"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"
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.
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.
(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.
If there is no subwoofer, the proper assignment
for LFE channel signal above the crosover 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.
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 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.
"Rusty Boudreaux" wrote in message
"If they are really small satellites you may have integration
issues. What you want is a smooth frequency response from
where
the sub drops out to where the mains pick up. With small
satellites at high volumes their low frequency ability is
reduced. You can end up with a dip in the response because the
satellites loose output near the crossover frequency."
This is one of those "depends on" statements without some
unstated
dependencies. These days we have subwoofers with 10, 8 and even
6 inch
drivers. These speakers can easily have relatively smooth
response up to say
300 Hz, which is the highest "subwoofer" crossover frequency I
can conceive
of in a system with pretensions to sound quality. My point is
that with a
driver like this pointed at the listener and a
decently-designed crossover,
a dip due to the acoustic properties of the sub and satellite
is unlikely
for any reasonable crossover setting.
The point I was trying to make is small satellites will be
excursion limited in their lowest octaves. In my case, I have a
massive IB subwoofer that has 15 liters of displacement at Xmax.
With my original satellite speakers I adjusted levels to achieve
a flat response at low and moderate SPL. However, when cranked
to high SPL the satellites couldn't keep up on their low end and
a dip in the response appeared. Even with the crossover at 160Hz
the dip would appear at the highest SPLs. I upgraded to mains
with better bass capability and no dip even at 110dB at 80Hz.
More likely, the bass and perhaps even the mid-bass imaging
will be upset.
We can argue all day as to whether the ear hears directionality
at 60 Hz,
but by 150 Hz there's very little doubt. For example, the
intention of the
recordist might be that the bass come from either the LF or RF,
but if the
crossover is at 150 Hz and the subwoofer and LF & RF speakers
aren't
positioned very close to each other or if they are close but
you are sitting
close to them, you're going to hear a lot of that bass coming
from the
center. I call that bass imaging failure.
Agreed.
"One way to combat this with small speakers is to set crossover
at
a relatively high frequency. However, you'll have to have a
really good sub that doesn't throw harmonic distortion into
higher audible frequency region...otherwise you'll easily be
able
to pinpoint the sub location."
It's true that a sub that is distorting will generate output
above the
crossover frequency and therefore be easier to locate. However,
you don't
need to presume substandard equipment to explain why a high
crossover
frequency will simply allow the listener to localize sounds to
the subwoofer
because the crossover point is too high for the application.
The ear
localizes the sound source better and better as the signal
frequency goes up
from 60 to 80 Hz. One way to partially circumvent this is to
put the
subwoofer very close to the satellites and to put the
satellites closer to
each other. However, this approach to reducing bass imaging
failure causes
some bass imaging to be lost.
Good point.
"If your really serious about getting a good match I recommend
upgrading to more full range speakers and/or adding midbass
drivers to pick up the slack."
Good advice. I've seen this work many times.
"I recommend setting the receiver to 0dB and adjusting the sub
amp
until the level is as close as you can get. Then use the
receiver to fine tune if necessary."
Generally speaking, more good advice. However, it's
non-specific about what
the receiver's LFE channel control is called and what it
actually controls.
I frequently see a LFE control, not a subwoofer control.
There's a big
difference because the LFE is effectively an input to the bass
management
subsystem, while the subwoofer is an output from the bass
management
subsystem.
Yep. You're right.
No need to comment much on the remaining comment where we
agree.
For a counterpoint, I consider the following which showed up in
my research:
http://www.abluesky.com/m/p/bs10011b.pdf page 10:
"The LFE Channel was originally designed for film applications
as a way to
extend the low frequency "head-room" (not frequency response)
of the
playback system. This additional headroom was created by adding
+10dB of in-band gain to the LFE channel. This channel should
only be
used when no additional headroom is available in the other
channels for
low frequency effects. As an example, you may use the LFE
channel to
increase the dynamic low frequency content of a movie that has
many
large explosions. This is rarely the case in music, although
there may be
some creative reasons to use the LFE from time to time. It is
important to
note that no "significant" audio should be sent exclusively to
the LFE
channel. The reason for this is that if a Dolby Digital audio
track is
folded
down to 2-channels, which can happen if a consumer doesn't have
a
surround system, the LFE channel will not be added to the
fold-down mix
(all other channels will be added to the fold-down)."
Yes, this is verbatim from the Dolby manual.