What frequency do I crossover subs

Due to way too many variables, there is no way to figure out on paper what is the optimum crossover point for subs in your room. I followed this method successfully: set the point at which my mains were rated -3db on the low end, dialed in phase and matching volume on sub, then adjusted crossover +/- using an SPL meter for smoothest integration. Not difficult, just time consuming.

As low as possible as Danny points out but I'd recommend setting volume by ear as the off the shelf SPL meters don't work well at low frequencies. A correctly integrated sub is the one that calls attention to it self, in most systems with a sub its always set too loud, IMHO

Best of luck

Peter

Making sense at 60 hz: Maybe....your speakers are rated at 45 but how many db down....3,6, 10 db? Some manufacturers stretch the lower reading.

Scientifically: Your ears are the best instruments. Imagine someone looking at a row of TV's and asking someone else which one looks the best. Even then, if you ask 5 people you might get 5 different answers.

Advice (but using "your" ears): Interpolate. Set the x/o around 60 and listen to the lower midrange. Remember it's not a brick wall at 60. The sub will be putting out 120 and 180 hz also, how much depends on the slope. Then try it at 30. Keep doing that at lesser amounts above and below 45 til you get a sound you like.

My guess is that you'll find the best spot somewhere around 30 to 40 but there are many variables. Might be a good idea to invest in a SPL meter (Radio Shack around $50) to help with the volume and phase settings but start with your ears first.