Bracing and Voicing a Classical Guitar Soundboard

[@chriscrevelsguitars]

If anyone is interested to know more about how I measure and voice the soundboard, drop a comment with your questions!

[@ulyan079]

Thanks for your video. Have you ever measured old Spanish guitar? Very interesting know their frequency modes. Thanks and sorry for my English ❤

[@chriscrevelsguitars]

@@ulyan079 don't worry about the English, it is not my mother language as well. I personally have not measure old Spanish great guitars myself, but I have studied the information others have published about such guitars.

[@ulyan079]

@@chriscrevelsguitars If it's not a secret, could you share a link to some article, please? And thanks for the answer🙏

[@chriscrevelsguitars]

@@ulyan079 i can't recall of any online article right now, but there is good information on Classical Guitar Delcamp Forum. I recommend books like the ones from Giovano Nocoletti and Trevor Gore

[@chriscrevelsguitars]

@@oscarjagal1081 once you know the density and resonant frequency of the plates of the top, you can use an equation to derive the Young's modulus of that piece. It's a number that relates to the piece stiffness. After that, you then use another equation to figure the thickness required to sustain the load of the strings you use.

[@Mental_hygenics]

I just built a acoustic baritinr out of free scrap and I stumble upon this craftsman. I am so humbled by the precision ans techniques. Im so blessed that i get to watch this...

[@chriscrevelsguitars]

Thanks so much, I am glad you liked it!

[@Mental_hygenics]

@@chriscrevelsguitars of course I hope you keep making awesome videos like this. I used to work for Marco Basses and he gave me so much insight. I really love the ways people voice their soundboards but its also interesting to learn how the sound comes from so.many places. I've heard from my 12 string extending the headstock 6 inches and creating a 2 degree difference created longer lasting harmonics and significantly changed the resonance. Is there a golden ratio to scale length and string height over the the soundboard ?

[@johnlay3040]

This is a truly handmade guitar. Amazing handyman.

[@chriscrevelsguitars]

Thank you! Glad you liked! It!

[@stavrosa8772]

Thank you for the great video! Such beautiful and detailed work...

[@chriscrevelsguitars]

Thank you! I really appreciate that

[@guerraz]

After you figured out the thickness of the top with yr calculations, what was the frequency of the top before the bracing was glued on . The frequency of the non-braced top must surely be part of the calculation . Also what was the frequency you were trying to achieve with the braced top . It wasn’t glued to the sides yet which is another frequency all together. The frequency you noted was your final , right? 170 Hz which is good for acoustics .

[@chriscrevelsguitars]

The exact frequencies are not as important as what they say of the plate: it needs to be stiff enough, but not too stiff. Of course, bracing adds stiffness and that's why I do the test braced. The sides do change the frequencies after the box is closed.

[@dalloguitars]

It looks like you got exellent results in the chladni test 👍👍

[@chriscrevelsguitars]

It does. So much of it does not goes through in the video. The most resonant frequencies I didn't even set the speaker to full power, which is great news.

[@csterea]

What would be interesting as a video follow up is what decisions you make based on these frequency patterns. I mean some of it are "luthier secrets", but roughly, I want to know how you alter the braces based on those "dust" patterns. And how you choose the balance between durability and resonance. And how you decide upon the thickness of the top (without the braces). I also saw some people tap on the guitar top and listen for sustain and the fundamental tone. Maybe you can shed some light on that. Thanks.

[@chriscrevelsguitars]

That's a great idea. Though maybe it is a little difficult to convey such a delicate process on camera. What I do is pretty much access which areas aren't as responsive as the others at those resonant frequencies: they present themselves either as a "bump" on the patterns or a "smear", making the pattern less symmetrical and crisp. This means that the area is too stiff relative to the overall top. So the goal is to make it less stiff, i.e. take away some material. If there is a brace at that point, then shaving the brace it is. I thickness my top using an equation for the stiffness required to sustain string load. For that you need to measure density and resonant frequency, and then you can figure out the target thickness for that specific piece of wood.

[@csterea]

@@chriscrevelsguitars Thanks for the straightforward response, you condensed a lot of information in it. I don't think I need a detailed video of endless brace adjustments, I understand what you mean. Is there also a measurement of how those frequencies sound together, or do you just voice the top based on request? For example, strummers may want a guitar which produces chords that sound "together", while fingerstyle players may want single notes to ring out. I ask because I tried different acoustic and classical guitars, some of them sound good on chords, while the ones that sound good on fingerpicking individual notes and less complex chords, they sound "all over the place" when strummed.

[@guerraz]

@csterea while some of us think there is builders secrets ( for a time anyway) there is non . The patterns you are referring to are frequencies (Hz) there is the before Hz and the after Hz . The calculations in question are useful if you learn how to use them but not necessary. In simple terms if you thickness yr tops ( classical) to 75 ish Hz that’s your best start regardless of the thickness. Of course the quality of the board is of big importance, if you can put a number on that maybe 5% not how it looks either . Awful looking boards work good too if the sustain is there to begin with . If it’s decided that a completed top will work by tapping then what is that frequency? Right ? Has to have a frequency. Some think that’s good some bad . Perfect pitch is probably what some people have to be able to hear or at least match the thump to a 6th string note like G , I certainly don’t . At this point after you determine the 75 Hz you brace and do some preliminary trimming. Don’t go crazy. In the mold and using an frequency analyzer (any) you trim to about 155 Hz - 160 Hz . In my tops I glue the bridge bindings fretboard before the test . So I stop at slightly above 190 hz Tape the back no glue . Start adjusting to 90 hz Air 190 Top Go to work . There is always speculation and doubt about this type of work . But whatever floats yr boat . Thank you

[@llanedeyrn5]

Excellent work. What are you looking for with the tea leaf patterns? Symmetry? Specific patterns at certain frequencies? Thanks.

[@chriscrevelsguitars]

In short, yes and yes. Symmetry, for one, shows me how much the stiffness is well distributed, so I look for that. I save a record of the patterns and frequencies and then compare to other instruments. Some of the patterns I do look for in some frequency range. This tells me if the overall stiffness is too high or low.

[@kingofskateop]

I'm really curious what happens if you brace the guitar in the shape of the Cymatics that you did at the end of the video?

[@chriscrevelsguitars]

Interesting line of thought. Conjecturing here, because I ultimately don't know. My educated guess would be that nothing special happens. After the soundboard is attached, all the modes change due to the edges of the plate being held by the sides of the guitar. For one, it is already braced when the pattern is formed, and the preexisting brace influences the pattern itself. It wouldn't be there without the brace in first place. Moving forward, it would depend on which pattern one chooses, a lower frequency one would have deeper acoustic impact (I suppose), because in higher frequencies the vibrations tend to ignore the shape of the bracing and 'see' only its stiffness. Finally, bracing is also a structural feature designed to increase the integrity of the guitar in holding itself against string tension.

[@sinaTonewood]

nice job with hands tools, thanks for the video

[@chriscrevelsguitars]

Thank you very much, glad you liked it!

[@XDdrox]

I'm a physicist, I understand the harmonic vibration modules you encounter, but for what purpose and what are you looking for? Do you define specific frequencies and force the top to have these frequencies as fundamental?

[@chriscrevelsguitars]

Bear with me, I am actually not so interested in the frequencies themselves, as long as they are in a certain range, which they normally do after the thickness of the plate. I am more concerned with (and acting toward) the even distribution of stiffness throughout the whole braced top. Second: the frequencies provide objective information that I can compare with my other guitars

[@XDdrox]

How incredible! I wanted to thank you for your reply and your attention! I wish you every success! @@chriscrevelsguitars

[@ulyan079]

hello. in the first mode, which you showed us at 12:04 min., what was the frequency? Thanks🙏

[@chriscrevelsguitars]

Hey. Sorry for the delay, had to check my notes for this one. It was at 173Hz

[@ulyan079]

@@chriscrevelsguitars Thank you very much and I'm sorry for the inconvenience. I am very pleased that you are sharing your experience. Good luck to you in everything

[@FrancescoSpina84]

I just discovered you channel and I LOVE the great videos you posted! Excellent quality and super nice to see your building methods and the precision you can achieve with hand tools. One question: where did you purchase the fiberglass bars for the go-bar deck? I would like to build a go-bar deck as well to build my first guitar! :)

[@chriscrevelsguitars]

So glad you like the videos! Stay tuned, soon I'll post some more. As for the fiberglass, these ones I got back when I lived in Brazil, but it seems Stewmac sells some very similar ones

[@chriscrevelsguitars]

Don't hesitate to get in contact if you need some tips for your first guitar build. I'm happy to help!

[@stephenrimmer5629]

Hello Christian, thank you for all your videos they are amazing. Can I ask at the start of this video you place the sound board on a set of scales my question is why, was you weighing it for a reason or was you just resting it on top for safety?

[@chriscrevelsguitars]

Hello Stephen. Glad that you like the videos! I weight the soundboard in several different moments as I work with it. Reason is that I aim for some specific weight relation between soundboard and braces.

[@stephenrimmer5629]

Hello Christian and thank you for replying I am currently in the process in purchasing the tools needed to build a guitar so I’m a novice but your video is the only one I have come across that includes sound and frequency and it’s gone way over my head how can I learn about sounding a top board?

[@chriscrevelsguitars]

@@stephenrimmer5629 a good beginning is Roy Courtnal's book on guitar building. You can find it online relatively easy. It doesn't go into voicing the soundboard, though, but gives interesting measures. Irving Sloane's book is also very good for overall construction. If you really want to dive deep into resonant modes and the science of guitar sound loof for Trevor Gore's books, but they might be a lot to digest if you are only starting on it. I recently received the book of Giuliano Nicoletti, from Iulius Guitars, and the information there is also very well presented and it gives you extra tools for start measuring modes and frequencies yourself. I personally recommend it. Feel free to email me at [e-mail] if you want further details!

[@vgfjr505]

If you change your bracing, will that produce a different pattern of nodes?

[@chriscrevelsguitars]

Yes, most certainly. Some of the patterns may be the same, but in different frequencies

[@jameslabs1]

Cool!

[@chriscrevelsguitars]

Glad you liked it!

[@OkanTandogan]

Hello, Thanks a lot for sharing your amazing work. I have a question; being an acoustics and vibration engineer and an aficionado of guitars (particularly flamenco) I wonder one thing. Have you ever made a study comparing objective resonance frequency measurements with how they subjectively sound when the guitar is played? We sometime want guitars with less sustain which are usually for accompaniment to a singer, or sometimes a balanced one if you also play solo. Sometimes, like some traditional flamenco guitars we want bright treables but without too much sustain still and so on. I am trying to understand, what sort of bracing/thickness etc and consequently the first 3 resonances of the guitar leads to which sort of certain sound. Have you ever made a conclusion as to "keeping the air reaonance, soundboard reasonance and back resonance at "..." frequencyies give a subjective result like high sustain/low/sustain/high treable sounding etc.? Thanks in advance.

[@chriscrevelsguitars]

A lot to unpack here, but let's go. The short answer is "it's complicated": I do keep notes on the frequencies and sound of my guitars, or better yet, recordings, as the memory does not do a good job with sound quality. But those are only good so far: a guitar's sound changes over time, especially when it is very young. You are right, most of the sound of the guitar comes from the lower frequencies, but the higher harmonics make a good portion of 'timbre', if you like, because our hearing is much sensitive around that area (for distinguishing consonants in speech, for example). So quality of sound depend also in the relation on harmonics: fewer harmonics give a more 'focused 'sound, "root pure", while more harmonics sound brighter, "richer". Much of what we think of sustain is also related to harmonics. Overall, the exact frequency of the top in itself doesn't matter that much as long as it is in a specific range and not in the exact frequency of any scale notes. The efficiency of the frequencies, and relationships between them are more important.

[@chriscrevelsguitars]

There are some general rules of thumb, though. As we are dealing with a limited amount of energy in a pluck, it needs to go somewhere and we can't have it all: so a guitar with stronger, faster attack will normally have shorter sustain (like a flamenco). This relates to the physics of the top: a heavier top will take longer to put in motion, and 'attack slowly', but once moving, will take longer to dissipate all its energy due to its greater inertia, i.e. 'sustain' vibration for longer.

[@OkanTandogan]

Hi Chris,@@chriscrevelsguitars Thank you again for your comments. I would like to give a sumamary on the several guitars in which I measured the first three resonances and I also played them to note the differences. Is there somewhere that I can write you about those to have your opinions also? Email, social media etc if that is also okay for you?

[@chriscrevelsguitars]

Hey, of course! I'm on Instagram as well, or you can email me at [e-mail]

[@mamaslostsoul]

@@OkanTandogan Beautiful work. if you have published it anywhere, pl share the link, will be more than happy to see those numbers to get a feel of the modes.

[@vgfjr505]

I’ll take your offer. What was that vibrating instrument that you used? Also, did you have to touch the top with it, or does it blow air into the board to get it to vibrate? Lastly, aside from being able to see the vibration mode pattern lines on the top of the board, do you adjust the braces afterwards if you see the patterns not as you like? Are you looking for perfect symmetry in the patterns?

[@chriscrevelsguitars]

Many questions! I'm happy to answer. I am guessing that you mean my audio monitor that I hover over the soundboard: it's a speaker, not a vibrating instrument nor air blower. The work here is done by resonance. Though the source of the sound must be loud and close to the soundboard, it must never touch. I'll do a sweep over the frequencies from 50 to around 400Hz, then the soundboard resonates when I get to one of its resonant modes. Positioning of the speaker matters also. Each mode at a different frequency and with a different pattern. I then write down those frequencies and photograph the patterns. I look for different things: some specific patterns to be inside of a frequency range; symmetry of the patterns; the shape of the most important modes. Last but not least, it is also documentation for future reference: if the guitar sounds particularly great, I'll try to emulate the patterns in the future. Yes, if I find that some things are not quite as I like, I do adjust the braces afterwards. Cheers!

[@vgfjr505]

Awesome… This is so interesting. Does the speaker need to be positioned at the center where the bridge goes? Also, do you ever repeat this test once the guitar is fully assembled to see the effects of the rest of the body on the top’s resonance?

[@chriscrevelsguitars]

@@vgfjr505 the bridge position happen to be (not accidentally) on the center of one of (if not the) most important mode, but otherwise no, the speaker needs to me at the 'nodes', the center, of the vibrating area. Basically I hover it around until I find the sweet spot. I personally do not do this after the guitar is done. Some people do, but I find it a little cumbersome. I do make a tap test and analysis of frequency response, which gives me part of the same information.

[@vgfjr505]

@@chriscrevelsguitars curious… Do you measure the mass before or after before or after you complete the shaving the top, or both? Also, is there a way to measure the top vertical displacement or the top response frequency as you hit it with the speaker? I think a nice mic could measure the response frequency? That would be interesting to get other information about the top vibration properties.

[@chriscrevelsguitars]

@@vgfjr505 Hey there! I actually measure mass many times as I am voicing the top and shaving bracings, before, after and during. Regarding the other questions let's go through them: Yes, there is a way of measuring top vertical displacement, with static weights. It's valuable info. I don't hit the top with the speaker, though, I just let the sound make the top resonate from a short distance. The "response frequency" I get you mean the resonant frequency? Those frequencies are exactly the ones where the patterns show. I start at a low frequency and go up slowly until the tea leaves start to bounce, then write it down and continue. You can also know them by recording a simple tap test and run it through a spectrum analyser. A nice mic will help, but it is not entirely necessary. These are different tests, for different data. Measuring displacement with weights tells you about stiffness and volume, tap test informs the resonant frequencies, and Chladni patterns show the resonant modes and distribution of stiffness. They are all connected of course, but each holds their own value.

[@jesussivira9711]

Saludos Desde Venezuela , quisiera saber las medidas de la tapa.y más barras armónicas gracias , buen trabajo.

[@chriscrevelsguitars]

Buenas! Esta tapa en particular se quedó algo como 2.8mm de espessura. Las barras harmônicas (las grandes), tienen 14 mm, e las pequenas empiezan con 5mm pero las esculpo hasta el tampo tenga la resposta que busco. Espero que ayude!

[@tomaslupia]

Exellent. What materials are the bars pf the go bar Made off? Thanks .

[@chriscrevelsguitars]

They are fiberglass.

[@shblesaleem8169]

Hello dear, nice work and am deeply glad that i found your chanel, i have one one question about the exact wood you used for the bracing! it seems that it is the same wood from the rest of the soundboard! it makes me wondering about it and why haven’t you used q-saw bracing wood? goodluck and am looking forward for more videos.

[@chriscrevelsguitars]

Hello! Glad that you like the channel, welcome onboard! The fan bracing is the same wood as the soundboard, yes. It is quarter sawn though, the whole soundboard is quarter sawn indeed. I am considering using spruce instead for future builds with cedar. But let's first listen to how this one will sound

[@shblesaleem8169]

@@chriscrevelsguitars Thanks fr responding dear friend, what i thought about was more related to wood grains for bracing wood! is it 90 degrees on the top ? well, forgive my dumbness haha but am trying to build my first Oud and everything from this angle seems very interesting and worth to be known .

[@chriscrevelsguitars]

@@shblesaleem8169 yes, it is 90º (or very close) on the whole top! I don't know much about ouds, but I suppose you want your top close to 90 as well in a oud

[@EmmanueleDaPonte]

@@shblesaleem8169all the great sounding ouds I’ve played had very similar to Australian instruments which want a very stiff back and sides and a lattice braced top

[@dassouki]

Nice work .. where did you get that circle cutter from?

[@chriscrevelsguitars]

I ordered it online from Dictum. Search their website for 'hole cutter'

[@sniperpelangi1988]

❤❤❤

[@chriscrevelsguitars]

❤️❤️

[@Rotary_Phone]

This guitar is going to be A LOT higher quality than those cheap "Esteban" guitars that you could buy from the QVC network about 15 years ago...That, I can tell you!

[@chriscrevelsguitars]

That's the goal!

[@Rotary_Phone]

@@chriscrevelsguitars You going to do a French polish on it, or some kind of lacquer?

[@chriscrevelsguitars]

@@Rotary_Phone this one os going to be French polished, yes.

[@Rotary_Phone]

@@chriscrevelsguitars Nice! I know i've read it's a tedious process, but It's nice you're sticking with the old school techniques!

[@chriscrevelsguitars]

@@Rotary_Phone it sure take some time, but is relatively straightforward (once you trained the technique), don't require many gizmos, and, most important I my opinion, it is non-toxic.

[@riccardomoni3598]

😮

[@chriscrevelsguitars]

😮

[@phoenixses]

No explaination of the voicing process, so essentially, we're not ment to learn anything, only watch you. Look at me, look at me.

[@chriscrevelsguitars]

Well, this is KZbin, not a class. Anyhow, look for Trevor Gore's or Giuliano Nicoletti's books if you aim to understand the voicing process better.

[@riccardomoni3598]

Siamo su scherzi a parte...🤔

[@chriscrevelsguitars]

😃

[@riccardomoni3598]

Non scherziamo per favore😂😊😅

[@chriscrevelsguitars]

🤣

[@juliocesarcardoso8516]

Excelente trabajo

[@chriscrevelsguitars]

Muchas Gracia's!