Best way of filtering bass into my subwoofer?

[Mal P]

Hi there,

My newly acquired pair of speakers (Dynaudio C1s) use first-order crossovers and are are phase-coherent and time-aligned. They sound great, but their extension, while not bad, starts to drop off below the 45hz mark. I have a HSU VTF-2 subwoofer that I'd like to mate with the speakers, to not only get more extension, but also to reduce the stress on the 6.5" woofer and the amplifier, by relieving the bass.

I'm having all sorts of trouble coming up with valid high-pass crossovers to do this, without distorting the phase of the signal that is sent to the speakers (which I believe would nullify their phase coherent nature). A good quality Linkwitz/Riley active crossover set at around 50hz and placed between my pre-amp and amp would certainly remove the bass quickly enough, but the phase-shift to the high-pass portion of the signal may interact negatively with the crossover in the Dynaudio. Likewise, a simple capacitor placed at the inputs to my amplifier would roll-off the bass somewhat starting from say 80hz (then I could use my sub's low-pass to meet that roll-off), but again, cause phase-shift to the high-pass portion of the signal.

Do you guys have any other options on how to do this? I guess the only real way is to simply use the low-pass on my subwoofer to come up to meet the roll-off of the speakers, but that wouldn't prodide the benefit of relieving the stress on the speakers and amp.

Are there any decent digital crossovers that implement good FIR filters? Perhaps with a DAC built-in so I can have both in one! I understand the DEQX unit has this, but my goodness, it costs an arm and both legs!

Or am I getting this whole thing completely wrong, and the phase shift using a Linkwitz/Riley crossover or even a simple capacitor won't affect the Dynaudio's phase coherent nature?

Thank you very much,
Mal

[bzdang]

Hi Mal, borrow an active crossover if you can and try it, or buy one with an agreement to be permitted to return it. The fancy crossover in the Dynaudios will keep its drivers working together properly, and relieving the Dynaudios of deep bass duty will do wonders for everything that comes out of those 6.5" woofers. 24dB/octave(or steeper) and 40~60Hz, you'll not want to hear the sub so much as to be freed of the artifacts of overworked small woofers.