Why MDF so Bad???

your experiment is very interesting & I believe that you may be pleasantly surprised by the results. I used a similar rack arrangement for many years & have always liked it. Not sure where your perception that MDF is undesirable came from, but I disagree with that conclusion based upon my own experience. I don't think that you'll need to treat the shelving at all. My shelves weren't even that thick: closer to 5/8" is all that mine were. And the whole thing was assembled from pieces in a Sauder Furniture kit; fastened with steel screws & the shelves sit on adjustable side pegs that plug into a column of holes such that the shelving heights are adjustable. Quite solid & rigid, it doesn't even have spikes which (I'm guessing) may not be very effective for this type of high mass rack anyway. Rather it has casters which are fantastic for rolling away from the wall & accessing the back of equipment for cabling changes or tweaks, but spikes could be installed in place of the casters (I have the spikes on hand, but I love the casters for convenience). It also had smoked glass doors which looked great, but I eventually removed them because I figured that it sounded a little better without them resonating, at least that was my perception. If you're interested in trying this rack it's now available cheap; it is shippable. I only replaced it because it has 7 shelves & I need 10 for my larger system now. It's double wide & even has compartment storage for records or accessories.
So I think that you'll have no problems with your new rack. You might find for certain pieces of equipment that audiophile shelving such as Black Diamond, Zoethecus, Symposium, Neuance, etc. placed atop the MDF shelves still enhances performance. Pods or cones placed between the MDF rack shelf & the audiophile equipment shelf sometimes enhances or even degrades sonics, or has no perceptible effect at all, so experimentation is required. Same applies for cones, footers, etc. placed between the components & the MDF shelf or the audiophile shelf when used. The whole thing responds quite well to these kinds of tweaks. My new larger rack is also made of wood, which I find much more attractive & WAF-friendly than black steel etc. Good luck with your project!

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
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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.