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Discussion Starter · #1 ·
I am very interested to know how effective the "Bass Enhance" feature of Lexicon is. To make any meaningful conclusions from this thread, please read the documents in these links carefully. I assure you that you will have a different perspective about Bass Management after you have read these very interesting links.

http://www.smr-group.co.uk/pdf/Bass_Enhance_FAQ.pdf


I did not have any major issues with the theory behind "Bass Enhance" but I started having some doubts after reading this article

http://www.hometheaterhifi.com/volum...rs-9-2002.html



If the information in "hometheatrhifi.com" is accurate, Dr. Griesinger's recommended ideal speaker configuratoin will basically discard most of the LFE channel, i.e., 40Hz to 120Hz !. That is about 80% of the LFE information encoded in the LFE channel. THX assumes that discarding 40% of the LFE information is acceptable by setting the sub-crossover at 80Hz because most modern movies do not have much information encoded in the 80Hz to 120Hz band. However this is not true for LFE info below 80Hz. Please note that this issue is only with the LFE output (subwoofer output in pre-amp/receiver).



Hometheaterhifi.com

====================

Strictly speaking, any processor with a sub/sat crossover frequency set lower than 120 Hz is "discarding" the upper end of the LFE channel. THX units are NOT exempt from this. With the standard THX 80 Hz 4th order crossover, the top of the LFE channel gets chucked.

====================


Lexicon's BASS enhance

********

As an “ideal†speaker configuration, Griesinger recommends:

– Sides set to Large

– Fronts and rears set to Small / 40Hz crossover

– Center set to Small / 120Hz crossover

– Subwoofer crossover set to 40Hz

********




If the whole idea behind "Bass Enhance" is to enhance the bass.... it does not seem to be addressing this, at least theoritically. I am sorry that I have to directly question a theory from a reputable company, in fact, I have an MC-1 that I really love for its Logic 7, but I do need some answers for these claims.

Thanks,

Sincerely,

-Jai
 

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What actually should happen in standard bass management is that the LFE should be fed to the subwoofer output after the low-pass filter rather than ahead of it. I don't know if anyone does it that way, though. Lexicon is pretty fastidious, so if anyone were to do it, I expect they would be in the group. The most puzzling setting to me is the one for the center channel.


Anyhow, the point of "Bass Enhance" is improved spatial reproduction at low frequencies, so despite the name, it is not about getting more bass. I don't know enough about the inner workings of this particular process to say for sure, but my guess would be that the processor can figure out from the crossover settings where it needs to route the information high-passed out of the various non-full-range channels in order to preserve it all. On the other hand, any time you have bass being reproduced from multiple locations you have opportunities for cancellation, so I expect it would be harder to get smooth, flat bass response with the setup described than with a more typical one in which low frequencies from all channels go to the subwoofer.


Before embarking, the question you might want to ask yourself is how acutely aware you are of the sort of spatial effects Griesinger is concerned with here. David is more attuned to that sort of thing than anyone else I have ever met--certainly more than I am. At the same time, if I have ever met an actual genius in my life, he is probably it. In short, I dunno!
 

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MDRiggs,

Quote:
What actually should happen in standard bass management is that the LFE should be fed to the subwoofer output after the low-pass filter rather than ahead of it.
Why do you think it should work this way? Where else will LFE go (modulo extra information like height put in Telarc and dmp SACDs) if not the subwoofer? Lexicon feeds LFE full-range into the sub, no matter what the sub's xover setting is.

Quote:
The most puzzling setting to me is the one for the center channel.
The recommended center channel setting at 120 Hz for bass enhance is to supress excitation of median standing waves that would disrupt ITD fluctuations necessary for bass enhance's effect. I've found that this depends on the system and room in use. I don't like this setting because lower registers of male voices become lost or less solid, and BE can already be overdone in my room.

Quote:
I don't know enough about the inner workings of this particular process to say for sure, but my guess would be that the processor can figure out from the crossover settings where it needs to route the information high-passed out of the various non-full-range channels in order to preserve it all.
That's not how BE works, and as explained in the other thread, BE is entirely orthogonal to bass management, which is what you're describing.

Quote:
On the other hand, any time you have bass being reproduced from multiple locations you have opportunities for cancellation, so I expect it would be harder to get smooth, flat bass response with the setup described than with a more typical one in which low frequencies from all channels go to the subwoofer.
This would be true if the bass information were coherent. Since the point of BE is to make essentially uncorrelated bass, this isn't necessarily true.


--Andre
 

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Quote:
Originally posted by AndreYew
Why do you think it should work this way? Where else will LFE go (modulo extra information like height put in Telarc and dmp SACDs) if not the subwoofer? Lexicon feeds LFE full-range into the sub, no matter what the sub's xover setting is.
Not following you. What I said was that it should be done the way you say Lexicon is doing it. Actually, re-reading what I wrote, I see how you could have taken it the other way. Anyway, many manufacturers seem to feed the LFE through the crossover filter on the way to the sub, which is wrong but probably easier than doing it right.

Quote:
That's not how BE works, and as explained in the other thread, BE is entirely orthogonal to bass management, which is what you're describing.
Okay. But if the setup is as described, how do you wind up with all the bass in the soundtrack being reproduced?

Quote:
This would be true if the bass information were coherent. Since the point of BE is to make essentially uncorrelated bass, this isn't necessarily true.
Pretty long wavelengths you're dealing with. Not obvious to me how you could jigger the timings to ensure good amplitude response. I know Tom Nousaine tried BE once, and set up according to instructions, he got a huge suckout in his room.
 

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Quote:
Originally posted by jmcomp124
MDriggs, Andre and Shawn,

YOur expert insight into this related topic will be invaluable. Please take a look at this thread. I would like your inputs.

http://www.avsforum.com/avs-vb/showt...hreadid=210817


Mono bass from LFE output of Stereo bass for HT?
Leaving apart Lexicon Bass Enhancement for the moment: The best approach to bass reproduction usually is to send everything below about 80 or 100 Hz from all channels to a single subwoofer (or to multiple co-located subwoofers). And usually the best location for the subwoofer is in a room corner away from room openings, such as doorways. (Not always, but in most rooms.) In most cases this will yield the smoothest low-frequency response without compromising imaging.


I didn't read the thread you reference very carefully, but I did notice the argument that summing bass from multiple channels will cancel out-of-phase signals, which is true. But: (1) Even though modern media can easily carry true stereo or multichannel bass, it usually winds up being mono anyway because of the way the recordings are made. (2) Using separate subwoofers rather than summing doesn't get you out of the woods anyway, because the same sort of cancellation can occur in the room. In fact, with multiple spaced subs you can get that problem even if the bass is mono. So I think it's a seriously flawed argument.
 

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MDRiggs,

Quote:


Pretty long wavelengths you're dealing with. Not obvious to me how you could jigger the timings to ensure good amplitude response. I know Tom Nousaine tried BE once, and set up according to instructions, he got a huge suckout in his room.
Two points to consider here: bass is phase-shifted 90 degrees relative to the other side. All bass on one side (say the left), is +45 degrees, and bass on the other side is -45 degrees. This turns out to be a good compromise in exciting ITD fluctuations without causing a major suckout at the listening position.


The second point is that BE is very room-dependent, so different people will get different results depending on their speakers and room. The Lexicon suggested setup is only the starting point, and one should experiment to get the best response in a room.


--Andre
 
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