MDF STC ratings please?

MDF STC ratings please? I have not been able to log in for ages, (my fault) anyway, I have searched here far and wide and goggled but I can’t find and sound proofing ratings for MDF (medium density board). Any leads would be greatly appreciated. Thanks in advance. :D P.S I have ordered John Sayers book and can’t wait to read it. :wink: :idea: Extra info’ I have decided to go four A two leaf system for my walls comprised of two layers of Fibre/partial board and two layers of MDF on the inside of my extension for my studio.

John has a book ? :roll: Hai and re-welcome ;) 'bout MDF. It's about the same weight/density as Gypsum/plaster-Board.

Ro wrote:

John has a book ? :roll: Hai and re-welcome ;) 'bout MDF. It's about the same weight/density as GypsumBoard.

External image, not preserved — original: http://www.klusidee.nl/Forum/afb/topic11664/stc.gif

Thanks mate I really appreciate that :D

the differences between MDF and drywall are mostly cost, weight, and stiffness. MDF is generally a bit heavier than drywall here in Fargo, thickness for thickness (i usually buy MDF at Home Depot), and costs 2-3 times more per pound. MDF has the advantage of strength, its really flat, holds screws, etc., and the disadvantages of higher $$$/pound and higher stiffness. The higher stiffness results in a situation where MDF will have a lower critical frequency than drywall for a given thickness/weight. This means the coincidence dip will happen at a lower freq for MDF. To summarize my ramblings, I simply submit to anybody debating between the two that if you don't need the screw holding or strength of a wood product, drywall is always the best choice because its less $$$/lb.

Brian, higher stiffness should create a higher resonance frequency...I seem to remember the equation for simple resonance being: omega = sqrt(stiffness/mass) Or do you mean something different by 'critical frequency'... I've always heard that 24" spacing of studs has better low frequency TL than 16", but the reason eludes me since the 16" spacings make a stiffer wall that is will only want to resonate at higher frequencies. Perhaps the 24" spacings act somewhat like a bass trap allowing the wall to vibrate, but disipating that vibration in the insulation. Cheers Kris

Hi Kris, I believe it comes down to mass... the larger the mass (MDF being heavier) the lower the resonant frequency. Regards, Dave.

for low-frequency panel resonances, a stiffer panel will drive resonance frequency up. But for the high frequency coincidence dip, the opposite occurs. The defining characteristic for a simple panel (not a double leaf wall, which is more complex) is mass, and the behavior of a simple panel is very nicely predicted by Insul software (though that software has limits when predicting double leaf walls). You can model (may have to convert to metric) drywall panels and MDF panels (at least the grade of MDF for sale here) with these properties: drywall --flexural modulus = ~370,000 psi for normal types and 420,000 psi for type X board --damping ~0.006 --density ~650 kg/m^3 MDF ---density ~720 kg/m^3 ---damping ~0.015 ---flexural modulus ~700,000 psi

Ah, so the stiffnes of the panel offsets some of the mass... interesting. Thanks for the information. Dave.

Well thanks to all again. I will have to read this a few times to absorb the information here (pun intended). :D Thanks for all the great information guys :D Yea, my extension for my studio is two layers of floorboard (glued with normal glue) and two layers of MDF sheets on the inside with glass batts compressed within. I know now that I should have made two rows for the studs (the bits of timber that holds the walls up.) but it is kind of too late now. I figure that if the STC is not great enough, I may insert pipes to allow the pressure to escape thereby achieve equilibrium though the roof so a can lay another wall in front of the existing wall without the dreaded third leaf appearing. :idea: Hey I might post that as a possible solution for others to read.

hey again all, ek well, the primary low-freq resonance of a decoupled wall like RC or double studs isn't affected much by panel stiffness. its the weight of the panels that is important there. but resonances in the panels themselves are driven up by stiffness, except this coincidence phenomenon, which lowers in frequency from a stiffer panel (or, more accurately, a panel with higher stiffness/weight)

I appreciate your feedback guys. :D I am a little slow to respond (had troubles logging on) :oops: