MDF vs PLY (Acoustic properties)

in theory MDF/HDF would be better because its more dense than ply, but it all depends what you want it for...

Simple, inside MDF outside PLY

You would never hear of HIFI cabinets being made of ply.

The BBC did at technical report back in the early 1970s on the pros and cons of chipboard v ply. They concluded ply was the best option because it was available in a greater number of thicknesses. Sonically they didn't find that much difference. The disadvantage of ply is that it also comes in a bigger range of qualities. The bad stuff is worse than chipboard or mdf and the expensive stuff is..... well.... expensive. Contrary to popular belief baltic birch is not the best quality ply by far. Look for Lloyd's certified ply for that. Anyone that uses such ply for loudspeakers (unless it is a custom build for your private yacht) has more money than sense and don't even think about anything but varnish as a finish. An 8 x 4 sheet of 18mm BS1088 Rotary Sapele mahogany faced board is about £180 + VAT. Given this summers weather it might be worth it if you live on a flood plain. It is guaranteed for 25 years.

For PA applications I would go with ply but the particleboard route won't be that disastrous. I am sceptical of the stories of cabinets falling if used in rain. Unless they are stored long term in wet conditions the paint should prevent too much moisture absorption and why don't the paper cones fall to bits too. Didn't one of the old Malcolm Hill PAs have problems with soggy cones many years ago at a monsters of rock festival? I've still got speakers and cases made from chipboard that after several years of use are showing no more signs of wear than the ply cabinets of a similar age.

Mykey's suggestion of ply faced mdf works well but is something I have given up on because of the hassle. It is also possible to use different materials for different panels in the cabinet. If no edges are exposed the surface of particleboard is quite resiliant.

On a slightly different note, has anyone used Wickes structural ply. It is about £22 per sheet and advertised as exterior grade. When I looked at it, it was stamped as class 1 which is for dry conditions, but a scrap that I was able to test didn't de-laminate after spending two weeks in water.

Wehay! MDF lovers unite!

one of the old wicked ones was unpainted mdf and was used outside directly on the floor many times, usually involving dew in the morning, dog pissing on it and beer being spilt onto it.  it had started to get a little fuzzy around the edges but was structurally fine... plus its not that much heavier and does sound better, if painted with comething decent i cant see it being a problem unless the cvab is going to be used for touring all the time...

This question of dropped cabs isn't entirely as clear cut as you might think. The last pair of ply cabs I made were fane 12" dual concentric monitors. I sold them on e-bay and despite loads of packing they didn't arrive safely. Conan the DHL driver had obviously decided to test the cabinet strength........ the cabs passed Conans test but unfortunately the one that he dropped face up the magnet parted company with the rest of the driver.