Multichannel Subs?

[TheCrypt]

I was wondering if it would be beneficial to use subs on my surrounds and centers? I currently use 4 Paradigm Studio 40s for surrounds and a CC-690 center. Thanks for input.

[IndyKlipschFan]

There is some new info at THX that suggests this too. Part of the reason is THX specs go to 80 Htz only.. Anything below that, goes to the subs..

OBVIOUSLY, there is some info lost in your sides and rear speakers too. I recently saw some layouts with subs all around.. (Yes below the sides and in the rears too...) hmmmmm It makes me wonder????? Is it a conspiracy to make us buy more speakers... going to a 7.1 - 9.1 system?

Or are people demanding fuller, full range speakers for the sides and backs too? Could this be where this where it is all headed?

[TheCrypt]

Ah, yes. If I wanted to extend each channel to 20hz with musical subs what should I look at? I could budget maybe $1500 a sub for each surround and the center. What are the more musical subs? I do a lot of multichannel music listening and think musical subs are the way to go. [] I also game and watch TV, movies, etc.

[TheCrypt]

These look promising. http://www.us.martinlogan.com/speaker_intro/depth_i.html

[TheCrypt]

For those wondering, I ordered this 5ch amp to power each sub individually and build my own subs to save money.

http://statement.anthemav.com/HTML/Technology/P_Series/P_Series_Tech.html

I'm going to start with just an 18 Q for the center channel in the cabinet right under the TV screen powered by 2 channels of that amp (1 for each VC) for maybe 1700w and see how that does until I save the funds to get some for the surrounds. I can't wait to try it out.

[Guest BobG]

I use 3 subs in my AV system. One for main, one for center (this was a great addition to the RC-7) and one to supplement the RS-7s. You have to set the surrounds to "large" if you go this route and need a sub with speaker level input and a high pass xover on board.

[T2K]

I know nothing stays the same
But if youre willing to play the game
Its coming around again

Carly Simon

A few years ago some of the resident experts here poo-pooed the idea, but I still like my Klipsch speakers with built in subs in front and rear. There is never any thought of needing more bass. I'm still impressed with their sound.

Keith

[mas]

To offer a simple answer: No.

The surround channels are bandwidth limited and do not have the lower two/three octaves.

[T2K]

Heck, and I thought all this time that this BobG guy knew what he was talking about, what with that Klipsch avatar and all.

Keith

[leerocker]

Surround channels aren't full range? Where is the limitation, in the encoding?

Really??????

Please forgive me for sound skeptical. I'm not saying your wrong it's just that that goes against what i've been told and thinking in my head for the past few years.

[oldtimer]

I guess putting Forte II's all around isn't overkill after all.

[mas]

Dolby Pro Logic exhibits a limited bandwidth whereby the surround channel response is from
100-7,000Hz.

With systems such as Dolby Digital and DTS that utilize LFE or Bass Management (more properly referred to as bass redirection) restrict distribution of the lowest several octave signal (typically) below 80 Hz to the LFE/Bass Management system.

This, by definition, constitutes a bandwidth limited signal.

And below is a statement, which while I do not agree with everything stated in the manner stated, like it or not, is consistent with the implementation of the surround format encoding with which we get to live.

From Rich Walborn, VP of Engineering &
Pascal Sijen, Director of Technology Marketing Miller & Kreisel Professional:

"In small studios/monitoring rooms ..., the frequency response of a speaker system in the region below 100Hz is dominated by the modal response of the room. Room modes, also known as standing waves, occur in all rooms at frequencies where the wavelength of sound is an integer fraction (i.e. 1/1, 1/2,1/3,1/4, etc.) of the distance between two walls, or the distance between the ceiling and floor (this is a slightly over simplified explanation). This means that invariably, some frequencies are reinforced and some frequencies are canceled, resulting in peaks and dips in the frequency response at the listening position. These
peaks and dips are affected by the relative position of the speakers to the boundaries in that room. Because of this, it is virtually impossible to get consistent bass response from multiple full-range speakers located around a room (such as in a 5.1 monitoring setup).

One solution to this problem is to employ a method called Bass Management, also referred to as bass redirection. Bass Management uses electronic filters to extract the low frequency information (typically below 80Hz) from the main five channels and then reroutes that information to a single subwoofer channel (reproduced by one or more subwoofers). Since the low frequencies will now originate from a single source (a subwoofer) this source can be placed in the optimum
location for bass reproduction in that room. And, because the main speakers are not required to handle frequencies below 80Hz, they can be reduced in size and easily placed for best imaging and coverage. The end result is that the overall frequency response of the entire audio system is considerable improved, without any sacrifice in performance or imaging.

One might ask, wont I perceive a difference in imaging if the sound of one channel originates from two sources (subwoofer and satellite)? The answer is actually no. Bass Management works by taking advantage of the ears inability to determine the direction of frequencies below approximately 150Hz. Provided there is no audible distortion or sonic artifacts at higher frequencies (port noise etc.), and the sound emanating from the subwoofer is limited to below 100Hz, it will be
impossible for the listener to identify the location of the subwoofer in the room."

[TheCrypt]

I do a lot of multichannel music listening and this addition has improved everything somewhat. I'm satisfied for now, but I've got 3 channels of power left and don't know what to do with them?

Thanks for your input guys.

[T2K]

You could look around for some Klipsch SW12 Series II or Klipsch SW15 II subs. They sell for a reasonable price and have line level and speaker level inputs, as mentioned by BobG. Of course they're powered, which I gather from your comments you wanted passive subs. And they're great music subs. I used two with Chorus II and they blended perfectly. Good luck to you.

Keith

[Roc Rinaldi]

I guess putting Forte II's all around isn't overkill after all.

That's exactly right oldtimer.

Take a minute and reflect on the evolution of sound in the surround mode. First they simulated a center channel, then made it discrete. Then they simulated the surround channels, then they made them discrete. They put a single speaker in the rear (6.1), then they made left & right rears (7.1). They started out saying "limited range" for the surrounds, then they began saying "full range" for the surrounds. Doesn't it make sense that eventually they will want to put all kinds of sounds for music and movies in any and all channels? I am certain that we are going to wind up with needing full range speakers for every channel and I'm sure they won't stop at 7.1 nor 9.1 nor 10.1 nor 14.3 nor 14.4.

Let's face it, they are not going to stop until we are surrounded completely by speakers everywhere including ceiling and under floor locations. They are not going to stop until they have all of our money.

[DrWho]

Spreading a bunch of subwoofers around the room opens the possibility to yield less bass instead of more...pretty simple acoustics, but no need to go there if everyone is already set in their ways.

Fundamently, what's most important is that for the amount of money being spent, the approach of subs on every channel usually does not yield the most performance. There are plenty of other "free variables" available that the money would be far better spent on - usually resulting in a better sound.

[Guest BobG]

I respectfully disagree with mas and the good Dr. Who.

MAS

Dolby Pro logic was definitely band limited in the rears, not the center. This is ancient technology. Dolby Digital and DTS are NOT band limited in any channel unless you choose to limit bandwidth by means of LF redirect to your sub. Why would you do that if all your speakers were capable of full-range reproduction? Redirecting bass from full range speakers to a single sub minimizes total system dynamics. Using subs with the center channel speaker and surrounds, or truly full-range speakers in those locations eliminates the need to redirect bass and provides the total system with greater dynamic headroom.

Dr.

Using multiple subs distributed around the room reduces the intensity of standing waves by filling in troughs and yields smoother bass. Also, bear in mind that the signal coming from the center and rear subs is not the same LFE signal sent to the "main" subwoofer. Using multiple subs in such a manner minimizes IM distortion in the bass.

OK, I feel much better now. Let the flames begin!

[DrWho]

Well if you don't have the same signal being sent to all the subs in the room, then you're not going to realize the real benefits of filling in the nulls...instead, you end up with a percieved frequency response that changes depending on how many speakers are reproducing a given sound. The only way to do deal with this is to treat the acoustics of the room, but then you're already going to be solving the standing wave issues []

As far as headroom and all that....I'd argue that X dollars spent on a single subwoofer unit should be able to outperform X/7 dollars spent on 7 subs. I suppose one might argue that bass is directional to an extent and I suppose you could add more subs to address that issue, but you'll probably only need 3 at the most? In that case I think you'll get more bang for the buck with 3 subs than you would with 7...

Do I need to put on my fire suit too? lol

[tenzip]

All that's lacking now is a discussion of what kind of wires to use to hook it/them up!

*ducks and runs* []

[mas]

I respectfully disagree with mas and the good Dr. Who.

MAS

Dolby Pro logic was definitely band limited in the rears, not the center. This is ancient technology. Dolby Digital and DTS are NOT band limited in any channel unless you choose to limit bandwidth by means of LF redirect to your sub. Why would you do that if all your speakers were capable of full-range reproduction? Redirecting bass from full range speakers to a single sub minimizes total system dynamics. Using subs with the center channel speaker and surrounds, or truly full-range speakers in those locations eliminates the need to redirect bass and provides the total system with greater dynamic headroom.

Dr.

Using multiple subs distributed around the room reduces the intensity of standing waves by filling in troughs and yields smoother bass. Also, bear in mind that the signal coming from the center and rear subs is not the same LFE signal sent to the "main" subwoofer. Using multiple subs in such a manner minimizes IM distortion in the bass.

OK, I feel much better now. Let the flames begin!

Regarding Dolby Pro, I should have said that the surrounds were limited to 100Hz-7KHz.

But much of this begs the question which was addressed in the posts.

And all channels may be band limited if you emply the LFE or bass management system. Seems like I have heard that stated somewhere...

And why would you chose a bandwidth limited configuration if your speaklers are full range? One might have asked than when the formats were proposed and developed.

Good question, but as I posted a portion of the response from a current discussion of mixing for surround sound, many feel that there is a good reason. (And aside from the 'political' recording protocol issues, I guess that we should also ignore the problems with multiple sources reproducing identical LF signals that are NOT necessarily mixed independently resulting in superposition and comb filtering and polar anomalies.

And now we are suggesting that there may be various mixes available simply on the basis of selecting "large" or "small"! As if things were not confusing enough already. And this does not extend only to the issues regarding the use of multiple subs, but also to how the various studios are actually mixing the sources. And no, all are NOT doing it the same! Exactly how to handle the material in the surround channels that may be handled by the LFE/Bass Management System is an ongoing discussion in the mix community. (A darn good reason in my book to be aware of the differences in approach.)

If they are assuming a bandwidth limited employment of the LFE/Bass Management system, one just might ask what one expects to find in the lower 2-3 octaves that the engineers assumed would not be needed - as it is being played back in the LFE/bass management system. Especially as many are actually recommending and employing a high pass filter to insure this is done.

I also stated that I have fundamental differences of opinion with the assumption and opinion that ALL LFs are non localizable below 150Hz. Oh sure, situtations can be constructed where this is the conclusion, but come on over and I can readily demonstrate that they are localizable - especially in a smaller listening spacem and certainly if the mixing engineer actually makes the channels different.. I am very tired of the 'LFs are omnidirectional and thus LFs are non-localizable' syllogism. That ranks right up there with "you can EQ room anomalies."

Why would you want to do so, you asked?

I don't know that I would! But unfortunately the studios are not calling me to ask (and I even have a bunch of infernal machines so as not to miss their calls!), and they are not calling many others whom I know. And I haven't even noticed any of them asking for forum input. So the reality is that we need to acknowledge what others in the industry are doing and deal with it accordingly. And there is no strict consensus on just which channels to natively bandwidth limit, if at all. Reading the mix guides is a fascinating journey into a land where the Scarecrow in the Wizard of Oz is providing direction. And there are still more opinions to deal with!

So, even if we pick a protocol we like, there does not seem to be a uniform consensus of engineers regarding exactly how one processes the various channels.

And if you do happen to decide on a configuration that satisfies you (and you are not bothered by the variety of source variations), we can come back to the basic issue of room modes.

So as far as a flame war, it would be a great diversion and maybe even a bit of fun,but only IF we can simply identify exactly what protocol and applicable variant that we are flaming. Just pick ONE! ;-)

But format nonsense aside, I do have a more basic issue with the 'solution' of room mode anomalies with lots of subs. I would describe this technique as more one of masking the fundamental problem. And it does nothing to reduce the boominess associated with room modes, which is far mire critical than the apparent distribution of LF energy about the room.

While multiple subs can introduce a few 'additional' peaks, they do not solve the fundamental standing room mode issue any more than Bose's direct reflecting system corrected the intelligibility problems fundamentally created by later arriving reflected signals by simply introducing additional reflected signals at higher gain!

All they did was to reduce the obvious nature of the fundamental issues by adding additional anomalies, making the entire listening area more chaotic and thus more evenly distributed with a more uniformly mediocre response - E.G. Instead of having a very noticeable variance as one moved from a 'good' to a 'bad' listening position, they homogenized the space and made it uniformly mediocre - thus the radical and noticeable changes from 'good' to 'bad' were not as noticeable - and thus many interpreted that as being better, as they did not find the "bad" spots to compare it to. Not that's an advancement in acoustical science! Not!

So with lots of small subs. The room modes are not lessened and the boominess is not reduced. It is increased, but you just don't notice it as dramatically as you move from one spot to another as the variation in intensity is lessened.. Is that an improvement? In my book, hardly. You still have the fundamental problem that has in no way been resolved. But that is precisely the approach - the methodology - employed by Bose to increase the perceived response and to 'widen' their soundstage and image. I guess it all depends on what your goal is...

(Sorry to pull the absurdly overused Bose card, but this is perhaps the one time it is valid!)

So I guess the question is, what are we trying to achieve? Are we trying to minimize a problem, or are we trying to solve the fundamental problem? I am not a fan of simply homogenizing a poor response and making it a tad bit more uniform. I am more concerned with solving the fundamental issues and then optimizing the space in a real manner.