Just got a new sub a little while ago (Dayton 10) and would like to use my old Onkyo sub for a dual sub set up since the dayton sub has audio out and i can easily connect another sub to it.
My new sub is a '10 and the old one is an '8. When i put them right next to each other i was actually getting less base, i think.
Would it be better to put the Onkyo at the rear or put it on the other side of TV? Any benefit to dual sub set up?
How do i tune the subs without SPL meter to sound better together?
Should the phase be set the same on both of them, or should they be out of phaze?

IMHO dual sub setups are hard to calibrate, definitely hard without an spl meter.

They would only be opposite phase if they were on opposite sides of the room facing each other.

you can also stack them... that is how THX recommends you do two subs.

but what would be the benefits of two subs vs one? if one is better then the other. My onkyo destorts too much on really low base.. but if i turn the gain down low it does not but then the base is not enough.. so if i use both am i gaining anything?

Again, IMHO, nothing.

Multiple subs in a home theater are usually used for large rooms that require alot of spl. Also if they subs are not the same driver, same design crossover, it will be very tough to get them to sound good together.

Personally I would use the better of the the two.

well, you can gain something if you are using two subs correctly. if you have variable crossovers on both, you can set the bigger one to handle bass from ~50 and below, and the smaller one to handle bass ~50 and up.

How do you set it to 50 and above? I do have a variable crossover on both but there is no way to limit the frquency at the top. meaning if i set it to 90 it will pick up everything below 90 including below 50 and therefore would distort with really low base.

the reciever cuts the top at 80 or 100 or 120.

To subs can deal with standing wave problems in a room. Every room had peaks and nulls. By messing with room position you can minimize this problem. Very time consuming and difficult though. I have this but with two of the same subs. I think I would also just go with the better sub.