Originally Posted by tkntz
I have a similar question regarding the crossover as I am running some old 603s in front, LCR 60 center, ASW1000, and 601s in the rear. I've also never felt like I had the volume set correctly either. It is either too boomy or non-existent.
Any suggestions would help.
This will be long...
Before you set your crossover you want to understand how 5.1 AVR or Pre/pros distribute sound to speakers from a AC3 (or other newer codec) signal. The following is my understanding, but I do not profess to be an expert, so please take this with a grain of salt.
With a 5.1 signal there are obviously 6 discrete channels of sound, and all but the sub channel are full-range (from 20hz-20khz, at least). The sub channel carries low-range information like sound in the 20hz-200hz range, typically explosion and other similar noises on a movie soundtrack. It's the AVR's job to make sure that all (or as much as possible) the information in those 5.1 tracks gets played, no matter what your configuration of speakers. So when you select which speakers you have, it will attempt to redistribute information from speaker channels you don't
have into those channels you do
have. When you set your speakers to large, it assumes they can play a full range of sound (20hz-20khz) and it won't worry about adding a crossover to limit the range of sound coming out of them. When they are set to small, it doesn't mean they are necessarily physically small (i.e. like bookshelf speakers), but that they should have some
kind of limit on the range of sound that is sent to them so that they aren't unduly taxed. This means adding a digital high-pass crossover, usually at a frequency that you can select. My Onkyo 805 lets me select from 40hz to 200hz in 20hz increments, most current AVRs are similar. If I use 40hz, this does not
mean that the speaker will get nothing
below 40hz, but that the frequencies below 40hz will get rolled off at some db/oct (depends on the receiver, usually either 12, 18, or 24) until you DO get nothing.
Example: Setup - you're sending your speakers THX reference level noise (75 dB equivalent in signal); you're sending them full-range pink noise; you have an 18dB/octave crossover; and you have and you set your crossover to 60hz.
Then at 30hz, you're going to be getting only 57dB of signal, and at 15hz, 39dB. Remember, an octave is a doubling/halving of frequency, and 3dB is a doubling in perceived loudness from a driver.
With that in mind, you want to set your crossovers on the speakers according to their ability to reproduce sound. This is where the +-3dB range spec comes in handy. So with a speaker that has a -3dB of 49hz (pretty common for a ported bookshelf), you might want to set the crossover at 60hz or so to make sure that your speaker is really performing in its optimal frequency range.
The other key to this is that if you have any of your speakers set to small, whatever information the AVR filters out from sending to the "small" speakers gets sent to the sub instead. So you have the sub playing not just the ".1" track information, but the stuff that's been high-passed filtered out. Clearly, if all of the other 5 speakers are set to "large", then the sub only gets the ".1" information and nothing else.
The crossover on the sub works the same way, but it's a low-pass crossover, filtering information above
the selected freq. This is to help your sub also stay within it's "comfort zone". Larger drivers typically have more difficulty moving quickly enough to play the higher frequency information, so a crossover for a speaker with a 15" driver is typically going to be set at a lower value than one with a 10" driver(s). Again, the +-3dB freq. point comes in handy. Another factor is that most people use 80-90hz as the "rule of thumb" point at which sound starts to be directional. This means above those frequencies (they are not hard numbers and are affected by many things) the wavelengths for the sound waves are short enough that the human ear can locate their origin. I tend to believe this number is a bit on the lower side of that range, if not a bit lower still. Above about 90-100hz, the male voice dips into the range played by the subwoofer, which (IMO) starts to sound terrible. This is where a lot of subs sound very "boomy". There is typically a LOT more information in the 100-120hz range than the 40-80hz range for most sources, so the sub starts working very hard. This is also why the sub/sat home theater systems usually sound very bad. The main drivers can't go low enough to unburden the sub from playing where it's very uncomfortable, so there are either big holes in the frequency response (read: Bose) or the sub takes up the slack anyway (many of them go up to and beyond 200hz).
So in order to set your sub crossover properly, you have to know
1. what are my speakers capable of producing (match crossover points to speaker +-3dB range)
2. what do I have my small speakers crossed over at (match the low-pass on the sub with high-pass on the speakers, if possible)
3. what are my personal tastes (if you like a very subtle sounding subwoofer, go lower with crossover freq, if you like a lot of boom and loudness to the sub, go higher)
This probably didn't answer your question directly, but the THX spec for the subwoofer crossover is 80hz, so you can use that as a guide. For your specific setup, I'd recommend setting all speakers to small, run 80hz crossovers on the center and rears, 40hz crossover on the fronts (may be pushing a bit, but 603s can handle it I think), and 80hz on the sub.
Note: please don't crucify me for any misinformation in here. Again, I'm not an expert. Feel free to correct where I've undoubtedly got errors.