(Back to Newsletters and Press Releases)

RealTraps News: Lossy Walls, Artifact Detroit
RealTraps acoustics expert Ethan Winer busts the myth that "lossy" non-rigid walls are bad for acoustics, plus another fabulous RealTraps professional studio installation.

Many people believe that for the best bass response, a room should have massive rigid walls that don't allow any of the sound to escape. But that type of construction is useful mainly for sound isolation between rooms and to the outside, not sound quality within a room. In truth, rigid reflecting walls create response peaks and nulls, as well as modal ringing that extends decay times. So lossy walls that "leak" sound through them actually give better results inside the room because the reflections are made weaker. Lossy walls are especially helpful at bass frequencies where the response and ringing are most difficult to tame.

The popular Room EQ Wizard (REW) software includes a Room Simulation utility that calculates the frequency response for any location in a room based on multiple parameters including the amount of absorption by the walls, floor, and ceiling. A wall that absorbs 10 percent of the sound affects the room's acoustics exactly the same as a wall that "leaks" 10 percent through it. The main purpose of the Room Simulation tool is to find good starting locations for the loudspeakers, before measuring to finalize their placements. But it's also a perfect way to show what happens as walls are made more and more lossy. In Figure 1 below, the "leak amount" for each boundary is set to 0.10 (10 percent) under Surface Absorptions. Figure 2 was set for typical locations of the speakers and prime listening seat.

Figure 1: The Room EQ Wizard Room Simulation tool accepts a room's dimensions, as well as the estimated amount of absorption by each surface.

Figure 2: The next step is to position your speakers and listening position within the room. REW can accommodate up to four subwoofers, though that wasn't needed for these examples.

When this came up in a Facebook audio group, I was surprised to see several people argue that "leaky" walls are best avoided. Even after I explained the logic as clearly as possible, they continued to insist that rigid walls are preferred. Not only for better sound in the room, but some claimed another benefit of rigid walls is that it's easier to predict the modal behavior of rooms being planned but not yet built.

The first graph below in Figure 3 shows the predicted bass response in a typical bedroom size space with the walls and ceiling absorbing 10 percent below 200 Hz. In most rooms the walls and ceiling flex a little at low frequencies, and the energy taken to move them provides a small amount of absorption. So assuming 10 percent absorption is reasonable. The next two graphs in Figures 4 and 5 show the same room with the walls and ceiling set for 30 percent pass-through, then 60 percent pass-through. Note that no room absorbs 60 percent of the bass waves via lossy walls alone. Only bass traps can give that much absorption! But for the purpose of these examples, the response clearly gets better and better as the boundaries leak more of the sound through. And when the starting response is better, you get even better results after adding bass traps. So this busts the main myth that rigid reflecting walls provide better sound inside the room.

Figure 3: With the room's surfaces absorbing only 10 percent of the low frequency energy, the response at low frequencies is far from flat.

Figure 4: Increasing the room's absorption to 30 percent makes a noticeable improvement.

Figure 5: When the room absorbs 60 percent of the low frequency energy, the response is even better.

As for whether lossy walls makes the response less predictable, it's clear in these graphs that the peak and null frequencies barely change as the walls become progressively lossy. It's true that absorption tends to lower the mode frequencies ever so slightly. But as is evident here, that hardly throws mode calculations way off. So that myth is now also busted.

Artifact Detroit

RealTraps recently completed a major upgrade at Artifact Detroit in Bloomfield Hills, MI, a music and sound design partnership co-owned by multi-instrumentalist Les Schefman. Over the years Les has composed and produced music for national clients including Casio, Jeep, Carrie Underwood, Minutemaid, Volkswagen, Ford, La-Z-Boy, Cadillac, and many others. Visit his website linked above to see an amazing amount of very high quality work.

Artifact Detroit in Bloomfield Hills, MI.

RealTraps was founded in 2003 by Ethan Winer and Doug Ferrara, and is now owned and managed by longtime employee Sean Kollar. Sean handles the day-to-day operations at the factory, and Ethan still pitches in to help customers with technical and pre-sales advice by phone and email. Ethan is well known throughout the audio industry for his technical articles in audio and computer magazines, and his popular book The Audio Expert published by Focal Press is now in its second edition. Sean is amazing whether playing the drums or the electric guitar.

General product information: http://realtraps.com/
Contact by email: Ethan Winer
By phone 10:00 am to 5:00 pm eastern time: toll-free 866-RealTraps (866-732-5872, local 860-210-1870)

# # #