Why MDF so Bad???

Of course wood, in my book, is MUCH nicer to the eye than the proverbial metal rods, pipes, shafts etc... MDF is a mixed bag of goods, not a priori bad; the thicker IMO the better.

About the rack/shelves: (Not being a specialist, take my comments w/ a grain of salt...)

I think the positive effects that Bob refers to are, that you may have the whole rack (shelves included) being vulnerable to less frequencies on the vertical plane. The rigidity of the rack would restrict vibration on the horizontal plane -- albeit its height looks like it would make it more vulnerable to resonances there.

OTOH, the wood mass may be "friendly" to low-frequency --higher amplitude level resonance. This is important, I think, and can only be addressed at each shelf-to-component level, by either DAMPING (i.e. find s/thing that turns some of the vibrational energy into s/thing else say, heat) or TUNING each component (using cones, pucks, etc that alter the resonant frequency of the component-rack system).

Strange though it may sound, I get better (subjective) results when resonant frequencies are higher than lower -- probably due to the lower amplitude of higher frequencies even though they play well within the critical audible spectrum (lower mid-range...). Whatever.

As Bob implies (I think) start out with components directly on the beautiful wooden rack, maybe putting sources/pre closer to the bottom (less prone to vertical movement) just for starters. Then change around. Take notes. Then play around with devices between component & shelf. If you can, try out a damping device such as Neuance shelf: sit the component on a Neuance, couple the Neuance to your shelf with s/thing rigid (cones?). Jadem6 has been successful(and so have I, copying his epxeriment) using bubble wrap b/ween Neuance and other shelf.

Input on sound & pics appreciated! Cheers

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
>

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.