EQ MAGAZINE: ELF-M2 REVIEW

After experiencing the original ELF-1 Low Frequency Integrator from Bag End Loudspeaker Systems over a year ago (see EQ, October 1993), I realized that many of my preconceptions regarding bandwidth and quality relating to the size of subwoofers were false. A small box and driver can produce high-quality low-frequency sound. However, the ELF-1 was a laboratory-grade instrument. That fact was reflected in the range of exacting control switches on the unit, and in its cost. If you are serious about sub-bass and want to be able to tweak all the parameters of the crossover at a moment's notice, you will want the ELF-1. If you have slightly more modest requirements, the ELF-M or ELF-M2, the latter being subject of this review, may be a more practical choice.

The ELF-M2 is a single rack-mount box made of heavy-gauge steel and constructed to withstand the typical physical abuse of being on tour. Its unassuming front panel includes green power-on LEDs, mode indicators (green for two-way and yellow for three-way), and flush-mounted continuous controls for adjusting output levels in each band and protection limiting thresholds. The original ELF-1 unit used DIP switches that were quiet and extremely accurate for all the adjustments. The continuous controls may not be quite as accurate to reset, but they do allow you to easily adjust the balance between frequency bands while listening to your favorite test source. The continuous threshold controls, for the mid/high limiters and ELF Concealment, allow you to easily adjust for different situations, but these screwdriver-type controls prevent idle knob-twisting and would easily accommodate a cover plate to prevent any unauthorized changes in your setup.

THE SETUP

The crossover parameters of the ELF-M2 can be set to suit your exact needs. If you are adding subbass to your existing full-range loudspeakers, it is simply a matter of setting the high-pass frequency and operating the unit in stereo two-way mode. The factory default of a 100 Hz crossover frequency (-6 dB point) will fit many such applications (see fig. 1), but, by simply changing a few plug-in resistors inside, a wide range of crossover frequencies (at 12 dB/octave roll-off) is available. Internal jumpers toggle the unit into three-way mode, where the same fixed-resistor approach allows the mid-to-high-band crossover frequency to be chosen. These are operations that need only be done once per loudspeaker type, and using this resistor approach is both flexible and accurate. It is also safer than having pushbuttons or knobs select these frequencies.

There have been some trade-offs in the design of the ELF-M2 and ELF-M models. They retain the balanced XLR inputs, but unlike the ELF-1, both the ELF-M2 and ELF-M sum the stereo channels to mono for the ELF subbass output and roll-off below 18 Hz (factory setting -internally variable). The ELF-M2 offers a three-way mode for active multiway systems and therefore can replace a conventional crossover. All outputs are unbalanced but use XLR connectors. The unit also has front-panel level adjustments and protection limiters on the MF and HF outputs. If these features are not required in your application, you can save $200 and buy the ELF-M. Either unit would fit right in to multiway sound reinforcement systems, studio monitors, cinema systems, or even DC-powered (automotive) systems.

A LITTLE HISTORY

Briefly, the ELF approach was the work of Ed Long and Ron Wickersham, two creative individuals with an impressive background in audio engineering. They realized that if a subwoofer could operate below its resonant frequency, not only would it produce less colored (read: distorted) sound, but also exhibit more linear frequency response. By matching the roll-off of a low-frequency loudspeaker driver mounted in a sealed box (infinite baffle) with a circuit that boosted those frequencies at the same rate, flat frequency response to very low frequencies (less than 10Hz) could be achieved. There was the added bonus of working well with even very small drivers and cabinets. The limiting factor in choosing the size of the driver is the maximum output level and not the low-frequency cutoff.

I auditioned the ELF-M2 with Bag End's 10-inch ELF subwoofers and I was very pleased with theimpact of these tiny subs. To protect the subwoofer drivers from damage caused by overexcursion at these extremely low-frequencies, the ELF design also includes a protection circuit called Concealment. This circuit progressively reduces the amount of gain, starting at the lowest frequencies, once the (adjustable) threshold has been exceeded. For a more detailed explanation of the ELF (Extended low frequency) principals, dig out your back issues for my review of the ELF-1 in the October 1993 issue of EQ magazine or call Bag End and ask for its booklet on ELF.

Bag End has reduced the cost of using the ELF technology while maintaining the excellent audio quality and protection systems of the original unit. The review system sounded great when used with electrostatic Hi-Fi loudspeakers, studio monitors, or sound-reinforcement loudspeakers. There is a little less headroom than in the original, but the unit still provides a dynamic range of over 95 dB. There is the added bonus of using the ELF-M2 to replace those tired passive crossovers in your system, and whether you choose to use Bag End's optimized ELF subbass loudspeakers or build or modify your own, the results will be devastating to any preconceptions you have about subwoofers.

For more information on BAG END products, contact BAG END at 22272 Pepper Road, Barrington, IL 60010, or call BAG END at (847) 382-4550.

Bag End Loudspeakers, USA 847 382 4550     www.bagend.com