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?
It seems a long time since I was here. I have brought the answer to my problem. The excessive resonance I was getting that interfered with the music has a simple solution. I had some white plastic food bag clips .They have a 1,1/2 inch wide "jaw" more like a box shape on the clip end.I let down the strings and clipped some on the struts to see what would happen.I realised the high resonance sounds were coming from the bass strings.I tried it with 5 altogether.Then took away all except 3 on the bass side.One each strut.
Playing the music now is perfect.No howl on line 2 .Gaspar Sanz Espanoleta. Before the cure line 2 would build and build with an awful sour resonance.
One for the scrapbook there I think.
Hi John and Tim. I've been wondering where Bob has gone myself, since I last saw his comments back in August of '09 or thereabouts, so I emailed him directly. Turns out he's heavily involved with the Delcamp website, which is more directly involved with Bob's interests with classical guitar. Since there are only so many hours in the day, he's decided to limit himself to the Delcamp site. Too bad for us, as Bob's advice is dead-on and well thought out, and he's extremely generous with his knowledge. A good man to know. However, we'll have to go to the Delcamp site if we want to catch up with him from now on, I guess.
John, it was interesting to see how you eventually solved your resonance problem. Who knew that food bag clips could be put to such a noble purpose! Now that you know what solves the problem, I wonder if gluing wood blocks to the struts that are the same weight as the clips might be a more permanent solution?
Cheers (as Bob would say) Larry
I discovered that you can find the fundamental resonance of a classical guitar (or acoustic) by using an air nozzle. A guitar (in the bass frequencies) is a Helmholtz resonator and makes it's sounds by the deflection of the plates pumping an air column in and out of the sound hole. It's like the note you get blowing across a coke bottle or a jug.
Use and air compressor (or go to some friend who has one) and blow air low and across the sound hole with a fine nozzle. If the guitar is responsive it won't take more than about 20-40 psi some guitars may require 60-80. If you experiment with the angle across the sound hole (like 1 to 10 degrees) the guitar will suddenly let out a howling roar that can be measured. It is amazing the first time you do it, so much energy is released the guitar feels like it is going to jump out of your hands or start to break. Don't be discouraged if it takes a higher air pressure because there are many variables such as the size of the guitar and in my experience it is not a qualitative measure. It just gives you a benchmark for comparison (your mileage may vary).
It is an experiment every guitar builder should try just to see the power a resonant cavity can produce. Mr. Wizard would be proud.
This is the predominant resonance. I typically see low notes like somewhere between low D and E or as high as G. If the predominate resonance is exactly at a string note or very close it could cause a wolf note or a note that is out of timbre with the rest of the strings. I tend to build too light so I give up a flat top for a fuller sound.
Science and physics of guitars are really complicated and hard to model or predict, I think this is why it is an art and not a science.
David I have been doing a very similar thing with the resonance.I don`t use an air hosethough.I try to guess the note (somewhere like third fret on the low E.)Then I hum that note open mouthed by the hole.I vary the pitch till It resonates. You feel a complete lunatic when you try that. You are dead right about avoiding a fretted note. Your low D has puzzled me.Is that below the lowest string? I have been trying what another maker recommends ,between third and fourth fret. This is not making ,by the way, I vary the resonance by taping a piece of leatherette across part of the soundhole.Weak masking tape is safe enough.The guitar I have been sorting out is a thin body type.It has a large hole above any measurements I`ve seen for full body guitars ; Diameter 8.9 cms or 3.5 inches in old money.
Theleatherette blanking piece closes off a (lemon slice ) section one inch from the edge of the hole. That can be converted into a thin rim just inside the hole.
I shall enter this then read the helmholtz info.The site I read recently describes the combination of all the resonances.They say that one alteration on it`s own will not give automatic exact same results. It said even the thickness of the hole edge comes into the equation.Also depth of back from the hole edge.
Larry Thanks ,I was noticing a gap in the posts where Bob used to be.Just a minute ago I put three of these clips on the kitchen scales.Hard to weigh something so light.So two teaspoons equals One Ounce. One teaspoon equals three clips.That makes each one ----one twelfth of an ounce One one needs dots in between.It has a "pleasant " resonance now.You can hear it without the annoyance.Overall sound quality is very good.No drawbacks.
Each clip jaw is about 1.5 inches long (in contact with the strut.)I doubt if that contact length does much apart from keeping it in place.I imagine the small weight is sufficient.I have not tried fewer than 3.That might be interesting.
Hi John, last year i went to a luthiers meeting at Ervin Somoygi s shop , there was a luthier there demonstrating how to cure wolftones on classicals, he took small portions of modeling clay,very small and placed them in different spots on the guitar top until he found a spot that the wolfnote dissappeared when played, he marked that spot with painters tape, weighed the clay and fashioned a small rosewood or ebony diamond that matched the clays weight and glued it on the inside of the top in that spot. it cured the problem. cheers Mark
Mark I have used a small amount of Bluetack for the weight.I reduced the weight as much as possible to retain a lot of resonance.Just removing the excessive stuff.I found the best place for the weight was right on top of the bridge in the centre behind the strings. Here`s the measurements; 2 cms diameter (circle) and 0.5 cms thick. That`s it. I have no problems with excessive resonance now.
awsome, their were a couple othrs guys at the meeting that used the same method and it got them out of hot water with their customers, nice simple solution to a perplexing problem always helps in my book.