Specific Gravity

ukulelebadass · Jun 8, 2009

What effect does the specific gravity of the wood used in the soundboard of an instrument have on the sound of the instrument?

Am I correct in my understanding that woods with higher specific gravities make better sounding instruments?

How high is too high, and how low is too low?

Timbuck · Jun 8, 2009

ukulelebadass said:
What effect does the specific gravity of the wood used in the soundboard of an instrument have on the sound of the instrument?

Am I correct in my understanding that woods with higher specific gravities make better sounding instruments?

How high is too high, and how low is too low?

I've just had a quick look on google at specific gravities/mass of timbers ...and noticed that Koa ,Mahogany, Pine, Black Wallnut ( tonewood favourites) all have a specific gravity of around SG 550 (whatever that means)..so it's most likely it does have an effect on the sound.. "Ebony" is much higher in the 800's and "Red Cedar" is down in the 400's.

Moore Bettah Ukuleles · Jun 8, 2009

Most resources suggest that the SG of koa is around 55, however in practice that figure is ambiguous as it can be anywhere between 40 and 75. I only know the SG of my wood because I have to set my moisture meter to it. Other than that it's a useless number to me. When selecting wood I trust my senses more; touch, sound, sight, etc,. Maybe someone else has a more scientific approach.

RevWill · Jun 9, 2009

I'm only interested in general gravity - as in, "don't drop it."

Seriously, I know nothing of acoustic instrument woods other than I like 'em.

koalohapaul · Jun 9, 2009

The link between SG and tone is due to the density of the wood. Wood with higher SG, such as ebony will be harder and more dense, while wood with lower SG will be softer. This is related to, but different from the stiffness of the piece.

Higher SG doesn't necessarily mean better tone. Generally, hard/stiff sides and back combined with a softer top will yeild a nice, balanced instrument. The depth and sustain come from the back and sides, while the quick response and brightness come from the sound board. Spruce top/rosewood sides and back instruments are a perfect example.

As far as actual numbers, I have no idea what would be good or bad. I've never measured the SG of any board I've cut. Like Chuck, I use my five senses and experience to grade lumber. If my gut tells me not to trust it, I don't.

Kekani · Jun 9, 2009

koalohapaul said:
Like Chuck, I use my five senses and experience to grade lumber. If my gut tells me not to trust it, I don't.

Ah HA! So that's how you get the headstock shape of your instruments, using your sense of taste (or bite, actually)!

Sorry, couldn't resist. Wait till you see your SB - I'm sure you'll have something frisky to say. . .

Hobgoblin Steve · Jun 9, 2009

Moore Bettah Ukuleles said:
Most resources suggest that the SG of koa is around 55, however in practice that figure is ambiguous as it can be anywhere between 40 and 75. I only know the SG of my wood because I have to set my moisture meter to it. Other than that it's a useless number to me. When selecting wood I trust my senses more; touch, sound, sight, etc,. Maybe someone else has a more scientific approach.

lol sorry, I really couldn't help it.

:shakes head:

ukulelebadass · Jun 9, 2009

koalohapaul said:
The link between SG and tone is due to the density of the wood. Wood with higher SG, such as ebony will be harder and more dense, while wood with lower SG will be softer. This is related to, but different from the stiffness of the piece.

Higher SG doesn't necessarily mean better tone. Generally, hard/stiff sides and back combined with a softer top will yeild a nice, balanced instrument. The depth and sustain come from the back and sides, while the quick response and brightness come from the sound board. Spruce top/rosewood sides and back instruments are a perfect example.

As far as actual numbers, I have no idea what would be good or bad. I've never measured the SG of any board I've cut. Like Chuck, I use my five senses and experience to grade lumber. If my gut tells me not to trust it, I don't.

Thanks this is exactly the answer i needed.

Moore Bettah Ukuleles · Jun 9, 2009

Hobgoblin Steve said:
lol sorry, I really couldn't help it.

:shakes head:[/QUOTE
I'm not being inconsistent. Let me clarify for you.
For me knowing the specific gravity is only important in order to set my moisture meter. I don't change the SG input but rather I set it at 60 and leave it and forget about it. Getting an accurate moisture reading is important only in knowing when a set is ready to build with, in my case 6% to 8%. Those moisture meter readings are crucially important to me. But when choosing a particular set of koa for a uke however, I still only rely on my senses, in which case I am looking for acoustic values, not specific gravity.

Pete Howlett · Jun 9, 2009

I like reading these technical thingies - don't understand them anymore and don't use them. When I did timber technology, specifically looking at tonewoods and their microstructure SG didn't come into it. Like Chuck and Paul, most experienced lutheirs will go by feel - if you watch the David Byrne video where he is thicknessing sides he says - 'Now will need to take a few thou offthis one before it's ready' as he flexes the sides between his hands. Building is a tactile process - let's keep it that way. Oh, and I'm sorry; I have no Mojo for sale...

Hobgoblin Steve · Jun 10, 2009

Moore Bettah Ukuleles said:
Hobgoblin Steve said:

lol sorry, I really couldn't help it.

:shakes head:[/QUOTE
I'm not being inconsistent. Let me clarify for you.
For me knowing the specific gravity is only important in order to set my moisture meter. I don't change the SG input but rather I set it at 60 and leave it and forget about it. Getting an accurate moisture reading is important only in knowing when a set is ready to build with, in my case 6% to 8%. Those moisture meter readings are crucially important to me. But when choosing a particular set of koa for a uke however, I still only rely on my senses, in which case I am looking for acoustic values, not specific gravity.

Click to expand...

you didn't need to clarify, I clearly made a joke that did not pass.

Specific Gravity

ukulelebadass

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Timbuck

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Moore Bettah Ukuleles

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RevWill

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koalohapaul

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Kekani

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Hobgoblin Steve

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ukulelebadass

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Moore Bettah Ukuleles

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Pete Howlett

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Hobgoblin Steve

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