Revel Performa F30 surround speaker system Revel Low Frequency Optimizer
When I swapped out the front-channel Performa F30s and C30 for the Ultima Gem and Voice for the comparisons described in the review, I took advantage of the opportunity to recalibrate the B15 subwoofer's equalizers for the new speakers. Because of differences in the way front speakers interact with a subwoofer at the chosen crossover point, the correct subwoofer equalization for one set of main-channel speakers won't necessarily be optimum for a different set—even though the subwoofer location has not changed.
I downloaded the Revel LFO program from Revel's website. It was very slow to boot on two different computers, but, once up and running, provided clear step-by-step operating instructions (if you select Beginner mode). You can designate one of five sound-level measurement devices: two from RadioShack, any other “C-weighted" meter, a “flat" meter, or a microphone connected to a computer. I used the RadioShack analog model. To run the test, you set all EQ level controls to “0," start the test tones on the LFO CD (which comes with the B15), and write down the readings for each frequency.
At this point, if you have the flexibility to move your subwoofer around, do so and check the results in a number of different locations. This can be very time-consuming, but rewarding. The best equalization is as little as possible. In particular, seek out locations with a minimum of dips. Peaks are much easier to compensate for.
Next, insert the readings for the best location into the computer program and click on Analyze. The program will then tell you how to set each of the equalizer controls. You can go back and take a new set of readings to recheck the results, but be careful; after you set the controls as recommended and take another set of measurements to see how you did, it will give you another set of recommendations.
But these are changes from the first set of adjustments, not a whole new set of numbers. The LFO program is dumb; it assumes you have the level settings on the subwoofer set to 0, and that each new set of readings is the subwoofer/room response, not the subwoofer/room/equalizer combination. This makes it essentially impossible—or at least very tricky—to go back and forth with successive measurements to progressively fine-tune the result. Audiophiles tend to be obsessive this way, but here you're likely to be better off making one set of measurements, dialing in the settings, and leaving it at that.
But it is possible to fine-tune the equalizers if you use a little intuitive deduction after the first run-through. For example, the program told me to use the third equalizer band to cut the response at 22Hz by 2dB. Deep bass is hard enough to come by, so I ignored this advice. Instead, I added a +3dB boost at 33Hz to fill a small hole in the response at that point that the LFO had not completely addressed. As I note in the review, however: Be very careful when applying boost with equalizers; if the dip you're trying to fill is a room null, it can simply overload the subwoofer. In this case, it worked reasonably well.
Not surprisingly, the new equalization settings I arrived at for using the Gems and Voice with the B15 provided a tighter bottom end with those speakers than had the settings optimized for the F30s and C30. But the original setup—F30s and C30 with the equalizer settings originally derived for them—produced the best bass definition of all. This didn't surprise me either—Kevin Voecks had arrived at these settings with more sophisticated test gear than the LFO system. Still, the LFO-derived result was more than acceptable; with fine-tuning, a reasonably adept owner or a knowledgeable dealer will almost invariably end up with far better bass than even the best unequalized system can provide. That's simply the nature of the speaker/room relationship.
The LFO also allows you to measure the result in more than one location and aim for an averaged response based on those results. But this average will seldom provide as flat a response in the prime listening seat as a curve derived for that seat alone. Nevertheless, I recommend setting the system up for that “hot" or “money" seat, checking to be sure that the other seats sound reasonable; if so, go with that. But remember that this may not be the best approach if more than one critical listener will be sitting in at the same time.—TJN