"Rusty Boudreaux" wrote in message
"Arny Krueger" wrote in message
...
"Rusty Boudreaux" wrote in message
"Arny Krueger" wrote in message
...
The general rule is set the crossover as low as you can without
overloading the satellites with bass. That will depend on
your room
and the loudness you prefer to listen at, among other
things.
For audio (stereo) this is good advice.
Thanks.
For movie soundtracks
with speakers set to 'small' you will loose LFE content above the
crossover frequency.
That's an interesting claim. I'd like to see it supported.
For a preamp/receiver to sport the Dolby Digital or THX logos it
is required the processing be done this way. This is detailed in
their "confidential" design papers. I couldn't find a good
description on their public site. However, it is briefly
discussed in this document:
5.1-Channel Production Guidelines Issue 1 (page 31 of 83)
http://www.dolby.com/tech/L.mn.0002.5.1Guide.s.pdf
"Consumer decoders take the LFE signal and add any channels in
need of bass management, as determined either by product design
or user selection. The five main channels are then high-pass
filtered at either a fixed frequency of 80 Hz or a selectable
frequency of 80, 100, or 120 Hz. The summation of the LFE and any
other channels is low-pass filtered at the same frequency. If the
crossover frequency is fixed at 80 Hz, as is standard in lower
priced decoders, information in the LFE channel between 80 Hz and
120 Hz will be reproduced at a lower level than it is recorded"
I guess you lost me when you say that LFE content is lost. In fact, its just
reproduced at a lower level than recorded.
The design guidelines spell out in no uncertain terms that the
LFE channel must be summed with the full range channels first and
then LPF. Therefore, any content in the LFE channel above the
crossover frequency will be attenuated in the subwoofer output.
I don't read "attenuated" as "lost". I guess that's a matter of personal
interpretation.
As a side note, all THX certified speakers are designed to be set
to small.
I've seen two general ways that the LFE channel is handled"
(1) The LFE channel is sent to the subwoofer without actually being
changed by any bass management. If any other speakers are set for
"small", their bass content below the crossover frequency may be
added to the LFE info in the subwoofer feed. This is pretty crude
especially the ones where there is really no bass management.
Approaches like these show up in some low-end
implementations, including mid-end consumer PC sound cards.
Basically, if you have no subwoofer, you hear no LFE information. If
your LF & RF speakers
lack bass, the LFE speaker may or may not be able to help you.
This certainly violates the Dolby Digital licensing agreement.
Stuff happens!
(2) The LFE channel is distributed among all speakers depending on
their properties and the crossover point settings.
Dolby/THX licensing allows redirection of the LFE to all channels
only if no subwoofer. If subwoofer exists then LFE can only be
routed to the main left/right. However, some decoders have a
"super" mode that combines LFE and bass from small channels and
redirects to all large speakers. THX does not recommend this and
if done THX requires all THX processing to be disabled.
Compliance is tested during THX certification.
In no case is the LFE channel
above the crossover setting sent anyplace but the subwoofer except
of course if there is no subwoofer.
Further, the LFE content above the crossover frequency is being
filtered for the subwoofer output and content is lost.
I believe you just said "attenuated", which I interpret as being different
than "lost"
If there is no subwoofer, the proper assignment
for LFE channel signal above the crossover point would appear to be
the center channel, subject to the settings for that speaker.
see above for dolby/thx certification.
However, below
the crossover setting, the LFE channel's content is pooled and
divided between the subwoofer (if present) and all other speakers
that were identified as being "large*. This is a pretty
high-quality implementation, and typical of mid fi consumer audio,
and up.
Again, see above for dolby/thx certification.
Let me elaborate. My main system which is used for both HT and
music, has no subwoofer at all from the standpoint of surround
processor bass management. My surround processor's subwoofer output
receives no signal. A subwoofer is present, but it is part of the LF
& RF subsystem. The RF & LF speakers are defined to the surround
processor as being "large". An outboard 24 dB/octave crossover
splits the subwoofer signal from the feed to the LF & RF speakers.
This is one of the best ways to implement LFE and low bass from
the full range channels. Although, I'm not doing it now I intend
to shortly.
I don't know about "best", but it does seem to work. It also seems to avoid
some fairly widespread problems with reproducing stereo music on the same
system.
By all accounts and tests, the LFE channel is well-represented in
the sound field in the listening room even though this system
effectively has no LFE speaker. I note that my surround processor
has no level controls for the subwoofer, but it does have a level
control for the LFE channel. The LFE channel is obviously virtualized.
I arrived at this setup experimentally, because my surround
processor has only a single crossover frequency, and it is
inappropriate for the speakers and the room.
It also preserves all LFE content regardless of crossover
frequency...which is why I'm gonna do it soon 
I guess it does avoid the attenuation effect that is described in the
standard.
I think this indirectly contradicts the claim that: "For movie
soundtracks with speakers set to 'small' you will loose LFE content
above the crossover frequency." My system has no LFE speaker
whatsoever, and yet the LFE channel
is well-represented in the room. Not only is the LFE represesented,
but it is also clearly and logically imaged.
My comments were intended for the sub output on a pre/pro in
which there is loss. With an outboard crossover as you have done
it's not an issue.
Trust me, I blundered into this arrangement.
;-)