Did you know that in the majority of listening rooms there is more reflected sound energy entering your ear holes than direct sound from the speakers?

‍By reflected sound, I mean sound waves that go in directions other than a straight line from  your speakers to your ears. Sounds bounce off walls, ceilings, floors, furniture, or your belt buckle one or more times. They eventually pass your head later in time, and from a different direction than the original wavefront from your speakers. Your ear-brain system has to untangle the original wavefront from the reflection "ghosts" that emanate from all directions around your noggin to somehow make musical sense out of all this. Amazing, right?

Fortunately, we humans come equipped with a form of spherical echo canceling that allows us to differentiate all these sound images and pick the first arriving one as the real deal - as long as the reflections aren’t more than 10 dB louder.

This process takes brainpower. Your brain consumes about 20% of your body's energy and when it gets fatigued your whole body gets tired. So, the last thing you want while you're mixing a track, or listening to your favorite post-industrial grunge rock opera, is to apply more brainpower to just listening!

To clean things up a bit, you want to reduce the amount of free-floating reflections. Absorb some of them, then bust up the rest into smaller pieces by scattering them. The idea is to generally organize the shape and direction of the reflected sound so that it works in concert with your speakers, not against them.

‍How do you figure all this out?  Research shows most humans prefer a similar, predictable reflected sound character based on the size of the room! Work done about 30 years ago by some of the world’s top psycho-acousticians shows a strong statistical relationship between a room’s size and the specific amount of reflected sound that make most audiophiles and professional sound engineers go, "Ahhh…"

The work was done by placing individuals in many different room configurations, listening to many types of music. They were asked to judge the quality of what they were hearing. It’s like going to the optometrist and being asked, “Do you see better with lens A or B?” Out of all this profound work came a specific recipe that correlates sound reflection decay to room volume. It looks like this (sorry in advance):  Target Reflection Decay Time =0.3*(Volume in ft3/3532)1/3 . You can always just hit the“buy button.” The boss says we need an example, so let's take a room that is 22’x17.84’x9’. Multiply those three to get a volume of 3532 ft3, resulting in a target decay time of 0.3*3532/3532=0.3 seconds. The sound from your speakers in that size room should bounce around and fully die out after about 0.3 seconds. But you’re not done yet.

The next step is to plug this into an equation that will take your room surfaces and determine how much to cover with absorber panels to achieve 0.3 seconds. Hurts, don’t it? A Spanish acoustician called Arau-Puchades came up with a long-overdue improvement to the original 1930s calculations by the infamous Sabine (as in Wallace, not the female Mandalorian warrior):

Where:

• V is volume
• S is total room surface area
• α is area-weighted averaged absorption coefficient for each wall
• x is area of left+right walls
• y is area of front+ rear walls
• z is area of floor + ceiling

Bottom line? We've run this analysis over 1,000 times for our expensive room acoustics projects and figured out this basic recipe: If you cover about 15~20% of the wall and ceiling area with absorption, and assume that your floor has at least a reasonably good-sized area rug, you will find the calculated decay time lands right on the target of 0.3 seconds!

In all seriousness folks, that 15~20% absorption coverage is all you need (besides love). You may have expected or seen 50% coverage or more, but something bad happens if you overdo absorbers. The room won’t feel right and will sound like a loaf of wheat bread is on your head. Face facts, folks: The human ear-brain system has come to expect a reasonable amount of reflected energy in a room. If you eliminate too much of it, the music is no longer believable. On the other hand, if you underdamp the room, it will interfere with the clarity of your speakers. You will again not be happy. Just target the appropriate reflection decay time - or follow our shortcut called the “buy button.” Either way, you will like the results.

So what do you do with the remaining 85% of the room? Here again, experts agree that about 15~20%added coverage with scattering devices (a.k.a. diffusers) breaks up a fair amount of the residual specular reflections and smoothes out the reflected field into a more even decay pattern (Rehearse that last line to impress your friends.)

These scattering panels can actually make sound field appear much larger to your ear-brain and eliminate the sense of walls surrounding you- leaving you with the ability to transport yourself to Carnegie Hall, Vienna Philharmonic Hall, The Village Vanguard, or outer space.  Now go splash cold water on your face forgetting all the way through this.

By now it should be obvious that we love to talk about this stuff and help our customers get results, so drop us a line at help@sonitususa.com

Or call 1-800-497-2087 and ask for Anthony.