The Room Resonance Remover(tm) from Lonnie Bedell Electronics is a new audio notch filter specifically designed to cut in the 125-540hz range to counteract room resonances that degrade sound quality in PA Systems & Home Stereos.

At first glance professional sound reinforcement and home stereo may seem worlds apart, but they both suffer from the same room resonances that amplify certain frequencies as the walls vibrate sympathetically. This causes the sound system to feedback prematurely at those frequencies, as well as sounding “muddy” as the low mids are amplified by both sound system and the room itself.

Professional live sound companies commonly use a graphic equalizer in large systems to compensate for this by “ringing out the room”. To accomplish this, they raise the sound level gradually, carefully listening as the frequencies naturally supported by the room start to feed back first, and then reduce them with the corresponding frequency slider on the graphic equalizer. However since graphic equalizers typically only cut 12db, sometimes the engineer is forced to bring down more faders to try and cut the intended frequency, affecting more and more of the audio spectrum. The home stereo user or small PA system has even less at their disposal, typically bass & treble controls of a fixed frequency that affect large parts of the audio spectrum.

While the immediate goal for a PA engineer may be to get more gain before feedback, by “ringing out the room” they also inadvertently gain the additional benefit of flattening out the frequency response of the listening environment by working with the room’s natural characteristics instead of against them.
Home stereo and other consumers can benefit from the same subtractive equalization as well. Instead of boosting high frequencies, for example, they may find a cut in the the low mids they are amplifying might yield them all the high end they desire.

The Room Resonance Remover(tm) cuts up to 30db in the 125-540hz range on 2 separate channels. The RRR has variable settings for frequency, Q (filter width), and depth (amount of cut). Inputs & outputs are line level, and can be configured as RCA or 1/4″ jacks at the customer’s request. It is available in 9 Volt battery ($129.95 US) or AC powered ($149.95 US)versions. High performance 5532AP op amps are used throughout for low noise.

“I designed the Room Resonance Remover for my own live sound gigs where I would have far more 200-250hz than my graphic equalizer could cut. By cutting with the RRR I am able to get the gain before feedback I need to do the job” says owner Lonnie Bedell.

The Room Resonance Remover(tm) is available at The RRR increases clarity in Home Stereos & Stops low end feedback in PA Systems

Lonnie Bedell Electronics manufactures a line of electronic products assembled in the USA. Lonnie has been an active audio engineer since 1987, and operates the Goin’ Mobile mobile recording truck based in Boston.