Thanks for the additional info. I can’t say what the answer is at this point, but here are some thoughts and possibilities to consider:
1)You didn’t say which miniDSP model you are using as the crossover, but I see that the "2x4," which appears to be a likely possibility, has a maximum rated output of 0.9 volts. The sensitivity of the Crown amp is selectable as either 1.4 volts or 0.775 volts. If you have not set it to 0.775 volts that could certainly be a contributing factor. Also, my suspicion is that those two numbers apply to its balanced inputs, which could mean that the corresponding figures for the unbalanced inputs are twice those numbers. If so, it can be calculated that even if you are using the 0.775 volt setting an input of 0.9 volts would not drive the amp to more than about 72 watts into the 8 ohm nominal impedance of the woofer, which is about 1/3 of its rated power capability.
2)The miniDSP 2x4 has a very low input impedance of 6K. While your Modwright tube preamp has a specified output impedance of 300 ohms, I suspect that as with most tube preamps its output impedance rises to much higher values in the deep bass region, due to the coupling capacitor it most likely uses at its output. Many tube preamps having nominal output impedances of a few hundred ohms have output impedances in the area of 2K to 4K at 20 Hz. If that is the case with the LS100 (and you might check with Dan Wright on that), and if you are using the 2x4 or some other miniDSP model having a similar input impedance, it would certainly explain a weakness in the deep bass region.
3)Although you stated that "all the right adjustments" have been made, between the plethora of settings in the amp and in the miniDSP there is lots of opportunity to go wrong. So double and triple checking everything would seem to be in order. For starters, be sure of course that your settings result in the amps being properly gain matched. And be sure that the high pass, low pass, and bandpass filter functions the amp provides have been either turned off or set to values that would not contribute to the problem.
4)Regarding the comments by the others, the woofer you are using does not seem to be a particularly difficult load, and I would not expect it to require a particularly high current amp. See the impedance plot in
this datasheet, which shows its impedance as being at or above 7 ohms at all frequencies, and not having particularly negative (capacitive) phase angles at most frequencies. Although it should be noted that the rise to as much as 30 ohms in the vicinity of 30 Hz means that at frequencies in that vicinity the amp’s power capability will be far less than the 215 watts it can supply into 8 ohms. Although a similar reduction in power capability into the high impedances at those frequencies would occur with nearly all solid state amps.
Hope that helps. Regards,
-- Al
