Hi everyone, Dennis Foley from Acoustic Fields.
Today we're going to talk about barrier technology.
Barrier technology is the technology that keeps sound in the room, and from going out
of the room, and keeps sound out of the room from coming into the room.
There's a lot of misconceptions about barrier technology and it's often confused with the
processes that go on inside the room.
But there are some subtle differences and those subtle differences can cause major issues
when it comes to sound quality.
So let's get back to the basics, 3 things that happen to sound, absorption, diffusion
and reflection, those are the only 3 things.
I don't care what you read, I don't care what others say.
This is what the laws of physics that we currently have to deal with tell us what happens with
sound.
When we deal with barrier technology, which of those 3 is critical?
Which 2 of those 3 is critical?
Is absorption a process that we consider in barrier technology?
Is diffusion a process we consider?
Is reflection a process that we consider?
So we'll address that in the next step.
Thank you.
Alright, let's look at barrier technology in terms of our 3 things that can happen to
sound.
We have absorption, diffusion, and reflection.
What is barrier technology, and how is it used?
If we have a sound source and we have a listener, and we want less energy at the listener, then
we construct what's called a barrier.
The quickest way to stop sound from reaching our individual inside of a house, a building,
or whatever, is to construct a barrier.
We live and work and listen to music in rooms and we're surrounded completely by barriers,
some good, some not so good.
But a barrier is the quickest way to isolate sound between the source and the receiver.
Alright, now with our barrier, which of these 3 technologies apply?
Is it absorption, is it diffusion, or is it reflection?
Well, I think we can rule out this one (Diffusion) right away, because it's mainly not applicable
in this situation.
Diffusion is a term that must be used for sound fields and addressing the distribution
of sound within a room or within an environment, that's not what we're talking about here,
not talking about distribution, we're talking about isolation.
So what are we doing with reflection?
Well sound energy from a source strikes our barrier and what happens?
It's reflected back to the source, partly, and obviously partly goes through the barrier.
So there is some absorption occurring here, and there is some reflection occurring here.
So reflection and absorption are the two main things that we look at for barrier technologies,
and thus the isolation properties that those technologies produce.
Let's put some numbers to barrier technology, and try to get a feel for how the technology
really works.
We discussed reflection and absorption as the 2 main principles when it comes to barrier
technology, so let's look at some definitions and get a handle on it.
One of the terms used for barrier and isolation technology is sound transmission class or
STC.
What is sound transmission class?
It's just a decibel reduction in noise.
So when you see a STC number you know that the barrier technology that that's supplied
to reduces noise by that factor.
Now what does that factor mean?
Let's take a look at that.
First off, the measurements include frequencies from 125 hertz to 4000.
So that's not really low frequencies, it's more upper or more middle frequencies to the
higher frequency range, and this is a criticism a lot of times with sound transmission class,
it really doesn't include a low frequency.
So we really need with barrier technology to look at less than 125 Hz., and any manufacturer
of barrier technology worth his salt if you will, will have data below 125 cycles.
So it's a decibel reduction in noise, and let's site a few examples to help you understand
how that works because it's not linear and it's a little bit difficult to grasp, so let's
put some figures to it to help illustrate the point.
OK let's put some numbers to sound transmission class to get a feel for barrier technology,
and how it's measured and what it means to us in terms of perception of sound.
In terms of loudness if you will.
So a 10dB reduction is perceived as half as loud.
So like I said before it's not linear, it's logarithmic.
A 10% reduction in noise is perceived as being half as loud.
So if our barrier reduces noise levels by 10dB, measured one side versus the other side,
it'll be perceived to the people involved in the structures as half as loud.
If we take 40dB of measured noise in this particular example, and we know that it's
half as loud then as 50dB of measured noise, so just that 10dB difference contributes a
lot to perception and how we hear sound.
An 80dB noise on one side of a barrier measured 50dB on the other side is a 30dB reduction,
so that translates to an STC or sound transmission class rating of 30.
So that will kind of help give you a little bit of idea.
Barrier technology is difficult, it's hard to do.
You have to be very, very careful with the way it's constructed, the arrangements of
the materials, the layers, they're quite important because we're dealing with vibration acoustics,
we're gonna talk about that in our next video on barrier technology.
We're gonna talk about materials and their densities and how to arrange those materials
in the most appropriate way to get the best reduction in noise levels with our barrier
technologies.
Thank you.