SE Electronics: guitaRF Reflexion Filter

When SE Electronics invented the trademarked Reflexion Filter [Tape Op #56] in 2006, I recall many engineers in our industry thinking it was a groundbreaking product, while others were skeptical. Since then, the basic premise of the Reflexion, a curved acoustic barrier that surrounds the rear of a mic to attenuate sound waves approaching the mic from the rear and sides, has been copied by countless manufacturers. Why? Because the concept can actually work well to reduce bleed and control room ambience. These days, you’ll find a whole range of these kinds of filters — from simple, barely effective ones that are made only of low-density foam, to the impressive, multilayered systems in SE’s growing Reflexion line. One of my favorites is the sE Electronics guitaRF, a filter specially designed for recording guitar amps, but incredibly useful in so many other situations. The guitaRF is compact — about 8’’ tall, 10.5’’ wide, and 4’’ deep. It’s made primarily of 1.25’’ thick acoustic foam inside a vented, molded plastic shell, with what looks like a fiber membrane in between. A flexible rubber opening that’s offset by 1.5’’ from center allows you to push a front-address mic, like a Shure SM57, part way through the back of the guitaRF into the acoustically treated volume in front. Additionally, there’s a bracket with variable drop and depth that you can use to hang a side-address mic, like a Royer R-121 ribbon mic [#19] or even a large-diaphragm condenser. The whole assembly mounts onto an included stand that has a base uniquely shaped to fit underneath a guitar amp, which assures that even the heaviest of mics won’t hit the floor. You can also mount the system onto a mic stand or boom. So far, I’ve used the guitaRF to mic amps using the included stand, brass instruments using a straight stand, and live-tracked vocalists using a large boom. I’ve even used it sideways to reduce cymbal bleed in a kick drum mic, and vocal bleed in an acoustic guitar mic. Being the gear geek, I took measurements to see how effective the guitaRF actually is. As you would expect, attenuation is greatest at high frequencies. From 4 kHz on up, the guitaRF blocks at least 12 dB. In the midrange, from 150 Hz to 1 kHz, there is 2 dB reduction — not amazing, but still useful. Surprisingly, the guitaRF is actually quite effective in the lows, blocking 4–7 dB below 70 Hz, depending on the depth of the mic. What I like best about the guitaRF is that it’s often the perfect compromise — it reduces bleed and room ambience to a lesser degree than its bigger Reflexion siblings, but it doesn’t block sight lines or take up too much space.