connecting a sub to a 2-channel system

OK, got the sub hooked up. It's making the house shake as I write this. We'll see what my sister thinks, she'll be here Friday.
I used some old speaker wire I bought in the early 90's. Twisted it right into the AQ banana plugs at the amp. It's old, clear-coated, oxidized, flat speaker wire, supposedly 16 gauge. Playing with the phase, crossover and volume now trying to get it integrated. Seems to work fine, but my Quads sound different, I know the impedance of the sub won't affect my amp, but still...I guess the new sound just takes some getting used to!

Further listening proves that I have to turn the volume up louder with the sub connected to get to the same SPLs I was getting in pure two-channel. I have a decibel meter and mild tinnitis, so I watch this kind of thing pretty carefully.

The loading presented by the sub to the power amplifier is not the reason. To prove that, see what happens when the sub is connected but its volume setting is turned all the way down.

What you are perceiving could be the result of a phasing problem, perhaps in combination with too high a crossover frequency, or a placement problem, or a room reflection issue. Given that the sub only provides two possible phase settings (0 and 180 degrees), and you've probably already tried both, my guess is that it's a placement issue, which at some frequencies in the bass region is resulting in the output of the sub arriving at the listening position with improper phasing relative to the same frequencies arriving from the Quads, for both settings of the phase switch.

Best regards,
-- Al

I'll try it tomorrow night with the sub turned off, see if that restores the Quads' ruler-flat mid-range. I feel like I am missing some detail in the mids, like the sub is covering it up or something. This is only temporary anyway, I miss the sub in my home theater too much! Funny how I used to crave bass when I first got into this hobby, now I just...don't!

I think I know what was wrong, crossover was not set correctly, now the sub and speakers overlap pretty seamlessly. Thanks all.