OK, I have been looking into an amp to go between my (new to me)
passive
sub and my (6 mo old) A/V Receiver.


The Receiver has a single SUB output jack, but the speaker enclosure
has
both L & R inputs, in fact it has outputs as well for I assume
satellite
speakers if I so choose. (We'll ignore those.)
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The Reciever has an RCA connection marked sub out, correct?
If so just connect the RCA cables from there to the sub input which I
assume are also RCA connectors. Just to be sure, we are talking about
a powered subwoofer, correct?

The sub out from the reciever should already sum the LF to mono so no
need to worry further.

The only other setups I've seen are when the connections on the sub
woofer are for speaker wire input from the amp/reciever and outputs to
the main front speakers.

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My plan is to add this sub to an existing setup that already had decent

Front, Center and Surround speakers.


My question this time around is how best to deal with a single Sub
Output from the source through an Amp and on to a Stereo (perhaps dual
voice coiled?) Subwoofer.
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Just connect form the sub output on the reciever, to the input on the
sub. then you go about setting up the crossover on the sub to blend
with the main front speakers. It would be best (if you haven't already
purchased the sub) to get a sub that has both adjustable high and low
pass filter sections, failing that a passive sub with a separate amp
that has, (as many proamps do) a low pass filter and then add a high
pass filter. The reason for this, is to limit the LF output from the
main speakers and save them from working in their most difficult area.
Not having paid any attention to what the abilities are of an A/V
reciever I can't say if these sort of features are already built in,
but I'm sure the owners manual will tell you.
__________________________________________________ ____

If you buy a passive sub, or build one then you need an amp that can be
bridged to mono and preferably you need both high pass and low pass
functions to send only frequencies below a certain point (80Hz or less,
although the sub out will likely be 150-200 Hz) and send only
frequencies above a variable point to the main speakers. They need to
be variable and preferably the slopes should be 24 dB/octave to keep
the bass in the sub and not leak out.

www.hypex.nl has some of the best sub amps around.
Do a search for pro amplifiers and you will find there are many
affordable choices for bridgeable amps that will provide you with ample
power at lower prices than the typical sub amp. Then if you want to be
thourough, add a parametric EQ to smooth out probable FR bumps imposed
by the room.

Adire's Shiva and Tempest drivers are some of the best subwoofer
drivers available, and plans for cabinets are easy enough to find
through them as well. Another option in the DIY sub area is Rhythmik
Audio which also have a very godd product. If yo go the DIY route look
into the possiblity of using sonotube instead of an MDF cabinet. You
might wind up with a sub that looks something like a water heater, but
it will be at least as strong as a conventional cabinet and much
cheaper.

Adire also makes finished subs. Other good subs that are already
assembled are, HSU, PSB, NHT (who also sell there 12" woofer to the DIY
market for use in a sealed enclosure, the absolute easiest DIY project
there is), and SVS. All of these are good products and will give you
excellent bass.

Lastly you will need something that generates test tones so you can
match the sub to the mains, and an SPL meter to measure the levels so
you can match them for smooth integration.

You might want to check with the subwoofer section of www.diyaudio.com
and check the archives for some of the projects that have been done by
the participants.

There are plenty of online resources if you go the DIY route, which is
what I did. I'll never buy a ready made sub again, since I know you
can get equal or better performance by doing it yourself.