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Discussion Starter · #1 ·
I'm posting this here as well as the SMR-Forum, although it's a Lexicon question in part.


The MC-12 has three sub outputs. Bottom line is that a number of options exist, but I'm currently running stero subs which are set in opposite corners at the front of the room. The room is 20' wide.


I'm considering another matching sub, and, given the setup, it would only receive the LFE output from 5.1 material. The others would receive whatever low bass is crossed over as a function of the bass management in the Lexicon.


I really have nowhere great to place the third sub, however, except on top of one of the existing stereo subs. Thus, I'd have the "LFE sub" on top of either the left or right stereo sub.


I'm concerned about cancellation issues, and, generally, whatever less-than-optimal effects that might result from a sub not being placed on the floor.


I've certainly heard that subs can be stacked, but not in the configuration I'm suggesting. To any of the sub aficionados out there, I'd be interested in your input. The subs will all be the same brand and model, Velodyne HGS-18.


Is it hoping too much to hear from TV on this one?


Thanks,


Nick :cool:
 

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Nicholas,


There shouldn't be a problem placing your LFE sub on top of (or next to) one of your other 2 subs. In fact, having asymetric placement like that is usually better than placing your speakers symetrically in a room. As long as you're not placing it along the centre line of the room (which re-inforces the mono-sounding in-your-head bass), you should be fine.


BTW, is the bass from your two HGS-18s not enough for the room?


Best,

Sanjay
 

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Discussion Starter · #5 ·
Quote:
Originally posted by sdurani
Nicholas,


There shouldn't be a problem placing your LFE sub on top of (or next to) one of your other 2 subs. In fact, having asymetric placement like that is usually better than placing your speakers symetrically in a room. As long as you're not placing it along the centre line of the room (which re-inforces the mono-sounding in-your-head bass), you should be fine.


BTW, is the bass from your two HGS-18s not enough for the room?


Best,

Sanjay
Thanks, Sanjay. That is helpful. As to the 2d part of your question, here's where I'm coming from.


Knowing that the Lexicon permits the three subs to be configured in stereo+LFE, my main concern was that I would actually be diminishing my bass response in 5.1 material, such as DVD-A or Multichannel SACD, since in a three sub configuration, all of the ".1" would be routed only to the LFE.


To me, that meant that instead of the smoother bass response I achieved when going from one to two subwoofers, adding a third would actually put me back in a one subwoofer configuration for all 5.1 material. That I was definitely not interested in.


I spoke at length with Lexicon technical support, who advised that the third sub would not have the effect I feared. While it and only it would get the ".1" material, the other subs would still be reproducing low bass depending on the crossovers. I guess I had surmised that in 5.1 material, all low bass is in the ".1" portion, or the LFE. Apparently it's not.


So is there now enough bass? There sure is. The goal, I guess, is to get the benefit of separating the LFE bass from the crossed over low bass, something that the Lexicon rep suggested was desirable. Right now, the LFE is "mixed" with the other low bass, and, so I surmised from my discussion, there's clarity to be gained by separating the two. How much clarity and whether it's worth it . . . that's a different issue.


But I thought I had allayed my fear that I would lose bass if I go to 3 subs. If someone has a different impression, or just a general comment on whether I'm approaching this correctly, it would be much appreciated.


Sanjay, thanks for the helfpul response.


Nick :cool:
 

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i always wonder just what is the content of the LFE discrete channel? it is probably not musical only special effects, and therefore not of 'phile interest. this argues for getting it away from the more musical content being sent to the mains or L/R subs and for not needing such a high quality sub for lfe.


nicholas, i've got to wonder how much bass is enough?
 

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Discussion Starter · #7 ·
Quote:
Originally posted by jlm
i always wonder just what is the content of the LFE discrete channel? it is probably not musical only special effects, and therefore not of 'phile interest. this argues for getting it away from the more musical content being sent to the mains or L/R subs and for not needing such a high quality sub for lfe.


nicholas, i've got to wonder how much bass is enough?
I know what you're saying, but the LFE channel must be more than that. The LFE channel is the ".1" in both Multichannel SACD and DVD-Audio. Since these are music formats, we're not talking about its use there for the same things as are used in Dolby Digital or DTS for DVDs.


I'm concerned about whether I'm overkilling it, too. I'd really like to hear from others as well. Thanks for the comments.


Nick :cool:
 

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Hi Nick,


Interesting conundrum. I have to say that I myself haven't separated the LFE from the bass management of the processor in any system I've done. Of course there aren't that many processors which allow you to implement this effectively without external crossovers.


The question of how much bass is enough is an interesting question, not without its complexities. The biggest problem is that we need to keep in mind the difference between just plain loud and having headroom. Your HGS-18 throws another complicator into the mix as it does have an internal limiter for the cases when there is large very low frequency content. It is noticable when it kicks in... at least in my experience. Of course this isn't all that often with a pair in a moderately sized room, but different room sizes or fewer units can make it an issue more often.


As such, in configuring a system there are some decisions to be made. The question of which offers more benefits or fewer detriments is between having more shared headroom for high peak signal content on either the main channels or the LFE channel, vs. separating the signals. Personally, I find our ContraBass about sufficient to cover full headroom in most moderate sized rooms, and it has the output of more than 2 HGS-18s. One designer who specifies the ContraBass when possible typically uses 2 units if the room has enough space.


Hard as it is to comprehend as "necessary," if you consider that in the ideal the LFE channel will produce near 115dB at the seats, the combined signal of this and the re-routed bass management signal justifies as much as 10dB of headroom over this 115dB level to eliminate the chance of overdriving the system. The catch here is that it isn't very often that your mains will be able to support 105dB of clean, listenable output at the listening position, and you can/should scale things back accordingly.


Now, in making this decision you should also consider the goal in reproducing both signals. If your subwoofers for the mains are producing clean, flat bass at the listening position, I don't really see any benefit to trying to make another single subwoofer handle that same task for the LFE channel. The only difference in combining the signals is that the peak demands are a little higher. That said, if we consider the content we see that by directing the funds to the single subwoofer system you will almost ALWAYS be well within the system's "loafing" range, and you now have headroom available for BOTH signals, compared to having one with more headroom, and likely a different frequency response than the other signal.


Here would be an interesting experiment...

With your pair of subwoofers set to stereo, run a second line to the sub which you would stack upon, and plug it into the remaining channel input so the HGS-18 sums the two signals. Now set the MC-12 to the intended configuration. For best comparison keep the volume a few notches lower, as the one sub is now getting ALL of the LFE signal which before was distributed between the two. This will show you what sort of LFE frequency response you will be getting, and allow you to make some observations and judgements.


Keep us posted.
 
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