MDF vs Birch Plywood for 3 way tower

Hi, So after having some good luck upgrading crossovers on existing speakers over the years I am looking to do my first complete build from the ground up and have questions about cabinet materials. The speakers will be a 3way with the following. Scan-speak 18W/8531G as the driver ATC 150 Mid-range and a Scan-speak D3004 soft dome in a ported 1 cu ft tower rectangle enclosure with 4 horizontal shelf braces and two vertical kinda like a bowers nautilus bracing system. I am planning on using glue and cabinet biscuits for the construction.I was first considering using 3/4 birch but was told 3/4 mdf would yield less coloration and resonance effects. I am wondering on other opinions on this and am curios if MDF is the way to go than are there differences in quality or is the stuff my local Home Depot sells fine? Just trying to get started in the right direction. Thanks in advance for you input, Gavin
 
Count me in the Baltic birch plywood camp - and yes, there are substantial differences in the quality of plywoods and MDF -try to find a local distributor to the commercial millwork / kitchen cabinet trades - they samosa skyways have a better range of sheet good products available than the big box chains
 
Thanks for the quick reply. So there is a big difference in quality that's good to know.I have a few lumber supplies close by so guess that's going to be a better route than Home Depot or Lowes. I hear some people say MDF can sound dead and not sure if this is referring to quiet witch is what I would equate to a plus or if dead meaning a lifeless character to the music witch is very bad and the I hear people swear by birch plywood and others say they have experienced a decent amount of resonance occurring. I would think a the large amount of bracing I plan on using would move the resonance freq and amount in either material in a favorable way. Trying let the drivers and crossovers dictate the sound as much as possible so any needed tweaking and adjusting to the sound can be done as needed. Once the cabinets are done that's what am living with and x-overs can be worked as needed. Thanks for the heads up on the mega stores lack of quality.
 
AFAIC MDF is not a suitable material for speaker cabinets (i'll get lots of argument) -- unless it is the only thing you have.

Because it is cheaper (in many ways) the industry have done such a good job brainwashing about MDF even a lot of talented designers will specify it (bet they haven't tried anything else)

If you want a step up from quality plywood (we use Murphy Ply from Portland), have a look for stranded bamboo plywood (thats what Plyboo calls it, Cali calls it fossilized). It is exceptional and needs to veneer.

dave
 
I live in a city and sourcing quality Russian birch pine is a pain in the ***.
The one stockist who use to have goods quality ply has gone bust. The only other one who has decent stuff including hardwood faced, you need to buy a minimum of 10 sheets and @ £46 per 8' x 4' 1/2" + VAT that's way to much for me. I've had two sample boards from two timber suppliers and i didn't even need to rip them to see the voids and delamination. And I specifically asked for good one side furniture grade. The search goes on.
 
I live in an area where there is a lot of hi end residential construction so there is a few good sized lumber yards within a few miles and quite a bit of custom cabinet makers they need to service. I am hoping that works in my favor. I appreciate the input I am getting from you guys. Point well taken about the energy storage on MDF and the links on the plywood manufactures the Murphy Ply looks like some good stuff going to see if its available to order locally in small quantity. Thinking I will use high grade for the cabinets and scale back a little for the internal bracing.Will prob end up veneering over the cabs as well. I am going to have a few days of this week to hash out details on the cabinets as far as material amounts and design details as far as dialing the final driver placement on the baffle and final box volume and porting. I need to look at group delay issues and come up with a final freq to tune the ports at. I am not looking to go as low as possible and want to avoid searing from the venting not being a good freq to work with on my drivers.Using one of the box calumniator spread sheets available online to get a rough idea witch is a bit new to me> I believe it the one Jeff Baglby has online. Fivetide I think I will be able to relate to the pain of paying the VAT sure I will have to order the ATC mid-ranges from the U.K may have slim pickings in the U.S as far as supply goes for them.Thinking once I get things together and finish cabinet build I can use the Dayton Dats V2 to get actual measurements after installing the drivers I can import them into the excel spread sheet crossover calculator from Jeff's site and hop onto the crossovers That is the software I have been using to get an idea of things before the build. Cheers guys and thank you for your input.
 
Well if I'm going through the cost for the other parts spending a little more for better cabinets is well worth it to me. The original plan was plywood and somewhere down the way I got the idea that MDF would have less of a sonic signature and take less away but sounds like good quality birch plywood is the way I am heading. Will check on suppliers in my area. The active crossover tri amp sounds nice but will go high order passive for now. I just laid out a bunch of money 2 months ago on a Mark Levinson 334 and love it. Does a hell of a job driving my upgraded Ked Q75's witch drives a point home about parts quality and manufactures cost cutting and the effects on the sound. I re worked the cross overs with Mundorf Evo Oils using point to point connections with solid 14 gauge silver for the jumper connections between the components and a little better internal wiring(audio quest X2 I get cheap through work and what a difference! so I can certainly believe the big manufactures choice of MDF for cost cutting leads to like results.Just kinda going through the plan here to make sure I am heading in the right direction with my first DIY build. Been using the net and The Loudspeaker Cookbook as my sources of info. Appreciate the input guys . Hopefully in the next few days I can get some line drawings together for the cabs and some more things worked out. Planning on ordering the Dayton Dats V2 software this weekend. It looks nice because I can connect the drivers directly to my pc without a microphone and get measurements so the acoustics of my room getting in the way being I don't have an anechoic chamber to work with. Thanks and cheers
 

srinath

Member
2010-02-12 4:09 pm
Why MDF bracing ? I braced an MDF box with wood recently. I had MDF sitting around, but didn't use that. Well My thought was that, MDF is very heavy, much heavier than Plywood, which itself is heavier than wood. The box would have weighed a ton. Far worse than it already is. LOL.
IMHO weight is best to add as weight to the bottom, by putting in bags of sand if needed, and also as wool stuffing. I have so much stuffing in this thing, its ridiculous.

Cool.
Srinath.
 
MDF bracing because it is always a good idea to use a different material than for the box.

Everywhere ply and MDF meet you have a lossy impedance mismatch and as planet10 points out MDF in itself is a 'lossy' (soft) material making it an ideal and cheap candidate. Using a different material for the bracing makes the bracing more effective as Tannoy, B&W and KEF have found out nearly 30 years ago. Basically you are adding a form of damping to the bracing effect which you wouldn't get if you were to use the same material for box and bracing.
 
I must digress...

Hi,

IMHO there are two simple facts :

1) Plywood is much nicer to work with

on point 1) I think sreten is to the point. But in this case remember we are considering BB ply (or equivalent) which are multiple very thin layers glued together under heat and pressure, and if purchasing true to BB plywood specifications, is void free. someplace I have the 30-70 page specification book regarding the stringent specifications to allow the use of the term "baltic birch".


, 2) MDF is the most cost effective.

The rest is all politics and personal bias. Neither is technically a bad choice.

rgds, sreten.

On point 2, I disagree that "the rest is politics and opinion". Yes MDF is cheaper. And if treated in an appropriate manner can sound good (look a Vince Bruzzese and Totem Acoustics for an example of how to use MDF in an appropriate manner). But baltic Birch has been specified by some manufacturers (those making BBC monitors, JBL Pro and others) as the preferred choice. Good construction techniques are a must for any enclosures (except perhaps the simplest diy builds) where substantial internal pressures occur. The best way is to use mitre-locked joints, but few diy types have the machinery to do a proper job on these. Other ways are to use good glue/mechanical joining techniques such as biscuits, etc. Of course simple joints glued and clamped together (or glued and screwed) together while allowing adequate time is generally adequate as well, and is easy to implement. So the material and construction techniques should be thought as a system.

As chrisb states (or was it dave?), arguments concerning which is better can go on forever. But if you are planning a build using premium parts, why not spend a small percentage more on better (easier to machine, less toxic, etc.) materials. The enclosures are simply the largest single component in a loudspeaker build.

I followed the development of B&W's "matrix" systems fairly closely and still lust after the DM1600(?) low density matrix monitors. I've come to the conclusion that due to the requirements for good enclosure bracing in all but a few designs that rely on a "lossy" cabinet, in the future any enclosure I build will be a space frame design. basically a box made of 1" X 2" (or larger dimensional) hardwood and then attach the outer walls to that. Then a brace from the from baffle to the rear, and a brace from the side to the other side. this could be done with a similar box as the top and bottom "frames" with an "X" brace inserted. Any lightweight non-permeable stiff material could be used for the walls then, like maybe Ciba-Geigy's Aerolam sheet material (as used in the Celestion SL600 and SL700 loudspeakers) if I could get some. Even somewhat flexible thin BB ply (if fastened and supported adequately). So it is not just the material, but the material and construction technique that must be looked at as a construction system.

I do need to disclose that I am a fan of Dave and Chris and their efforts at planet10-hifi, but I have never heard a loudspeaker that they have built that I would not or could not live with myself.

Besides typical enclosed loudspeakers, the cabinet materials can be completely minimized if using an OB speaker, but I would still use quality materials. A local audio buddy has a pair of the Dick Oshler designed "Basszillas. These are considered to be "budget" OBs, but my friend has built solid wood bass enclosure and solid pine OBs. And I've used BB ply to very good effect in my copy of the Tube Kingdom OB's as promoted by Joseph Esmilla, even though it may not be necessary. With a little creative layout I built them with just a single sheet of birch ply (in this case I used void free, cabinet quality birch ply). I better end before I i run out of digital "ink".