Subwoofer for Harbeth M30?

Yes, those are great subs. They do require a highpass crossover I believe. so that means you need an amp and preamp or an integrated with pre-out and amp-in. This way one can free up the harbeth from anything below about 80Hz so it can concentrate on the mid-range. Search out what Bob Reynolds has to say about this type of set up here on agone. What he says makes a lot to sence regarding highpass filters (crossovers) and distortion. As for me, I think the sound of the radial driver is so delicious down to 45hz, I thought it a pitty to use a high pass--but I might try it in the future. Also check out the Vandersteen website, It will explain better than I can regarding the philosophy behind their subs and how they work.
Cheers!

I got my M30s today, hooked them up and listened to them for about an hour. Right off the bat, I'll tell you they seem to be cleaner than my B&W 801 Series III, but so far they seem less extended in the highs. Time will tell.

Hi,

I used a REL Storm with the Super HL5's in my room. They worked well together. My room was actually two rooms as I have a large listening room that opened into another large open space. I have subsequently sold both speakers as I bought a pair of Harbeth Monitor 40's. The 40's do not require the use of a subwoofer.

Good Luck with the Monitor 30's.

Will the use of a Bryston 10B active crossover improve subwoofer integration between the Harbeth Monitor 30s and a Rel active subwoofer?

I've mated Rel with the harbeths for years. They work great, integrated seamlessly.
Cant go wrong with the Rel B series or the St series w/ your M30s.