# 5.0 with LFE over Left/Right or 5.2?



## Wintermute (Jun 13, 2009)

I'm setting up a HT system with three 3-way speakers for Left/Center/Right. The Left and Right speakers will also have a subwoofer added to them to make them full range 4-way speakers. Each speaker will have a DSP active crossover. Careful attention will be given to phase alignment and polar response of the drivers at the crossover frequency. Room equalization will also be done in the DSP. The room has plenty of bass traps so I don't think I'll have to position the subwoofers to avoid room modes. 

So here's my question. I have 4 identical subwoofers. Two is enough for the room. Should I route the LFE to the L&R speakers or setup two more subwoofers for LFE only? I'm not sure how movie sound tracks are mixed. Is LFE totally discrete or are LFE sounds spread to all channels. What about sounds like explosions that contain a full spectrum of frequencies. I'm thinking I would benefit from having them all originate from a coherent source. Because the DSP is going to add a processing delay I will probably bypass the speaker setup in the AVR. (Most likely the AVR would think the speakers are 50ft away due to the DSP delay)

My current setup is passive cross-over tower speakers and subs with the AVR set to put all content below 50Hz to the LFE channel. But when I run REW I always see a wide dip around the crossover frequency. That's why I'm thinking to optimize the room response for the Left and Right channels and send LFE to them.

The project is with three NHT M-80 monitors and four S-80 subwoofers. 
-Dave


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## sga2 (Nov 14, 2009)

Wintermute said:


> I'm setting up a HT system with three 3-way speakers for Left/Center/Right. The Left and Right speakers will also have a subwoofer added to them to make them full range 4-way speakers. Each speaker will have a DSP active crossover. Careful attention will be given to phase alignment and polar response of the drivers at the crossover frequency. Room equalization will also be done in the DSP. The room has plenty of bass traps so I don't think I'll have to position the subwoofers to avoid room modes.
> 
> So here's my question. I have 4 identical subwoofers. Two is enough for the room. Should I route the LFE to the L&R speakers or setup two more subwoofers for LFE only? I'm not sure how movie sound tracks are mixed. Is LFE totally discrete or are LFE sounds spread to all channels. What about sounds like explosions that contain a full spectrum of frequencies. I'm thinking I would benefit from having them all originate from a coherent source. Because the DSP is going to add a processing delay I will probably bypass the speaker setup in the AVR. (Most likely the AVR would think the speakers are 50ft away due to the DSP delay)
> 
> ...


I believe the LFE are encoded as a single discrete channel in the media. If you tell the AVR there is a sub, it sends the signal through the line level sub pre-out. If set to "no sub", it will spread the same signal to the front L & R (not sure about C) channels. That is, it would not send different LFE to the left and right channels so no LFE would be associated with any single channel. If you have the gear, why not try? But I think you'll get better results with 5.1 material by using the subs with the LFE channel for the following reasons:

1. Since our ears cannot tell directionality at these low frequencies, there would be no benefit to coupling each sub with a front channel that I can see. The mid and upper level frequencies associated with the LFE events (these sounds sent to the other 5 channels) are what give us a sense of direction to the events.

2. Subwoofer placement is critical to smooth bass performance and the best results might occur almost anywhere on the 4 walls of your room If you are trying to sonically couple the subs to the L & R channels, you will have limited flexibility in placement and likely robbing yourself of performance potential. 

3. If the LFE channel is already discrete, I think you'll lose something (probably imperceptible, but not zero) by using the AVR to combine the signal with fronts and the separating again at the subs' crossovers. 

4. You'd have no direct control over the subs from the AVR. You'd have to manually adjust level trim, crossover, etc. at each sub any time you want to change.

5. One benefit of using a powered sub and AVR crossovers to limit low end signal sent to the other 5 speakers is that you take the burden of the power-hungry low frequencies off the the AVR's amps, giving you more headroom for the rest of the full range.

6. I think that with 4 well-placed subs you could get a very good, smooth room response over a large area - better than you could get with 2 subs. I went from 1 to 2 and the difference is amazing. And my original 1 (SVS PC12+) has enough output to take care of my small room, but the response now is much better over a larger area. Going from 2 to 4 would be nice.

All that said, if you are completely convinced that you only need 2 subs for the room, you might consider conecting two to the .1 output for movies and conneting the other two to the L & R speaker level outputs to "create" 4-way fronts with better low end. I could see this giving some benefit when listening to 2 channel music.

Regards,
sga2


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## Wintermute (Jun 13, 2009)

sga2 said:


> 1. Since our ears cannot tell directionality at these low frequencies, there would be no benefit to coupling each sub with a front channel that I can see. The mid and upper level frequencies associated with the LFE events (these sounds sent to the other 5 channels) are what give us a sense of direction to the events.


It’s not directionality that I'm concerned with. Its phase coherence and time alignment. The further apart the drivers are the more likely they will interfere with each other.



> 2. Subwoofer placement is critical to smooth bass performance and the best results might occur almost anywhere on the 4 walls of your room If you are trying to sonically couple the subs to the L & R channels, you will have limited flexibility in placement and likely robbing yourself of performance potential.


I prefer to solve room mode problems with dampening. Moving the subwoofers around may change the location of the room mode hotspots but the room modes still exists and sound at those frequencies will take longer to decay than non mode frequencies (aka ringing). Dampening takes the energy out of the room. I know there is a lot of disagreement on this topic. But I have done listening tests in my room and dampening is way better. Especially with kick drums and bass guitar. For example, if the bass guitar is strumming fast multiple beats of the same note it all blends into a single long note without room dampening. 



> 3. If the LFE channel is already discrete, I think you'll lose something (probably imperceptible, but not zero) by using the AVR to combine the signal with fronts and the separating again at the subs' crossovers.


Certainly if my crossovers are poor you have a point. But if they are not I feel I actually get an advantage. My understanding is that the LFE channel may contain content up to 120Hz. In my proposed setup I would be using the 8” woofers on the M-80 for this and letting the 12” S-80 handle only the bottom octaves.



> 4. You'd have no direct control over the subs from the AVR. You'd have to manually adjust level trim, crossover, etc. at each sub any time you want to change.


I'm replacing the AVR's processing with the external DSP. I'll have total control of cross-over frequency, slope, parametric equalization and delay.



> 5. One benefit of using a powered sub and AVR crossovers to limit low end signal sent to the other 5 speakers is that you take the burden of the power-hungry low frequencies off the the AVR's amps, giving you more headroom for the rest of the full range.


Let me clarify, the left-center-right speakers will be using a DSP as an active-crossover. Amplification is provided after the crossover. A separate amplifier is needed for each driver. I will need 12 channels of amplification for the LCR speakers. One for each tweeter, one for each midrange pair, and one each for the two eight inch woofers on the M-80. The subwoofers are self powered. I should not have used the term AVR (audio-video-receiver). In fact I'm using an Onkyo PR-SC886 AVC (audio-video-controller). I'm using three 5x200W external amplifiers. 



> 6. I think that with 4 well-placed subs you could get a very good, smooth room response over a large area - better than you could get with 2 subs. I went from 1 to 2 and the difference is amazing. And my original 1 (SVS PC12+) has enough output to take care of my small room, but the response now is much better over a larger area. Going from 2 to 4 would be nice.


I'm not sure the more subs = better. Especially since most AVR/AVCs can only do time alignment for one. My current setup has two subs on the LFE. I make sure that each sub is symmetrically placed. Newer AVR/AVCs have outputs for two subs and I assume they allow each to have its only delay.



> All that said, if you are completely convinced that you only need 2 subs for the room, you might consider conecting two to the .1 output for movies and conneting the other two to the L & R speaker level outputs to "create" 4-way fronts with better low end. I could see this giving some benefit when listening to 2 channel music


Yep, this is my question in a nutshell. If my fronts are truly full range is it necessary to have separate LFE subwoofers. I'm going to try it both ways but I'm curious is anyone else has considered this.


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## sga2 (Nov 14, 2009)

I'm curious how this will turn out. 

Regards,
sga2


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## ojojunkie (Jun 23, 2010)

Since you already have the gears it won't cost you anymore to try both configurations and from there you decide which sound best to your ears. 

Personally, I would prefer 5.2 setup i'll just make sure to lower the x-over of the L/R speakers to maximize it's capability in the lower region and integrate well with the subs.


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