baltic plywood or mdf for building 142.5L shiva?

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I am building the 142.5L shiva vented subwoofer as detailed on the Adire Audio website. They say to use 0.75" mdf. Is there any advantage to using 0.75" baltic birch plywood (many layers). The difference in price is $20 for a sheet of mdf compared to $50 for the plywood.

Any recommendations? Will it work better with plywood?

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Brian
 
I've used MFD and have gotten really good results (not with the Shiva, but the Titanic 1200). For a subwoofer I wouldn't bother with the added expense of baltic birtch. I have heard a lot from people who have used Baltic Birtch in full range speakers and the general consensus has been that Baltic Birtch does offer some slight improvement. If you are going to use Baltic Birtch, make sure that it is void free plywood, there are types of Baltic Bitch plywood that are not void free and would cause problems.
 
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It is from home depot, and has a lot of layers (more then 9, will count next time I go maybe 17?). I examined the cut pieces in the store (4'x8' sheets cut into 4'x2') and the edges of the normal sheets, and I could not see a single void.

It just takes 4'x8' one sheet of wood, and I don't mind the extra cost. I am just wondering if it will provide better results. Is it easier to finish baltic birch, as compared to mdf?

--
Brian
 
Retired diyAudio Moderator
Joined 2002
I found this in another thread. I guess I will try the plywood, unless anyone can give me a reason not to.

Originally posted by Nelson Pass
Baltic Birch = double ++ good.

MDF = double ++ ungood.

I have a problem understanding how a population obsessed
with oxygen free copper wire and teflon capacitors can
accept mutated cardboard.

Of course I use it all the time, myself.....

Thoughtcrime is death. Thoughtcrime does not entail death, Thoughtcrime is death....

--
Brian

"Anyone who challenges the prevailing orthodoxy finds himself silenced with surprising effectiveness. A genuinely unfashionable opinion is almost never given a fair hearing."- George Orwell
 
Laminates/veneers/baltic ply etc.

I cam across an architectural product which might have application in this area - ApplePly - whether it's appropriate for speakers I can't guess. However, they do have a distributor search engine which allows you to find retailers within a certain radius from your location. This might help in finding source of baltic fir, hardwood veneers, etc.

Try clicking on this link, then go into their distributor search engine to find links to retailers/lumber yards which carry exotica:
http://test.premierelink.com/statesind.com/prod/consumer_2b2.html
 
Brian, the MDF and Plywood argument has been coming up a lot recently. I had always worked under the assumption that MDF was wanted due to its mass and that plywood was bad. Now they're saying void-free baltic birch plywood or even solid wood is not bad?!?! I'm getting just as confused as everyone else.

As to finishing, I think you'll find that you will have an easier time finishing the plywood with paint or stain, as it won't absorb as much as MDF. However, you have the problem of the end grain on plywood showing through, so you have to take some extra steps to hide that. Basically I think it comes down to picking whichever you want to work with.

P.S. - You're in Atlanta, so why are you sticking with HD for plywood? You should have lots of sources around there to price compare with!! HD's prices are high and quality is low, compare to a real lumber yard, and you should get a better deal.
 
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Schaef,

I never read that solid wood is not bad for speakers. Here is the order of preference that I have seen the most common:

"Recommended building materials are void free plywood (such as marine ply, apple ply, or baltic birch), MDF, and particleboard, in that order."

The above is taken from Adire Audio, from the pdf on tempest subwoofer applications.

As for the lumber yards, I have looked with no luck to find one with better deals on wood. Home Depot is also very convienient. There are 5 Home Depot stores that are close to my home and work. If anyone around Atlanta can recommend a lumber yard, I will check it out. One more issue is that I don't have a truck, and HD sells plywood in 2'x4' sheets, and when I need big sheets, there is a Home Depot 2 miles from my friends house where I am working on my speakers, so I can get his brother to drive his truck to get wood for me. I agree that there prices might be high, but there is a price to convenience. My friends father, who used to be a professional woodworder, tells me that good lumber yards are a thing of the past.

--
Brian
 
No, solid wood is not for speakers

solid wood is not as dimensionally stable as plywood -- in plywood the veneers are built up at right angles so that as moisture is absorbed and released the wood doesn't change dimensions (or not that much compared to a solid wood.) Solid woods can split, S2S (smooth two sides) solid woods are very expensive, etc., etc. Further, woods like Pine have been getting less and less dense through time as forestry techniques push toward rapid growth, rapid fiber build up, but less dense fiber.

MDF is heavy, but relatively easy to machine and finish.
 
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Joined 2002
Hi Brian,

The plywood will be much stronger and stiffer then MDF, but MDF has better damping then plywood. If all your using it for is straight side, tops, and bottoms, you could use either, but the MDF will be less resonant. If you plan on a design that requires some structural strength (like horns), you might want to stick with the plywood.

Be careful with screws around MDF. It doesn't take much torque to strip the thread. Also, screws into the edge of MDF is a sure way to split the board.

I thought you've finished your Thors already?
Rodd Yamas***a
 
Retired diyAudio Moderator
Joined 2002
Thor is getting close to being finished, which brings me to research new projects. I have both of the main cabinets totally glued together. One is sanded down to be stained, and the other needs more sanding before I stain it. The bases still need to have their fronts glued on. For the bases, I made them out of plywood, then glued solid oak to them. The have lots of internal bracing, and are quite heavy. One more day, and I should be to the staining stage.

I figure that it will take less then a day to cut all of the wood to build a sub. With the table saw, I can cut them all pretty quickly, and with my new router jig, I can cut all of the holes out of the internal braces, and the woofer hole quickly also.

I am addicted to this diyaudio thing, and keep on starting new projects.

I really should finish my Aleph. I have all of the parts, and all that I have to do is drill the holes in the heatsinks and mount the transistors and then assemble. I just get sidetracked. I am also in the middle of working on my new PIC18F452 microcontroller based PGA2310 pre-amp (similar to Mark Hennessy's design). I am laying out the pcbs now. I also need to finish my new leach amp design with integrated to-3p devices. I have the pcb finished and the board tested, I just need to drill holes into a heatsink, and mount the board to the heatsink, and test with normal power supply. I also have 2 channels of a leach superamp finished, and I need to finish testing them. I have a chassis for one channel of the superamp, with transformer and caps, which could possibly power the subwoofer amplifier. I also have a BOSOZ almost finished (needs chassis and pots). Along with another 3-channel leach amp that needs a case and transformer.

I with I could go full time DIY like peter, but I keep on working long days at my job, and spend the weekends building speakers...

On top of all of this, I am trying to help a friend start a Georgia Tech diy audio club.

--
Brian
 
MDF vs BB

Just my two cents worth. Forget MDF damping for subwoofers.... just make it a stout box. At the frequencies which a subwoofer operates damping is problematic at best.

I'd use some form of engineering ply (Baltic ply, apple ply) and brace the panels such that their natural resonate freq. is outside the subwoofer's operating range.

Cyclotronguy
 
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Joined 2002
I went by HD today at lunch, and they had the birch plywood with 13 layers and void free in 2'x4' sheets for $13. This seems just about perfect for building an EBS Tempest (dimensions 24"x24"x48", so I picked up 7 sheets (one for each side, one for top and bottom, and 2 for internal bracing. The edges are cut perfectly, and they are quite square.

I will build the EBS Tempest. It should be quite easy with the wood cut into 2'x4' sheets, plus the sheets fit in my honda civic.

They are pretty heavy though. I am scared at the thought of having to move the EBS Tempest...

--
Brian
 
Ex-Moderator
Joined 2002
So Brian,

That's what happens with those DIY speaker project. First you start saying things like "I'll be bak", then you start to look like this::eek:

Rodd Yamas***a
 

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Baltic Birch and Tempest PICs

I recently used 3/4" Baltic Birch on my Tempest sub in an octagonal shape (135L sealed). I am very impressed with the rigidness. It is more rigid (less resonancy felt by hand) than my main speakers made with 1" MDF and 1/4" Baltic Birch veneer. I also used a marble top (3/4 Baltic plus 1/2" marble). The weight is quite manageable.
Pics: http://www.picturetrail.com/mch1/1159742
 
Retired diyAudio Moderator
Joined 2002
Rodd, Thanks for the advice and laugh.

I started building the 320L tempest ebs subwoofer today... I have all of the wood, and have cut the holes for the internal braces. I will try next week to get to a table saw and get all of the pieces cut to size. Now, all that i have is 7 - 48"x24" sheets.

It still boggles my mind that the finished size will be 48" high by 24" wide x 24" deep (including the 7.25" high feet on the bottom).

I am quite satisified with it. I have a new gallery for this up at: http://brian.darg.net/tempest
I will try to update the pictures as I progress on this project.

Here is a picture of the wood: (note... the burn marks in the cut out circles are from the plunge router going into the wood for the first time. If I went really slow, I could avoid this (by letting the saw dust come out as I go down), but I wanted to get it done and it will be in the inside of the sub. It took me an hour for each board, cutting 16 - 4" diameter circles in each. The jasper jig and plunge router worked great for this.

--
Brian
 

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