Hi Nick V,
Regarding your overarching question “Active Analog vs DSP Crossover” my experience is both can be made to work when enough effort and time is brought to bear. I have personally had good, no make that excellent results with Marchand Electronics Inc. (
http://www.marchandelec.com/) on the analog side and DEQX (
https://www.deqx.com/) on the digital.
It can be a long road because in the bass region the room is such a wildly varying influence. Something you wrote above jumped out as a potential wrong turn on that road. I am especially thinking of achieving a good livable 85% solution to enjoy now and as a baseline (or should I pun and say ‘bass line’) while you incrementally learn and tweak to get the 95% perfect result we all strive for. Disclaimer I am an engineer so 100% perfect never happens in my world.
You wrote “
I've played with the low pass cutoff frequency and the only place I seem to get good integration is where the speakers start to roll off between 30-40Hz. It doesn't make sense to use the subs from 20-40 Hz only, I want to cross them around 80-100Hz or even 150Hz maybe.” This line of thinking is I believe your potential wrong turn, or at least passing by a very scenic road less traveled.
In Nick V’s system we have three components that will significantly contribute bass energy.
1. Selah Audio Vigore’s SB Acoustics 8" woofers
2. Rythmik FM8 active subwoofers
3. Room acoustics primarily from the mechanisms of boundary reinforcement and room nodes.
SB Acoustics makes very good woofers and Selah Audio knows what they are doing in the implementation of bass alignments so I am making an educated guess the main stereo pair can output significant energy to at least 40Hz perhaps even 30Hz. As the woofers roll off the room boundary reinforcement will act to counter their roll-off lifting up the response. Same story with the Rythmik FM8 subwoofers except they play down to 20 Hz if not lower. Now you have lots-o-bass and along come the room nodes stirring the mix with big peaks and suck-outs based on the room dimensions. Typically the primary result is one or two or three big booming peaks somewhere between 60-100 Hz.
Only heroic measures will change the room acoustics below 150 Hz and you have stated these are not acceptable as the room is multipurpose family space. The trick I want you to consider is hinted at when you wrote “
seem to get good integration is where the speakers start to roll off between 30-40Hz. It doesn't make sense to use the subs from 20-40 Hz only”. It does make sense when we find the frequency of the worst offending room mode and pick the subwoofer to mains crossover frequency to purposely create a null at that frequency.
As an example say your room has a node at 55 Hz causing a 6 dB peak. With the subwoofers LPF at 40 Hz and the mains HPF at 60 or 65 Hz the energy to excite that 55 Hz peak is attenuated. The net response is smoother yielding the bliss of “
good integration”. I first encountered this after auditioning and purchasing a REL sub as REL has championed very low Hz LPFs for their subwoofers for years. It is counter intuitive but a smooth response with true response in the lowest octave is quite a nice result.
This is certainly more towards the audiophile ideal and admittedly does not serve the home theater side where in the 10 to 100 Hz range mo-bass always better. And looking at the Rythmik FM8 description on their website it is very capable of playing much higher and contributing to low frequency effects and maximum system output. Going there is where in my experience DSP plus lots of measurements and experimentation is required finding and nulling out those peaks.
Enjoy the journey and happy listening.
