Dreadnought interior air volume (I.A.V.)

JoePa and Son · #1 02-23-2018, 07:53 AM

Search here and Google...no luck.

Curious to know I.A.V. for:

Standard square shoulder dreadnought.

Slope shoulder 12 fret dreadnought.

Thanks...

Goodallboy · #2 02-23-2018, 08:02 AM

Can’t wait for this one to get rolling......We need another spec to obsess over.

Kerbie · #3 02-23-2018, 08:06 AM

Quote:

Originally Posted by Goodallboy

Can’t wait for this one to get rolling......We need another spec to obsess over.

I think this might be inciting a riot...

OK, just kidding. You know we never obsess over the small stuff here on the AGF.

llew · #4 02-23-2018, 08:43 AM

Quote:

Originally Posted by Kerbie

I think this might be inciting a riot...

OK, just kidding. You know we never obsess over the small stuff here on the AGF.

Certainly no more than 1/16 of an inch?!?

jweave69 · #5 02-23-2018, 09:00 AM

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phavriluk · #6 02-23-2018, 12:21 PM

To speak to volume, we need to know the dimensions of the chambers being measured. So...OP needs to figure out/find the surface area of the soundboard or the back, and the height of the chamber at the lowest thickness (probably the neck joint) and highest thickness (probably at the endpin). Average those two height numbers and multiply by the area of the top/back and you've got an unrealistic number owing to the hourglass shape of the guitars, but the relative differences will prevail. Just don't talk to an engineer about how those numbers were calculated.

Jaden · #7 02-23-2018, 12:51 PM

That’s a very interesting question and such a specification would be interesting to note and compare amoung all guitars. Complex math to figure out for the layperson.

SuperB23 · #8 02-23-2018, 01:02 PM

This would obviously be very brand specific info. The 12 Fret D that Santa Cruz makes would have a vastly different number than Collings or even than a Gibson style Smeck type 12 Fret Dreadnought.

Tico · #9 02-23-2018, 01:45 PM

Air volume is hard to measure; water volume is easier and will be the same volume.
Calculating volume inside simple shapes like perfect cubes or spheres is easy using simple formulae.
But because guitars have complex/changing curves, you need calculus.

Calculus proficiency is only a start.
You'd also need accurate measurements at many points (the more the better) of every changing curve of the body, even the outward bulge of the back and top.
Those measurements are not easy to obtain without an expensive laser-scanning gizmo.

An easier solution:

Acquire a trashy dreadnaught that you'd throw away.
Rest the guitar on it's back.
Place a level on the soundboard and prop up the head till the soundboard is level.
Remove the pins.
Plug the endpin hole if it goes all the way into the guitar.

Fill the body with water till it overflows out the sound hole and pin holes.
Measure the water as you siphon it out.

Among the inaccuracies will be air trapped between bracing glued to the soundboard, and the outward bulge of the soundboard.
Calculate that volume, best you can; add it to the volume of water you siphoned out of the guitar.

A good guitar for this test would be a 1936 Martin D-45.

ManyMartinMan · #10 02-23-2018, 02:14 PM

Quote:

Originally Posted by Tico

Air volume is hard to measure; water volume is easier.

The calculus is actually not complex especially if you calculate at STP. What you stated is true. You would need all the measurements - and I'm not doing it... because I'm a musician not an engineer (so I don't care). However, volume is volume so fill up your guitar with water, pour it in a bucket and measure the volume.

Okay, seriously, we have several engineers who will enter into this and argue about the answer, hopefully. Popcorn at hand.

Bronzeback · #11 02-23-2018, 02:22 PM

You could fill with something that's not going to harm the instrument, like foam peanuts, if you wanted to get a good guess. Said peanuts poured into something easy to measure, like a square box would do it.

Long Jon · #12 02-23-2018, 02:23 PM

Quote:

Originally Posted by ManyMartinMan

Okay, seriously, we have several engineers who will enter into this and argue about the answer, hopefully. Popcorn at hand.

Obviously filling it with water is impractical, so yes, popcorn, that could work, or rice.

Long Jon · #13 02-23-2018, 02:26 PM

I’ll bet there’s some software that could tell you the volume of any given 3D shape you could enter in.

Once you have the answers, keep a copy safe; an engineer once kindly worked out for me the exact capacity of a very odd-shaped water storage tank on my boat and I’ve lost his workings and forgotten the result !

ManyMartinMan · #14 02-23-2018, 02:30 PM

Peanuts won't conform to the guitar's shape. Rice, or similar, would.

Tico · #15 02-23-2018, 02:40 PM

Quote:

Originally Posted by Long Jon

I’ll bet there’s some software that could tell you the volume of any given 3D shape you could enter in.

Once you have the answers, keep a copy safe; an engineer once kindly worked out for me the exact capacity of a very odd-shaped water storage tank on my boat and I’ve lost his workings and forgotten the result !

The problem is, how do you measure a 3D shape with complex curves accurately enough for the software to give you an accurate-enough result?

... as they say about computers, garbage in garbage out.