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Hi all,

Building a 30s style advanced jumbo and decided using eir was a more ethical choice than other rosewood. Got a AA/ 2nd grade back and sides set from Spanish suppliers. Looks nice but taps like decent mahogany or walnut, nowhere near the brw, tucurensis or padouk I have here. Is this usual? I'm guessing it'll still make a decent guitar with a torrified red spruce top?

There it is

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I'd say yes.
I've build with some of the lower grades of EIR and they have all come out well.
A lot of the back's resonance can depend on thickness/radius/bracing and you can of course play with them to get the results you want.

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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.

I've measured the properties of a lot of different pieces (and species) of wood. On average EIR has similar stiffness along the grain, but is less dense than BRW. IRW also normally has much higher damping than BRW or Padauk, although it's usually lower in damping than walnut or mahogany. These are natural materials, of course, and there's a lot of variation and overlap in properties.

Damping is the rate at which the material dissipates vibration energy. It often seems to me that the damping of the wood sets a sort of limit on how low the damping of the structure that's made from it can be. It's very easy to make a guitar back that has high damping out of a good piece of BRW: factories do it all the time. A good maker can usually figure out how to get the best out of a piece of wood, and can produce a better instrument from (high damping) maple than some made out of (low damping) BRW or Pernambuco.

It also seems to me that the mass of the back can be more important than the damping. After all, it's only 'losing' energy when it's vibrating; if it's too heavy to move much it's not losing. I've heard some very good things about African Blackwood, but the stuff I've measured has high damping. The same is true of Morado/Pau Ferro, which is as dense as the ABW, and I've made some nice guitars from Morado.

If you're looking for a wood that's like IRW in terms of density and stiffness, but has the damping of BRW, go for Black Locust.

Thanks everyone, this will be my second rosewood guitar but I haven't put the finish on my first yet! Black locust sounds great but I doubt I'll find it in Europe.

Tap tone is more or less simply a test of dampening? I should have 3 backs to compare as I brace them, yellow meranti, black walnut and eir. If they tap well when thicknessed and braced then I'm on the right lines correct?

In the UK Timberline is a guitar timber supplier that many don't seem to have heard of. I have had some good material from them. But no, no Black Locust!

Cheers Dave

I used to visit timberline and David Dyke often in one day trip but Brexit has messed all that up since I moved to Ireland...

Can i simplify low damping as a boing and high damping as a thud?

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Hutch

Get the heck off the couch and go build a guitar!!!!

banjopicks asked:
"Can i simplify low damping as a boing and high damping as a thud?"

Pretty much. Low damping produces a sound that is more focused in pitch, and sustains longer. But...

Any piece of wood you're going to use for a guitar top or back will have a lot of different resonant modes that can be excited by tapping. Which one(s) you get depend on where you hold the piece and tap it, as well as on the size and shape and the properties of the wood. Depending on all of that it's possible that the piece will have more than one resonant mode that will come in at the same pitch, or nearly so. This can confuse the piece of wood almost as much as it does you, as the coupled modes can 'beat' in frequency, as well as changing the losses.

Not holding the piece right on one of the stationary 'node' lines adds damping, and when there are lots of modes they can overlap in such a way that it's hard to isolate them. I've had instances where a piece that looked and sounded like it had high damping performed much better when it was trimmed down a little in one direction, to shift modes a little further apart in pitch. This on advantage to working with Chladni patterns that allow you to see the mode shapes, rather than simply relying on tap tones.

Looking and tapping a lot less budget after 80 grit thickness and scrape to around 2.15mm/ 85 thousandth and a quick wipe of shellac

Hopefully visible here

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When I was going to build my first Black Tiger out of Tasmanian Tiger Myrtle and no one on this forum had built with it before my Tiger Myrtle tapped like wet cardboard. It was awful, the worst sounding wood in my stash.

I built with it anyway and low and behold if you thickness it properly, brace it with skill, experience and a methodology that works for you and the guitar that it helped produce was a big success. It produced a very loud box with lots of over tones and strong fundamentals that many said the OO size I built completed with dreadnoughts for volume.

Ya just never know and turning that wet cardboard into a musical instrument is what we are for, Loothiers...

Mike if you do your part this wood is capable of being a great guitar. So the bottom line for me is tapping is extremely subjective and you really can't tell much from it. Thickness, dimensions, how and where you hold it and even what you tap with are all variables that can skew results.

What we do know is only about 10,000,000 plus successful guitars have been built out of EIRW so if it were me I'd be bracing that puppy up by now and it looks like that's exactly what you are going to be doing. Good going!