question on matching subwoofers with main speakers

[2gumby2]

I purchased two Velodyne SMS-1 active crossovers to go with my two subwoofers. My main speakers are rated to achieve 32Hz, but the instruction manual for the SMS-1 recommends setting the crossovers at 80 Hz since this is "the THX standard". I read somewhere else that subs should be crossed as low as possible. For those that might have experience in such matters, should I go with the recommended 80 Hz crossover or perhaps try to cross at around 40 Hz or lower since my main speakers have that capability? I listen to 2-channel music only, no Home Theater.

[Grainger49]

I have been living with subs since the 70s.  I like them and they drive me crazy.  Here is why:

The rated response of your speakers will not be what is achieved in your room, unless you listen in an auditorium.  What is achieved in your room will be a higher roll off frequency.  So you will need to work with the crossover frequency, level, phase, speaker positions to achieve a smooth frequency response.

I don't know that THX standards (for movies) are applicable to a system where your main speakers might respond below 80 Hz the result will be a bloom of bass in the region between 80 Hz and where your speakers actually do start to roll off.

Then there is the matter of your speakers' roll off slope.  If it is a gentle slope there will be little more bass energy present when the sub adds to it below the roll off frequency.  If your speakers roll off steeply and the sub is a less steep roll off then there will be a bit of a hole where they crossover.  Neither are that offensive, you get to decide.  So I agree, crossover the sub as low as possible without a bloom or hole.  That is right, just not as simple as they state it.

I like to place the subs at the plane of the main speakers.  If you find the sub is slower than the main speaker, try it more forward.  If the subs are too aggressive, seem to play before the mains move them back.  This is assuming they are in phase with the main speakers.  That is the sub and the main woofers move forward at the same time.  (Sorry if that is insulting, it isn't meant to be.)

Even a cheap spectrum analyzer is a help.  If a friend has one get him to come over drink beer and show you how it works.

I use a sub and a year after I had it "set up" I discovered a hole in the response and had to increase the crossover frequency.  It is a process.  

Enjoy the trip.

[2gumby2]

The Velodynes have the ability to adjust phase in 15 degree increments so I'll try to get the phase set first and then experiment with the crossover points to see what happens.

[Grainger49]

That is a great adjustment.  Mine only has a 0 and 180 degrees switch.  

The problem is that you might move the sub to get rid of some modes, bass humps and then the phase is off again.  

There is a set up trick where you set a sub in your listening seat.  Play a test tone (Stereophyle's test disks) and walk around where you want to place the sub.  When you find a spot that most of the tones sound an equal level then the sub goes there.  You need to do it twice to place both woofers.

Oh, I just remembered, send your wife out somewhere else or she will lose her mind.

[xcortes]

the instruction manual for the SMS-1 recommends setting the crossovers at 80 Hz since this is "the THX standard

Thx doesn't care about the low frequency extension of your speakers because they're supposed to be high passed at 80 hz by the Thx Ht processor. You DON't want to do that and you only want the SW to enter the scene where your speakers leave it. Thus experimenting, or even better, measuring, is the way to go. Yu want at least a RS SPL meter and a set of test tones. If you want to reatin your mind, marriage and hearing, do yourself a favor and get some measuring software. There's some downloadble for free. You'll need a decent sound card and a mic.

I set up my SW through measurement and then on each record I adjust the volume up pr dow anyway :>)

[2gumby2]

Good advice all. My subwoofers have an internal volume of 9 cubic feet each and weigh about 225 ponds each so I will not be moving them around. However, I have them sitting near each speaker so hopefully this might help some. I printed off the Outlaw Audio SMS-1 guide so after I go through that I'll get serious about setting the subs up.