3/4" vs 1/2" MDF for sub box.

[george graves]

Looks like the norm is 3/4" for box building. (with some crazy guys using 1" - damn that must be heavy...

What about 1/2"? Too thin? Can you get away with it on a smaller box around 1 cu ft? I assume the box it's self starts to flex a bit the thinner you go. Does it start to resonate? Would that really be an issue if you are firing it through the ski pass hole?

I'm not trying to save money, just weight really.

[Schnitzer318is]

If you are going to use 1/2" be sure to use internal bracing to limit flex. I also wouldn't go bigger than a medium-ish 10" sub with 1/2". That's just imho though.

[Mtriple]

If you are going to use 1/2" be sure to use internal bracing to limit flex. I also wouldn't go bigger than a medium-ish 10" sub with 1/2". That's just imho though.

Agreed. It also doesnt hurt to to reinforce the inside of the enclosure with fiberglass for good measure.

[StereoInstaller1]

Another issue is splitting.

Bracing alone will not make up for the flex of the panels of the box.

Since I can build a very solid 1.5 cubic foot box that weighs 35lbs, I figure that the 1/2 would weigh 33% less, right? How much weight would that save, maybe 8ish lbs?

Nah, no thanks. I will go without ice cream for a month or whatever, I gotta have kick ass bass SQ, it is a HUGE priority for me.

(mine weighs about 65lbs empty, BTW. I care not)

BTW, George, you have a table saw, right? Cabinet stapler? Get busy, build both and compare!

Luke

[StereoInstaller1]

George, do you have a clear understanding of why the strength of the box is directly related to sound quality?

I just did a bit of reading on Young's Modulus. I wish I spoke math. I was looking to see if there were a simple way of determining what % more elastic it would be, but the math puts it out of my league.

I assume this to be accurate: http://en.wikipedia.org/wiki/Young's_modulus

[Jean]

Neither..... 1" HDF with bracing and 2" front :)

[george graves]

(mine weighs about 65lbs empty, BTW. I care not)

BTW, George, you have a table saw, right? Cabinet stapler? Get busy, build both and compare!

You personal box? Or the ones you sell are 65 lbs?

I've got all the box building stuff - but I'd rahter not buy two sheets. Although I have discovered that MDF is great for making jigs for building things - it's so easy to work with.

Neither..... 1" HDF with bracing and 2" front :)

God I love a r3v pissing match. I swear if there was such a things as 4" MDF someone would say to use it.

[StereoInstaller1]

Yeah, the beast that is in my E30, the 2.7 cubic foot beast.

Maybe someday you can hear it, hopefully.

LF

[Axxe]

George, do you have a clear understanding of why the strength of the box is directly related to sound quality?

I just did a bit of reading on Young's Modulus. I wish I spoke math. I was looking to see if there were a simple way of determining what % more elastic it would be, but the math puts it out of my league.

I assume this to be accurate: http://en.wikipedia.org/wiki/Young's_modulus

It isn't something that I have direct experience with (MDF) however in my opinion the amount of additional bracing required to maintain the same deflection as thicker board would negate most if not all of the weight savings, and introduce stress concentrations right in the areas of largest deflection, requiring a second piece of MDF to further spread it out. Not worth it from a weight perspective IMHO. Fiberglass would be a better method but again, you're adding weight.

[Jean]

God I love a r3v pissing match. I swear if there was such a things as 4" MDF someone would say to use it.

I know, me too! Actually, the least resonance and flex the better and you of course know this.

I went with 1" HDF and double that on the front for my home woofers....and also braced with 1" hdf internally .

[AndrewBird]

Just machine the box out of a solid block of aluminum. It's light, right? Maybe cover it in carbon fiber for added lightness (like a Lotus)?

[george graves]

I know, me too! Actually, the least resonance and flex the better and you of course know this.

That's pissing in the wind IMHO. Sure the walls of the box could blow out a tiny, tiny bit. But in the epic battle of speaker cone vs. MDF, I think 99.9% of that energy is going to be directed out the speaker.

[Jean]

Yep, it's car audio after all lol

[FredK]

Sure the walls of the box could blow out a tiny, tiny bit. But in the epic battle of speaker cone vs. MDF, I think 99.9% of that energy is going to be directed out the speaker.

That's also pissing in the wind IMHO.

:p

It may actually boil down to practical issues. 1/2" MDF has less surface area available for gluing, so unless your miters are PERFECT, your box will demolish itself fairly easily.

[StereoInstaller1]

That's pissing in the wind IMHO. Sure the walls of the box could blow out a tiny, tiny bit. But in the epic battle of speaker cone vs. MDF, I think 99.9% of that energy is going to be directed out the speaker.

Not so. In fact, that is the primary reason for a sturdy wall: it has a HUGE effect.

The kinetic energy of the flexure is released as "mud" as soon as that particular resonance has passed.

Hell, if flex isn't a concern, why not build them of cardboard, or even 1/8", right?

Flexure is the MOST important goal of a box material, thus insanity such as concrete boxes, dual layers of 1" HDF, etc.

The trick is to find that perfect compromise of weight, strength, cost, availability, sound quality...thus pretty much all installers use 3/4" for 99.99% of the boxes built worldwide.

Part of my story is that I have built boxes of 1/4" MDF with bracing, added Fiberglass, used hunks of allthread, all kinds of tricks...but I did all that crap 20 years ago. Nothing has changed, not even refined. 3/4" MDF is is still the most logical solution for me.

I still wanna see someone else build multiple examples of identical boxes and then do proper analysis. Not since the BBC and Celestion spent a couple years doing so in the late 70's has any known published work happened like that.

Celestion DID invent that crazy lead/aluminium/balsa/styrofoam composite material that they were building some crazy $10,000 speaker from back in those days, but that was when MDF was $50/sheet (think $50 a sheet in 1978!), not "cheap" like it is today.

LF