Spaciousness: The Final Frontier

Published On: June 26, 2020Tags:

Spaciousness is the Key to Making a Space Sound Big…

…said the Senior Chief CEO of Seniority at the Department of Redundancy Department.

But, how to make a small space sound big? In a word: ambience. This week we dive deeper into the answer while explaining how diffusion creates ambience, and tell you about our preferred type of diffuser. With an “e.”

One of our favorite toys for visualizing sound is the ripple tank. When lights are shone from underneath onto a ceiling-mounted projector screen, compelling acoustics/wave physics thesis presentations can be made.  Art Noxon wrote his Masters Thesis on this very topic.

These days, we use modern digital technology to have our fun and have found no better collection of tools in this vein than those created by the folks at In the above screen shot, we have a pair of point source speakers and a blue listening chair, with four poly diffusers on each side wall. Notice the expanding reflections enveloping the listening chair.

To see the animated version of spacious diffusion shown above, see the code at the bottom of this email to paste into the ripple tank applet.

What Exactly is Ambience?

Ambience is a time delayed diffuse condition of upper treble sound that is uniformly distributed throughout the room. Here ambience is depicted as sound going in many directions at one time, everywhere throughout the room.

The phrase “diffuse sound” has become commercialized. True diffuser panels scatter higher frequency sound. While skyline/phase grating type diffusers have become quite ubiquitous, the classic diffuser is the “poly,” short for polycylindrical diffuser. They are typically about 4 feet wide and easily 12 feet tall, and are found in the live rooms of old school recording studios, concert halls, and auditoriums. A “poly” scatters sound sideways but not vertically.

Why Horizontal and not Vertical? 3D is Better than 2D, Right?

Listeners hear lateral diffusion much better than vertical diffusion because of where our ears are located: on each side of our head. This is why a vertical poly is a good diffuser. Like most aspects of the human body, our built-in “stereo pair” is built primarily to respond to lateral movement and changes. Gravity keeps us, to a large degree, on a lateral plane, and most of our time is spent moving sideways. Thus, lateral sensitivities are strongest.

Specular Diffusion? Isn’t that an Oxymoron?

In the world of optics, the terms specular and diffuse are opposites. The former indicates a “hard” reflection where the angle of reflection equals the angle of incidence and almost no energy is lost, like a bathroom mirror. The latter indicates a “soft” reflection where the light is reflected at many angles instead of just one, with each reflection containing a portion of the original energy. Sound is a little different due to the longer wavelengths.

Many types of diffusers are designed to scramble the timing of the reflections they scatter. This introduces phase shifts that golden ears can hear, and that is not the ASC method. The “poly” is a specular diffuser which means the reflection sounds just like the incident sound, with no time distortion or phase alteration. It is mirror like, wherein the reflection is the same as the object being reflected. The “diffusion” comes from the dissimilarity between the angle of reflection and the angle of incidence; hence the use of the term “scattering.”

The reflected sound of a voice or loudspeaker played at a poly diffuser will seem to soften in energy as the many reflections are sent careening off at various angles. This multitude of reflections then bounce further around the room, losing a small portion of their energy with each bounce. As time passes, the phase and voice of the sounds remain intact while the energy drops, until they reach the ear of the listener as a smooth ambient tail coming from all directions.

Now this is a happy listening room!

How do TubeTraps Play into This?

Every TubeTrap (except a MonitorStand) includes a built-in polycylindrical diffuser. HalfRound TubeTrap use smaller diffusers, and their specular diffusion pattern is shown here.

FullRound TubeTraps, QuarterRound TubeTraps, and of course, StudioTraps all let you scatter sound around the room to provide a smooth ambient tail while also absorbing excess bass. Enjoy!

Read much more about coherent and incoherent diffusion in this article authored by Art Noxon from the 89th AES.

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