one 12in sub or 2 8 inch subs

In general, I'd always say that two is better than one. And (see below) four may be better than two.

There are many excellent 12" subs out there for which a pair costs less than a single r 528. Both Rythmik (my choice) and SVS (highly regarded by many) offer a pair of 12" subs that will outperform the Rel on the test bench (not necessarily the same as sounding better). In each case, a pair sells for under $1500/pr. IIRC, the SVS is closer to $1100.

Duke, who posted above, owns Audiokinesis, which sells the Swarm bass system with four 8" subs for $2500. That might be one more good option to consider.

Lots of people love Rel, but I question the value proposition. Not trashing the brand - numbers never tell the whole story and personal preference varies - just suggesting that you might wish to explore some alternatives that offer more measured performance for less $.

As always, YMMV.

Marty

neither, choose at least 15 inch. Subwooder need to be closed, no bass port. Rel is in Europe not that popular anymore. Many Rel sub's I tested are sooo slow. Even wenn people would give me extra free money every day by receiving a free Rel I would not want them in my house.

8", and even 10" sealed subs will roll off fairly high unless equalized or some sort of servo feedback is employed. Ported or passive radiator designs will give extra bass extension at the cost of larger cabinets and reduced transient response. If the subs are expected to play higher frequencies,say 100 Hz, that transient response becomes more apparent. Below a certain point, it's more just "rumble", not that that's a bad thing.

I agree with Duke but there are limitations of smaller sub drivers that can be reduced partially with multiples. That said, I'll be starting work on dual 10" subs soon.

Two is better than one in every way, especially if power is doubled with two as well.

Hey just curious... Which other speakers are you runnin with the sub.
That will probably help you decide as well. Just an after thought.