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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/volu...ers-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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Jai,


"If the information in "hometheatrhifi.com" is accurate"


It isn't.


"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. "


Unlike what that article says the THX standard was put in place years before there were DD 5.1 soudtracks. The LFE channel on DD isn't brickwalled at 120hz either, that is its -3dB roll off point.


"Dr. Griesinger's recommended ideal speaker configuratoin will basically discard most of the LFE channel, i.e., 40Hz to 120Hz !"


No it won't. The MC-1 will redirect the LFE from above the sub crossover point to your next larger speakers.


On the MC-12 if you are just using the L/R sub outs (and having the LFE redirected to them) the LFE portion of the signal bypasses the subs crossover point.


Shawn
 

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Discussion Starter · #3 ·
Quote:
Originally posted by sfogg


"If the information in "hometheatrhifi.com" is accurate"


It isn't.


"Dr. Griesinger's recommended ideal speaker configuratoin will basically discard most of the LFE channel, i.e., 40Hz to 120Hz !"


No it won't. The MC-1 will redirect the LFE from above the sub crossover point to your next larger speakers.


Shawn
Shawn,

Thanks for the info. Are you sure that "The MC-1 will redirect the LFE from above the sub crossover point to your next larger speakers". Where did you get that information ?

-Jai
 

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Jai,


The HTHF website assumes that your sub xover is 80 Hz all the time. That's not the case with Lexicons, or many other higher-end separates systems (Meridian, Theta, etc.). Set to the settings recommended by Lexicon (which should be considered just a starting point), you will lose no bass information with a Lexicon processor.


Second, you must separate the issue of bass enhance from bass management. Bass enhance is all about decorrelating mono bass for better envelopment and bass externalization. It's done by phase-shifting bass on one side 90 degrees relative to the other side. Bass management functions work independently of BE functions.


--Andre
 

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Discussion Starter · #5 ·
Andre,

I do understand/agree that BM works independently of BE, but the coverse is not true. BE relies on BM. If indeed, what you and Shawn say about bass management is correct (The HTHF website assumes that your sub xover is 80 Hz all the time AND The MC-1 will redirect the LFE from above the sub crossover point to your next larger speakers), I have no issues with the theory. Can you point me to some solid document that will prove what you emphasize. I gain knowledge by reading documents like
http://www.hometheaterhifi.com/volu...ers-9-2002.html

and through my own experiments. But in situations like this it is very difficult to find out through experimentation in a typical HT setup and hence I rely on information presented in documents. It is disappointing to see inaccurate information published like this. What the article says is


"Strictly speaking, any processor with a sub/sat crossover frequency set lower than 120 Hz is "discarding" the upper end of the LFE channel."


It says "ANY" processor. Wouldn't one be lead to believe that it woudl hold for high-end equipment like the MC-1 ?


Anyways, Thanks for all the info.

-Jai
 

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Quote:
Strictly speaking, any processor with a sub/sat crossover frequency set lower than 120 Hz is "discarding" the upper end of the LFE channel.
Any processor that works that way is a bad processor. Most of them either send the LFE above the crossover point to the mains or bypass the crossover with the LFE channel and send the whole thing to the sub. As long as you are letting the processor handle the bass management, and not using the built-in crossover in a powered sub, you won't have a problem with most current rigs. It's easy to test. Play the Avia DVD's test tones for the LFE channel and listen to which speaker(s) they come out of.
 

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Jai,


"Where did you get that information ? "


I had a MC-1 and a DC-1 before it. With my MC-1I had the system with the SUB out set to 40hz and the sides set at 40hz. L/R and rears at 80hz and the center at 120hz. I didn't loose LFE info, it was redirected to my sides.


"But in situations like this it is very difficult to find out through experimentation in a typical HT setup"


This isn't a hard test at all. Play any test track that is on the LFE channel only and adjust your crossovers around and listen to the results.


"It says "ANY" processor. Wouldn't one be lead to believe that it woudl hold for high-end equipment like the MC-1 ? "


Sure, reading 'Any' would imply 'Any.' But the author is plain and simply wrong. The whole article is based on how bass management *may* work on some processor somewhere and making the incorrect assumption that it applies to them all.



Shawn
 

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Discussion Starter · #8 ·
I read the bass management section of the MC-1 owners manual and as far as I understand, the bass being redirected to larger speakers and not just the sub is true "ONLY IN THE CASE OF THE CENTER CHANNEL". This is a big relief for me :) because the Dr. Griesinger's recommended settings will work with no loss of bass, despite the fact that the bass for the rear and side crossovers get redirected only to the sub. So there is a small element of truth in the hometheaterhifi.com document too because the summing of LFE info and redirecting the the sub is true in the case of front/rear/sides and not the center channel (for the Lexicon MC-1). Thanks guys for the clarification. Please feel free to add more insight into the discussion. The key here is that "THE BASS SPLIT FEATURE IS AVAILABLE ONLY FOR THE CENTER CHANNEL IN THE MC-1"




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

********



From owners manual


Center

Systems that utilize a full-range center speaker should select LARGE to

direct center information to the center output with a full frequency

response. Select SMALL for installations where the center speaker is

smaller than the left and right front speakers. This will automatically

engage the Bass Split feature which takes the low frequency content

from the center, and distributes it to the left and right front speakers,

reducing the risk of damage to a small center speaker without loss of

bass information. When SMALL is highlighted, press SELECT to display

and adjust the crossover point for the low frequency redistribution.

Available crossover points are: 40, 80 and 120Hz. Press DONE to return

to the Speaker Configuration menu.


SIDES

This menu sets the system for your particular side speaker configuration.

Systems with side speakers should be designated as STANDARD

(LARGE or SMALL) or DIPOLE (LARGE or SMALL). When STANDARD

SMALL or DIPOLE SMALL is highlighted, press SELECT to

display and adjust the highpass filter for the side outputs. Choices are

40, 80 or 120Hz. For any 5.1 channel inputs, selecting SMALL routes the

low frequency information to the subwoofer output.
 

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Jai, you are still misunderstanding the manual (I hate to guess but you seem to be confusing bass management vs. bass enhance and LFE vs bass from the other channels). The magazine article is 100% wrong with regard to the Lex processors. There is no way that it is even a little bit correct. Please reread Shawn and Andre's comments above and accept them as the real deal.
 

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Discussion Starter · #10 ·
Catapult,

Thanks for your concern. I clearly and precisely understand the difference between Bass Enhance vs Bass Management AND bass vs LFE. I don't think I am misuderstanding the manaul. What do you understand from the following ? At this point, I cannot accept anything as real deal as I can do that only after I understand the reasoning behind it.


CENTER

Select SMALL for installations where the center speaker is

smaller than the left and right front speakers. This will automatically

engage the Bass Split feature which takes the low frequency content

from the center, and distributes it to the left and right front speakers


SIDES

For any 5.1 channel inputs, selecting SMALL routes the

low frequency information to the subwoofer output
 

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Jai,


The Lexicon manual is correct, but incomplete. It does not say what happens if you do set your fronts to Small. In that case, bass is then redirected to the sub from the fronts, so there is no loss.


I had an MC-1 (MC-12 now), and did not experience bass loss when my fronts and center were set to Small.


BTW, note that Dr. Griesinger's recommendation is just a starting point. In my room, with largish fronts (Aerial 10T set to Small/30 Hz), and small sides, I will get too much Bass Enhance effect on some recordings. BE is very room and setup-dependent.


--Andre
 

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Discussion Starter · #12 ·
Andre,

The Lexicon manaul does say what happens when the fronts are set to SMALL. Yes, you are right, when it is set to small the bass is then redirected to the sub from the fronts. Whether there is no loss or not depends on your what you set the MC-1 for the subs. Here is a specific scenario where I believe there will be a loss.


Fronts: 80Hz

Center: 120Hz

Rear: 40Hz

Side: 40Hz

Sub: 40Hz


In the above case, any center channel info in the range {80, 120} will be split and sent to the Fronts without loss. However a Front left or right channel tone of 60Hz will be lost because it will try to send it to the sub which is crossed over at 40 (lowpass). It will not send this tone to the rears which are set at 40 (highpass), it will only send it to the subwoofer output. So as I understand, the rule of thumb for the MC-1 is "If you set your subwoofer crossover to value say X, the Fronts also have to be crossed-over at X, if the fronts are set to SMALL". Dr. Griesinger's recommendations also follow this rule. The reason why this is critical is because the "Bass Split" feature of the center channel crossover depends on the Fronts. The Lexicon manual clearly states that for all other channels except the center, the bass is directed to the sub-woofer output, but not split to larger speakers. MC-12 maybe different.

-Jai
 

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Jai,


"The Lexicon manual clearly states that for all other channels except the center, the bass is directed to the sub-woofer output"


I don't believe that is correct regardless of what the manual says. This has been a heavily discussed topic for years on the Lexicon forum. Bass management is also a little different depending on if you are listening to a 2 ch source vs. a 5.1 source.


Instead of going through all these theories why not just try it yourself on your MC-1? Then you won't have to worry about what theory to believe you will have heard how it works for yourself.


Shawn
 

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Jai,


" MC-12 maybe different. "


BTW, it is. In the MC-12, which has crossovers ever 10hz, you can set it up such that you have holes in the response of your main channels bass to you sub.


For example if you have all your main channels at 80hz and your L/R subs at 70hz you will be attenuating the region between 70-80hz.


This isn't any sort of flaw in the processor though, just a byproduct of a very flexible setup. You could use this to help tame a room boom in this region for example.


And even with this setup you will not loose any LFE info, the point of the article you linked to, since the LFE channel bypasses the L/R subs crossovers. Or if you are using a third sub on the LFE Sub out then it will receive the entire LFE channel alone.


Shawn
 

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Discussion Starter · #15 ·
Shawn,

The case that you are mentioning about wilfully creating a hole by setting the fronts to 80 and sub to 70 is a very simple case. It is very obvious how easy it is to create such a hole. I am not calling these bugs, BTW. But it is important for someone to understand that the "Bass split" feature is available only for the Center channel. So leaving a so called hole between the center and front speaker crossovers is not a problem, whereas leaving a hole between other channels can be a problem like in the case I mentioned. I am not sure if you understood what I was trying to point out as your example talks about a very different case where one can create a hole. Please read my post again where I present the scenario that creates a hole. Again, this is not a bug in the MC-1 but just its features/limitations.

-Jai
 

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Jai,

Quote:
Fronts: 80Hz

Center: 120Hz

Rear: 40Hz

Side: 40Hz

Sub: 40Hz
Yes, there will be bass loss, but this is improper setup of the MC-1 and MC-12.


--Andre
 

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Discussion Starter · #17 ·
Andre,

Another scenario where there will be a hole is

Fronts: 80

Center: 40

Sides: 80

Rear: 80

Sub: 40


Any info sent to the fronts that is has a frequency "f" such that 40
Thanks,

-Jai
 

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Discussion Starter · #18 ·
Rule of thumb for MC-1 crossover

"If you set your subwoofer crossover to value say X, the Fronts also have to be crossed-over at X, if the fronts are set to SMALL" to avoid any loss of bass information.
 

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Pardon the the OT remark, but the filter for the LFE is adjustable and much closer to a brick wall. In fact, from what can be determined from reading, frequently an 8th order filter is utilized. There is generic mention in the Dolby vs. DTS debate on the dolby web site that a steep filter is usually used (this comment was passed while discovering that there was significant energy in the LFE track at 700hz (2 against nature), an uncommon finding given the typical steep filter used).


On topic, having owned the DC1,DC2, MC1, and now the MC12B I second Andre's thought-BE is highly room dependent and produces a more spacious appreciation of low frequency information when it functions correctly.
 

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Discussion Starter · #20 ·
After all the theoritical derivations based on information available in the manual and articles, I decided to perform some simple tests to make sense of all of the cross-over debates. What I found proves that what Andre and Shawn said about bass being redirected to the next larger speaker for all channels and not just the center channel was right. My assumption that only the center channel has bass split, based on incomplete/insufficient details in the MC-1 seem to incorrect. I am not going to elaborate every detail of the experiments but instead give you a gist of the total setup. My front speakers are close to full range (built in subwoofer) and hence can go as low as 25 Hz. I used the AVIA test tones for subwoofer setup. I set the rear and side cross-over to 120, set the sub to 40 and Fronts to 40 and unplugged the sub pre-out. So if any LFE tone is sent to the rear speaker, it should not be able to drive the SPL high enough. The test tones were set for 75dB and the Surround right + LFE tone yielded bass info that read on the SPL at around 75dB. However, when I turned off the front amps, the SPL rapidly decayed under 100 Hz sweep proving that LFE information from the rear/sides were redirected to the Fronts and not just the subwoofer (note that I unplugged the subwoofer). Please note that the owners manual does not elaborate this. All that it says is that the LFE under the crossover is sent to the subwoofer output. I guess what happens is after it is sent to the subwoofer output (internal circuit), it sees that the sub is low-passed at 40Hz and the tone is greater than 40Hz and hence the tone takes a second hop being sent to the fronts. This second hop is just a speculation.

-Jai
 
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