Small Room Acoustics ~ Diffusion

[artto]

Diffusion is a property of a sound field.

A perfectly diffuse sound field is isotropic, which means
that at any point (location) within the sound field, sounds may be expected to
arrive from all directions with equal probability. It is homogeneous. In fact,
true diffusion exists only as an academic ideal. In the real world as soon as a
another material such as a chair or person are introduced into the space, it
ceases to be.

In small rooms there is actually not much diffusion present.
This is because of the size of the space. The size of the space physically limits
the critical distance between the sound source and the listener. The critical
distance is defined as the distance from the source at which the direct sound
equals the level of the reverberation. Because the critical distance is shorter,
and the reverberation time for small rooms is shorter, there is simply not
enough time nor surface area, regardless of what it is made of or how it is
treated for the sound to actually diffuse in an isotropic manner before
reaching the listener.

The majority of spaces we have to listen at home are
actually “transitional sound fields”, “there is still a perceptible transition
that occurs as a function of distance” This transitional sound field is more
related to the ratio of direct to
early-reflected sound and to the extent to which laterally reflected sounds,
especially, contribute to the perception of apparent source width, image
broadening, frontal spaciousness, and so on. (Toole, 2008)

All of the other acoustical measures employed in evaluating
performance (size) spaces such as early/late-decay rates, energy ratios,
lateral fractions and others having to do with impressions of articulation,
direction, image size, apparent source width, and spaciousness, so far as the
performance of the listening space itself is concerned, these are more
traditional acoustic measures that find themselves in the wrong place (in small
rooms). (Toole, 2008)

The numbers produced by traditional acoustical predictions
and measurements, while not totally irrelevant, are simply not direct answers
to the important questions in small rooms used for sound reproduction.

All of this leads to the fact that it is the small room itself
that is not diffusive. Or rather shall we say, not capable of being truly
diffusive.

Toole asks “What then are the important questions?” He says
they have to do with reflections, but not in a bulk, statistical sense. The
knowledge base must include the directivity and off-axis frequency response of
loudspeakers and the directional reflective, diffusive, and absorptive
characteristics of materials at the points of first reflection.

He goes on to say that “diffusion can be improved by using sound-scattering devices, irregular,
curved and angled surfaces, and especially designed devices, often called diffusors. Perceptually, a diffuse sound
field sounds spacious and enveloping.”

Quadratic Residue Diffusors are one of those “especially
designed devices”. They can be of benefit in certain applications, especially
where space is limited, like recording studios, and home listening rooms.
However be aware that as design bandwidth increases, so does the size and
complexity of the QRD.

Here is a link to QRDude, a Quadratic Residue Diffusor
calculator which will make designing and building your own QRD much easier and
faster.

http://www.subwoofer-builder.com/qrdude.htm

[Groomlakearea51]

"He goes on to say that “diffusion can be improved by using sound-scattering devices, irregular, curved and angled surfaces, and especially designed devices, often called diffusors. Perceptually, a diffuse sound field sounds spacious and enveloping."

That would be true; and is the basis for small room treatment methods, materials and techniques. [Y]

[H]

[KdAgain]

"He goes on to say that “diffusion can be improved by using sound-scattering devices, irregular, curved and angled surfaces, and especially designed devices, often called diffusors. Perceptually, a diffuse sound field sounds spacious and enveloping."

That would be true; and is the basis for small room treatment methods, materials and techniques.

Most of the forums on small room acoustics that I periodically check out refer to absorption, not diffusion. Most of the photos which are supposed to represent well treated rooms show primarily absorption. Artto is one of the few exceptions to this. For several years now I have read with great interest of his techniques and results. I only wish I lived closer to him - I would certainly beg a listen!

I have also wondered if Klipschorns (which I own) need different treatment considerations than most speakers? I have come to somewhat of a conclusion that in a typical room that a combination of absorption, diffusion, and heavy bass trapping is perhaps the best answer. But how to learn to implement all of that is my dilemna!

Rod

[Colin]

Do you really wnat to psread sound out in a small room? Won't it simply continue to reflect off the walls? Isn't absorption more effective?

[artto]

Do you really wnat to psread sound out in a small room? Won't it simply continue to reflect off the walls? Isn't absorption more effective?

No. A room with good and proper diffusion will actually sound "larger" than what is actually is without getting that "dead" quality.

[SSnyder]

is there a originil problem to soluton for or is this simple gobbildeegoock

[artto]

is there a originil problem to soluton for or is this simple gobbildeegoock

If you have no idea or don't care about how a room affects the sound produced by the speakers, musical instruments or voice, then it's simple "gobbildeegoock".

[SSnyder]

Just obvios that a small room sound like small room not a big room>>>>>do not need be a genious to tell that

[jacksonbart]

I think spelling the simple words helps otherwise you create diffusion

[Rudy81]

I have a large quadratic diffuser along the rear wall of my media room. Together with the hf absorption for primary reflections and large bass traps I get a really nice sound field.

Paying attention to and working on room acoustics just made all my other improvements that much better. I have spent many years messing with room treatments and finally have a solution that works very well in my room.

If you have a dedicated listening room, spending time and money on room treatments is a must if you are searching for the best possible sound experience.

[Colin]

right, diffuse, not deaden

not confused anymore