Hi everyone, Dennis Foley from Acoustic Fields. Today we're going to talk about diffusion
versus sound redirection -- completely different principles, completely different sound and
much confusion about this. A lot of sound redirectional devices in the marketplace are
called sound diffusers and it's simply not true and let's find out why. Let's look at
some definitions first. 5 conditions in a room before you have a diffused sound field.
There are 5 clearly defined conditions that must be present in your room before you can
actually say you have a diffused sound field within your room. 99.9% of the rooms I'm in,
not there, missing 1 or 2 or 3 of these 5 things and we'll get into those shortly.
Sound redirection, let's define that. Redirection is sound energy striking a surface and then
reflecting back in the opposite direction. Angle of incident equals angle or refraction
or reflection; not the same principle, not the same end result in a room, definitely
not contributing in a few situation and in many situations sometimes to a diffused sound
field in a room. Let's look at the 5 conditions that we must have present in our room in order
to call our room a diffused sound field situation within our rooms. Let's look at the 5 things
that we need. Let's look at the 5 conditions that must be
present in a room before we can actually say we have good diffusion within our room. We
have what's called a diffused sound field. Let's look at those 5 conditions. The first
one we have no frequency or spatial irregularities in the frequency response. No big peaks, no
big dips, +/- 2db, +/- 1 ½db, nice, tight peaks and toss, smooth, no spatial irregularities.
The second one, the beats in the decay characteristic of our room must be negligible. On a log scale,
and we'll get into that in another video, but it must be of a straight line in a log
scale. We have to have the beats in the decay characteristic negligible, not noticeable
at all. Third, the decays must be exponentially perfect. We can't have big pauses and hiccups
in the curve, so they must be exponentially perfect and we must make sure that that's
the case. The fourth characteristic, the decay characteristics must be the same every place
in the room, and have one room with a higher decay or lower decay rate than the other one
and finally the reverb time. The reverb time must be the same in all parts of the room.
These are the 5 criteria that you must have within your room in order to have what's called
a diffused sound field within your room. How do you get these 5 characteristic? You use
devices that are sound diffusion devices and not sound redirectional devices and let's
look at the differences. Okay, here we have an example of sound diffusion
versus sound redirection. This is our diffuser QRD series 7 based on prime #7, so we'll use
that as our prop here. We've all seen these sound direction devices. They're hemispherically
shaped, they're half rounds, there are tubes, there are things along that line that they
have this. Sound energy comes in at a certain angle, leaves at the opposite angle. That's
the function, that's how they work. We know that a sound diffuser works completely different.
It has a series of wells or troughs, different frequencies, the energy enters the wells,
comes out in a fan-like array, not reduced in time or amplitude; completely different
approach, really true sound diffusion and that's what we really need to have to contribute
to those characteristic. A sound redirectional device when they're put next to each other
in a room, really don't have a lot of diffusion or a lot of sound redirection even below 300
cycles. They're limited in bandwidth, so to speak, and also just the basic way they perform
is limiting. It's difficult with a sound redirectional device to get a true diffused sound field
in your room because of just the nature of the elements. Manufacturers call them sound
diffusers because they want you to believe that they have a diffuser in their product
line and technically they don't because it can't satisfy those 5 conditions that we went
over. Let me see if I can kind of put this to the
side and let's look at no frequency or spatial irregularities. Would a sound redirectional
device accomplish that? Maybe, but since it doesn't work really well below 300 cycles,
we probably would have some issues in that ring. Beats in decay characteristic negligible;
well if there's a spatial irregularity in the frequency response of the unit itself,
you're going to have difficulties with that. You're going to have difficulties having an
exponentially same decay rate. Reverb time and decay characteristics in the room must
be met and the device must be able to contribute to that.
The only diffusion device that we have found that really works well is the quadratic diffuser
because it can provide you with diffusion in 2 dimensions -- a vertically positioned
diffuser can diffuse sound in a horizontal dimension and a horizontally positioned diffuser
can diffuse sound in a vertical direction. You really can get 2 of possible 3 dimensions
of sound with 1 device. For us, as designers and builders and acoustic people that are
trying to create certain things inside of the room, it's a great tool because it's so
versatile. You can even choose the frequency response.
Thank you.