"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.
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.
(2) The LFE channel is distributed among all speakers depending on their
properties and the crossover point settings. In no case is the LFE channel
above the crossover setting sent anyplace but the subwoofer except of course
if there is no subwoofer. 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. 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.
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.
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.
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.
See my other post and links.
OK, let's do it.
"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.
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.
"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.
"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.
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)."
The document I quoted relates to a dedicated bass management product for use
in audio production. The manual seems to make interesting reading.
Other similar tools:
http://www.smr-home-theatre.org/surr...image_13.shtml
http://pdf.outlawaudio.com/outlaw/docs/icbm_manual.pdf
Also, various online audio-related discussion groups where various
controversies related to these products have been logged. Google seemed to
find a good selection of these with the search words: bass management
controller .