Creating "true" full range 7.1 speakers using multi subs..?

ATTENTION!!! This subject is broken down into about 12 posts back-to-back and says "CONTINUED.." accordingly, to bring up my post count past 10 posts. Otherwise it would not let me post the link below. Apologies, but I could not think of anything else...



According to this passage from the article found here:
http://www.hometheaterhifi.com/volum...pril-2000.html

"With the generous bandwidth and headroom in each digital channel, an appreciable amount of bass can reside in the screen channels themselves. This can spread things out nicely or can be used to enhance directional cues. When the sound engineer wants even more, they can elect to put additional bass information in the LFE channel, tapping into those big 18" drivers and what essentially amounts to more bass headroom. In an all out assault, with deep bass in all channels, the LFE channel makes possible an extra 6 dB of headroom over and above what the three screen channels can deliver as a group. In a nutshell, the LFE track is that extra kick in the pants!
If you are doing the math right now, you may have already concluded that in a text-book Dolby Digital theater, one heck of a subwoofer system is called for! Let me explain.
In a movie theater on the island of Utopia, with ideal hardware, any single screen channel should be capable of a clean 105 dB peak with it's own respectable bass. The LFE channel should be capable of a 115 dB peak. Drive all channels to the max and the system should be able to slam you with approximately 120 dB of bass information. Thank you Dolby."

And so...


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Re: Creating "true" full range 7.1 speakers using multi subs..?

My current setup:
2x Infinity BETA 40s (Floorstanding)
1x Infinity BETA C360 (Center Channel)
4x Infinity BETA ES250 (Surrounds)
1x SVS PB12–Plus/2 (set to 16Hz extension mode)

I want to get 3x BIC Acoustech Cinema Series H100 Powered Subs for the fronts and some smaller 10" Subs (that go down to at least 24hz) for the rears to crossover at about 40-60Hz. I am doing this because:

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Re: Creating "true" full range 7.1 speakers using multi subs..?

A. I read somewhere that REAL movie theaters not only have discreet amps per channel, BUT ALSO discreet amps per Bass, Mids, and Highs per channel... and then ANOTHER sub for the LFE only!! Is this true..?

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Re: Creating "true" full range 7.1 speakers using multi subs..?

B. Most people crossover ALL speakers (even full range) at about 60-80Hz .. but I notice a difference between doing this and having all LARGE settings and letting the SVS Sub handle ONLY the .1 LFE channel. The Bass seems more "dynamic" and not as "muddled" this way.

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Re: Creating "true" full range 7.1 speakers using multi subs..?

Example = In Jurrasic Park 1, when the T-Rex walks around, ONLY the footsteps kick in the .1 LFE Channel and seems more distinct vs when I have ALL speakers crossed over at 60-80Hz, which just just carries ALL bass including closing car doors, deep voices, etc., to SVS Sub giving it a "generic" rumble. The dynamics of various bass disappear..

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Re: Creating "true" full range 7.1 speakers using multi subs..?

When I hooked up 3 spare Yamaha 10" subs, that were laying around, to the fronts and then dedicated ONLY the LFE to the main SVS Sub, there was a feeling of discreet bass coming from the LFE sub (SVS). Some sound effects had this LFE.. while others did not.

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Re: Creating "true" full range 7.1 speakers using multi subs..?

Example A: Jurrasic Park 1, there is a lot of bass in this movie as it is, especially the T-REX Roars but... the T-REX footfalls seem to have "additional" bass. I could easily tell. And the footfalls seemed disctinct from the REX roars or jeep doors slamming. It had more "presence" and was louder. All of a sudden.. it sounded to me like discreet bass I was hearing in movies for years! Not directional bass mind you, but an extra "Oohm!" in bass reserved for only CERTAIN sound effects. When all was crossed-over to 60hz or 80hz... Bass still sounded great but seemed to blend more and did not seem to have a 6db BOOST on "certain" effects.

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Re: Creating "true" full range 7.1 speakers using multi subs..?

Example B: Empire Strikes Back, In the begining, when Han & Chewie go to search a meteor and find an Imperial Probe Droid, when they started to fire at it, the laser blasts and intial small explosions sounded good (front mains+yamaha subs in front), but when it self-destructed.... It gave HUGE bass hit to the SVS sub in dedicated LFE mode (giving the feeling of a larger explosion than the previous ones).

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Re: Creating "true" full range 7.1 speakers using multi subs..?

In both examples, playing the same scenes again while letting the SVS bass-mange everything, it did not have the same dynamics in explosions and bassy effects (all explosions/effects sounded about the same db).

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Re: Creating "true" full range 7.1 speakers using multi subs..?

I always noticed when watching movies in theaters.. that some explosions and bass effects sounded more "dynamic" and louder than other explosions and effects. Before I could never create this dynamic variance in movies at home no matter what the wattage. I could never explain it and all my friends thought it was in my head. But the article, I linked to earlier, BETTER explained WHY this was happening, more than I ever could.

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Re: Creating "true" full range 7.1 speakers using multi subs..?

"When the sound engineer wants even more, they can elect to put additional bass information in the LFE channel, tapping into those big 18" drivers and what essentially amounts to more bass headroom."

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Re: Creating "true" full range 7.1 speakers using multi subs..?

Anyway, in the past, I never even bothered to set speakers to anything past small since I always used tiny satellites before as mains and surrounds. Since I got these new infinity towers, a big center, dipole surrounds, one day I attemted to use them as large setting and do ONLY LFE for the SVS sub. The result was that dynamic extra kick that I felt in movie theaters all along. Yet I was puzzled as to how this would make a difference anyway. Especially since in theory... A "great" sub should be able to produce bass for all channels AND do LFE as well with no problems. Also, since home Dolby Digital circuitry added the +10db boost automatically.. the soundtrack should play the extra "peek" in certain bassy sound effects the same as dedicated LFE in real theaters right..? RIGHT..??!! ..

hehe well in theory yes.. but not as I have heard in practice.



so because of the differences in "bass DYNAMIC" in certain effects rather than "bass localization (never an issue to begin with)", I want separate subs for main channels + LFE sub.



But since the Infinties are not REALLY full-range speakers (fronts all roll off at about 45hz, surrounds which all roll off at 60hz) I wanted to add the "mini-subs" to each channel to make them play safely at high volumes.



One thing I forgot to metion was that: even though I'd set all main channels to LARGE, I would use the individual sub higpass crossover/filter to cutoff the highs past 80hz to the speakers and leave the rest to the subs respectively per channel.



Like I said before, If I had 7 GENUINE full-range speakers (20hz-20khz) then I would not bother with the subs. But as is, leaving the speakers large will obviously dammage the speakers at high volumes, with no cuttoff.



For the fronts I was looking at 3x 12" subs.

For the rear channels, 3x 10" subs going to 2 Lside Surrounds, 2 Rside Surrounds, and 2 Rear Surrounds.

OR... 2x 10" subs for rear since most speaker level subs are in stereo so 2 subs would cover four channel rears.



I would probably use cheaper subs as I don't really care if they go down to 20hz or just to mabe 30hz. I guess my prespective on that is that a cheaper POWERED (100W RMS) sub that can comfortably go down to even 24-35hz with a 10-12" driver is still putting less effort than a bookshelf sized surround that goes to only 60hz using mere 5.25" drivers.



PS: I am not thinking about this for bass localization (..as most bass is nondirectional under 80hz anyway), but rather, for dedicated bass for ALL channel PLUS the "discreet" SUB for the +10db bass effect from LFE channel as DOLBY's original theater specs intended for 110db SPL.

Re: Creating "true" full range 7.1 speakers using multi subs..?

I mostly just skimmed your post(s), but my initial reaction is that you'd probably run into problems with the subs canceling each other out and creating some rather odd nulls and nodes. Still, you might get lucky. Also, have you tried moving your SVS around to see if you just had it in a bad spot when you weren't satisfied with the bass? You might also be exciting a room mode with the SVS that the Yamaha's weren't hitting, which could cause the SVS to sound muddy. Have you done any frequency sweeps?

Re: Creating "true" full range 7.1 speakers using multi subs..?

The interaction between the subs as mentioned above was my first thought.

Another reason you might want to use bass management with a single sub is that your main channels can carry a lot of bass that is not sent to the LFE channel.

Check out the waterfall plots from revenge of the sith

Anybody up for an AVS waterfall thread? - AVS Forum
avsforum.com /avs-vb/showthread.php?p=6575290#post6575290

That shows the center channel goes down to 10hz. Are you going to put equal subs on all 7 channels that can play that low? It all depends on the movies mix if its needed. With bass management you could always double up on your subs on the 'sub out' channel if you think that one is not up to the task of handling all the channels base.

I havn't verified any of this, just something to think about.