettLeeLuthier have you shown your record keeping in any videos? It might be in this one, I have to watch again.

[@GarrettLeeLuthier]

@@PaulMcEvoyGuitars Yes, in Episode 6: Notetaking.

[@66Gollum]

Thats realy interesting, thank you verry much for showing and explaining this so well!! I'm always thinking about building a probe guitar with a easy removeable deck, but dont know how to do and will it be helpfull?

[@GarrettLeeLuthier]

Do you mean removeable neck? If so, you can use any number of bolt-on designs, such as those used in steel string guitars. I find it helpful for fretting and finishing separately from the body.

[@66Gollum]

@@GarrettLeeLuthier sorry - no, I meant a removable soundboard. For a beginner it's to hard to finish the complete guitar an then realize the sound is not good

[@garylee6266]

@@66Gollum The idea is that through correlations to good sounding guitars, you will be able to use surrogate measurements to tell you before you finish the guitar if your top assembly has potential to sound good. Deflection, tapping and impulse analysis are some of these surrogates. If you feel that you need to model something that is structurally closer to a finished guitar, try using the approach taught by Brian Burns Guitars using partial side/top/back assemblies that can be manipulated.

[@66Gollum]

@@garylee6266 yes, that's wy i like your method so much - a real good starting point. Thank you again so much!

[@markgrimm3564]

what does the top measure out to .115''

[@GarrettLeeLuthier]

I don't think I understand your question. What's the significance of .115"?

[@dogboyy2k12]

wow thx......

[@GarrettLeeLuthier]

Thanks for watching. You are very welcome!

[@MegaMandrake99]

The only way to know now is to continue the building and actually play this guitar

[@JoseEduardo-vb6ko]

Hi! I watch yours videos but i dont undertand english. I need subtitles.

[@Today_I_Want_To]

You can activate automatic subtitles in the definitions. Do you speak portguese?

[@JoseEduardo-vb6ko]

@@Today_I_Want_To thanks! Yes, portuguese

[@Today_I_Want_To]

@@JoseEduardo-vb6ko me to. Welcome. Nas definições tem legendas automáticas e normalmente dá para configurar português nas definições.

[@GarrettLeeLuthier]

If you are not able to get the translations, please let me know. I was able to get my video to play Portuguese closed caption.

[@JoseEduardo-vb6ko]

​@@GarrettLeeLuthier consegui acessar as legendas, obrigado

[@riccardomoni3598]

😂😂😂😂😂😂😂😂😂

[@robertbdesmond]

Gary- I enjoy your scientific approach, but we need to talk sometime! Thanks for sharing your methods and beliefs. Bob

[@GarrettLeeLuthier]

Sure, Bob. feel free to contact me by email through my website and we can schedule a time.