Natural Science Forum / Physics / Acoustics / July 2005

For starters, young's modulus for iron and steel is about 30 million psi
(3x10^7 pounds per square inch). Aluminum is 10^7.

GPa sounds like gigapascals (10^9 pascals). Pascals and psi are the same
entity (pressure). Likewise for Kg/m^2. It looks like all you have left
to do is to figure out what Hertz is doing there.

Damping, when expressed in percentage, refers to percent of critical
damping (single half-cycle response to an impulse).

That's all I can relate at the moment.

Angelo Campanella

Pa = N/m^2 = (kg m/(s^2 m^2))= Hz^2 kg/m. Perhaps this definition?

STC = Sound Transmission Class in dB corresponds roughly weighted sound
reduction
Rw defined in  ISO-717-series standard.

I expect that INSUL expects material damping  known also as dissipation
or (internal, material) loss factor (bellow n, usually symbol is Greek eta)

n = 2(C/Ccr) = ln(10^6)/(wn T60) = 2.20/(fn T60)

C = viscous damping coeff. N s/m,
Ccr = critical damping coeff. N s/m,
fn = natural frequency Hz
wn = natural frequency rad/s
T60 = reverberation time s (time within that vibration is damped 60 dB or to
10^-6)

for one degree of vibration systems:
Ccr = 2 sqrt(k m) = 2 m wn
k = spring constant N/m
m = mass kg

For steel n = 0,001...0,006 or 0,1...0,6 % (infinite plates in flexural
vibration)

Kari Pesonen

Your posting is full of misunderstandings.

Modulus has units of force per unit area like pressure.  Pa is such a unit
in the metric system equivalent N/m^2.  However, commonly in metric
countries, units of mass multiplied by the acceleration of gravity are used
instead of force units such as Newtons.  Thus, you get units like
kg-m/(sec^2) instead of N.  From this it looks like you are getting a Hz
into the units but I believe it works out as Kari Pesonen suggests rather
than the units you get.  I do not have access to my copy of INSUL right now
to check just what it says.

Though there may be some relationship, I do not believe Durometer is the
same thing as Young's modulus.

STC is not a measure of damping.  It is a single number rating of the sound
blockage ability of a partition.  It is one of the results that INSUL
provides rather than an iput parameter.  Damping of the material is one of
the input parameters.

The damping you are referring to in percentage is probably that input
parameter which is the actual material damping, that is the true meaning of
damping related to the ability of the material to damp vibrations.  This
influences the sound blockage at the coincidence frequency of the panel.

I think part of your problem is the common misuse of the the term "damping"
to mean various things acoustical such as sound absorption or even sound
blockage, rather than confining its use to the proper meaning.