By George Petersen

PRODUCT CRITIQUES AND COMMENTS

Sabine FBX-900 Feedback Exterminator

Two years ago Sabine introduced the FBX, a revolutionary product that automatically detected the onset of feedback and assigned a notch filter to eliminate the offending squeal. Now Sabine has unveiled its second-generation product, the FBX-900.

Housed in a one-rackspace chassis, the FBX-900 is a single-channel unit that combines nine independent, narrow-band (0.1 octave) -50dB filters that are under DSP control. Depending on user needs, any of the filters can be either fixed or dynamic. During the initialization procedure - when the unit determines the problem frequencies in any setup - the FBX assigns fixed filters to the strongest resonating frequencies. The dynamic filters are left unassigned to control any intermittent feedback that can occur during a program. Filter activity is indicated by an LED display on the FBX front panel. Controls are minimal, consisting of an input level adjust pot (with 4-step LED indicator), reset button and power and bypass switches.

Setup is straightforward. The FBX is placed between the mixer and the power amp, using either its balanced XLR (pin 2 hot) or unbalanced 1/4-inch connectors. Stereo operation requires two FBX units, and each monitor mix output from the console requires its own FBX, also placed between the mixer and power amp. If equalization is used for room correction, the FBX can be placed either before or after the equalizer in the chain. A simple initialization procedure (outlined in the manual) requires the operator to raise console master levels until feedback occurs, which allows the FBX to "learn" the problem frequencies and set its filters to counteract them. Once the filters are set, the unit retains the setting in nonvolatile memory, protected against power losses and saved even when the unit is off.

Clearly outlined in the manual, the procedure is fairly simple once you've done it a few times. While the FBX-900's setup is more straightforward than its predecessor, the original FBX had the instructions silk-screened on the top of the unit. Perhaps Sabine could do the same for the new model, just for those occasions when the manual may not be handy.

The power supply is an outboard wall block with cable terminating in a 3-pin DIN plug which can wiggle out fairly easily. A bit of gaffer's tape took care of the problem, although Sabine should look into finding a more robust connector, or preferably an internal power supply. The latter is a must in many permanent installations, as local codes often prohibit outboard power supplies or require that all installed gear be UL-approved. (According to Sabine, future units will have 5-pin DIN plugs that should hold more securely - Ed.)

Over a period of weeks, I had the opportunity to use the FBX-900 on a variety of situations, both as mains and monitors. Like its predecessor, the FBX-900 is an extremely effective feedback suppressor, adding another 6 dB - 9 dB of gain-before-feedback in any system. The difference is really amazing, as a 9 dB gain increase is the equivalent of an eight-fold increase in amplifier power.

The FBX-900 yields a noticeable improvement in any feedback-prone situation. As an added plus, Sabine improved the 900's signal-to-noise ratio (now typically 86 dB, which is 16 dB better than earlier FBX models). The filter action is fast - typically in the half-second range - and the nine filters can handle just about anything. For those cases when you're mixing 120 dB rock monitors in a glass room, you can always run two FBX-900s in series for 18-filter action. This one's a winner, a powerful tool for anyone seeking a simple yet elegant solution to feedback problems.

Sabine Inc., 13301 Highway 441, Alachua FL 32615-8544, (386) 418-2000.

Copyright 1992 by Mix Magazine.

Reprinted with the permission of the publishers.