Jackman,
Nice speakers. Philip Bamberg knows how to design non-CD speakers extremely well. As to your subwoofer question, I looked at what he published on his website. The nominal impedance for the woofer is 8 ohms, minimum is 5.1 ohms. The driver is only 84dB efficient as you already know.
The
maximum LINEAR output for each sub (I'm assuming you have a pair) is 102dB with a power of 165 watts, when you have a high pass filter of 23Hz with a 0.7Q. The maximum LINEAR output for each sub without the high pass filter is only 100dB with a power of 100 watts. He didn't mention which frequency the maximum output was measured at, or if it was an overall average. When you look at the impedance graph from 20 Hz to 50Hz, it has a peak of 40 ohms. That will severely decrease the amount of power available to the subwoofer (as it is with all subwoofers due to the impedance peaks) and so more power is better. So Phil went the next step and plotted for you all the possible power curves from 6 watts to 162 watts with high pass filter and without. So to be honest with you if you have anything more than 200 watts into 8 ohms, it should be plenty!
All of the answers are right there on Mr. Bamberg's excellent graphs
Series 5 XLS subwoofer power curve.
As to which solid state amplifier sounds better? I'll pass on that question.
He also states this on a separate page on his website which is wise information:
Subwoofers' output is generally limited by excursion of either the woofer or the drone. A gradual compression of the output is heard as a "softening" of the bass. BESL subwoofers are designed so that both woofer and drone reach their separate excursion limits at the same drive level. Rather than limit the 1st octave bass as a means to increase mid and upper bass max SPL, BESL subs’ SPL response tracks the same curve shape at all operating levels. We recommend the use of multiple subwoofers for systems requiring extra high output levels.
Be wary also of claims for extraordinarily high output SPL and high input power for other manufacturers’ subwoofers. Often, their subwoofer is placed in a tri-corner, which boosts the output by about 10-15dB! The max power may be that of driver failure, or because of the use of drastic 1st octave electronic limiting. In other words, they don’t say that the SPL does not remain flat at all operating levels.
Another claim to fame from manufacturers is that of subwoofer amplifier power. Such high power may be truly required for the radical EQ necessary to boost the 1st octave output from small, sealed subwoofers. This is a crude, and brute force approach to getting output from a poorly designed bass system.
BESL designs drone-assisted subwoofers as a mean to boost low frequency output acoustically, and without requiring extraordinarily high amplifier power.
Suffice it to say that to provide a truly meaningful set of specifications for subwoofer performance would take an entire page, and not just a few lines.
Lastly, provided it is operated under the specified max power conditions, a BESL monitor or subwoofer will never produce severe distortion.
So basically you don't need a tremendous amount of power, but if you want more spl, build more subs!
Anand.
