Hi everyone, Dennis Foley from acoustic fields.
Today we are gonna talk about absorption coefficient and sabins.
These are 2 forms of measurement that we use for sound absorbing products.
There are guidelines we use when we consider the total amount of absorption inside of a
room.
There are also guidelines we use to measure the absorption power if you will of a particular
technology and a product.
You see these two measurements in the literature quite often so let us explain them and get
some examples of how they work and I think you'll get a handle on what they actually
mean.
They are often misused and mislabeled, so hopefully this will help you get a better
understanding.
Let us deal with absorption coefficient.
To determine the absorption coefficient of a product, which is always expressed in percentages,
you take a sample size and you inject energy against it from the speaker and part of that
energy goes into the technology and the sample size that's being tested, and part of it is
reflected back.
So we have absorption into the product and then we have a percentage of the energy that's
reflected back.
So in the particular sample size, and you always have to look at the sample size in
test results, that absorption coefficient which is expressed in a percentage, is a ratio
of absorbed vs. reflected.
So if it is a 66 percent absorption coefficient, then you know that 60 percent is absorbed
and 40 percent is reflected.
So that's the testing procedure and the interpretation of absorption coefficient which is always
expressed in a percentage.
Now let us look at sabins.
We just discussed absorption coefficient, now let us look at sabins.
Sabins is a smaller domain, we are gonna work with just one square foot when we are talking
about sabins.
So when you see an absorption coefficient data of a particular product expressed in
sabins, you know you are talking about domain or surface area of one square foot.
That's the percentage, the number represents a percentage of absorption in that one square
foot domain.
A value of one is equal to 100 percent absorption in that particular domain.
Of 1 square foot.
So if we have a Sabin value at 50 cycles of 30, we know that in that square foot, we have
30 sabins of absorption going on.
So it is a little bit different than absorption coefficient which is based on a ratio in the
sample size.
This defines the absorption in the technology that's being sampled and tested in a one square
foot domain.
Similar but a little bit different.
You see, some test results that are greater than 1, well, you can say, well, how can you
have more than 100 percent absorption.
Well, you cannot.
But the value to the right of the decimal point is really due to test bias and edge
to fraction errors during the testing procedure, but we do not really consider that to be an
issue.
We know that a value of 1 or anything larger to the right of the decimal point is 100 percent
of absorption.
Another way to think of sabins is okay, if we have at 50 cycles, 77 sabins is our number,
which is very high.
Then you can use as rough estimate in your absorption calculations when you design rooms
you can say to yourself, okay, I have a powerful absorber, that represents 77 square feet of
absorption capacity, at that particular frequency.
So sabins and absorption coefficient, a little different in how they enter sound absorption
data, but both are useful tools in helping you realize the power and the sound absorption
capabilities of 2 different technologies when you are comparing them.
If you are going to compare two products from two different manufacturers, sabins is the
number you want to look at.
That's the max amount of absorption of each technology being sampled.
Thank you.