Cinema sub-bass

Discussion in 'Archived Threads 2001-2004' started by Bill Fagal, Jul 11, 2002.

  1. Bill Fagal

    Bill Fagal Stunt Coordinator

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    Here's a question for you industry insiders and movie enthusiasts alike:
    Do you see any current/growing/future demand in modern theater-land for extreme sub-bass reproduction?
    I understand that current movie soundtrack bass content doesn't really go south of 20Hz, and most theater bass reproduction is probably running out of steam around 40Hz. However, I'm wondering if soundtracks might be changing as moviemakers push the limits as they try to keep wowing jaded viewers.
    It seems to me that the ability to reproduce, say, a decently loud 12Hz effect on a movie bass track could give movie producers a whole new palette of psychological tools to grip viewers. Though inaudible, infrasound creates a tactile, palpable sense of foreboding, dread, and/or power that you can turn off and on at will.
    I recognize the technological/practical hurdles to reproducing loud infrasound, but I'm wondering if the market would be there if such a device were available in a reasonably priced transportable package.
    Is the market driving cinema subwoofers, or would a good cinema subwoofer drive the market? [​IMG]
    Bill
     
  2. Ryan Schnacke

    Ryan Schnacke Supporting Actor

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    I'm guessing you haven't seen the waterfall charts on the SVS site. There's quite a bit of sub-20Hz content on recent DVD's. http://www.svsubwoofers.com/faq.htm and look for "10) What are some great bass demos?" and then click on a few of the links to waterfall charts.
    In particular, check out:
    Antz
    Fight Club
    The Haunting
    Iron Giant
    Super Speedway
    Titan AE
    Toy Story 2
    The Phantom Menace
    U571
    As for an affordable device to reproduce these signals ... just check out the rest of the SVS website.
     
  3. Bill Fagal

    Bill Fagal Stunt Coordinator

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    Ryan, thanks for your reply and the SVS links.

    Sorry, I don't think I was clear enough in my first post. What I'm curios about is *cinema* sound. I know it's a tad off topic on this forum, but it seems to me that home theater performance has quite outstripped most cinemas, in terms of bass reproduction. I'm curious if y'all think cinemas intend to catch up.

    That soundtrack info at SVS is interesting. I honestly hadn't realized that new movie releases were getting into the teens of Hz. I guess that answers the soundtrack part of my question. It sounds like there should be some real call for for theater infrasound. Without it, we're not getting nearly the full picture!

    By the way, can anyone tell me if DVD soundtracks differ from the large-venue cinema versions?

    Bill
     
  4. Ryan Schnacke

    Ryan Schnacke Supporting Actor

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    Okay, I see what you're saying now. And I agree, I'm at a point where I actually prefer my home theater audio more than the local multi-plex. Probably for the reasons you're stating and the fact that I calibrate my system to my preferences. If only I had a better display.

    As for your question - its a tough subject. A theater has a LOT of space to fill. Getting anywhere near reference performance at 20Hz would be a huge undertaking. Below that you could use bass shakers. Still it would be quite expensive and you have to prevent those sounds/vibrations from bleeding into the next theater. Some places already have enough trouble keeping their 30-40Hz bass contained.

    I could see this as a specialty feature at a few theaters. Sort of like DLP projectors right now. But I wouldn't want to pay bloated ticket prices to pay for this every time I saw a flick, especially when I've already paid for my own HT.
     
  5. Mike Strassburg

    Mike Strassburg Second Unit

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  6. Lewis Besze

    Lewis Besze Producer

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    I think that the avarage movie theater goer already thinks that the bass is very good in theaters now.
    This "opinion" comes from a fact that most people never heard real 20hz and below bass, period,so have no comparison for them.
    I also think that movie houses have no interest in such "device" if would indeed exists.
     
  7. Bill Fagal

    Bill Fagal Stunt Coordinator

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  8. Rory Buszka

    Rory Buszka Supporting Actor

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    some Bag End Bassault-R's with their 21-inch cones and ELF integrators...
     
  9. Bill Fagal

    Bill Fagal Stunt Coordinator

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    I couldn't find any excursion specs on those Bag Ends. However, a 20Hz tone at 134dB/1m anechoic (about what you'd want in a decent-sized theater?) requires that you displace 2200 cubic inches of air per half cycle, I believe. That's 7 21" woofers blasting at 2" of p-p excursion. If you wanna dip to 15 Hz, it's gotta double!
    So, if the Bassault's drivers can swing 2" of excursion, a cluster of four units might work nicely [​IMG]
     
  10. Rory Buszka

    Rory Buszka Supporting Actor

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    Well, now we know how Bose Acoustimass can seem like the movie-theater experience: It doesn't go below 50Hz, much like the bass in many nearby theaters (except for the Lucasfilm-THX theater in the United Artists 12) and it has poor transient response (like bass booming around in a theater)
     
  11. Griff

    Griff Stunt Coordinator

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    I went to see Blade 2 last night, although it was a great movie, with an equally good soundtrack, the cinema just didnt do it for me. I was waiting for my chair and the whole theatre to start shaking roller coaster style, i kept thinking to myself, "turn it up!". Another disappointment was the lack of surround sound believe it or not. There was one scene that had a hint of rear or side effects, and even then it was easy to pinpoint the speaker in use. I just cant wait until the movie comes out onto dvd, let my brahmas have a go at it!
     
  12. Dennis XYZ

    Dennis XYZ Stunt Coordinator

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    I'm surprised Mark Seaton hasn't jumped in here and mentioned the Servodrive Contrabass. They have been available for some time and are used at places like Disney World.
    http://www.servodrive.com
    Hmmm, I just checked the site and it's being overhauled. Anyway, their patented technology uses servo motors rather than voice coils to get some ridiculous amounts of clean excursion. Do a web search and you may find some pics/specs on other sites.
     
  13. Bill Fagal

    Bill Fagal Stunt Coordinator

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    From all I hear, Contrabasses are sublime. However, I believe they are properly targeted at serious home theater. According to specs listed on the "Contrabass Corner," they displace about 600 cubic inches per half cycle and claim about 114dB at 16Hz--earthshattering in a home theater, but in a decent-size theater, you'd probably need about a dozen to reach that 134dB/1m reference point below 20Hz (that I picked out of thin air...anyone have a better idea of what 1m SPL should be in a decent-size theater?)

    Bill
     
  14. Greg Monfort

    Greg Monfort Supporting Actor

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    It's an accurate claim. [​IMG] The two I had pegged a calibrated 120dB SLM with modest power at 16Hz in a 16ft x 27ft x 8ft room that opens into a hall and dining area.
    If the standard hasn't changed in recent years then you need 110dB out into the middle of the theater, so to use the large theater at the local Hollywood 24 which I guessitmate at ~100,000ft^3, JBL figures 40 acoustic watts (136dB)/m is required after reverberation energy is factored in.
    Considering that a cinema sub system is -10dB/30Hz and the reference is 5dB less than it is for DD/HT, it's no wonder it pales in comparison.
    Since I've never bothered to do any reverberation calcs on true sub frequencies I don't know how they would affect the SPL requirements, but I imagine there's probably not enough room behind the screen to stack enough direct radiator sub cabs to EQ a system to the DD/HT 115dB/20Hz/listening position reference in this size cinema, though with the CB's rather high efficiency down low you could do it with 23 (assuming a constant reverberation energy factor).
    GM
     
  15. Mark Seaton

    Mark Seaton Supporting Actor

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    Hi guys,
    I've seen this thread, but been a bit busy. As Dennis and Greg noted, ContraBasses do certainly deliver in ways most cinemas have never experienced. For a theater like mentioned here, where you want 136dB ContraBasses can be figured to deliver a solid 120dB @ 1m in an enclosed room. As such, I would say that 8, close coupled ContraBasses would easily reach this goal with ~500W each.
    Of course a pair of BassTech 7s would achieve the same thing with less than 1000W total. [​IMG]
    A long while back, Michael Leader did a pretty sweet system for a Canadian premier of Terminator 2. Our main speakers didn't exist at that time, but he did have 4 BT7s in the room. The response from all those who attended was significant praise of the low end effects and great sound. If I was going to do a Cinema house I would probably use 2-4 BassTech 7s with flare exensions as this would be a permanent install. With a little EQ, flat response to 20-25Hz at silly levels would not be a problem.
    Anyone know someone putting together a cinema? ;-)
     
  16. Bill Fagal

    Bill Fagal Stunt Coordinator

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  17. Greg Monfort

    Greg Monfort Supporting Actor

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    >For a theater like mentioned here, where you want 136dB ContraBasses can be figured to deliver a solid 120dB @ 1m in an enclosed room. As such, I would say that 8, close coupled ContraBasses would easily reach this goal with ~500W each.
    ====
    Hmm, has the design changed since the basslist kits I had? Mine could only do ~118dB/20Hz/450W each (500W only makes a fraction of a dB difference) in a tiny volume compared to a ~100kft^3 cinema where there's no 'room gain' and little reverberant soundfield at 20Hz, so I don't see how you figure only eight for this application.

    Regardless, we'd want to pump it up to 141dB to meet the DD/HT 115dB peak/listening position equivalent which requires ~another doubling of CBs/power.
    ====
    >Of course a pair of BassTech 7s would achieve the same thing with less than 1000W total.
    ====
    I don't remember the specs in detail and the site is down, but this seems a bit optimistic too, so what am I missing here?

    GM
     
  18. Mark Seaton

    Mark Seaton Supporting Actor

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    ====
    Hmm, has the design changed since the basslist kits I had? Mine could only do ~118dB/20Hz/450W each (500W only makes a fraction of a dB difference) in a tiny volume compared to a ~100kft^3 cinema where there's no 'room gain' and little reverberant soundfield at 20Hz, so I don't see how you figure only eight for this application.
    Regardless, we'd want to pump it up to 141dB to meet the DD/HT 115dB peak/listening position equivalent which requires ~another doubling of CBs/power.
    ====
    Well, 141dB would infer about a 65' distance without any addition from reverberation. Fair enough though. Depending on where they were placed, this should require 12 to 16 ContraBasses. For such a large application, I would probably get close enough to the corner such that below ~25Hz it was less than 1/4 wavelength away. I probably shouldn't have said only 500W, as when I do proper installs we usually put 800-1500W available to each ContraBass to prevent any clipping and allow proper headroom. It should be noted that the specs for short term power handling of 500W is with a pink noise signal with 6dB of headroom(noted in the manual). Yes, this exceeds the boilerplate rating, but there is a reason we give specifics for the measurement. So long as the continuous ratings are not exceeded, peaks to 2kW are not a problem, but this requires proper design and some understanding of the system. In an installed system, limiters can be set to help contain this, and in a calibrated system, we know what the max settings will yeild so far as output. 114dB is the approximate excursion limit of the PRs at 16Hz. This is the number we want to design with for long term output, but the sub can easily peak to 120dB above this frequency.
    Fortunately in most applications we are placing a ContraBass near or against a wall, which spacially helps us with another 3dB of output jumping to 117dB continuous. The ContraBass is 1-3dB down in the 16Hz to low 20Hz range, so in the meat of the range, figuring 119-120 is not a problem with the rear wall confinement. Then, it is not very difficult to place a sub such that it will be coupled to another boudary in the 20Hz range, which starts to give more boost and an eventual ~3dB of gain more. In a home the ceiling is almost always in this range, and even placing for modal distribution usually puts this in the proper range.
    ==========
    ====
    >Of course a pair of BassTech 7s would achieve the same thing with less than 1000W total.
    ====
    I don't remember the specs in detail and the site is down, but this seems a bit optimistic too, so what am I missing here?
    GM
    ==========
    I was going off the 136dB suggestion made before. A pair of BT7s are rated on our spec sheet to produce and average SPL equivalent of 136dB at 1M, ground plane. 4 Units extend the effective low frequency output and can produce the equivalent of 142dB at 1M ground plane. Again a rear wall will confine the radiation. I did also mention flare extensions. Increasing the horn length and mouth area of a pair of BT7s will extend and smooth the response, as well as increase the efficiency. Likewise, simply placing a pair of BT7s against a solid side wall can provide a mirror for the mouth which results in 2 units performing like 4 in open space/ground plane. Mouth area is key for the BT7s. Tom Danley and I have been talking a lot about using corners and walls to form the flare extension recently, and there are some very interesting possibilities. Previously though, there was no one here to educate the users other than Tom, so this wasn't pushed much, and isn't very practical for touring use which was then the majority user base.
    Now, about the BT7 specs...
    Specs get a bit tricky here because we are dealing with a 10.5' path within the horn itself. Likewise, as you get the mouth area larger, it no longer is a an ideal point source and you have to consider the size of the effective mouth. So the first issue is that in a conventional subwoofer, going from 1m to 2m drops 6dB in open space. In this case, at 1m you are already ~13.5' from the driver, so you have to go back to approximately 27' to see a 6dB drop in sound level! I recall that the measurements which were done by an outside contractor years ago(in the desert) showed ~122dB(with only about 2dB of compression) at 10m from 4 BT7s at 10m or 32' to 33' away. Two BT7s against the wall would produce very similar, and a flare extension would make it even better. This would imply that we would indeed be near 115dB at the ~65' meter distance mentioned here. 4 BT7s with some creative loading would be beautiful and down right scarry when appropriate. [​IMG]
    Damn, now Tom and I both want to find a theater to try this in... [​IMG]
     
  19. Mark Seaton

    Mark Seaton Supporting Actor

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  20. GaryM

    GaryM Agent

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    I want to submit a warning here. In the early 1970's I got a campus job working for one of my EE professors who was in turn supporting research on infrasonic sounds conducted by the Psych Department. (I never found out who was providing funding, it may have Psych or possibly even some Federal source.)

    We built several infrasonic speakers based upon the Electro-Voice EV-30A musical instrument speaker, essentially a 30" diameter subwoofer driver, driven by some early high output solid state amps and laboratory audio oscillators - these systems had significant output below 10Hz. (Aside - the sound of 5Hz from one such speaker is akin to the sound of closeby telephone poles through an open car window at highway speeds - something felt in your chest rather than heard.)

    Once you get well below the threshold of hearing, high volume infrasonic sound has a variety of effects on different people. One common effect is a sudden almost uncontrollable urge to urinate, RIGHT NOW. Another is severe fear, accompanied by distress because you don't understand why it's happening to you. Occasionally in enclosed spaces your diaphram will spasm, leading to difficulty breathing.

    Now I don't know if any of you are even approaching the same infrasonic sound levels as the above experiment with your ever bigger/lower frequency/louder subwoofers. I just want to urge caution upon you. Like most things in life, it is possible to go over the top and HAVE TOO MUCH low frequency sound. Be carefull!

    Gary
     

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