If a system was set up with the FL, FC& FR using sub woofers with electronic crossovers and setting the speakers to large in the 950 then each of the 3 front speaker channels would be capable of full frequency response. Any two-channel source or multi-channel source would have full frequency response in the 3 front channels. For the ultimate system, I would think that a 4th subwoofer only channel should be added for LFE with sub set to "yes" in the 950. This would send any multichannel movie LFE to the 4th subwoofer channel. Since I do not fully understand how various formats (stereo music, two channel movie, DVD 5.1 movie, DVD-A, DTS, etc., etc.) are mixed, does this seem logical? By building a system in this configuration, it seems to me that it would play every format without reconfiguring subs or 950 switches. The 4 subwoofers would not be there to blow the room completely apart but to put the sound in its proper location. I would assume that the 4th subwoofers placement would not be as critical as the other 3. The 3 that are associated with the 3 front channels should be as close to the 3 front channels as possible. I would like to hear the three front channels with full frequency response. I am just in the planning stage at this time but I value everyone’s opinion. Thanks.

While I agree with your final conclusions, I think your approach can be questioned. First, the Newtonian laws you reference refer to inelastic collisions; air is very much an elastic medium and its compressibility does affect the energy transfer (albeit considerably less than it might under other conditions). Second, you seem to infer that a driver's distortion-limited X(max) is defined by its suspension. I don't think this is the case nearly as often as you might think. Rather, the distortion-limited X(max) is defined by the driver's motor geometry; the suspension, hopefully, serves primarily to keep everything in line. And even in the lowest-compliance designs, where the suspension supplies a significant portion of the damping, it can behave in a remarkably linear fashion if properly implemented.

I agree that the advantage enjoyed by the larger drivers results from the shorter stroke necessary for a given pressurization, but I'd argue that it derives primarily from motor geometry. The increased X(max) required for the smaller driver to yield an equivalent pressurization would require, assuming equal gap heights, a longer voice coil. This creates two problems. First, the lower gap height/X(max) ratio of the smaller, longer-throw driver means that the BL will drop off much sooner and more quickly than it would with a larger gap height/X(max) ratio. And it will take the motor's ability to control the cone's motion with it; increasing distortion at a given level. Second, the longer voice coil contains more wire and, presumably, more turns than its shorter counterpart. And since this greater number of turns is moving through a longer stroke, thereby breaking more flux lines, the back-EMF increases considerably, further diminishing the driver's output for a given (open-circuit) input.

Or I could be completely wrong...

The collisions I used illustratively ARE ELASTIC collisions: where both momentum and kinetic energy are conserved. Although air is not an ideal gas, where collisons are close to ideally elastic, it is close enough for this discussion.

What I stated in my post was an attempt to illustrate some priciples that place an upper controlling bound (elastic collison is an upper bound) and yet give some explanation (not intended to be exhaustive) on why things are the way they are.

In my comparison of a large woofer and a smaller one, the part that says:

"...two woofers that have identical motor assemblies..."

will allow for the larger coned woofer playing at the same spl output as the smaller woofer to be producing lower distortion due to taxing the suspension less and, as you state, less distortion due to the (identical to the smaller coned woofer) motor operation more linearly.


Paul




[This message has been edited by Paul J. Stiles (edited April 18, 2003).]

Nothing could be further fron the truth. Carver Sonic Holography is based on crosstalk cancellation. There is a similar mode, called PANORAMA, in Lexicon processors which does crosstalk cancellation for 2-channel sources; albeit with much more sophistication than Sonic Holography.

Bass Enhance works by constantly varying the phase between the low frequencies on opposite sides of the room. This helps externalize the in-your-head, mono-sounding bass often found in studio recordings (especially pop music); makes it sound more like the bass you hear at live acoustic events.

Taking advantage of Bass Enhance is simple: you need two subwoofers placed at opposite sides of the room. Ideally the subs should be directly to either side of the listening area, but I've heard good results with the subs placed in the two front corners or anywhere along the side walls. The closer to the room centre line the subs are, the lesser the effect. With flexible placement allowed, Bass Enhance never "requires PRECISE placement of both speakers and listener's ears."

For more information, read the first few pages of the following Bass Enhance FAQ (quite interesting)...

http://www.smr-group.org/pdf/Bass_Enhance_FAQ.pdf You guessed wrong; the Bass Enhance feature is not dependent on multiple subwoofer outputs. The MC-12 is the only Lexicon processor with multiple sub outs. More than for Bass Enhance, these outputs are actually designed to allow MC-12 users to treat derived bass and discrete bass as separate entities. EVERY OTHER Lex processor (including their new MC-8) has a single subwoofer output; yet they ALL have the Bass Enhance feature (a feature that predates the MC-12 by a number of years). On the contrary, LFE content is precisely what Bass Enhance was intended to be used for. The .1 LFE channel contains mono bass that has the potential to be perceived as coming from inside the head. This content is perfect for splitting into two channels and applying Bass Enhance in order to externalize the sound for more enveloping bass. This makes absolutely no sense whatsoever. What does a process to externalize bass perception have to do with a discrete Low Frequency Effects track? Both co-exist quite well in Lexicon processors and aren't at odds with each other, either conceptually or in practical implimentation.

Best,
Sanjay

this is from the sited FAQ article:

"You might be tempted to use only 2 subs-one at each side-and eliminate the third LFE sub, since Bass Enhance will route LF to the sides. Be aware, however, that this strategy entails the following limitations:


...In 5.1 recordings, you will lose the LFE channel since it is not used in Bass Enhance processing..."

so...please tell me what i'm missing here?

also from the same article: "...Bass Enhance processing is predicated on those[laterally placed subs] being located to each side of the listener. It never hurts to experiment, but moving the side speakers fprward or backward more than 15 degrees (1-2 feet) will likely compromise the effect past the point where it's beneficial to use it."

as far as the over simplified explanation of carver's holograph generator, which is not crosstalk cancellation (as well as the limited explanation of dr. G's bass enhance process), my understanding of the 2 systems pinpoints the arrival times of sound from 2 sources as the basis for both.

whether or not you use phase, crosstalk or split signal/delay, you are doing basically the same thing, which is psycoacoustic processing using time-arrival manipulation.

dr. G admits that the process is very room-dependent, but offers no explanation as to why that is so. i've offered one for you...placement of speaker systems and ears is critical. you may feel free to prove me wrong.

bass enhance (which only works with a center-placed LF signal, and not with the stereo-recorded bass as described in the beginning of the thread, and is nothing more than an alteration of the source to change it to suit a particular whim...and not with very much success at that) is of little significance to me. therefore, i have no desire to purchase the white paper to fully understand the process.

my position on the importance of having a discrete LFE system to multi-channel audio is the result of many hours of research.

lexicon mentions 1 advantage in the manual, stating that the "more demanding LFE is separated from the 'crossed over' bass", allowing for 'smaller' subs to be adequate. (BTW, this in itself is reason enough for all pre-pros to offer a discrete LFE output with it's own processing options). the 2nd advantage they list is that of being able to level adjust the LFE separately from redirected bass.

unfortunately, they haven't explored the other numerous advantages (or if they have, they haven't made them public), such as arriving at production and labeling standards, as well as better reproduction options.

[This message has been edited by bossobass (edited April 20, 2003).]

[This message has been edited by bossobass (edited April 21, 2003).]

You're missing clarifications about Bass Enhance that came from Lexicon after this FAQ (which is not an official Lexicon document) was written. Not your fault, but it is the reason why I specifically suggested reading "the first few pages" of the FAQ. This newer information is also why I stated things that were contradictory to statements made in the last few pages of the FAQ: e.g., subwoofers need not be directly to sides of the listening position in order to take advantage of Bass Enhance. Also, you don't lose the LFE channel; it is simply folded into the derived bass being sent to both subwoofers. In fact, you don't even lose control of the LFE content; even when it's not being sent to its own dedicated subwoofer, Lex processors still allow the user to control the volume of LFE channel (discrete bass) independently of the subwoofer (derived bass) volume. Oh yes it is, and that's all it is.

From a 1998 interview that AIG's Gordon Brockhouse conducted with Mr. Carver himself:

GB: Is sonic holography essentially crosstalk cancellation?

BC: Yes. The crosstalk cancellation has been adjusted to produce a realistic presentation on regular stereo recordings. Years ago, Harry Pearson wrote a wonderful series of articles on generating a soundstage with a stereo system. What you want is a sense of layered depth on a soundstage that extends behind the speakers and is wider than the speakers. I've adjusted Sonic Holography to really give a soundstage in spades using Harry Pearson's treatise as a model. In real life, for every sonic event we have two sound arrivals: one for the each ear. Every time I snap my fingers, you hear two sounds: one in your left ear, one in your right. In three-channel playback, every time I snap my fingers, you might hear six Ä one in each ear for each of the three speakers. Those unwanted sounds need to be cancelled if we're to generate a replica of real life.

You can read the entire interview here:

http://www.audio-ideas.com/interview/carver.html

The Ambiophonics web page also discusses Sonic Holography, and other crosstalk cancellation technologies:

http://www.ambiophonics.org/welltuned.htm

"Polk, Carver and a few other companies took up the challenge of spatial realism in the "80s by, for example, supplying the right speaker with a "shadow" version of the left speaker's sound, timed and tonally shaped so that it cancels it at the right ear. Among the limitations inherent in Polk's early "Stereo Dimensional Array" and Carver's "Sonic Holography" techniques is the fact that the shadow signal not only appears, in this case, at the right ear, where it's needed, but also, at the left ear, where it's decidedly not. Modern digital processing, like that used in the "Panorama" in Lexicon's CP-series surround processors, can cancel this new distortion by supplying the left speaker with a shadow of the right shadow, then the right speaker with a shadow of the left's shadow of the right's shadow. It sounds crazy, but it works rather well, considering it really a new take on the old cat- chasing-its-tail theme, an provided you keep your head in just the right spot."


Also see the description of Sonic Holography here:

http://www.bmwworld.com/audio/carver.htm So what? Dialing in speaker distances, during initial set-up of a pre-pro, uses "time-arrival manipulation" (signal delays) to give the psychoacoustic impression that all your speakers are the same distance away. Does that make time alignment the same thing as Sonic Holography or Bass Enhance?

I don't understand why you continue to insist that Sonic Holography and Bass Enhance are similar. Bass Enhance does not generate ANY crosstalk cancellation signals. Listening space parameters such as room size, bass modes, and surface reverberance all serve as perceptual cues contributing to realistic bass. A room where all these parameters are contributing to terrible bass response could easily swamp the effects of Bass Enhance (just as an overly reflective or oddly shaped room can kill proper soundstaging and imaging). Elsewhere, in rooms where asymmetry and/or other factors contribute to naturally "stereo" sounding bass, the Bass Enhance circuit will do very little to improve the situation. I mean, the stereo effect already exists. It is rooms and set-ups, which conspire to create monophonic sounding bass, where Bass Enhance will really help.

However, room interaction is not the same thing as precise placement of speakers and listener. They may work off each other, but they are separate parameters. To that end, Bass Enhance is less affected by imprecise placement than it is by the contributions of the listening room. Truth be told though, the effects of Bass Enhance are most dependent on the recordings. I've heard well recorded live classical music where Bass Enhance's effect was negligible. I've also heard studio pop recordings where the effect was very pronounced and easily noticeable. Bass Enhance works with more than "a center-placed LF signal". It works with stereo bass too, especially in situations where a bad room is reducing the effect of well recorded stereo bass. Keep in mind that Bass Enhance is simply a tool to correct problems that may occur when playing back audio in less-than-optimal, real-world rooms. Nothing more, nothing less. For what it sets out to do, it is extremely successful. But you would have known that had you ever heard the effect. And with all due respect to your many hours of research, your "position" is of zero significance to me. I simply posted in this thread to correct inaccurate statements you made about Dr.G and Bass Enhance. I'm not (nor do I have any interest in) debating the importance of a discrete LFE system. I'm confused by the second advantage that Lexicon apparently lists in their manual. Follow: take any Lexicon processor, hook it up to only 2 main speakers (no sub) and play any source with a .1 LFE channel. The processor will fold down any number of channels into two, and mix in the LFE. However, the user can adjust the LFE level; there are separate parameters for discrete bass (labeled LFE Mix Level) and derived bass (labeled Subwoofer Level). Agreed, they haven't. But they may not have that sort of clout in the industry.

Best,
Sanjay

[This message has been edited by sdurani (edited April 21, 2003).]

though i appreciate the links, i've owned a C-9 since it's first arrival. in fact, my manual is hand written and illustrated by BC. i understand the process implicitly.

to clarify, it's interaural crosstalk cancellation. 'crosstalk cancellation' implies that there is something wrong with your equipment that needs corrected.

on the other hand, i don't understand bass enhance any more than i did before your posts and, apparantly, the FAQ article actually contains wrong information on the subject. i think that if it's all you think it is, the manual might have given the subject a bit more ink than the paragraph that 'covers' the subject.

if you have the ears to be able to properly level adjust and select the proper LP point and slope for, in any given multi-channel format, the LFE when it's summed with redirected bass into however many subs, then you have extraordinary ears. and, it's simply unnecessary to attempt.

our viewpoints here are basically opposite.

soundhound's original post describes a method to best reproduce a stereo mic'ed bass signal. i agree with that method, and any method that best plays back the original content. bass enhance seeks to alter a studio mix of direct-injected bass so that it sounds more like a live recording...not my preference. just as misguided, would be an attempt to place the bass signal of a stereo mic'ed mix into the 'center of your head'. the subject is reproduction of stereo bass, not post production creation of stereo bass. thus, my comments.

bass enhance is well enough documented by it's owners to convince me of it's limited success. to imply that it is not at all placement critical is incorrect.

lexicon is at the top of the heap, worldwide, in the field of reverb and delay processing on the production side. you underestimate their clout. certainly, at least, they have as much clout as apogee's rich elen.

i personally believe that the MC-12B is the best pre-pro available today. one of the reasons is the LF output config and processing thereof (bass enhance notwithstanding).

soundhound has said that he would prefer multi-channel audio be produced in a 5.0 format. that makes more sense to me than to say summing the .1 channel with redirected bass is perfectly fine. THAT makes no sense whatsoever.

I was using the term 'crosstalk cancellation' in the same exact way that both Brockhouse and Carver himself were using in the interview I cited. Maybe they were implying that there was something wrong with Carver's "equipment that needs corrected"? The manual is probably the wrong place to look for a thorough explanation of Bass Enhance; after all, it doesn't give much "ink" to how LOGIC7 works either. To be fair, it is just an operational manual (with a lot of ground to cover) rather than a 'theory and design' white paper.

Since you claim that Bass Enhance is "taking a page from bob carver's holograph generator", then could you please provide some documentation that shows where BE generates interaural crosstalk cancellation signals as part of its process? Yes, Bass Enhance is simply a post processing option specifically for situations where the you don't have the type of recorded bass that soundhound's original post described. It's like Pro Logic II: many people prefer not to use it, especially at a time when more and more discrete multi-channel recordings are being released (movies and music). However, this misses the point that PL II is an option specifically for situations where you don't have a discrete multi-channel source.

Ultimately it does come down to personal preference; some people like the effect, others don't. Understood. As I said before, I have no argument one way or the other with your position on the subject of stereo bass reproduction. I was simply responding to particular comments, such as your accusation that "dr. 'G' spent too much time developing bass enhance." Nothing personal, but I felt that bold statements like that needed addressing. What documentation discusses the relative success (or lack there of) of the Bass Enhance process? Which is why I never implied that it was "not at all" placement critical. However, not everything affects Bass Enhance equally. While it varies by situation, in most cases BE is more dependent on the original recording and listening room than critical placement of subwoofers. I'll defer to your better knowledge of Lexicon's industry clout. In which case, their inaction implies that the matter has little to no interest for them. It makes sense to me because, in the artificial construct of home audio playback, compromises sometimes have to be made. Most consumer audio systems don't have a dedicated LFE subwoofer that can afford to sit idle when no discrete .1 channel is present. Sorry, that's the real world. In those situations I welcome the option to sum LFE content with redirected bass; especially where I retain independent control of the LFE and the redirected bass.

Whether it makes sense to you or not, I prefer having these options now rather than waiting in hopes that the industry will someday adopt some sort of discrete LFE system.

Best,
Sanjay



[This message has been edited by sdurani (edited April 21, 2003).]

fwiw, i'll give it a (cursory) stab...

bass enhance is a process that uncorrelates, or decorrelates a correlated LF signal by applying a constant phase shift (i'm guessing quadrature, but i simply don't know the degree value) to the signal in each of 2 channels. this serves to add a spatial psychoacoustic quality to some source material in some rooms.

hologram generation applies a fixed time delay to each of 2 signals and routes each to the opposite speaker (actually adding crosstalk).

though 1 widens an already psycoacoutically spread sonic image and the other widens a psycoacoustically narrowed sonic image, the end result with both processes is that the signals are delayed as to arrival time to the ear from 2 sources in a controlled manner to give the illusion of a wider or deeper or more 'live' source. in fact, someone with the inclination should try a C-9 with stereo subs...it may even work better, as bass enhance lessens bass output.

as for documentation of the success of bass enhance, i read evey post i could find using "bass enhance" in the SMR search engine when i heard of the feature a while back. there were numerous posts with words like 'exasperating', 'my back is killing me from moving these subs', 'very source dependent', 'not everyone likes it', 'doesn't work in every room' 'doesn't seem to track as well as...', etc., etc. this, to me, is far from resounding success.

i apologize for any undue 'boldness' i may have conveyed in my posts. i assure you, i meant none. i find it difficult to express myself with only a typewriter as the means. i've read many of your posts, here and otherwise, and have always found them to be accurate and helpful.

i've been a fan of dr. g and lexicon for years. as he puts it, he was dragged kicking and screaming from the pro side to the consumer side. i don't think it's that lexicon isn't interested in influencing the industry with it's unique properties. i also don't think they haven't tried. (logic 7 as an encoded format comes to mind). in the case of the merits of a separate LFE output, i honestly believe that it was born of a way to increase the effectiveness of bass enhance, and lex really hasn't explored the many other benefits. i could be wrong, that's why i used the word 'maybe'. in re-reading it, i can easily see how it may have been mistaken to be flip or condescending. again...apologies.

to me, logic 7, DPLII, bass enhance, sonic holography, etc., impede the progress of discrete, multi-channel audio. that would mean i'm not a fan. i know you like these modes, so...i'm apologizing in advance for any future dumb ways i may convey my thoughts.

This may come down to how we each view the two processes: I see the similarities you mention, but I see greater differences. Yes, both processes are trying to widen the soundstage, but then so do other processes, like matrix decoders. This doesn't mean that LOGIC7 is the same thing as Sonic Holography or Bass Enhance.

Besides, I think the differences are significant. Holography uses crosstalk cancellation (Carver's words), fixed phase, exacting placement and specific delays. Bass Enhance doesn't use any of these technologies, relying instead on constantly shifting the phase (from 60 to 90 degrees) of the low frequencies between the speakers on the left side of the room vs the right side.

The effects of Holography are more noticeable as you use less monophonic recordings. The effects of Bass Enhance are more noticeable as you move towards recordings with more monophonic bass. The results are also quite different: Holography produces better localization with almost shockingly precise imaging in the front soundstage; Bass Enhance actually does the opposite, as bass becomes less localizable and more enveloping.

Going back to your original point about precise placement of speakers and ears: that may sometimes help Bass Enhance but it is an absolute neccessity for Holography. Confusing the two processes will result in placing a requirement on Bass Enhance that is not really, well, required.

As mentioned before, Lexicon has a mode similar to Sonic Holography, which does have all the requirements you've described: users have to dial in distance, angle and position of the listener relative to each speaker. Talk about precise placement! None of this is required with Bass Enhance, as there is nothing in the menu for setting it up. Also, the Holography-like "effect" can be adjusted over something like 62 steps; Bass Enhance is simply and on/off parameter. Again, the two processes are significantly different. I've read similar quotes from people trying to locate and intergrate a subwoofer (or worse, multiple subs) seamlessly with the rest of their speakers. This hasn't made me feel that the addition of subwoofers to home theatres was a less than successful idea.

Maybe we're using the term "successful" to mean different things. Properly set up, Bass Enhance delivers as advertised. I don't see what's particularly unsuccessful about that. Griessinger is definitely an interesting guy. Like many scientists, he can sometimes be an odd bird, especially in person. Lately he's been so obsessed with optimising LOGIC7 for cars that Lexicon, once again, has to drag him kicking and screaming to work on their home theatre products. I don't think Lexicon has ever really made an effort to push for LOGIC7 encoding for 2-channel material. Ironically, due to the equpment used in one mastering house (MiCasa Productions) there happen to be more L7 encoded DVDs than EX encoded titles. More a fluke than anything Lexicon actively attempted to do. BTW, these soundtracks decode incredibly well on the Outlaw 950 using the PL II CES modes.

As for influencing the industry as far as a discrete LFE system is concerned, it may simply not be a high priority for a company that does the kind of work that Lexicon does. Keep in mind that their speciality is signal processing (turning 2-channels into 7, turning mono bass into stereo, etc). Just a guess, but they seem like they'd put more effort into figuring out a proprietary solution to an industry problem rather than try to change the industry itself. From what some of the folks at Lexicon have told me, the reason behind the separate LFE output was to allow users to treat derived bass and discrete bass as separate entities. For example: the two sub outputs can be run as dual-mono, real stereo (bass filtered from all the left speakers vs all the right speakers), or even have Bass Enhance applied to the signal. In comparison, the LFE output is simply a passthrough; not even a crossover in the signal path!

Interestingly enough, I heard Bass Enhance work well in a system with no subwoofers. While on a quest for suitably "mucical" subs, a friend of mine temprarily set up his system with 6 floorstanding speakers and a small centre channel speaker (standard 7 speaker placement). While the floorstanders were by no means full range speakers, they had enough bass to show off Bass Enhance. Ultimately, Bass Enhance is not as much a process for subwoofers as it is a left bass vs right bass process. Likewise, apologies for anything I posted that may have come off as harsh. As I said in my previous post, nothing personal meant; even (especially) when our views are at odds.

As for surround processing, yes I'm an obvious fan; mostly because I use my processor 80% of the time for music listening, most of which is 2-channel CDs. It's been almost a decade and a half since I've listened to 2-channel material using only 2 speakers. I don't hear everything in the real world between two points in space in front of me. At this point in my hobby, I find it very distracting to listen using only 2 speaker. I guess that makes me the anti-purist audiophile?

Is surround processing an impediment to discrete multi-channel? I'm not so sure. Keep in mind that the best matrix decoders (LOGIC7, PL II, Circle Surround II) came out after DD 5.1 was already established. The argument could be made that discrete multi-channel is having a bigger influence on surround processing, rather than the other way around. Once consumers get a tase of discrete multi-channel, they start to want that same sound for everything in their library. Companies respond by creating surround processing that tries to bring 2-channel legacy recordings as close to possible as the discrete multi-channel experience.

One place where matrix decoding may be hampering the desire for more discrete channels is with Griesinger himself. His "ideal" playback system has 5 speakers up front (main L&R pair, centre, a pair at the first reflection points), 2 side speakers, 2 rears, 2 overhead speakers and a pair of subs. However, he doesn't advocate going beyond 5.1 discrete delivery channels for his 11.2 channel playback system. The bulk of the channels will be matrix encoded and recovered upon decoding during playback. If he didn't have such strong convictions towards processing, he'd probably be advocating more discrete channels (full range and LFE).

BTW, don't know if you've seen these yet, but for some interesting reading, check out this interview with Dr.G:

http://www.smr-home-theatre.org/Lexicon/dg_qa1.html

As well as the good doctor's own website:

http://world.std.com/%7Egriesngr/

Best,
Sanjay




[This message has been edited by sdurani (edited April 22, 2003).]