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I'm not sure 'wolf tone' is the correct term but the two lowest E notes on my dread are causing problems. They have a loud thump but then they decay really quick. I notice this happening on the open low E(6th string), 4th string 2nd fret, and 5th string 7th fret. Also the 12th fret harmonic on the 6th string doesn't ring out like it should. The guitar has been strung up for about 3 weeks I think.

I'm guessing this has something to do with the interaction of the resonant frequencies of the top and back plates. I wouldn't be opposed to shaving the braces some but I wouldn't know where to start. The braces on the top could have a little more triangular cross section but other than that they are pretty much close to specs. The back braces are a little heavier, the upper two are about 1/32" wider than the plans(typical Martin 5/16"x5/8") and they could be much more triangular. The lower two have a little extra meat on them. Any advice on what I should do?



And if it matters...
I don't know what the resonant frequency of each plate was before gluing them to the body but before I glued the neck and bridge on I'm pretty sure the lowest resonant frequency of the closed box was around F#. Now when I hum into the soundhole the lowest note I get is E but I don't know if that E is actually 82.407Hz or an octave above. I did try and use a speaker in the soundhole and sweep through the frequencies and record it with a mic. It seemed like it was resonanting around F or F#. I also did this with a big speaker next to the guitar, because I didn't trust that tiny speaker so much, and the loudest note was F# in this case too. I could also feel it resonating much louder at F and F#. I did record both speakers away from the guitar as a control. I also did this with the guitar laying on its back so that probably raised the resonant frequency too.

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Jeremy Douglas

Jeremy, I don't have any advice as I am only a keen beginner in the realm of acoustic guitar construction. However I am very interested in gaining more understanding in this area of building so will be listening carefully to the more experienced when they chime in.
I do remember Al Carruth and others saying that if the main resonant pitch of the back is too close to the main top pitch the wolf tones can be a problem. I am planning on using chaldni (not sure of the spelling)patterns to determine the main pitch of both braced plates before and after gluing to the rims on my current build.
I'm sure there will be a fix for your problem.

Regards

Craig

I have occasionally changed quiet guitars by selectively adding weight here or there. In determining where, I have applied a Bulldog Clip (or binding clip...you know, the spring clips that some use to hold kerfed liners when gluing) to various points along the lower legs of the x brace or tone bar. Make sure the clip itself doesn't buzz during your trials. Once I've found an improvement, I've glued a piece of spruce having the same mass with HHG to the same area. I don't know what the rogue frequencies were, but it made an improvement in each case. The trials are kinda fun and enlightening. Give it a try.

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JJ
Napa, CA
http://www.DonohueGuitars.com

Thanks guys, I was hoping Alan would chime in here. I found an old post where he talks about adding weight in certain spots to see where it would be best to remove wood(decrease stiffness to lower the pitch). So I'll probably try what JJ and Alan have suggested today and see what adding some weight does.

"BTW, there is a reasonably safe way to try out some of this stuff. You can add weight to things to drop the pitch, rather than shaving them down, and it's reversable. Get some poster adhesive; 'FunTac' and 'BluTac' are a couple of brands. You can stick a wad onto the back or the headstock to hear what would happen if you shaved something to drop the pitch. By moving the weight around you can find the most effective spot to remove wood. If you don't like what you hear with the weight on, there's no damage done. DON'T use modeling clay: that has mineral oil in it that can get into the wood."
viewtopic.php?f=10102&t=13342&hilit=wolf+tones


Btw, does anyone know about where the main air resosnance should be on a dread?
The one in question is based on Martin pre-war style(adi top,forward shifted X ,scalloped braces,low back braces,etc).

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Jeremy Douglas

Finding the 'main air' resonance (close enough):
Lay the guitar on your lap or a table top face up. Pinch the low E string (tuned to pitch, of course) between the thumb and finger of your left hand. When you pluck the string you should get a pitched 'thunk'. Move the pinch point up and down to find the loudest tone: that's the 'main air' resonance. Damping the back may change it a bit, but not too much.

Dreads usually have their 'main air' resonance below G, and often around F or F#. E would be pretty low, and I'd suspect a very loose top or a really small soundhole if I saw that.

It's hard to hear the 'main top' and 'main back' pitches, in part because they are masked by the 'main air' resonance. I like to hold the guitar up with one hand, pinching the shoulder brace and fingerboard end through rhe soundhole. Try to block off as much of the hole as you can with your fist, but without touching the top any more than you have to. Tap on the center of the bridge and try to get an impression of the pitch. It will often be someplace near the open G string.

Tapping more or less in the center of the back with the guitar held in the same way will give you the 'main back' frequency. The best spot to tap will vary depending on the way it's braced and so on: look for the strongest and lowest pitched tone.

If the 'main top' and 'main back' tap tones are less than a semitone apart you will get a very strong couple, and often there will be problems too. These can range from the sort of short sustain you've got to something that sounds like fret buzz but isn't. Anyway, check the resonant pitches and then you'll be in a better position to figure out what to do.

Craig:
The patterns are names after the guy who found out aobut them: Ernst Chladni. He was active in the late 18th and early 19th century, iirc.

What are Wolf tones?

Thanks Alan, I'll try and find out what these pitches are later.



Meaning pinch the string with my left above the frets to determine the pitch? It would be hard to find if the resonant frequency is E though right? Because you can't really dampen the string as well at the nut.

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Jeremy Douglas

But you would still get the same effect at the octave location at 12.

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Waddy

Photobucket Build Album Library

Sound Clips of most of my guitars

I heard the term Wolf tone before but never had anyone explain what it is or sounds like???
So I'll ask again.

But all the strings ring out more when I pinch at the 12fret than the 11th or 13th fret. What about doing that test on the 5th string?


Chris, defining what a wolf tone is has never been clear to me either, which is why I'm not sure what I'm describing is technically a wolf tone. Wikipedia has an entry on it. Most of what I read on the net concerns instruments played with a bow and the wolf tone makes a howling sound but I think with guitars this maybe a note which sounds like a loud thump with little sustain; which is what I'm expereincing.

Btw, I did clip some clothes pins on the two upper back braces(2 pins each brace). They helped quite a bit I think. The clothes pins on the number 2 brace made the biggest contribution.

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Jeremy Douglas

Do those two statements seem to conflict with one another or am i missing the point?

Ok, I don't think I have to skills to do it. I tried but I can't figure out what the resonant frequencies are. With the strings loosened and humming into the soundhole the strongest note really seems to be F#.

The soundhole is 4" in diameter. I'd be surprised if my top was looser than average. The top is Adi, it seemed stiff, I left it about .118" thick in the center and .112" around the perimeter of the lower bout. The bracing is 5/16" on the X and lower tone bars, the finger braces are 1/4" and the UTB was 3/8". Forward shifted, scalloped.

The back braces are also based on pre war Martins. Tall thin upper braces and low wide lower braces.

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Jeremy Douglas

Jeremy like you I struggled with this as my ears just are not experienced enough to hear what i need ,so on the advice of others here on the forum I downloaded a software tone generator from the net. I dampened the strings with some paper towl , sprinkled some poppy seed first on the top(just behind the bridge) then the back(approx the middle).Then holding the guitar by the neck with one hand I slowly scanned through the frequency range starting at about 170Hz and through to about 230Hz . I noted the frequency at which I observed the most movement of the seed.
I would highly recommend reading through some of older posts relating to this topic. It really is fascinating as well as being extremely helpful.

regards

Craig

They actually agree with each other as to the cause but the solutions are of course different. The point is that disrupting the resonance solves the problem either by adding mass or removing it...both methods change its resonance frequency. My addition of mass was intended to be reversible should I need to change. That is entirely born out of inexperience and a desire "to first cause no harm". Alan's is born out of much experience resulting in the confidence to take the irreversible path. We should all strive to make decisions with such confidence.

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JJ
Napa, CA
http://www.DonohueGuitars.com

Ask 500 luthiers about how to go about determining where mass should be removed or added to
eliminate dead notes or wolf tones, which, by the way, are two different things, and you'll likely get
500 answers.

The very best time to determine whether or not a top is properly voiced to provide even, balanced
notes across the entire register is during construction, not after. Even though some change or improvement
can be achieved on a finished guitar, it is negligible. Once a guitar is built and finished and a player
wants to change or improve a particular characteristic in its tone, it's really a crap shoot in every case.
There are those guys who remove mass from as much of the brace system in a guitar as they can in an
effort to fulfill their claims of creating a louder, better sounding guitar, but I've heard enough of them after
the fact that are boomy and have lost whatever articulation or note separation that they may have had.
It's more than material removal that bring improvement.

I believe that that much of what is considered fact is, in actual fact, more subjective in nature than
many builders will ever admit. Much of the absolute, formula based deduction offered is speculation
at best and you really have to treat each guitar as an individual system of cooperative parts.

I apply a lot of what has been ignored and abandoned from the violin building community, especially
of the past to the construction of my guitars just because I've found it to work in presenting positive
contributions to balance, response and volume. Weight distribution is one of my chief concerns when
voicing a top, not symmetry and tapping while listening to the top is just a secondary part of the overall
voicing process.

Enjoy trying to locate the trouble area and do your best to learn from it, but understand that removing
mass is not always the answer just as adding mass is not always the answer. The correct location for change
is always the most important thing to nail down.

Regards,
Kevin Gallagher/Omega Guitars

Just a thought on the fretted notes. Have you checked to see if the fret aren't loose?

I tried it with pepper the back really showed some movement at F# and G with more movement at G. The top I'm not sure about; without the soundhole covered I got a lot of movement at E, with the soundhole covered all I got was a little movement at E.


Thanks Kevin, this is my first one so hopefully I'll learn something and do better next time.

Chris, the frets aren't loose, and the problem is only on the E notes.

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Jeremy Douglas

I think it was Al Carruth who explained the term “wolf tones” as originating from classical instrument construction.
A violin for example, can have one particular pitch that seems louder than the rest when it is bowed. If you were to pluck that pitch, it would “bark” out loud for a millisecond, then dull out quick with little sustain. It’s the bowing that is like a continuous pluck that makes the bark stretch out. So on a bowed instrument, the wolf is loud but on a guitar, it barks but has no sustain like the other notes do. The main wolf is directly related to the inner air volume of space inside an acoustic instrument. It can be slightly altered by sound hole placement, body shape, bracing choice, bridge density and many other changes you could make but you are still going to have a wolf there somewhere and it seems many of these changes also affect tone and responsiveness (and not always in a Good way).
Some don’t hear it. Some don’t care. Some, like me, are bugged by these things and have chased the wolf around for a long while.
One of the things that helps to spread the wolf out rather than having one big bad wolf tone, is to be sure your top and back are tuned to something other than the “main air” pitch that you expect to have once the box is closed. This can be difficult for the first time builder but enough info is here to keep you on the correct path. You start to get it after a few builds along with a few other useful things, thank goodness.
This is how “I” understand the wolf tones but am willing to bet there is much more to it!

You can de-tune the strings and play the same note farther up the frets, if it still wolfs at the same pitch, than you know it's the wolf and not the frets.
Good Luck,

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Wade
Nashua, NH
http://www.wadefx.com

'Wolf tone' is a term that has several meanings, depending on who (and when) you ask. The original meaning, back in the Middle Ages, was based on the type of temperament they used, which caused the interval from C to F# to be even more dissonant than it is now. They called it 'the wolf', and never used it in music unless they were trying to make fun of somebody (i.e. Locrian mode).

Some of the violin crowd insist that the real 'wolf note' only happens on thier instruments, and that we should find some other term for our problem. Actually, there are several things on the guitar that are called 'wolf notes', but the most common one happens for exactly the same reason that the wolf does on the 'cello. The outcome is different because, as has been pointed out, they're driving with a bow.

You have to remember that a string only vibrates 'properly' when both ends are 'fixed': tied to something that doesn't move. Obviously you can't do that on an acoustic instrument or you'd never hear anything, so we're stuck with some level of compromise. You try to make the top stiff enough and the bridge heavy enough that the end of the string is more or less held stationary most of the time, and hope for the best.

The problems arise whan there's a strong resonance that causes the top and the bridge to move a lot at a particular pitch, and you want to play that note. There are two ways to think about this; in terms of the effect on the vibrating length of the string, and in terms of the way energy flows from the string to the body of the instrument. These are actually two equivalent ways of saying the same thing, but they do bring out different aspects of the problem.

Say you've got a fairly light top, and the 'main air' resonance of your guitar is at 100 Hz, just above G on the low E string (97.9 Hz). The top will move most easily at 100 Hz, but it will move quite well when you pluck that G note, too. In this case the top will move in whatever direction the string is pulling it. With the bridge moving the end of the string is no longer stationary, as it's suposed to be, so the vibrating length can be different. In this case the string 'thinks' it's a little longer than it's supposed to be, and thus sounds a little bit flat. If the 'main air' resonance was at, say, 96 Hz, a little below the pitch of the note, the bridge motion would be such as to make the string think it was _shorter_, and it would sound sharp. But ONLY for the fundamental of the note: none of the overtones of the string would be effected unless there is another resonance near their pitches.

So what happens when the 'main air' pitch matches the note exactly? That's the classic 'wolf'. The top may move so much that the string essentially can't tell how long it is. Even if that doesn't happen, it extracts all of the energy from the string in a hurry, and turns it into sound. On a guitar you get a solid 'whump' with no sustain.

On a 'cello the situation is more complicated because they keep dumping energy in with the bow. As long as the top and bridge aren't moving the string knows how long it is, and can sound the fundamental of the note. But as the top gets moving there comes a point where the string 'loses track' of it's end for that pitch, and can no longer sustain the feedback with the bow that keeps things going. However, the overtones work fine, so suddenly the sound jumps up an octave. Now that the bow is no longer putting energy in at the 'wolf' frequency, the body vibration dies out, and, hey presto, the string discovers it's end again. The fundamental starts to build up in the string, and the whole circus starts over. This pitch shift happens even more rapidly than it did with your voice when it changed, and you can get a 'roaring' or 'bleating' sound.

Notice that the main difference is that we're dealing with a plucked string, while the 'cellist uses a bow. If you bowed your guitar at the 'wolf' pitch you might very well get the same bleating response. It's that same mechanism, and deserves to be called by the same name.

There are a couple of other things that can happen on a guitar that are also in the 'wolf' class. For example, if the 'main top' and 'main back' resonant pitches are too close together, and both are very active, they can trade energy back and forth. I believe the top may actually stop and start several times a second, causing a sound for all the world like a fret buzz. All of these feature strongly coupled resonances at close frequencies.

'Wolf' notes of whatever sort tend to be most common on lightly built and responsive instruments. If you look closely at the spectrum of one or another played note on almost any good guitar you'll see some evidence of 'wolf' behavior. This is much less common on heavily built bad guitars. So there you go; any time you build a good guitar you're risking a wolf note. If you can't stand the wolf, get out of the den.

Thanks Alan, I'm printing that out.
Jeremy you might try reading some of this stuff to see if it can help lead you in an area to look.
http://www.vanlingeguitars.com/Bio-BraceTalk.html
Some don't agree with it but I'm open to ideas.

I'm starting to think I must have made the top too loose. It occured to me that while my top thickness and bracing dimensions matched well with the specs I got from John Arnold and others for pre-war Martin dreads, I didn't inlet the lower tone bars or the finger braces into the lining, I also didn't tuck them or the bridge plate into the X brace. I don't know if not tucking them into the X matters much but I definitely could see how feathering the finger braces and tone bars to nothing could make the top too loose around the perimeter.

Chris, that chart van Linge posted is interesting. He states "The basic idea is that when a brace that has too much mass for the job passes through a ring, it dampens an arc of that ring, reducing volume." My problem is the lower E notes are too loud and as I stated above I didn't tuck the lower tone bars which is right where his low E ring is.

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Jeremy Douglas

Jeremy,

I just found this thread after someone visited my website. This sounds like a problem I've been dealing with for years, on both my builds and re-voices.

If I understand this correctly, the low G and F# are loud, but the low E thuds with no sustain. In my work, I've found it necessary to ignore concepts such as pitch of the top and back, and focus on how the braces impact the various rings with which any given note resonates. The problem could be caused by the top, but it is my suspicion that it comes from the back.

My Sound is Round diagram shows the rings each string resonates with on the top. The back operates as two, overlapping systems of rings--the upper and lower bouts. The upper bout can, if braces allow, reinforce the G and D strings. The lower back, the low E, A and D, sometimes the G.

While the 3rd and 4th braces have major impact on the lower bout's ability to reinforce, I've been focusing on the 2nd brace after I have the lower ones shaped parabolically so that each ring can be felt to be vibrating over them on both sides. The ring the low E resonates with usually lies just inside the perimeter, and would like to cross from one side to the other through the waist (where it overlaps the ring system of the upper bout) but the 2nd brace invariably dampens it, and no vibration can be felt over it--no continuation of the ring just inside the lower bout.

However, the F# and G rings are slightly smaller in diameter than that of the low E (in my model, ring diameter is inversely proportional to the frequency) and can be felt to vibrate through the waist area just below the 2nd back brace. The intensity of these notes I believe is due to the brace pushing back on the rings just below it, causing them to over amp, perhaps like waves surging against a sea wall.

To test this idea, try putting a capo on the F# or G, plucking that string and feeling over the area just below the 2nd brace. My guess is that you'll find a great deal of vibration there. But playing the open E, virtually none there or just over #2. Another test is to drop the E down to a D, which might be loud and resonant, like the G. If so, you can feel vibration just above the 2nd brace because the D, being a lower pitch, resonates with a ring larger than the E and lying above brace #2. This depends a great deal on placement of that brace.

Overall, I think the guitar soundbox is saying, basically, that it won't accept the energy from the low E because there isn't enough possibilities for it to find resonance. Especially as I get close to having the braces balanced on the top, such a problem seems to emerge where it wasn't there beforehand.

Not accepting the energy can happen to other notes or strings, too. Perhaps you've run across a problem with one string buzzing when the others don't? Just last week, the D string started buzzing on one of mine when it hadn't before I reshaped the X brace legs more radically. I could see that the amplitude of the D was about twice that of the other strings, which seemed a likely cause.

Plucking the D and feeling its ring on the top, I found a spot over the upper tone bar where there was no vibration. I could also feel a tiny imperfection in the shaping of the tone bar in that location, and when properly flowed into the rest of the brace, the buzzing was eliminated and the D's volume increased to that of its neighbors.

In correcting the low E problem, I find it necessary to lower the height of the 2nd brace to no more than 5/16" tall in the middle with parabolic shapes both in length and cross section. To know how low to make it, I tap over the brace, working from one side to the other. The pitch of the tap tone is irrelevant. What's important is that it remain the same over the brace's length (with the exception of the very ends, which should at least be clear and sustained). If the pitch drops some through the middle area, the brace isn't low enough. It needs to become transparent to the way the back wants to vibrate to allow the low E its full potential, and at the same time, the wolfness of the F# and G notes (and often that of the G string) is gone. And the low E can be felt to vibrate over the 2nd brace with even volumes and sustain up its frets.

I recently played a build of a colleague who uses parabolic bracing and noted that the low E wasn't as loud and resonant as the A, D and G. I observed that the back braces were parabolic and low over their lengths, but the ends had been given the same squared off scallop standard on most guitars. Those ends absorb vibration, IMHO. And, plucking the low E, I could feel no vibration over the four ends of the two lower braces, some in between. Whereas, the A string's ring, being smaller, vibrated over the parabolic cross section of those braces, about 2" in from the ends, and was louder for the reinforcement. I could feel a complete ring for the A and D on the lower bout.

In my earlier work, I was able to sometimes dampen wolf notes by gluing in extra braces where there was too much vibration, but also lost some "life" the guitar had. I never tried to add volume this way. Overall, I believe that when the top and back braces are balanced properly, they get out of the way and let the soundboards vibrate completely most everywhere, which is when I get max volume, sustain and headroom. And clarity, too.

Works for me,

Scott

Thanks for responding Scott. Actually the two lowest E notes are louder than everything else. The E notes do lack some sustain but it's mainly the loud thump that sticks out. I'll have to read through your post more carefully but I have to be honest, at some points I can't tell if you are talking about notes or strings. I'll poke around though and see how the back braces feel when I pluck the E notes compared to others.

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Jeremy Douglas

Jeremy,

I was writing about notes on the low E string. In the cases I was referring to, the F# and G were thumpy and louder than the rest. However, the density of the back wood and thickness both determine the size of any ring resonating with a particular frequency. It's a mass-at-a-distance factor that is involved. A thicker back would have more mass per unit length, and thus, a smaller ring would result. Which is to say, that maybe the low E is butting up against just below the 2nd brace, not the F#, as in my example, giving it an unwanted boost. What happens when you drop the E to a D? If the thud goes away, brace #2 is highly suspect. With a low D note, the ring might just be larger enough to pass through the 2nd brace, dampening it some and not reflecting the energy back.

Scott

Thanks, Scott. It does go away when I drop the 6th string to D. It's just on the E notes that are thumpy including the 4th string 2nd fret and 5th string 7th fret. The resonant frequency of the body is around E and I believe the top is too.

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Jeremy Douglas