"The Sublimator" An Infinity 1260w 18hz Tuned Offset Driver Folded Horn. - Page 3 - AVS Forum | Home Theater Discussions And Reviews
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post #61 of 142 Old 04-12-2015, 10:02 AM
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Originally Posted by diy speaker guy View Post
Voidless ply is the best option. You don't want voids because sometimes there's knot in a void that shakes loose and will rattle at certain frequencies and there's not much you do to fix it.

The only voidless plys I've seen are baltic birch ($55 for a 5x5 sheet) and Arauco sanded pine from Mexico ($35 for a 4x8 sheet). The Arauco factory in Mexico burned down a few years ago and Arauco became pretty hard to find but I think it's making a comeback. Haven't seen any up here in Canada yet but hopefully it will be back soon. There are probably more voidless plys I haven't seen (Appleply?) but this stuff gets expensive.

Baltic birch is just as heavy as mdf (but several times stronger), Arauco is a good bit lighter and still a lot stronger than mdf. OSB is heavy like mdf and you have to watch out for pieces that aren't embedded properly, if there's a piece that's not completely glued in it could rattle at certain frequencies. And it's really tough to finish nicely, but not impossible if you aren't too picky. My buddy made these and just painted them with black rust paint.

...

The problem with 1/2 inch ply (especially Arauco) is that it starts to twist and warp as soon as it's cut. It doesn't stay flat for long. So I wouldn't cut it until I was ready to glue it.
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post #62 of 142 Old 04-12-2015, 10:23 AM
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I don't get it, am I in trouble? Which part is the problem?
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post #63 of 142 Old 04-12-2015, 10:29 AM
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I don't get it, am I in trouble? Which part is the problem?
He's apparently got a thing for MDF.

Over the past few days he's been on many-post rant in the Martsub FAQ thread about how MDF is sonically better than BB, because it's common sense.
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post #64 of 142 Old 04-12-2015, 11:00 AM
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Originally Posted by Stereodude View Post
He's apparently got a thing for MDF.

Over the past few days he's been on many-post rant in the Martsub FAQ thread about how MDF is sonically better than BB, because it's common sense.
MDF is a fine material, but it's unreasonably heavy given how weak it is compared to Baltic birch which weighs about the same. It's also incrdibly susceptible to water damage in ways that almost no other sheet goods are, and sonically superior is a matter of opinion. It certainly sounds different but for a subwoofer it hardly matters. MDF's weight will provide a lower resonant panel frequency, stores more energy (mass stores energy and releases it like jello at the panel's resonant frequency) and the ringing will last longer. Plywood has a higher resonant frequency and doesn't store as much energy or ring as long because the panel is much stronger and stiffer and usually has equivalent or higher resonant frequency than same size mdf panels.

It's pretty simple physics.

Martysub isn't THAT big, but it's getting up to a size where I would never even consider using MDF. Personally I wouldn't use MDF for anything larger than about 1 cu ft, unless I wanted some really big and heavy dead sounding mains.
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post #65 of 142 Old 04-12-2015, 11:12 AM
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Strength and stiffness are facts, not anything that is open to debate. All MDF has over BB is just a slight edge on density. Does that make it better sonically? I don't know.

MDF-
Modulus of Elasticity - 348,090 psi
Strength - 3,480.9 psi
Density - 46.7 lb/ft^3
Specific Stiffness - 0.328 Mx10^6
Specific Strength - 3.28 Mx10^6

Baltic Birch-
Modulus of Elasticity- 1,099,386 psi
Strength- 4,351.1 psi
Density- 44.9 lb/ft^3
Specific Stiffness- 1.07 Mx10^6
Specific Strength- 4.25 Mx10^6
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post #66 of 142 Old 04-12-2015, 02:34 PM - Thread Starter
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Originally Posted by Kubbie View Post
Strength and stiffness are facts, not anything that is open to debate. All MDF has over BB is just a slight edge on density. Does that make it better sonically? I don't know.

MDF-
Modulus of Elasticity - 348,090 psi
Strength - 3,480.9 psi
Density - 46.7 lb/ft^3
Specific Stiffness - 0.328 Mx10^6
Specific Strength - 3.28 Mx10^6

Baltic Birch-
Modulus of Elasticity- 1,099,386 psi
Strength- 4,351.1 psi
Density- 44.9 lb/ft^3
Specific Stiffness- 1.07 Mx10^6
Specific Strength- 4.25 Mx10^6
Does proper bracing not make all of these facts irrelevant?

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post #67 of 142 Old 04-12-2015, 03:08 PM
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Does proper bracing not make all of these facts irrelevant?
Well, it all depends what you mean by proper. What's necessary for BB isn't what's necessary for MDF. The stiffer the material, the less bracing it needs.

So, if you take a design that was "proper" (ie: minimum necessary) for BB and make it out of MDF you're going to end up with an inadequately braced box.
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post #68 of 142 Old 04-12-2015, 03:11 PM - Thread Starter
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Originally Posted by Stereodude View Post
Well, it all depends what you mean by proper. What's necessary for BB isn't what's necessary for MDF. The stiffer the material, the less bracing it needs.

So, if you take a design that was "proper" (ie: minimum necessary) for BB and make it out of MDF you're going to end up with an inadequately braced box.
I was more referring to properly braced bb vs properly braced mdf. And properly as in liberally as opposed to conservatively.

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post #69 of 142 Old 04-12-2015, 03:17 PM
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I was more referring to properly braced bb vs properly braced mdf. And properly as in liberally as opposed to conservatively.
Well sure, you can build an adequately braced / robust enclosure out of either.
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post #70 of 142 Old 04-12-2015, 03:47 PM - Thread Starter
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Well sure, you can build an adequately braced / robust enclosure out of either.
Ok. Now we have arrived at the point of which we can discuss the pros and cons of said bb vs mdf enclosures. Are the two materials sonically different?

Eg, does one offer more damping (for higher frequencies) or is that even a thing?

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post #71 of 142 Old 04-12-2015, 04:04 PM
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All materials resonate at their resonant frequency. All materials store and release energy based on their stiffness and mass. So yes, different materials will sound different.

For subwoofers the different sound is hardly important most of the difference is well outside a subwoofer's passband. Weight and strength is more important. 1/2 inch mdf is VERY weak and very heavy compared to other 1/2 inch sheet goods. And if you measure it's usually not even 1/2 inch, it's closer to 11 or 12 mm.
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post #72 of 142 Old 04-13-2015, 08:27 AM
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Isn't lower price the reason for using MDF? With the correct bracing does it matter if it's bb or mdf?

Is the difference more important with horns vs other subs? Even though I've used mdf in previous sub builds I think I would use plywood for a horn.
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post #73 of 142 Old 04-13-2015, 10:03 AM
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if my "limited" building experience . . .
with the BF 1/2" ply subs and in general, 8" is considered a maximal spacing between braces and edges


i.e. a 24"internal-25.5 external wide sub is braced at the 8" and 16" mark on the interior


a 30" width is braced at 7.5", 15" , 22.5"
this seems to be a accepted" standard range and it show up very consistently whether folks use 1/2 or 3/4 material


there are some who will argue that such stringent uniformity "may" induce more internal panel harmonics because of the symmetry and suggest slightly offsetting of braces to "reduce/mitigate/eliminate the possibility of "harmonically sympathetic yadda yadda yadda . .


and wrt windowing braces for less weight/internal "turbulence", the ROI for time/effort involved especially for a pieces never to be seen again is strictly a personal call,
the real science may be out there somewhere but for me "The Truth is out there" and a well performing sub is right here

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post #74 of 142 Old 04-13-2015, 11:59 AM - Thread Starter
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Well I suppose it's settled. Ply it is. Now. Is it imperative that I buy the most expensive ply? Assuming that the enclosure is adequately braced?

Asphalt Empregnate pine board?



It says "regular pine board from Georgia pa if I c is designed for above ground application s to provide rigid reliability extra insulation value and sound deadening properties in a cost efficient panel".

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post #75 of 142 Old 04-13-2015, 01:19 PM
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More plys is better than less. If the face veneer is paper thin it's probably less than ideal. (There might not even be a face veneer at that price.) Make sure it looks like the plys are glued together well, I've seen stuff that bubbles up between the plys over time and you can physically rip the plys apart with your hands.

Above all, void free is highly desirable. By looking all the way around the sheet you should be able to see if there's voids or not. Sometimes they fill the voids (like BB fills problem areas with football shaped patches) and that's ok, but if you see big holes in the plys at the edges you are just asking for trouble if you use that.

So no, it doesn't have to be the most expensive plywood. But there are things to look for. You don't want construction grade but you don't need furniture grade.

Also if weight is an issue, go for sanded pine. BB is much heavier but it's also stronger. Pine is pretty soft. It's still strong compared to mdf but you can dent it with a fingernail. Duratex is pretty hard so if you use that for a finish that isn't an issue.

Also as I mentioned, 1/2 inch pine starts to twist and warp almost immediately as soon as it's cut up. The smaller the panel the more it will warp. Unless you want to straighten panels as you build, don't cut it until you are ready to glue it.

At $10.35 a sheet that's probably construction grade, so probably only 3 ply, probably no face veneer, probably badly glued plys and probably very rough face and full of voids. But check it out at the store, you might be pleasantly surprised. But I doubt it, that's very cheap. Arauco is pine and it's very nice, I think it sold for about $20 - $25 for a 1/2 inch sheet last time I saw it for sale.

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post #76 of 142 Old 04-13-2015, 01:33 PM
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"The Sublimator" An Infinity 1260w 18hz Tuned Offset Driver Folded Horn.

Asphalt impregnated board? What on earth is that? Why would you want to use tar covered materials? How do you paint that? How do you even glue it? What does it smell like? Is it actually actually plywood?
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post #77 of 142 Old 04-13-2015, 04:10 PM - Thread Starter
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So my wife just told me that she just realized how tall 81.5 inches is. She completely shut down the projects. Looks like the tiny marty is the next best thing.


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post #78 of 142 Old 04-13-2015, 04:15 PM
 
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Without knowing anything about it...NO on the asphalt stuff.

I am a fan of MDF, It actually measures .75" thick and you are guaranteed void free. (plywood doesn't come in standard thicknesses, 3/4 will be 21 or 23/32nds, BB might be real dimensions) It doesn't warp, is easy to cut without splintering, and is plenty strong. The sheets are bigger 49x97 too.

The only decent ply that I have found at home depot is oak veneer 3/4 for $50/sheet and it still has a couple voids. MDF is ~$30 for 3/4".

Don't spill water on raw MDF and it works great.
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post #79 of 142 Old 04-13-2015, 04:17 PM
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Well she just made your life a lot simpler so thank her for that and pretend you believe it.

IMO that's an ugly little thing, looks like the Monsters Inc monster. You should paint it like that and give it little arms.



Gary so sad he can't have a real sub. Make her stare at that for a while and re-evaluate the importance of 81.5 inches in the general scheme of things.

Good luck.

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post #80 of 142 Old 04-13-2015, 04:30 PM
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So my wife just told me that she just realized how tall 81.5 inches is. She completely shut down the projects. Looks like the tiny marty is the next best thing.
It's better to ask forgiveness than permission.
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post #81 of 142 Old 04-13-2015, 04:31 PM - Thread Starter
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I never asked permission..... I just told her.
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post #82 of 142 Old 04-13-2015, 04:43 PM
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Sounds like she told you.
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post #83 of 142 Old 04-13-2015, 04:46 PM
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I never asked permission..... I just told her.
And why would you discuss dimensions?

Built it, then let her complain about how large it is.
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post #84 of 142 Old 04-13-2015, 04:50 PM - Thread Starter
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And why would you discuss dimensions?

Built it, then let her complain about how large it is.
She wanted to build shelved for all my blurays in the location that I wanted to build my horn. But I just pointed to another(better) location to build the shelves. THE SUBLIMATOR WILL LIVE!!!!!!!!


Edit: it's all settled. I can haz horn.
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post #85 of 142 Old 04-13-2015, 04:52 PM
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You could always build the forum's first media shelf sub. You'll just need to use velcro on your blu-ray cases so they can't fall or rattle.
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post #86 of 142 Old 04-13-2015, 04:57 PM
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Originally Posted by More is Better View Post
I am a fan of MDF, It actually measures .75" thick and you are guaranteed void free. (plywood doesn't come in standard thicknesses, 3/4 will be 21 or 23/32nds, BB might be real dimensions) It doesn't warp, is easy to cut without splintering, and is plenty strong. The sheets are bigger 49x97 too.
A few thousands of an inch variation makes no difference. "Plenty strong" is relative. Even bad plywood is plenty stronger. Cardboard is plenty strong too for some purposes.

Quote:
The only decent ply that I have found at home depot is oak veneer 3/4 for $50/sheet and it still has a couple voids. MDF is ~$30 for 3/4".
Arauco is $35 for 5/8 if you can find it. It's great stuff.

Quote:
Don't spill water on raw MDF and it works great.
Last time I used mdf it was deep summer and a drop of sweat got on it. By the time I was able to wipe it off (almost immediately) it blistered like it had some kind of plague. I've got a scrap of 5/8 mdf that's been outside for awhile. It's currently about 3 inches thick.

Mdf sucks moisture right out of the air. It needs to be sealed airtight on both sides (inside and outside the cab) or the joints will swell and show joint lines. There's tons of forum posts about trying to get rid of these lines. I don't even bother trying anymore. I sand it ruler flat and two days later the line pops back out. Sand it ruler flat again, 2 days later the line is back. ALL exposed edges of mdf really need to be sealed with something toxic, and right away after finish sanding. Even then, the moisture in the sealer is often enough to pop the lines back out.

It's not impossible to do a piano finish but it certainly isn't easy. I had a 5/8 mdf box I sanded so many times trying to get rid of the lines it ended up 1/2 inch. I finally realized it wasn't going to happen unless I got some toxic sealer. I thought my oil based paint would seal it. No. You need a real toxic sealer.

Fun stuff.
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post #87 of 142 Old 04-14-2015, 03:07 AM
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A few thousands of an inch variation makes no difference. "Plenty strong" is relative. Even bad plywood is plenty stronger. Cardboard is plenty strong too for some purposes.



Arauco is $35 for 5/8 if you can find it. It's great stuff.



Last time I used mdf it was deep summer and a drop of sweat got on it. By the time I was able to wipe it off (almost immediately) it blistered like it had some kind of plague. I've got a scrap of 5/8 mdf that's been outside for awhile. It's currently about 3 inches thick.

Mdf sucks moisture right out of the air. It needs to be sealed airtight on both sides (inside and outside the cab) or the joints will swell and show joint lines. There's tons of forum posts about trying to get rid of these lines. I don't even bother trying anymore. I sand it ruler flat and two days later the line pops back out. Sand it ruler flat again, 2 days later the line is back. ALL exposed edges of mdf really need to be sealed with something toxic, and right away after finish sanding. Even then, the moisture in the sealer is often enough to pop the lines back out.

It's not impossible to do a piano finish but it certainly isn't easy. I had a 5/8 mdf box I sanded so many times trying to get rid of the lines it ended up 1/2 inch. I finally realized it wasn't going to happen unless I got some toxic sealer. I thought my oil based paint would seal it. No. You need a real toxic sealer.

Fun stuff.
So which "toxic" sealer do you recommend?
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post #88 of 142 Old 04-14-2015, 03:13 AM
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Has anyone heard of this stuff called Advantec plywood? It's not exactly plywood per se, and it looks like typical OSB at first glance, but, it is the strongest, stiffest and most dense sheet wood that you can buy, plus it's pretty much water proof and absolutely will not bend or bow even if you wanted it go!

I know that this would not be very popular in the DIY community due to the OSB look of the sheets, but for those that want to build an enclosure that won't ever be seen, or as a covering for baffle walls, stages and risers, this stuff is the holy grail of stiff, ridged, dense and unworpable sheet wood!
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post #89 of 142 Old 04-14-2015, 03:24 AM
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Originally Posted by Tip24/96 View Post
Has anyone heard of this stuff called Advantec plywood? It's not exactly plywood per se, and it looks like typical OSB at first glance, but, it is the strongest, stiffest and most dense sheet wood that you can buy, plus it's pretty much water proof and absolutely will not bend or bow even if you wanted it go!

I know that this would not be very popular in the DIY community due to the OSB look of the sheets, but for those that want to build an enclosure that won't ever be seen, or as a covering for baffle walls, stages and risers, this stuff is the holy grail of stiff, ridged, dense and unworpable sheet wood!
Nice find, I may try it out. I'm sure it looks fine finished with duratex.
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post #90 of 142 Old 04-14-2015, 05:06 AM
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Quote:
Originally Posted by Tip24/96 View Post
Has anyone heard of this stuff called Advantec plywood? It's not exactly plywood per se, and it looks like typical OSB at first glance, but, it is the strongest, stiffest and most dense sheet wood that you can buy, plus it's pretty much water proof and absolutely will not bend or bow even if you wanted it go!
The comparison I saw was to standard OSB and some low grade 4-ply plywood. I'm not sure it would be all roses compared to BB 13-ply.
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