Which is heavier/stronger?? 1/8" steel or 3/4 MDF??

Well, I've got this idea for a toolbox/subbox/shelf for the rear of my Jeep, but I can't decide what to make it out of. I've settled on MDF for the subbox portion, but for the rest, 3/4 is DAMN thick, and eats up a lot of room. I think 1/8" steel would be strong enough w/ the correct gusseting and reinforcement ribs, but will it end up being heavier than MDF do you think? What I'm asking is, square inch for square inch, which is heavier. I don't have the foggiest idea where to look for that info. Thanks for any help. Peace

Ary

The steel will be way heavier. Why don't you use 3/8" or 1/2" real plywood?

Sean

I can't tell you for sure which is heavier. I built mine out of 5/8 plywoood. I planned on 3/4" MDF but it was just too heavy. The plywood was a lot lighter. Here is a breif write up with the cad drawings I did.

http://home.earthlink.net/~jkorda/mods/box.html

Rolled steel weighs 495 lbs/cu. ft. The heaviest pine (yellow) weighs 45 lbs/cu. ft., which is 11x lighter than steel. You were questioning 1/8 vs 3/4, which is a factor of 6, so you can figure the steel plate will be almost twice as heavy per square foot as the plywood, and that's without bracing. That's why they use aluminum on aircraft.

Well, the reason I wanted to get away from wood is that it's not nearly as durable as steel, and my design would waste a lot of space if I used something as thick as 5/8 or 3/4. Perhaps I need to redesign :laugh3: Thanks

Ary

I like your design ideas. 1/8" steel is used in very very very high end home audio speakers costing around 70k. They build the box out of mdf. Coat the whole thing in 1/8" steel and then put another layer of real wood on top of the steel. The end result is the finest looking, sounding, non-resonant box you can design.

If you brace the steel sufficiently, you should be able to get away with it easy without it resonating. How big of a sub do you want? Some 10"s need less then 1/2 a cubic foot of volume to work correctly. Oh, by the way, most audiophiles consider the 10" to be the most natural sounding speaker. Anything bigger requires considerable more volume and has a much different sound.

Just some input to consider

I was actually considering 2 8's firing towards the ceiling, maybe angled towards the rear hatch. I don't want them to fire sideways 'cause my design would "trap" the sound under the shelf. I chose 8s cause a 10 would be too wide. My design is to put a shelf across the cargo area level with the back seat. Under the shelf would be a full-width tool drawer. I figure that should be enough for most of my tools, and the other ones will be secured under the shelf in the unfortunate event of a roll(GOD FORBID!!). Well, that's the idea. I was planning to remove the trim on the passenger side and build the box for the sub to fill that cavity. Dirk, were you suggesting that I just build the sub box out of 1/8" steel?? Thanks

Ary

P.S. When you said you liked my designs, were you referring to this, or something else that I'm unaware of.

They actually would probably weigh pretty close to the same. 3/4" MDF is very heavy and dense stuff. You could also consider making it out of apply ply. It comes in 5'x5' sheets and is very thin veneered plywood that has many layers. It is very stable plywood, usually comes in 1/2" or 3/8" and is maple for a nice finish if you want.
With that said I would probably use steel (I did on my tool box for space reasons). I would rather weld a peice of steel than cut some MDF any day- nasty stuffuke:

I thought it was rad that someone was actually considering building a sub box out of steel, which is what it sounded like you were doing. Because it could work very well.

Understand, I have no first hand experience building a box out of just steel, I have always used MDF and plywood, but the theory is sound. The purpose of a box is to fine tune the total resonance of the speaker as a system. It does this by being made out of dense, non-resonant materiel to trap and reflect sound waves. Steel is very very dense, hence its weight. Thus it is ideal. This seems to serve your purpose because it takes up less space than MDF.

If this is the route you want to take, remember: A sub box has to be absolutely air tight, or low end will suffer. Also, no matter the size or shape, you will want to brace the box internally with either more steel or a strong wood: plywood would be ideal since it is stronger than MDF. You could glue this or somehow fasten it to the steel so that the individual panels of steel do not resonate like a diaphram.

As for your placement. I too eventually want to put a sub in the wall cavity of the passenger side trunk. I think it will fit perfectly if the sub doesn't have a huge magnet. Your idea of the two eights firing towards the rear hatch would work as well.

But also consider this. Bass is omnidirectional below a certain frequency; this is why you can put your home theatre sub anywhere. If you aimed your subs into the back seat, the sound would no doubt be different, but not necessarily worse. Dr. Amar Bose of Bose speakers did alot of research as a kid about speaker placement in a setting or surrounding and came to the conclusion that sometimes a speaker sounds better if it is in another room, or facing a wall. Bandpass subwoofers function on this theory to a certain extent. In fact, your whole trunk, your whole car acts like a speaker enclosure, amplifying and attenuating certain frequencies.

Ideally, experimentation will give you your best results.

I'm sorry I'm long winded tonight. If you have any other questions, feel free to ask; I love talking about sound almost as much as jeeps.

Don't make a box solely out of steel, steel may be dense an strong, but it is NOT acoustically dead, it will resonate. The very top-end boxes (www.wilsonaudio.com) actually use special resins, often with MDF frames. Notice that anyone that uses steel or aluminum uses wood on both sides of it. If you need it thinner than 3/4" then use 1/2 and fiberglass the outside (or inside). use more resin than you usaully would. Bondo works well also. Making a steel or aluminum box is EXTREMELY difficult to do correctly for a number of reasons. The most important of which is that you have to coat it with something that is aucoustically dead or your sound will be very colored. It is possible you could use fiberglass resin - but even that will not be as dead as just good ole' MDF. The design of the box is more important than the materials, bottomline. Build it out of MDF like you planned and spend some extra time researching box design.

I think you need to look at what you intend to use it for. If you're going for sound, MDF is definately the way to go, hands down. Without some very serious design of the enclosure, steel would be an extremely poor choice for a sub, especially steel so thin. Now if you need a tool box or something for storage, we're talking a different animal entirely. Ever seen when someone's used MDF in a bathroom? It's not pretty when you spill something on it and soak it, or even just the humidity. Put one cooler in the back of your Jeep and it leaks and you can plan on spending next weekend rebuilding it. I can't imagine what the results would be with a solvent like a gerry can that leaks a little, but I bet it wouldn't be fun. I am a carpenter and use MDF frequently; it's great stuff. But it's not for universal applications. Perhaps you'd consider a combination of materials?
Hope this helps.

Kelly, I definately am, I was just wondering if I could get away w/ using steel for the shelf and drawer. I always planned to make the sub box out of MDF. Thanks for your input. Peace

Ary

How concerned are you with sound quality? I deal a lot with sound reproduction/reinforcement pro audio stuff. One thing I fight a lot is resonance from rooms and stages. I personally think that a vehicle is a lousy platform/enviroment to be trying to find high fidelity . If I read you correctly, I suspect that you're not looking to sink $30k+ into your jeep looking for that 'perfect' sound. A seperate steel shelf with some decent bracing should be just fine and not resonate too much. You've got a lot of other issues to address before this becomes a major consideration. Good luck.
-kelly

I am by no means an audiophile. I JUST got my two blown speakers replaced, before that I was listening to just the rears(talk about horrible imaging). I used to think I cared a lot, but I've realized that I'd rather spend my money on other stuff. I just hate not having ANY bass whatsoever. Thanks for your input. Peace

Ary

P.S. About Bose, I run Bose 901's in my house, and I know all about how they work reflecting sound and such(those speakers are such a PITA to place).