Hi MARC!
> I have been following this echo for some time now (yes, all the way
>from Sydney!) with increasing frustration at the car audio vs home
>audio debate (I enjoy both).  In a vain attempt to distract everyone
>with a question,  I was wondering if anyone could help answer the
>following about my home theatre setup.
Glad to see you and New Zealand back with us again. Now just wish we
could get the Hong Kong crowd back in here again. They REALLY were
into the high end home stuff! We missed all of you.
>1.  I have a pair of small 2 way vented speakers as my mains in my
>  home set up and a single sealed 12inch sub running via a small
>  dedicated amp from the lowpass output of the Yamaha Pro Logic
>  decoder (VSX1050).  Even though the main speakers are not
>  particularly "bass heavy" do I need to run some sort of high
> pass filter on them to prevent interference from the sub?
No, I don't believe that you will need to bother. The small mains
probably have a built in high pass due to the nature of cabinet size,
et al. A lower sub frequency crossover Fc could leave a hole in
frequency response coverage on that system. Locate the sub at the
center front location, which will minimize the displacement effects
since it's coming from the "window on the wall" is a more natural
direction for that band of bass.
> 2.  The lowpass output of the decoder has an Fc of 400HZ and there
>   are lots of directional clues coming from the sub - what is the
>   best Fc to use and how do I do this  - at line level (before the
>   amp) or at speaker level?
That Fc does sound much too high... but then you didn't say just what
the
response of those main speakers are, and I agree, directional info is
there.
Subs work best below about 200Hz where the fundamental frequencies made
by the source material reproduce as pressure changes in the room and are
nondirectional and diffuse, even throughout the room except where room
node cancellations cause the sound to wink out which needs room
treatment
to cure.
My current "main studio monitors(and keyboard gig/personal sound
system",
if needed)" starts to fade at 120Hz (3db down point and loses about 6dB
the first octave below,that and about 12 more the next octave down, so
I have the 18" woofers of the (2-1-18" Gauss) currently setup at for
about
90 Hz, on a 6dB/octave electronic crossover and running an EV 100 WHAT?
per channel in the studio or in mono mode as a live system though with
the cabinets tied in parallel.
At this crossover Fc, I use stereo subs in the studio, since the slope
is not as steep as I would like normally (digital crossovers are much
better than what most can get at right now), but would use them together
for acoustical coupling and maximum power output.
I am running Klipsch 250A's on the top end of things,(a fine portable
sound
system cabinet with a 10" woofer, a mid and high horn (90*40)),highly
efficient, directional, with that horn "in your faceness" and Klipsch
kleanliness. Some like to go lower on the crossover like 80Hz, but that
would be more like large concert and installed systems normally.
> 3. I want to replace the dedicated amp I have with one built into the
>   sub box itself - does anyone have a good cheap amp design (about
>   100Watts) I can work with?  It seems the power supply requirements
>   are more expensive than the active components on most of the kits
>   I have seen.  A decent 200VA transformer runs to about $80 here.
Can't think of one off hand, but a well equiped library (or website)
that
has back issues of some some of the hobby magazines should be a place to
look.
> 4.  Lastly (is this off topic Bonnie?) How do the commercial sub
>     manufacturers get their subs to turn off after 10 minutes or
>     so of inactivity.  I keep forgetting to turn mine off and its
/     driving me nuts?
Since some consider things like this to be a "feature" (I do if I can
selectively disable the damned things, which are frequently a nuisance,
such as a portable DAT machine that I use that wants to shut itself off
-
about the time that I really want it to be on when plugged into the
wall,
not on battery power.
Idle current shouldn't really be THAT bad! I seldom power down my studio
any longer, and never power down the computers. The time it takes to get
it all warmed up and talking to each other is to much bother.. besides,
the air conditioning cost is the big factor to me this time of year
here!
As long as everything is surge (and/or brownout) protected on critical
digital stuff (like considering a UPS), I just leave it all on, almost
all of the time, unless it just isn't regularly used.
Bonnie *:>
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