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RE: Request Help for Audio Equipment Set Up (Non Pro User)

Posted by Dave_K on January 19, 2017 at 11:33:58:
Sorry for the late reply.

SPL = sound pressure level. I mentioned it in regards to how loud you need the system to play, because the subwoofer crossover settings that produce the best sound quality and probably not the best settings for maximum SPL. You may find for example that using a lower crossover frequency (e.g. 50-60 Hz) and/or a shallower crossover slope provides better sound at moderate levels. But as you increase the level you might end up pushing the Wharfedales into heavy distortion in the bass. If so a higher crossover frequency may give you a little more headroom. 80 Hz LR24 is a good compromise to start with, but I would experiment a bit and see what sounds best.

Here's an example calculation using Ohm's law:

Power = Voltage^2 / Resistance
Power = 500W RMS
Resistance = 4 ohms
Voltage RMS = sqrt(2000) = 44.72V

dBV = 20*log(V)
44.72 Volts RMS = 33 dBV at the amplifier's output

Now subtract the amplifier's voltage gain to get the voltage at the amplifier's input. For the Crown, according to the owner's manual the voltage gain is 32.9 dB. 33 dBV - 32.9 dB = 0.1 dBV

Finally, convert dBV to dBu. 0 dBu is defined to be 0.7746V. 0 dBV is defined to the 1.0V. Converting gives me 2.3 dBu.

That means 2.3 dBu of output from the Driverack will produce 500W RMS output from the Crown amp into 4 ohm speakers.

By repeating the same calculation for 1000W into 8 ohms with the Cerwin-Vega's gain of 35 dB, I get 6.25 dBu. So the Wharefedale speakers are the limiting factor.

Real loudspeakers are not a flat resistive impedance, so the actual output into the Wharfedales won't be exactly 500W. Also, loudspeaker power handling specifications are also approximate, because the stress on the loudspeaker depends on the frequency content of the signal. So if you're going to use the limiter, I would set it a few dBu lower to be conservative, at least until you know your system's limits.