Can't Find 1/8" ply, how about "tempered hard

Posted: Sun Mar 30, 2003 3:03 pm

Having problems finding 1/8" plywood. How about using "Tempered Hardboard"? It's a chocolate brown compressed wood stuff. Smooth and shiny on front, rough on back. Would this work just as well for the 1/8" and 1/4" panel traps or perhaps just 1/8" panel traps? If not I'll have to find a specialty wood store.

Thanks so much.

Posted: Sun Mar 30, 2003 3:52 pm

Jason,

> How about using "Tempered Hardboard"? <

Sorry, but that won't work. Ask for 1/8th inch Luan plywood, which is just as good as other types of 1/8th inch plywood. Keep looking. You'll find it. 1/8th plywood is definitely out there.

--Ethan

Posted: Sun Mar 30, 2003 4:31 pm

They stock 1/8th" Luan at Home Depot... Kurt

Posted: Mon Mar 31, 2003 1:53 pm

Actually, Jason, you CAN use the Masonite - it will just change the frequency to a lower value, all other dimensions being equal. See my post in this thread (today) for the formula - 1/8" plywood is listed as having a density of .35 lb/sq ft, or 11.2 pounds per sheet.

Oops, almost forgot the link - here it is

http://www.recording.org/cgi-local/ubb/ultimatebb.cgi?ubb=get_topic;f=34;t=000176

If you used 1/8" Masonite instead of 1/8" ply, both mounted on the edge of 2x4's (3.5" air gap), and the Masonite panel weighed (say) 14 pounds, then the density/cu ft would be .4375 instead of .35 pounds, and the frequency would center at about 135 hZ instead of 150.

I don't have a sheet of 1/8" Masonite handy to weigh, so keep in mind that was a "ferinstance" - still, you get the idea... Steve

Posted: Tue Apr 01, 2003 7:52 am

Steve,

> you CAN use the Masonite <

You bring up an interesting point. I always assumed that density is not the only property that matters. And assumed plywood is better than masonite because it is stiffer and flexes "better." But maybe that's not valid? Is mass really the only thing that matters?

I sure wish it was easier to actually test this stuff!

--Ethan

Posted: Tue Apr 01, 2003 9:19 am

Quote:

Originally posted by Kurt Foster:
They stock 1/8th" Luan at Home Depot... Kurt

The Home Depot by my house stocks 5 mm. Luan plywood. It looks like 1/8" plywood, but is actually 3/16" thick. If you are thinking of buying Luan plywood from Home Depot, it may be a good idea to measure the thickness.

Posted: Tue Apr 01, 2003 12:12 pm

OK, I did not realize that ... I wonder what the difference would be in terms of the center frequency? Knightfly??? Very Happy

Kurt

Posted: Tue Apr 01, 2003 1:55 pm

Intuitively, I would think that mass was not the only concern. As an extreme case, think about super-rigid, fairly low mass graphite, or high-mass, droopy loaded vinyl. 1 pound per square foot loaded vinyl is probably similar in mass to a number of much stiffer materials, but I wouldn't think they would vibrate the same. I don't know, though- it would be an interesting thing to find out.

Quote:

Originally posted by Ethan Winer:

You bring up an interesting point. I always assumed that density is not the only property that matters. And assumed plywood is better than masonite because it is stiffer and flexes "better." But maybe that's not valid? Is mass really the only thing that matters?

I sure wish it was easier to actually test this stuff!

--Ethan

Posted: Tue Apr 01, 2003 4:54 pm

Hello, I'm lovin' this site, what a candy store of information. This is my fist post, I want to shake off that LURKER status.
Ok, I REALLY do not know the math, but in my guitar building, density and stiffness mean everything to getting the plates to respond properly. With plywood you've got X number of wood veneers glued up at right angles to each other which give it it's stiffness. Masonite is just some sort of pulp fiber saturated with glue and just ain't that stiff. For my work the stiffer materials sustain/sing better. It's hard to imagine that this doesn't carry over to these bass traps.
But I've been wrong before.
IThat's my 2cents.

Best Wishes, Julius

Posted: Tue Apr 01, 2003 5:07 pm

One other thought;

If these traps do respond in a similar fashon to a guitar box--you might be able to tweak it's freqeuncy response by thinning the plates perimeter.
It's just an idea.

Julius

Posted: Wed Apr 02, 2003 5:08 am

Guys, I posted a nearly complete paraphrase of the pertinent section from the Master Handbook here - (including the formula, but not the chart)

http://www.recording.org/cgi-local/ubb/ultimatebb.cgi?ubb=get_topic;f=34;t=000176

And I agree, intuitively there should be more to it than just mass - Although Mr. Everest mentions SQUAT about characteristics such as surface finish, # of plies, hardness, etc - if you take him at face value, a 12 inch thick sheet of balsa wood would have the same characteristics as a 1/4" sheet of Amazonian Iron wood (too heavy to float in water) - somehow, I think something is missing from that section of the Handbook.

Mr. Everest (or a helper) has left out or mis-typed minor things in a couple of his books before, but I wonder how that got by... Steve

Posted: Wed Apr 02, 2003 6:09 am

Hi Julius,

Welcome aboard.

> For my work the stiffer materials sustain/sing better. <

Yes, absolutely, which is why my instinct says that masonite might not be as good as plywood. And even plywood is nowhere near as good as "real" wood for cellos and basses.

Of course, in a wood panel bass trap you do not want the trap to sing. The fiberglass is used to damp the wood specifically to prevent that. And the purpose of the membrane is to provide mass, not a spring. But it still seems that a limp material might be less efficient than a stiffer material that's then damped with fiberglass.

--Ethan

Posted: Wed Apr 02, 2003 1:21 pm

Quote:

Yes, absolutely, which is why my instinct says that masonite might not be as good as plywood. And even plywood is nowhere near as good as "real" wood for cellos and basses.

I would think that the membrane is there just to convert the pressure wave (vector?) into pressure (scalar?) inside the trap, where it causes air to pump into the fibreglass and heat up, thus converting the low frequencie sound energy into heat.

If I think about that, the limper the material, the better this conversion (since it doesn't work against the sound pressure by resonating)

or am I completely on the wrong track here?

Hans van Dongen

--
this is a non-profit organisation-
we didn't plan it that way, but it is

Posted: Wed Apr 02, 2003 2:18 pm

O.k. guys I did find some 1/8" and 1/4" Marante plywood. It's made of Mahogony. Think this stuff is just as good as regular ply? It's either this or use Tempered Hardboard, or custom order 1/8" ply from Home Depot which is fine too. What ever is the most recomended. If I go with the Marante should I use it for the high bass and use regular ply for the low bass? Thanks for all your help.

Jason

Posted: Wed Apr 02, 2003 8:26 pm

Mahogany's going to be a little denser (here we go again....), but I bet it's not all that different. Bet it looks great.

Quote:

Originally posted by Jason James:
O.k. guys I did find some 1/8" and 1/4" Marante plywood. It's made of Mahogony. Think this stuff is just as good as regular ply? It's either this or use Tempered Hardboard, or custom order 1/8" ply from Home Depot which is fine too. What ever is the most recomended. If I go with the Marante should I use it for the high bass and use regular ply for the low bass? Thanks for all your help.

Jason

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