Official Luthiers Forum!

Think you need a better spectrum really.
At a guess, body ~100, top ~ 165 (not typical frequency for a top, nor well defined) Back I'm not seeing anything, may not be a live back.
What are you using for a microphone?
Any other offers?

_________________
The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

It is a greek bouzouki not a guitar this instrument... i have a condescent usb microphone c 1U behringer and visual analyzer. i tried it with audacity too...i can see three frequencies 50 hz 100 hz and 172... but they are not excactly peaks...as you can see....i dont know what is wrong...

You might have mentioned it was a Greek bouzouki................
I don't have clue, but I do like Retsina and Ouzo

_________________
The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

Haha i also do...but i like making inatruments too!!Well maybe not while i am drunk from ouzo!

I think OP is chasing ghosts. Martin can't make any two instruments of the same nominal specifications sound identical. Wayne Henderson's been chasing instruments that match a Martin he remembers from his adolescence. I think a first-time builder has zero chance of success in doing this, but an excellent chance of making a good instrument that sounds just like itself. Technical discussions can extend till doomsday and I think none of them points to a cookbook process to copy a guitar's voice. Might as well try to figure out what music them angels dancing on a pinhead prefer.

_________________
Peter Havriluk

More information is usually better. Controlling the way you get it helps.

I've been doing 'impulse spectra' for at least 30 years; more regularly as time goes on. The responses of the room will color the spectrum you get, so, at very least, you need to always do them in the same place. Microphone placement also has an effect, particularly in a 'live' room; moving the mic even a few inches can alter the spectrum chart. I finally got tired of trying to account for all the differences and set up a 'semi-anechoic closet' ; a space about 4' x 10' x 6' that is well padded on the inside, with a fixture to hang the guitar from and turn it to different angle when I want, and provision for driving the guitar by dropping a small plastic ball in a string to hit the bridge. The microphone is mounted in a specific spot, and feeds into my computer. It's not perfect, but it's pretty good, and always the same.

I also use Chladni patterns on the assembled instrument to look at the resonant modes of the top and back. For this you need a signal generator (such as the one in the 'Luthier Lab' Android app, an amplifier that can put out 12-15 W, a compatible speaker, a few foam pads and some sawdust or glitter. The 'main air' resonance is read off using my old analog dB meter, or you can use a small electret mic and a digital volt meter. Getting the resonant modes tells you where the peaks and dips in the spectrum chart are coming from.

The important thing is to come up with tests that give reliable, repeatable information, and are easy to do. You won't do them if they're not easy, and non-reproducible data is useless. Note that, for simple impulse tests, you're not always going to be able to get the same amount of power input every time; the heights of the peaks will tend to vary from one test to another. What counts is that the overall shape of the curve matches pretty well, as do the frequencies of the peaks and dips. There is a way to get a more controlled input (the 'wire break' method, which I have also used), but its a little harder to do, and tends to accentuate the low frequencies. Again, keep it simple...

I print out the spectrum chart, and add in the Chladni information by hand in the margins. I've been doing this for over twenty years now, which gives a lot of data that can be more or less directly compared, which is a big help. Again, this is a long road...

A song line keeps appearing in my ears at this point: It’s a long and winding road.

Also for Brits of a certain age there is a song: You should have listened to Al.

I have probably had a glass of Merlot too many but I reckon that sums this discussion up!

Cheers Dave

"The important thing is to come up with tests that give reliable, repeatable information, and are easy to do. You won't do them if they're not easy, and non-reproducible data is useless."

I laughed when I read this because it's so true and obvious to anyone who ever even approached such methodology.

KISS - Keep It Simple Sweetie.

Use the KISS principle. Break it down to it's native parts and start from there. And that is not to say that keeping it simple is easy... No no no it's hard work. It's hard work to design an experiment that is simple and that you can replicate under the same perimeters to yield similar results.

I mean..... even the humidity will affect how an instrument resonates in testing right? It would seem a humidity laden instrument would move different than a dry one


Sent from my iPhone using Tapatalk

Exactly what I was thinking…

I think the solution is to build about 100 instruments maybe 200 and you might start getting the hang of it…


Sent from my iPhone using Tapatalk

Its ok humidity will affect it but i cant believe that with using physics there is not a way of knowing or tuning an instument to play its best...we have mics we have computers...we have knowledge...maybe there is a way to make a good instrument by copying one and then trying to manipulate its sound. i have built maybe ten or more intruments and repaired more than fifty. But i need something more to than feel and luck.I need to incorporate science in my building. I make good instruments already as players say...but i need to be sure an instrument is going to sound good before even put on the strings.I believe it can happen i just dont know how yet....Till know i tune the intrument alot after i put the strings on.

Sorry but i will disagree with this statement...I have spent a lot of hours tuning an instrument so as to play good.I think this is the way and not just building more instruments. I know i can tune an instrument after it is built but i want consistency and a way to know excactly how to do it and not just getting lucky after hours of manipulating the sound....

I've concentrated on trying to get them to work well 'off the bench', without requiring a lot of post-production adjustment. As I say, with some practice you can get 'arbitrarily close' to the desired sound this way reasonably consistently: 'perfect' matching would require later fine-tuning, if it's even possible (which I doubt).

You have to have some sort of model in your head about how the guitar works; you use that to devise measurements to guide you. If you think that tickling the strings makes leprechauns laugh, and that's where the sound comes from, then you have to figure out a way to count leprechauns, and find out what entices them into guitars. I go with the 'standard model' that relies on Newtonian physics. Since my math chops are weak I don't go in so much for deeply mathematical models, such as Gore uses.

Several people have, in the past, endeavored to design guitars from first principles; starting out by defining the 'ideal sound' and then working out designs to produce it. They have not been terribly successful in the market. Partly this is due to limits in our understanding of what constitutes the 'perfect' sound, but we can solve that problem by looking at more agreed-on 'great' guitars.

Partly it's due to the shear complexity of the beast. This has been stated as a paradox. The builder has very little direct control over the way the guitar works above, say, about 600-800 Hz, but we know from playing and listening tests that the difference between 'average' and 'superior' instruments is mostly in the high frequency range, particularly between 2 kHz and 4 kHz. So how is it that some makers can consistently make superior guitars when they have no direct control over what makes them superior?

Obviously there must be some sort of indirect control. Many good makers (but not all) use some sort of 'tap tone' method to assess the state of the top, in particular, before assembling the box. The 'tech' method of doing this is to use Chladni patterns to look at the resonant modes of the 'free' plates, both the frequencies and the shapes. This is very hard to justify on a theoretical level, since the assembled box is manifestly much more than the sum of it's parts. It would take a very sophisticated computer model to track the contribution of the 'free' plate modes to the modes of the assembled box that actually shape the sound. Even that would be limited in it's accuracy, given the inherent variability of wood, and especially in the high frequency range. But you have to try something.

The saving grace is that what seems to count in the high frequency range is the number of modes and their associated losses. Because they overlap so completely in pitch and couple so promiscuously the actual output peaks you see in the high range are not the output of 'pure' wood or air resonant modes, but rather the products of complex coupling. However, it us possible to think of things in a statistical manner: if there are ten major output peaks in an octave (say between 2000-4000 Hz), there must be ten major wood or air modes that are coupling to produce them. Also, the ratio of peak height to the level in the lowest dips is a function of the overall loss in that range. Judgments of overall 'quality' of sound appear to be linked to the number of peaks and the peak-to-dip ratio rather than to precise pitches, particlarly in that high range. Frequency differences are perceptible, and allow listeners to differentiate instruments that are otherwise 'identical', but produce no agreed ranking in 'quality'; some people might prefer one over the other, but there is no consensus.

It turns out that, so far as I and others can tell by using the Chladni method, there does seem to be a correlation between the number and clarity of 'free' plate modes of the top and the overall quality of the assembled guitar, as judged by listeners and players. We have to be careful about this. Richard Feynman pointed out the :"You are the easiest person for you to fool". Logically it makes sense that setting up the stiffness and mass distribution in the 'free' plate so that it divides up into smaller vibration areas at higher frequencies in way that is not 'lumpy' and has low losses should allow it to do so effectively once it's glued down, even given the large change in edge constraint. But that's not 'proof' and proof may be impossible to get, particularly give the limitations of the research budget...

Again, there are other ways that seem to work about as well, but I have some evidence that suggests they are all different means of approaching the same end.

So; using normal good building practices you can get the lower range peaks (up to, say, 600 Hz) to match more or less well which establishes the overall 'character' of the sound. The more things you have under control, the closer you'll get. Getting the parts, particularly the top, to work 'better' within themselves improves the 'quality' of the sound without necessarily altering the 'character'; a rosewood/spruce Dread will sound like a rosewood/spruce Dread, and not a mahogany/cedar one, but you can improve the rosewood one by getting the parts, and particularly the top, to work 'better'. It's easier to do this before you close up the box, so that's what I try to do.

sound is subjective,what sounds good to one person may not sound "good" to another...

"we have mics we have computers...we have knowledge..."

All of which are imperfect. Not to mention, what was already mentioned, that wood is not perfect either. This is the beauty of instrument making as an art. It's almost as mysterious as it was when Strad was making them. Yes we have better tools now technologically speaking but as Alan mentioned, on this research budget, we probably aren't going to get too far.

Maybe when nano chip technology becomes mainstream we will get a bit closer. But to model a panel of wood?

But that would take the fun out of it, wouldn't it?

_________________
formerly known around here as burbank
_________________

http://www.patfosterguitars.com

Well i have looked everywhere for a second hand trevor gores book and nothing!This book is really hard to find!!

Think that many builders are aware of the books, and I for one have said it would have to be pried out of my cold dead hands.....

_________________
The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

Hehe i see!it must be very good if you say this!Do you believe i should buy it?

I do, and as I said SM members ($40 for a year - which you can easily get back on delivery charges) get it half price ($174), and I don't think you would be much less buying second hand.
It also includes full size plans for 4 guitars covered in the book - a SS Falcate build, a J-45, a lattice braced classical, and another (I can't remember off hand)
Really don't think you could get much better bang for your buck in a book on guitar design and building.
I use several of his jigs (or at least adapted his suggestions) and some of his construction methods, and I have several other good building books on my shelf basically for reference

_________________
The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

Thats good! I am more interested in the chlaldi paterns and tap tuning...i hope it gets me there...

Gore doesn't look at the 'free' plates (not glued to the rim) using either tap tones or Chladni patterns, so far as I remember. They're basically the same thing except that Chladni patterns give more, and more objective, information, but take more time. I ran Chladni patterns on several tops in a tap tuning workshop that was run by Dana Bourgeois, and confirmed that we're doing much the same thing.

I wrote a series of articles on 'free' plate tuning in 'American Lutherie' magazine back in '91-92 (issues 28-29-30). I also was the 'talent' in a video put out by Micheal Collins on plate tuning steel string guitar tops. I don't know if that's still available: I haven't heard anything from him is several years. We've learned a few things since then, I think, but those sources will get you started. Note that I don't get anything from either source at this point.

Copying the 'free' plate modes from an existing instrument won't produce another with the same sound, but it can help you get close. You need the 'free' mode information on the original to do this, of course, and you don't generally have that, since relatively few makers use this technique.

So far I've found the method I spoke of in my June 3 post to work fairly well; basically using Chladni patterns to show the modes on an assembled instrument, and correlating those with an impulse spectrum. The spectrum by itself won't sufficiently constrain things: you can't tell for sure what's causing any specific peak or dip in the output. The Chladni patterns give you most of that information, but, by themselves, don't say much about how effective a particular mode is in making sound. The spectrum also gives you 'air' mode information, which you won't get directly from a Chladni pattern.

It often happens that, when I've made a particularly nice instrument, I'll go back in the records and realize there was one more thing I wish I had measured. At some point you just have to go with what you can do: you can spend al kinds of time on this getting information that doesn't help much. The important thing is to set up tests that compliment each other and are easy to do, so that you can get a lot of data in a short time, and keep it on file.

Simples.

_________________
The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

Anybody planning on winning the Tour de France first learns to ride a bike. All the competition planning in the world has no value without world-beating basic skills.

_________________
Peter Havriluk

You can use Luthier Spectrum Analyser (LSA) to easily compare 2 instruments. The software allow to save and load multiple recorded tap tones. You can then easily identify the frequencies which are differents. You can get a copy at: https://alainlambert.wixsite.com/lutherie/luthier-spectrum-analyser

Attached is a screen of a comparison I made of 2 instruments.