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I have a custom build that's about 8 years old or so, and it's always had the characteristic of being exceptionally boomy on the A string. It's almost as if the box was tuned to that freq. It's fitted with a soundboard transducer pickup, and I'm playing in our worship band. The feedback is starting be an issue, and I was wondering what ideas you fine folks would have in helping to reduce or resolve the problem. I was going to try a soundhole cover at one point, but my soundhole is larger than normal, so none would fit. I then read through some threads here about tuning the box to frequencies that fall between notes, and got to thinking about ways to slightly raise the resonant frequency of the box.

I build electrics, not acoustics, so even though I'm familiar with the basic mechanics of the build, I'm definitely not up to speed on the principles.

Thanks for any help

Rog

Unfortunately, raising the pitch can be rather difficult. To be able to help you properly, we would need a frequency plot of your main top monopole, main back monopole, and air chamber resonance. Otherwise it's all just guesswork.

You might do a search for wolf note, as there is a lot written on the topic that can help.

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http://www.Harvestmoonguitars.com

Yeah, I haven't the slightest clue as to how I would go about that or if I have the means to do so. I'll do some digging around to see about finding the methodology.


It's not actually a wolf note, which I understand to be a weak note. When I pluck the A string, it's considerably louder, and the entire box seems to boom.

Yes, it's ACTUALLY a wolf note. Wolf note means it gets very loud on that note.

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"Act your age, not your shoe size" - Prince

Then I understood incorrectly. Thanks for the clarification.

Just found Trevor's post on setting up a tap test. Reading through that now...

A simple check to find the 'main air' pitch is the 'pinch test'. Lay the guitar down in your lap. Pinch the low E string between your thumb and finger down near the nut, and pluck it with your other hand. You should get a sort of pitched 'thunk'. Move the pinch point up and down a little at a time while plucking as evenly as you can. The sound should gewt louder and softer as the pitch is changed, and the loudest sound will come on the 'main air' pitch.

If that's really close to A (and you can check it with a tuner) the guitar is likely to extract all the energy from the string at that pitch in a hurry, and turn it into sound. The result is a note that's much louder than usual, for a short time: it 'booms' on that note. Often the change in power is less noticeable than the reduced sustain, which is, perhaps, why people tend to think of 'wolf' notes as 'weak'.

Once you've found the problem you have to figure out how to fix it. There are various ways to go about that, some simpler and less invasive than others. The first thing is to be sure of what the problem is.

As said earlier, it's easier to lower the frequencies than to raise them. If you find your main air resonance indeed is centered on the A note, here are some options (I'm sure there are more). Remember that you'll be lowering the top main frequency and the back main frequency and the main air frequency so these aren't independent.

- Enlarge the sound hole (raises the frequencies)
- Add weight to the rim below the bridge (maybe on the tailblock.....lowers the frequencies)
- Sand/plane the braces on the top or back (lowers the frequenies)

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Formerly known as Adaboy.......

That sounds like a simple enough test, so I'll be doing that when I get home tonight. Thanks for giving me something practical to help trouble shoot.



Thanks a bunch, Darryl. This is a guitar that was built for me awhile ago, and it holds a great deal of meaning as it's a memorial guitar. If the problem is indeed an issue of air resonance and can be fixed by some of the methods you describe, I'll definitely want to get lots of input before doing anything. I don't think I'd want to shave the braces because it's already built pretty lightly, and I don't want to mess with the structural integrity. Likewise, I wouldn't really want to enlarge the sound hole because of the need then to refinish.

Thanks a bunch, guys. This is exactly the kind of information I was hoping to get.

Hi Rodger,

Let us assume it is in fact a wolf note on a flat top and not an arch top.

The easiest and quickest way to deal with this is to change the air volume of the box. Try various size Styrofoam blocks on the tail block and then the neck block. Also try different strings.

Then try little plasticine or clay chunks stuck here or there on the top till the wolf disappears. Then substitute the exact same amt of weight in wood glued directly underneath the clay or plasticine. This sometimes helps.

There are a few luthiers who will even shave a brace here or there...but they are few and far between with that skill and knowledge.

If it is an arch top...then readjust the string after lengths between the bridge and the tail piece. Also try fishing weights on the A string.

A wolf note on a cello are very common...a lot of players simply learn to adjust the attack on that note with the bow. If your a finger picker this might also help.

And a word to buyers of custom instruments...insist on a 10% hold back for a min 30 days to cover such pesky situations. You would be surprised how fast something gets fixed if your holding back 10% on a $5k instrument. If your builder refuses, my suggestion is to find another builder.


good luck Rodger and let us know what worked for you.

HB

How much larger than normal is your soundhole? That may be part of the problem.

Ok, so I was able to attempt the string pinch test last night, but unfortunately I wasn't able to tell much. I thought I could tell a difference in volume, but then I noticed that it just got consistently quieter as I went up the fret board. I think what was happening was that I was able to pinch the string more firmly as I went, so that didn't give me any consistency. I'll try a few more things tonight when I have a bit more time.

You can lower the frequency of the main top resonance by using a heavier set of bridge pins.......or go lighter and raise the top frequency.

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Formerly known as Adaboy.......

This is a pinless bridge, so no option for replacing pins.

I think Clay may be right. From your description, it doesn't sound like the main resonance is too low, rather, that the resonance is right at "A". That's a bit high for most peoples' taste, and having it right on a note (and "A" in particular) is a problem. A large soundhole raises the main air resonance. Shaving some braces, or adding some mass to the top (and perhaps the back) would lower the main resonance. Poster putty is an easy way to experiment with mass. Magnets can work too. Don't start shaving braces if you're not sure you understand the structural implications.

For playing amplified you will want a soundhole plug. It's not difficult to cobble up something that does the job and looks okay. An under sized circle of thin wood, plywood, plastic, whatever, and a bit of foam weather stripping for a snug fit will suffice.