Sub/Speaker Crossover?

Do your Spendors go down to 45hz...in YOUR room? Probably not. I would cross them over at 60. I also agree to listen for yourself and determine the best crossover point for your speakers and sub...in YOUR room.

With a sub, your placement doesn't have to be next to the mains. You may find that because you can move the sub to an adjacent wall your perceived bass may improve a lot (in the mains). I'd try 60hz to start, with the sub on an adjacent wall. Unfortunately it eventually comes down to trial and error. Keeping the crossover low will allow maximum bass to come from the mains, which in conjuction with a sub (a second source of low frequencies) may help even out room nodes. That works even better with stereo subs.

I use SP-1s and S 100s with a pair of REL Stadium subs, I use 25 Hz. I would never go above 40, 60 is for HT set ups. I let mine go full range whether I am using the RELs or the Hsu I use in my HT or the Nelson Reed 1204s.

I cross over my mains into my sub at 80Hz. I tried everything from 50Hz to 100Hz, and found that 80Hz resulted in the smoothest integration. However, I cannot say that 80Hz would necessarily work best for you, since, after setting up several mains/sub systems in several rooms, I came to the conclusion that the choice of crossover frequency is very system/room dependent.

Another thing to keep in mind is that the perception of of the "best" crossover frequency will be influenced by other parameters of subwoofer setup, such as placement, phase, level, and time alignment. All of those parameters interact psychoacoustically, so it is often challenging to identify which parameter needs to be adjusted. In my case, it was a frustrating process that took several full days of experimentation distributed over a couple months.

Having offered those words of discouragement, I will say that it is totally worth it, so hang in there!