View Full Version : Box Building Question
03-10-2004, 01:25 AM
I have an Orion H2 sub that I want to build a box for to go in my new Frontier extra cab. Orion says it's pretty critical to use at least 1" thick MDF in building the box to make sure it won't flex. I'm just wondering if there are any other materials I could use that would be as strong as this but not cost so much money. 1" MDF costs like $60 a sheet, and weighs about 1200 pounds. Any advice would be great.
03-11-2004, 12:19 PM
1" mdf for 60 bucks ? shop somewhere else.
3/4" is 16 bucks a sheet here and doesn't way no even 100 pounds... so 25% thicker is certainly not over 125 pounds... and last itme i saw 1" mdf it was about $25 a sheet
other materials that are lighter and better -- 3/4" cabinet grade birch plywood will be as strong if not stronger than 1" mdf, and it'll be an all around better box-- cost is about $40 per sheet... but may be more.
03-11-2004, 04:36 PM
pbd - i assume you mean home audio cabinet, not like kitchen cabinet? (i realize this is a stupid question, but better safe than sorry :D ) and i thought mdf was good because it eliminated resonances; does cabinet birch plywood do that?
03-11-2004, 05:24 PM
Cabinet grade or furniture grade as some places call it is plywood that has no voids, unlike a sheathing or construction grade which will have knots galore and often times, uneven glue dispersion between the layers. If you go to your local Home Depot or lumber yard, you can walk through the plywood sections and you can see the differences.
You can use it to build kitchen cabinets but it is often sold as a veneer plywood with one side having a veneer of birch, ash, oak, cherry, mahogany, etc etc... As the veneer gets more exotic, teh cost goes. The cheapest is birch veneer. Birch has a very even grain to it and it accepts all kinds of finishes well. It can be made to mimic more expensive finishes too.
The benefits to using cabinet grade plywood is durability, strength and weight. Depending on the materials used, plywood can be lighter than MDF. Usually they are pretty close in weight.
The drawbacks are, there is always a chance of splitting teh wood accidentally and/or the glued layers seperating and causing issues. I have yet to have it happen to me and I have made several enclosures out of the stuff with great success. The plywood in a 3/4" thickness is often overkill for a speaker in terms of structural integrity. But using the 3/4" thickness just means that the sides will have less flex and further help to eliminate any resonances you might get.
As opposed to MDF, the plywood looks better IMO and you can always finish it off nicely with a stain and polyurethane rather than carpeting or paint.
The benefits to MDF over the plywood are cost, sonically dead and ease of use. The reason is that MDF is basically paper fibers like you would see used in corrugated carboard, pressed together under high pressure to form the sheets. Given that, if you get it wet, it's done for. On top of that it can make gluing and screwing the box together difficult. Mainly because MDF does not hold on to a screw or nail like wood fibers will. Also, MDF will tend to soak up glue rather than be held together by it. The fibers in MDF do not act together like they do in wood and plywood and that causes the joints to not be as strong as the joints in wood or plywood. Overtime, they can weaken to a point where it could cause a problem. Most people usually have no issues though.
Both materials are good and have thier pros and cons. Every carpenter I know would prefer the plywood over MDF out of structural concerns. Most stereo shops and installers like MDF, including Polk Audio. Truth is, it comes down to personal preference and budget.
04-16-2004, 08:42 PM
Well if you are going for good looks and sturdiness look into the birch or maybe even oak plywood. Oak is very strong but $$ too.
As far as MDF is concerned...
I use anything from 5/8 to 3/4 and have good results. I would reccomend the 3/4 for subs over a few hundred watts. Additionally. if you are going for quality AND cheap.. Build the main enclosure from 3/4 mdf, then the face where the sub will mount from a hardwood birch or oak piece... Home depot is a good place to look for partial cheets, they come usually 2'x4'. The harwood plywood will be superior for sucking your subs tight to it with a non-hardening sealant or foam. you just can't get that seal from mdf without calking in the sub. (which makes a horrific repair job later)
When building from MDF, remember it is glue and paper... so your primary bond in making the cabinet should be... GLUE! I reccomend liquid nails, as it seals, caulks, glues, and hardens very well. Use screws to bring the joints together, but remember.. that is their only purpose in MDF.
Also.. even though it is overkill... if you can get a tube of industrial air-duct sealant to seal your inner seams... but let the fumes evap for at least a week!
04-16-2004, 08:45 PM
I always seem to forget something...
Little trick... Use car underbody coating in the inside of your box as a cheap alternative to dynamat for reducing your relfected sound waves.. essentially spraying rubber on the inside. NO.. this will not seal air gaps, and Yes, air the box out for a week.
05-01-2004, 02:50 PM
Baltic Birch and MDF are the two big woods used for making cabinets. If you need reinforcement, make some bracing or add some fiberglass.
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