Why MDF so Bad???

An all wood rack can be both a thing of beauty and sonically excellent in my experience. I would stick to using 2 x 2's or "mega duty" dowel rods ( rails ) for the frame and risers and then use suspended shelves resting across the support rails. Stick with wood that is lightweight but offers a high degree of internal damping when it comes to shelves. Added mass ( the thicker you go, the more mass you have ) is noticeably poorer sounding when it comes to shelving in my experience. This definitely hurts "prat" and bass definition.

Another factor in such a design is that the shelves should NOT be a stressed member of the frame ( if at all possible ). In other words, the rack should stand on its' own in rock solid shape without the shelves being in place. You also want to keep the rack open ( no closed sides or back ) as this allows far greater ventilation and will affect room acoustics the least. Otherwise, you've got a large reflective surface to deal with. If you want to put the equipment into an enclosed rack, make sure that you have adequate airflow around the amps / other heat generating components and get the rack out of the room. Mounting it into a nearby closet, etc.. would be a good choice. I think that Dekay is doing something like that. This should also help to reduce the amount of airborne vibrations that the equipment has to deal with too.

I went from a "home brew" rack of this nature to a very heavy commercially built rack in one of my systems. The commercially built rack used two sheets of .75" MDF sandwiched together for each shelf. These 1.5" shelves were then coated with some type of poly for cosmetics / protection by the manufacturer. The difference in sonics between these two racks was astounding. In effect, it was one of the worst mistakes i had ever made but it did teach me a BIG lesson i.e. bigger is not always better, things that cost more are not always better and things that you don't think have that much effect on the sound really do.

Learn from our mistakes and do some digging in the archives both here and at AA. It's a lot cheaper that way and you'll probably end up with better performance. I think that you'll find that most people that have tinkered with multiple racks and have greater experience in this area are shying away from what you are thinking about having built. If you look at a rack as more a piece of your system in terms of tuning & resonances rather than being a piece of furniture that you can stack your equipment on, you'll probably have a better idea of the why's and how's of what works best. Sean
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Just a comment about MDF in speaker boxes: It's used so much because it's readily available, cheap, easily machined, assembled, and veneered, and has moderately good internal damping. That said, there are VASTLY better materials for cabinet construction, and the best ones are virtually NEVER used because the cost is so high (not just the materials costs, but the cost to the manufacturer of the learning curve that is required to use them properly). So MDF is probably here to stay, limited as it is.

Sean, interesting report on the thick MDF rack. It makes me wonder whether really thick shelves, say 4" to 6", would be better or worse. The stiffness goes up a lot faster than the mass. It may be that 1.5" MDF just isn't enough, especially for heavy components.

Oh, I forgot! I'm also getting some 2 inch thick maple shelves (they are actually made of one piece of maple, like the mapleshade). I guess the maple shelves will go on top the the MDF shelves and I will be using some cones or points to separate the maple shelves from the mdf base shelves...

In this rack, the MDF shelves are only used as a bracing for the rack and as a support to the maple shelves... The back of the rack will be fully opened...

The only thing I am worried about is reflection. Since the sidewalls are closed, I will probably end up with some sound reflection... I was thinking of putting the rack between the speakers but I have pair of Verity audio Fidelios which has rear firing woofers (I have no other place to put the rack)...

Sean (and everybody else for that matter), do you thinks I'm better putting the rack directly in the middle of the 2 speakers or leaving the rack a bit behind the speakers...

Worse comes to worse, the rack will become a nice plant table in my office :-)

thanks again

do you think I'm better putting the rack directly in the middle of the 2 speakers or leaving the rack a bit behind the speakers...

I would think that the rack placed somewhat behind the speakers is the more typical approach, but with the rear firing woofers you might find it works better otherwise. However when placed directly between speakers, staging may be degraded.

Karls: The tests that i've seen on speaker cabinets shows that going from .75" to 1.5" does reduce resonance and ringing, but not by what one would think. When one gets up to 2.25" to 3", the differences really come into play. As such, your idea about "super thick" shelves may have some validity but i'm not about to try it out myself : ) Personally, i've had much better luck with relatively low mass yet rigid wood that offers good internal damping. The shelves on the other "double thick" rack weighed something like 23 lbs apiece whereas my current shelves clock in at about 4 - 5 lbs each. The other rack also had the shelves acting as part of the support structure whereas these shelves are free-floating. I think that these are the two major differences in what i'm hearing / experiencing.

Lgregior: I basically agree with what Bob had to say. If you can get the rack behind the speakers, that would work much better than having it on the same plane. If you can get the rack far enough back so that the rear of both speakers is visible when looking from the side with no interference from the rack, you should be pretty good in terms of soundstage, imaging, etc... As far as the woofers pushing air / vibrating all of the gear situated behind them, that may be another story. Moving the rack to another part of the country might reduce this, but the cables would have to be awfully long : ) Sean
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