Wondering about mixing Baltic Birch with MDF

[Tim Morton]

I am going to build a subwoofer for my Home Theater. The carcus will be made from 3/4" Baltic Birch, but I will be using 3/4" MDF as internal bracing and also as the bottom and top. I will then trim out the sides with some type of hardwood to give it a raised panel look. And I will use something as of yet to be determined for the top. Is there anything I should be aware of when mixing these three types of wood? I will dado the braces into the plywood...but I will also need to glue and screw the plywood to the MDF to make a box. I will probably be using internal stringers to give a stronger joint.

Just looking for advice and things to be on the look out for. Here is a picture of what it should look like when I am done...of course it will probably end up being about 40% as nice:o

[Jim Dunn]

Just make sure that you pre-drill the MDF.

But Tim I'm wondering if you wouldn't be better off to reverse the materials? Using the BB as structural materials and the MDF for the raised panel look.

As to your other materials it would be less stable than anything else you've mentioned.

[Karl Brogger]

I built alot of sub boxes in highschool. don't use plywood. The bass will literally rattle it apart. MDF works well, as does regular particle board. Use PL400, or Liquid nails on all the joints and caulk all the joints on the inside to get it air tight. If you want the outside to be woodl, veneer the outside. Melamine actually works really fricken well too. Its more reflective than bare particleboard and helps keep the sound trapped in the box longer.

[Phil Thien]

Not to start an argument, but quality plywood is fine for subs. In many ways it is superior to MDF because at these very low frequencies you want the walls to be ridgid.

[Jim Becker]

MDF is an excellent material for any form of loudspeaker due to it's density. I'm with Jim...build the box with MDF and trim it out with the ply, veneer and solids for looks.

[Phil Thien]

MDF is an excellent material for any form of loudspeaker due to it's density. I'm with Jim...build the box with MDF and trim it out with the ply, veneer and solids for looks.

MDF is important for full-range speakers because the density helps w/ resonances in the 300-1000-Hz range. However, it doesn't help in lower (20-Hz) frequencies. I've hung-out at audio discussion forums enough to learn that lower frequencies need stiff cabinets and that high-quality plywood is preferred but nobody likes the cost.

Here is a quote for a better source than I:


In the deep bass range, cabinet damping is less important than sheer rigidity. Cabinet-wall resonances typically occur between 300 to 800Hz, well above the recommended crossover frequency. Since the self-damping properties of MDF are not required in a woofer cabinet, a stiffer and more rigid material like plywood is a better choice. (Apple-Ply or Baltic Birch are the best grades of plywood for speaker cabinets.) Since plywood has a much higher speed of sound than MDF, the panel resonances will also occur at a higher frequency than MDF, which is desirable in a woofer cabinet (but not in a 2-way system where the midbass goes up to 3 to 4kHz.)

From this page: http://www.nutshellhifi.com/ME2txt.html

[Jim Becker]

Thanks for the clarification, Phil.

[Greg Narozniak]

Back in my sounds days all the rigs I worked with like Claire Brothers, EAW, etc, all had one thing in common, the boxes were built from multiple layer Plywood.

Now one big factor for that is that when you 'fly" loud speakers the cabinets need to be as strong as possible to withstand the pounding of Set up, hanging and running during a show, tear down and packing. So that may be a large part of it.

Now higher end home speakers may be different but that is my experience with them.

[Jim Becker]

Oooh....EAW cabinets are wonderful! A number of years ago when I was doing some sound reinforcement that exceeded my own equipment capabilities, the rental firm I used supplied some EAW boxes. I have to say, they made "me" sound good making the performer sound good! LOL

And yes, multi-layer ply makes sense, both in strength and stiffness, but also because it can also result in reasonable weight...one downside to MDF unless a totally stationary situation is at hand as in a home setup.

[Karl Brogger]

My experience is limited to car audio, but the plywood was always "not recomended". Maybe people were using CDX? How would hollows in the plywood effect things? I can't imagine much, but??? Car audio shops always used particle board, or mdf as well.

[JayStPeter]

Sounds like you're on the right track there. No worries with those materials. BB and/or MDF are the best two materials to build out of (in that order). My personal preference is to use butt joints with glue and brads/screws for speakers. It's too easy to get little gaps when you dado things if you don't get the dado depth perfect within thousandths. For the internal braces, biscuits work well. Once you glue and nail/screw everything, dress it up to cover the fasteners with the nice joinery. Use silicon caulk on the inside to seal the cabinet.
What driver are you using?

[Jim Solomon]

Not to start an argument, but quality plywood is fine for subs. In many ways it is superior to MDF because at these very low frequencies you want the walls to be ridgid.

I believe you'll find tha MDF is denser than BB. Google any speaker construction site an you'll see they are made almost exclusivly of MDF, especiall subs. If you want a hardwood look, veneer it.

[JayStPeter]

I believe you'll find tha MDF is denser than BB. Google any speaker construction site an you'll see they are made almost exclusivly of MDF, especiall subs. If you want a hardwood look, veneer it.

Ask the question at any speaker building site. Specifically BB ply. Most builders don't use it because of cost and difficulty finding it, but will rate it as superior to MDF. Regular ply isn't good.
You've got to remember that most of the DIY builders are after the best bang for the buck. Once you use something at least twice as expensive for the cabinet the cost savings of building your own cabinets starts to fade.

[Tim Morton]

Ask the question at any speaker building site. Specifically BB ply. Most builders don't use it because of cost and difficulty finding it, but will rate it as superior to MDF. Regular ply isn't good.
You've got to remember that most of the DIY builders are after the best bang for the buck. Once you use something at least twice as expensive for the cabinet the cost savings of building your own cabinets starts to fade.

Thanks Jay, you said that better than I could have:) I am building whats called a LLT subwoofer. (Large low tuned). Its going to be about 40"x22"x30". Give or take a few inches. I think I have decided to use just the BB and buy 2 5'x5''s. Cost will be right around 100 bucks and I don't have to breath any MDF dust:)

The driver is made buy a company called TC sounds and it is a 15" TC2000.

I'm using the Baltic birch because i have never worked with it before and I want to try to make it look like furniture instead of the usual crap I produce:D

[Brian Kerley]

Have you thought about using a Sonotube (round concrete forms) as the enclosure for the sub? A lot of home theater guys have had a lot of success with those.

[Tim Morton]

Have you thought about using a Sonotube (round concrete forms) as the enclosure for the sub? A lot of home theater guys have had a lot of success with those.

I have....but it won't pass the WAF.:cool: I am basically building a box with the same air space as one of the sonosubs you mentioned.