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Separate sub for the rear channel
#323155 09/18/10 03:36 PM
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So - would 2 subs - one for the front channels and one for the rear (or surround channel) be better for movies?

http://www.audioc.com/library1/subprimer.htm

A single sub provides a major and cost-effective improvement for most people in most rooms with most music. However, there are a number of reasons to consider more than one sub.

-Stereo subwoofers, are more important if the main speakers need a rather high crossover frequency. Some very careful listeners may want stereo subwoofers with crossover as low as 60Hz while many others might be more than happy with a single subwoofer crossed over above 100Hz. Many of the popular three-piece satellite-subwoofer systems in the $500-$1000 range have crossovers above 160Hz! Some listeners hear the problems immediately while others never even notice them.

-Multiple subs can increase output levels and lower distortion. People with large rooms and those who need higher than average output levels might want to use more than one sub. Two smaller medium cabinets might fit your space better than one large box. For large spaces, and or very high volume requirements, any number of subs can be added to a system.

-Multiple subs can yield smoother in-room response than a single subwoofer. Loading the bass into the room from two or more points can give a better balanced bass throughout the room. However: if the crossover frequency is low, (usually below 80Hz or even lower), the best bass may be with the multiple subs placed next to each other.

-A third sub may be used for the rear surround channels. Many films now have significant low bass in the rear channels. Some processing modes require extra subs for the ultimate experience. Some film lovers feel that having a subwoofer for the rear channel improves impact and realism with such films.

Re: Separate sub for the rear channel
cvictorg #323161 09/18/10 04:37 PM
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Pretty soon, the sound will be perfect but there will be no place left to sit.


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Re: Separate sub for the rear channel
cvictorg #323180 09/18/10 08:07 PM
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Originally Posted By: cvictorg
So - would 2 subs - one for the front channels and one for the rear (or surround channel) be better for movies?. . .

Hi cvictorg'

Definitely not, if you use two subs they should be feed with the audio signal from the LFE dedicated channel which (when well configured) will also include all the lower requencies for all the channels (including front and rear). Having one sub for the fronts and one for the surrounds (rear and/or sides) could easily result at not only missing good bass information but at having a single sub working at a time (rarely in unisson).


jc
Re: Separate sub for the rear channel
cvictorg #323191 09/18/10 11:53 PM
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Given that frequencies below ~80 Hz are non directional, there is no benefit to a rear channel sub. I'm not even sure how you would redirect bass from a surround channel specifically to one sub.


Fred

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Re: Separate sub for the rear channel
fredk #323196 09/19/10 12:51 AM
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I think it might be interesting if you could setup a midbass unit for the rear channels. You could set the crossover in your AVR to 40hz and then use a sub-woofer with an internal high level crossover to have a second crossing for the rear channels at say 80hz. This way you wouldn't be missing out on any lower frequency surround effects that your average rear channel speaker is unable to reproduce.


M22 VP100 QS8 RX-V665 DMP-BD55 SMS-1 LFM-1+ LG47SL90

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Re: Separate sub for the rear channel
cvictorg #323197 09/19/10 01:04 AM
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No.


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Re: Separate sub for the rear channel
JohnK #323198 09/19/10 01:13 AM
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No.


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Re: Separate sub for the rear channel
terzaghi #323237 09/19/10 09:02 AM
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Oh oh, somebody did a no no.

The -3 db point of the QS8 is 65 Hz. You can't localize bass below ~80 Hz (probably a little higher in most rooms). Unless you have a surround speaker with a -3db point of 100 Hz or higher, I just don't see the point of a sub or mid bass unit for surround duties.

If your surrounds are not that good, spend the $500 on better surrounds rather than an MBM.


Fred

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Blujays1: Spending Fred's money one bottle at a time, no two... Oh crap!
Re: Separate sub for the rear channel
fredk #323249 09/19/10 01:33 PM
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Frankly, I don't totally believe the often quoted 80hz non-directional figure. This is why I said it might be interesting. I honestly don't know of any "surround" speaker that can even approach 40-50hz at meaningful levels of pressure. I suppose if I had deep pockets and 2 pair of M80s or a second subwoofer then I could try it. However, I don't have these things. Just because it's "taboo" doesn't mean it wouldn't be fun to try.


M22 VP100 QS8 RX-V665 DMP-BD55 SMS-1 LFM-1+ LG47SL90

Depression is merely anger without enthusiasm.
Re: Separate sub for the rear channel
prototype3a #323252 09/19/10 02:13 PM
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cvictorg, and all,

Whoever wrote that "sub primer" is deeply misguided and does not understand how movies are mixed. The following is simply wrong:

"A third sub may be used for the rear surround channels. Many films now have significant low bass in the rear channels. Some processing modes require extra subs for the ultimate experience. Some film lovers feel that having a subwoofer for the rear channel improves impact and realism with such films."

The whole point of the " .1" Low-frequency effects channel used in all cinema systems (mainly Dolby, dts and some Sony) and movie/TV show mixes is for deep bass frequencies below 100 Hz.

Regards,
Alan


Alan Lofft,
Axiom Resident Expert (Retired)
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