Are there wolf notes on classical guitars and is it the same as unwanted resonance

[John Cadd]

When I play some simple chords on a flamenco guitar the A string starts a little howl going.If I drop the tuning down slightly on all the strings this nuisance stops .Is the cure to remove some wood from one of the bars,and which one?

[Bob Webster]

Can you make a recording in the form of a .wav file? If you can, make one of an E scale on the treble string, nut to 12th fret. Place the microphone about 10-15mm above the soundboard just up from the end of the bridge. If you can do this and post the file to this thread, I can do an analysis of it and see if the howling A is caused by a top resonance issue.

As for what to do about it, the two options are to shave a brace or two or to thin the perimeter of the lower bout of the top. The recordings might provide some clues as to which is appropriate. Also, if you could look inside with a light and an inspection mirror and describe the bracing pattern and general dimensions of the fans, etc., that ;would be further help.

At first blush, if the problem really is due to a top resonant issue, the fact that you're experiencing right at an A110Hz note already says that the top might be overbuilt in one aspect or another.

Best,
Bob

[John Cadd]

Well Bob I `m not very hot on new technology,I can`t even work an mp3 player.I think my symptoms are mild compared to the ones I was reading on the Delcamp guitar forum.I found it interesting that I could minimise the Resonance by slight alterations in tuning.The Delcamp people were saying that their teachers told them you just have to accept this situation.My guitar is a modern version of the standard Spanish flamenco.Seven fan braces .Normal cross bars. I might have exagerated calling it a howl but the topic seemed ripe for your expertise and maybe for lots of makers picking up your "gold-dust" tips.
I expect you shave braces with those reverse blade spoon planes made of brass.I always wondered what they were for. I never play flamenco (yet) but as a classical fan I love the clarity and serious (not wooly)bass notes.What notes do you recommend for tuning tops and backs before gluing together?

[Bob Webster]

Hi, John. I don't even look to closely at what my backs and tops tune out at before I glue them up into a box any more. The vibrational modes must bear some relationship to what the eventual box modes will be but they are so different and varied relative to the box. It makes it very tough to know which modes to target for manipulation especially given the interconnectivity of the effect of plate thinning and brace adjustments. In brief, it's pretty tough to know how the manipulations will play out at the box level.

Further, some of the modes that one can visualize at the box minus bridge stage go away when you glue the bridge on. And some of the modes that you can make happen when the bridge is glued on have no relevance to how the strings make the bridge make the top move when you pluck a note.

Brian Burns, a very experienced luthier in Fort Bragg, CA, has a dummy set of sides and back that he clamps his tops to when he does mode testing. He then works to get the numbers close to those of a reference guitar that he built previously that he thought was an excellent guitar.

I know that what I've said doesn't sound very helpful but it does reflect the reality of the situation. What I do is stiffness testing of all my tops blanks. I use the numbers to arrive at a starting thickness for a specific set relative to a reference guitar build for the particular design I'm using. When the box is together, I compare numbers again with the reference guitar at that stage and decide whether I want to do any adjustments.

As for brace shaving, I actually use one of those Schneider planes that are available from LMII. I don't have alot of different boutiquey sorts of tools like you can get from specialty woodworking outfits. An issue of budget.

Bob

[Russell Vance]

Thanks, Bob, nice to hear a bit of clear thinking on this vexing subject - I find it very hard to convince punters that everything changes everything and that those who talk a lot about the esoterics just seem to confuse the issue - you end up with "it is what it is" works for me. Good ingredients and build consistency seem to be the best insurance against getting too far offa track. But, I see from scrolling down the posts that the lid is off the can of worms. Good luck mate. Rusty

[Tim Mace]

What is the tap tone of your guitar?As compared to a standard pitch?

[John Cadd]

Well Tim the top is about Aflat and the back is a semitone lower.I have a Spanish mahogany guitar which has a top at G and the back is about one tone lower. I have only a basic small clip-on diode thingy and pinning down low notes exactly is not easy for me.

Bob`s method reminds me of a very good course run in USA where they put all the bars on the outside of a test instrument so they can play around till a good result is established .then that is what they use for comparisons.That becomes their standard. I have only tuned in violin plates but a guitar top is a much wobblier thing .Then the varnish finish changes it all again.

[Tim Mace]

Now , if you proceed but the closer you get to A or G would be my guess to remedy.The in between is probably not good vibes....at least that's my theory and I'm guessing.You tested under tension? W/dampened strings?My instruments generally tap an a or g before assembly.And as yet have done no aftershave( is that a luthier term?)so I'm probably not your best source for experience but I like thinking about this stuff.Good luck!

[Bob Webster]

Actually, Tim, it can be more beneficial to locate the resonance between a couple of notes. If you land dead on one, that note can become a wolf tone. That happens because the energy transfer is most efficient at the resonant frequency. The resulting note is much louder than neighboring notes but has much lower sustain because it all blows out very quickly.

Aftershave? Are you watching too much ESPN? :)

Bob

[Tim Mace]

Bob ,do you have ESP? I've always thought the opposite.I know that for instance A box that sounds at a good A440 rings full on w/an A chord though never considered that to be
wolfish.Since he indicated that lowering the tuning negates the problem I figure the box is
some where "between" sharp & flat. How much can a box be adjusted.I would think no more that 1/4 to a !/2 tone.And can it be sharpened?

[Bob Webster]

I don't know of any way to sharpen the box resonance by removing wood. However, if the resonance is as high as an A, then there's no harm at all and much to be gained (particularly in bass response) in going lower. What I'd do next would depend on the size of the braces and the thickness of the top. If the braces look particularly massive, expecially over the bridge, I'd be tempted to thin them. If the situation is that the braces are relatively delicate, I probably start by thinning the perimeter of the lower bout. You can do this while the guitar is strung up so that you can check progress relative to tonal response.

Bob

[John Cadd]

Bob the idea of minor tuning adjustment sounds fascinating and dangerous as well. what kind of tools would be used .How would you avoid damage to strings and soundhole. I pictured a sanding block on a wooden handle wiggly enough to reach through the hole.But what would I be aiming at in tuning terms?Reminds me of early experiments on a carburettor with my first m/cycle.Mind you one of my most useful tools is a thin screwdriver with3 or 4 bends and twists and a filed out end that will do things nothing else will do.It just evolved!

[John Cadd]

I forgot to say the flamenco has delicate bracing,so no point spoiling them.