Subwoofer crossover - for what purpose?

Posted by Philip Brandes [IP: 152.163.206.189] on October 26, 1998 at 12:34:54:

In Reply to: Subwoofer crossover - for what purpose? posted by Phil Miller on October 26, 1998 at 10:19:24:

Phil,

I take it you're referring to the DC-1's sub crossover, not the external one built into the sub. But either way they both serve the same purpose in limiting the freqs sent to the sub.

Here's why it's a good idea to use the DC-1 sub crossover as well as the other speaker crossovers. Since there is no discrete sub channel for Pro-Logic and other non-5.1 formats, the DC-1 follows the typical practice of generating the sub output by summing the front L & R signals. (This will also include the bass routed to the fronts from small center and surrounds).

Without a sub crossover, you can end up with overlap between your fronts and the sub, resulting in too much bass. Say you set your fronts to small w/80 Hz xover. Unless you set your sub crossover to 80 Hz as well, your sub will duplicate the freqs from 80 up to (I believe the sub signal tops out at 150 Hz) that are also going to your fronts.

The only way to keep this from happening is to set your sub xover to the same freq as your front channel crossover (80 Hz per THX specs).

Although theoretically this limits the LFE channel to 80 Hz & below, Lexicon claims that in actual practice the LFE channel (which only duplicates other channel info) is never mixed above 80 Hz, so you're not losing anything.

Note that Lexicon will be making changes to bass management in the next software upgrade, so it may work differently then.

Hope this helps,
Philip

: I was reading an article on the LFE channel over the weekend and I began
wondering exactly what purpose the sub x-over serves. The x-overs on the
fronts, center, rears and sides clearly serve the purpose of routing
bass to the sub below the x-over but what is the sub x-over filtering
out/in and where would the filtered out signal be produced? If, in
addition to material routed to the sub from the front speaks, etc., the
LFE channel potentially contains 20-120 hz of material -does that mean
we should set our sub x-over to 120 hz which would mean we would pick up
all material filtered from the fronts, etc. (i.e. below 80HZ) plus all
of the LFE material. The inclusion of a sub x-over may have something to
do with the THX standard and the usefulness of it may be very obvious
-but not to me at this time. Thanks. Phil M.

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