What frequency do I crossover subs

This decision also depends on the listening room, the shape of the FR of your sub(s) vs. your main speakers in the lower frequencies, and whether you're using digital room correction ("DRC", like Audyssey, ARC, or similar).

Without any DRC:

It's very likely that your carefully located, single subwoofer will produce notably smoother bass than your main speakers. This is because you can place the sub close to a wall where reflections of low frequency, long wavelength signals (destructive interference) are minimized. If you are using a pair of subs, their output is almost surely much, much smoother in the bass because, while each sub will still have small FR irregularities, those irregularities are likely at different frequencies and will tend to average out to a very smooth summed response (vs bass from main speakers out on the floor). IME, this difference will usually be pretty dramatic.

In this case, cross the subs just high enough to allow the subs to handle response where the room does its worst damage. In an effectively treated room (bass busters, etc), I've found that this will generally be somewhere around 70 to 80 hz, although it's obviously dependent on the characteristics of your specific room. In an untreated room, the worst issues usually persist up to +/- 125ish hz. I'd suggest that you experiment with frequencies between 70 and 100 hertz and see what sounds best.

If you're using DRC, then it's a different story. IME, the software will effectively smooth bass response wherever the subs are placed and wherever they are crossed. In this case, you have a lot of flexibility and the choice will be more dependent on the specific qualities of your subwoofer(s) vs your main speakers. Try it at 50hz and try it at 80 hz and see which you prefer.

Good Luck

Marty

db,

If you're using the SMS-1 in auto mode, you're only scratching the surface of that unit's potential.

The SMS-1 will output FR <200hz to any video monitor. You could hook that up to get a visual take and see how it correlates with what you're hearing. You'll also see the FR thru the x-over point that you've chosen. If you tweak the parametric DRC settings and slope, phase, etc. (assuming that you haven't already done so) to achieve the flattest FR around that point, you'll hear a really seamless hand-off from the main speakers to the subs.

You should also manually adjust for smooth FR below that point. Unfortunately, Velodyne (IMHO) mangled the auto-correct software and the cumbersome manual set-up is really mandatory for best results.

Marty

Audionuts,

The OP asked for a "scientific" approach - which I took to mean he wanted an alternative to set-up by ear. I described one such "scientific" approach; set for flat FR at the listening position. In the end, he may prefer the "tune by ear" approach that you recommend, but now he has a different approach for comparison purposes.

BTW, my experience is that the "scientific" approach has yielded vastly preferable results, but that may only indicate my own shortcomings at setting up a sub by ear.

Marty

Wolf,

I don't think that your point is lost on most people. Lots of records suck in lots of ways - including too much/too little bass. Some folks tweak their systems for each record, but I'm probably just too lazy for that. Like the chicken head idea, though.

Marty

PS Even when the record has issues, there's always the purists's question of whether you want to hear what's on the record or whether you want to "fix" what's on the record by tweaking the system.

Personally, I'm already there with systems that correct for the room. When they start selling the system that can adjust itself for the recording flaws, I'll be first on line to sign up.