Hi everyone Dennis Foley from Acoustic Fields.
Today I want to focus on the room and the noise if you will that the room
makes. Our rooms contribute over fifty percent of what we hear
inside of them, so it's important to understand just what their contribution
is to the sound that we're hearing in the room.
It's always that balance between direct
and reflected energies but
all that energy in a box, the room, produces distortions and today I want to
focus on the four
main distortions that our rooms cause.
First one is room modes. These are the high and low pressure areas as a result
of
long wavelengths, low frequency energy not fitting into our smaller rooms.
SBIE, Speaker Boundary Interference Effect. This is the
distortion that's caused between the speakers in our room
and the surfaces of our room, so we need to be
cognizant of those issues. Comb Filter,
a series of reflections between two surfaces that looks like a comb
the teeth of a comb on a graph, so this is why it gets its name.
And then finally poor diffusion, probably the most
misunderstood and just not understood at all
concept in room acoustics and it's so very, very important.
It's the sound we want to get
but don't have because of our room. So today we're going to elaborate on each of
these four
and give you a little bit more information on each one to help you
understand their impact and effect.
Okay
Our first room distortion that we want to focus on is room modes.
These are those high and low pressure areas in our room, and they're caused
by long wavelengths, low frequency energy, that simply doesn't want to fit
correctly inside of our room. A 30 cycle wave 37 foot long
20 foot longest dimension of a room,
some is gonna fit, some is not. So some will go through the wall,
a lot will go through the wall, and some will be reflected back into the room and
contained within the room.
It's this energy that we need to focus on because it's this energy that creates
the pressure areas.
If we look at this pressure map
you can see that the
pressure areas are everywhere throughout the room and
these are pressure areas that we need to be aware of because they can
mask, smother and blur, certain frequencies that
are present within them so to speak. So we really need to be careful of those
pressure areas and how they interact
with what we're trying to accomplish. There's ways to reduce them, there's
technologies that we can use to reduce them.
First you have to find out where they are in the room and then you have to
apply the correct treatment.
So room modes, first type of room acoustic distortion that must be dealt with
and we do have the technologies to deal with it but location is
critical and then magnitude; defining how big they are so we can assign the proper
technology to absorb it.
Our second room distortion that we want to look at
has a long name SBIE
which stands for Speaker Boundary Interference Effect, so it's an acronym
for
the issues that go on
between our speakers and our room
boundary surfaces. These can be all kinds of issues
they can produce comb filters which we will discuss in
the next room distortion. We can also look at pressure areas created by low
frequency energy that gets
trapped and built up in these areas. So the distance from the speaker or sound
generating
device or source to the room boundary surface
has a huge impact on what you hear. If you want to test this out
it's really easy all you have to do is measure the rooms frequency response
when you have your speakers set up in a certain position
and then just go ahead and move your speakers maybe a foot forward
more towards the center of the room and look at the
frequency response of the room now and you'll see a big difference.
So there's a lot of energy in this area
and it also always needs to be controlled with the proper acoustic
technology.
And this energy that's trapped between a speaker and the room boundary surfaces
can also be the ceiling and the floor. Produces what we call phantom images so
kinda has a sound if you will of its own.
Now it's not audible, I mean it is audible but it
and it doesn't sound like a speaker but it has a particular coloration and
quality to it
because when it's not there and treated correctly you can definitely hear the
difference.
So speaker boundary interference effect that the
distortion if you will that occurs between the speaker
and your room boundary surface so we need to be aware of those issues also.
Okay, our third room distortion
that we want to talk about in regards to
rooms and the noise if you will, that they produce,
it's something called the comb filter. A comb filter is a series of reflections
back and forth, back and forth, back and forth, between two
opposing surfaces. So
if we take our speakers here and we look at
left and right channel we can notice that energy from a speaker is always
radiated out of the cabinet
front, sides, rear especially with the lower frequencies, omni directional
out of the speaker.
Mid's and the highs pretty much out at the front but
low frequency energy out of this and of course
we have our side wall reflections with middles and highs. But its this back and
forth
trapping if you will of energy that creates another
phantom image situation as similar to speaker boundary interference effect
that we just discussed.
So all of these areas are
trapped energy and noise if you will
in and of and by themselves probably not too big a deal
but its the accumulation
of a lot up these little issues that add up to a big
room distortion issue in your playback in
and recording environment. So we want to be a little bit anal and address all
these little issues so that they don't add up to
be a big issue.
Another area
that's completely misunderstood and overlooked is diffusion.
I think people just don't understand diffusion, they don't understand how to
apply it
but it's really necessary in all our small rooms and even larger room
environments.
Diffused sound energy
is present in free space or outside if you will.
There's objects everywhere, there's the Earth, there's trees, there's
buildings, everything is diffused. Energy is bouncing everywhere
and our brain and ears
are trying to localize all this energy and does a pretty good job of it.
When we take that outside world and we shrink it down into a room, or a small
box,
we change all the physics. We change all the physics of our ear
so we we have to compensate for
going from an outside large environment,
that's really diffused in terms of Sound Energy,
into a small box with small dimensions
and restricted
distances for frequencies to travel.
People just don't understand the power of diffusion and what it can do in
a room.
It can do many, many things. One of the things it can do is it can add separation
to your instruments and vocals because if you're talking outside to three or
four people,
five feet away, they're able to understand all your words and
hear everything intelligent intelligently hopefully
and acoustically but when you get into a small room you have
early late and direct Sound Energy's impacting upon the listening
environment. So
you need to create an environment that has difusion in it and one of the ways to
do that is
is with diffusion technology. Separation,
definition, definition is another thing that it will do for you
and it helps define the
the mid-range area quite nicely, and it also adds what we call
air or spaciousness. So diffusion, and we like to use quadratic diffusion because
it's predictable and consistent,
you can actually choose the frequency response you wish to defuse
and this is really helpful in certain rooms depending on usage. So
I'm gonna show you a diffuser
and we'll talk a little bit about quadratic diffusion.
This is our
our DIY diffuser kit. This diffusion sequence is based on the prime number
seven
we will be offering this shortly on our web site. It's a kit that you actually build
yourself. It's very easy all you need is glue and a little bit of masking tape to
hold the pieces together while they dry. We finish each piece for you, we cut it
to fit in and and you can watch the videos on that
and how to assemble it. We'll have three sequences for you right out of the
gate shortly
3 kits, one based on prime 7, one based on prime 11 and one based on prime 13.
Just a little bit as the numbers go up the
the diffuser gets wider, the wells get deeper the diffusion frequencies get a
little bit
more involved. So you're gonna have three to pick from but
this is a quadratic diffuser and and four these across the back wall
in a recording studio or control room, amazing what it will do to the rear wall
that bounce back, you won't even believe there's a rear wall there.
Front and rear wall in listening environments, oh my gosh it just opens up
the
presentation, there's definition and separation, there's all kinds of
good things that go on with the diffusion. So
diffusion is not that hard if you have the right kind of tool and quadratic diffusion
is a really, really good tool because it's predictable and consistent
and now in kit form you can just buy it and
assemble it in your studio or home and have a
finished unit and then using three or four five units
positioned in your room, you you can achieve a nice diffused soundfield in
your room.