Designing (And Constructing) Your Reflection-Free Zone

In part three of this series, we looked at the three components of acoustic treatment: acoustic panels, bass traps and diffusors. Now I’m going to show you how to put them to use. First, let’s go over the thing that will instantly improve the sound of any room, regardless of its size: the Reflection-Free Zone (or RFZ).

Creating a RFZ is the most critical step in creating a pleasing listening environment. Simply put, the RFZ is an area surrounding the listening position that absorbs the first reflections from the speakers so that they don’t randomly bounce around the room. The idea is that all you hear is the speakers’ direct sound as a result (see above).

In order to create an RFZ, sit in the listening position and have a helper move a mirror over one of your room’s side walls. Every inch of space you see in the mirror’s reflection of either speaker requires acoustic treatment to tame the reflections. Repeat this from the opposite wall and the ceiling, and you’ve defined your RFZ.

It’s a good idea to treat a larger area of the wall than you identify with the mirror. That way, you’ll be free to move around a little without leaving the Reflection Free Zone. If you’re wondering how the heck to slide a mirror around on the ceiling, try attaching a hand mirror to a broomstick with rubber bands. Just by treating this area alone, you can improve the sound of your room by a surprising amount.

The floor of the RFZ can stay reflective with hardwood (which everyone likes because it’s easy to roll your chair around) as long as the ceiling is absorbent. Even if you have a rug on the floor, you’re still better off to have the ceiling absorbent in the RFZ to eliminate any chance of early reflections from the speakers reflecting back onto the listening position.

The acoustic treatment that you’ll use is several of the acoustic panels that we spoke about in the previous installment of this series. You can easily make enough of these panels yourself to cover the RFZ in a typical room for less than $100 if you’re handy (see this video from The Studio Builder’s Handbook to learn how to build your own), or you can buy them pre-made from companies like Ready Acoustics, GIK Acoustics, Real, MSR and many more.

Sound panels are very simple to make. They’re based around an absorbent material like Owens Corning 703 rigid fiberglass board (or, to a lesser extent, Rockwool Rockboard 60). Both come in standard 2×4’ panels and in 1- to 6” thicknesses (2” is what’s used the most). A ridged fiberglass panel differs from normal fiberglass batting in that it’s a lot denser because it’s tightly compressed, and although it’s not made specifically for acoustic control, it works perfectly in that application.

It’s also possible to use acoustic foam for treating your RFZ, but it’s a poor choice because it has a limited frequency response, burns easily, and is actually more expensive than the acoustic panels made from ridged fiberglass or Rockwool.

The 703 is framed with simple 2×2 or 2×4 inch wood strips, and then covered with a fabric like burlap (the most popular) or Guilford of Maine, which is flame resistant but a lot more expensive. The reason why you might use a 2×4” frame instead of a 2×2” (the size of the 703) is the air gap, which adds to the effectiveness of the panel by lowering the frequencies that it absorbs.

Burlap works well as a cover because it won’t sag and bag over time, it’s cheap, looks good, and is available in a very wide range of weaves and thicknesses. When selecting panel cloth, the best way to evaluate it is to breathe through it. If you can feel your breath on the other side, it’s good to go, because sound can travel easily through it.

There are other products that work as well as 703 for absorption. Owens Corning also makes a model 705 that has twice the density of 703, but costs more as well. Speaking of cost, 703 costs approximately $12 a panel (sometimes more and sometimes less, depending on where you buy it) and comes in packs of 6. Knauf ECOSE, Johns Manville, Roxul Safe and Sound or Rockboard 60, and Certainteed all have the same absorption characteristics or better, and can be even less expensive than their Owens Corning equivalent. Personally, I prefer Rockwool.

You won’t be able to find 703 or Rockwool at your local Home Depot though, so look in the phone book for a supplier of “Industrial Insulation” or HVAC. Sometimes they call it “industrial furnace insulation board,” so be sure that the thickness and density is the same as 703 if you’re not getting the real thing. Then just place it on the walls and ceiling to create your Reflection Free Zone and enjoy your improved listening space.

You can find out a lot more about how to build a home studio effectively and inexpensively by consulting The Studio Builder’s Handbook. You can also read some excerpts from the book on my website.