Ultra low Shiva sub

Discussion in 'Archived Threads 2001-2004' started by MarkoV, Jan 15, 2002.

  1. MarkoV

    MarkoV Auditioning

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    I just ordered Shiva 12" element and I planning for my first sub.

    I created a model using LspCad from Adire Audio:

    120 L Vented box with tuning to 13 Hz using 10,2 cm or 6,8

    cm reflex tube. Then I created Bass boost to 7 Hz with

    -15.6db att (R11 = 10 KOhm, R12 = 50 KOhm and C11 = 470 nF).

    I got incredible response. -3 db point is at 13 Hz.

    Group delay is 12 ms at 20 Hz, 20.3 ms at 15 Hz.

    Everything sounds too good. Is there something wrong with my

    model ? Any opinions ?

    Marko
     
  2. JerryW

    JerryW Supporting Actor

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    Wow... that's great, but something doesn't sound correct, how do you get a tuning frequency that low in an enclosure that small? How long is the port (looks to be 4" in diameter)?

    Also, I don't think B Boost will help in a vented enclosure like that. The rolloff is just too steep to allow for much adjustment.
     
  3. Greg Monfort

    Greg Monfort Supporting Actor

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    Sounds like you used the default power/configuration settings as GD, excursion, vent mach, will go through the roof with more than ~ a fraction of a watt if a really low note is reproduced. The vent's a bit long too, so PR's would be needed. IOW, not a viable design for HT even without bass boost.

    GM
     
  4. Dustin B

    Dustin B Producer

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    Could you ellaborate on how you modelled that boost please. I don't understand that part of LspCAD at all, I understand the result, but I need how to get that result spelled out :p) Is that a 2nd order HP? What is the C12 value?

    And what are you planning on powering it with?
     
  5. ThomasW

    ThomasW Cinematographer

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    My question is why bother?

    Remember one can't hear a signal that low. All you'll be doing is turning the driver into a bass shaker. One can also do that with a higher and more sensible tuning.

    Also except for the occasional test disc and signal generators, there's virtually no software available that has anything below 15Hz.

    To create boost at 7Hz you're going to need a VERY expensive EQ. The Symetrix 551 can be forced to boost as low as 8Hz by using a combination of filters. But other than that a custom build unit would be necessary. Creating boost at 7Hz will take CUBIC horepower for any significant output. A slight hiccup in the system and your Shiva will be toast.
     
  6. Scott Simonian

    Scott Simonian Screenwriter

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    Maybe its because he would like to experience this octave in our spectrum of hearing. I personally havent heard such low tones before, that I know of.
     
  7. ThomasW

    ThomasW Cinematographer

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    7Hz is inaudible, but certainly detectable via bone conduction. But again there's nothing out there to play except for a disc or two. Playing test tones that low is interesting for a day or so. Eventually it starts messing up your vestibular system. Then you get dizzy and barf.....
     
  8. Brian J Dupuis

    Brian J Dupuis Second Unit

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    Hey, now you're talking. It ain't fun 'til someone blows chunder. [​IMG]
     
  9. Michael R Price

    Michael R Price Screenwriter

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    My friend Philip Ries built a sub with a Shiva, 120W amp in about 290L (10 cuf) tuned to 10-10.5Hz.

    First, it sounds amazing. Very clean and tight, can shake up your insides. But I'm sure any other more conventional alignment can do the same.

    I agree about the fact that there's very little real world use for such a subwoofer. But experiencing such infrasonic sounds is really something. Phil says that when he played a 10Hz tone, things rattled in his brother's room two floors up (not to mention that the room the sub is actually in pulsates strongly, creating a pretty weird sensation). Of course, in real music I dont think there's any point to this except maybe organ music and other 'hall sound' that may create an interesting ambiance to the sound. I'm sure movies have some information down in the 10-15Hz range... mainly, it's a psychological thing: knowing that if there is anything down there, you're feeling it.

    I can ask Phil more about the project if you're interested... but I don't know if thats what you want. (With him, budget, depth and quality were the most important things)

    With that project, space (or the small amount of lost output) wasn't an issue so going for such an extreme alignment was a 'what the heck, why not' sort of thing. I wouldn't bother if I was looking for a conventional HT sub. I'd also stay away from using equalization to extend bass... it might cause you to clip your amp or bottom the driver easily (not to mention causing more distortion).

    Scott, at my school the air conditioning system causes a small area (a few rooms) to vibrate at maybe 6-10 Hz. Most of the time you don't really notice it, but when you do, it's a pretty disconcerting and unique feeling.
     
  10. MarkoV

    MarkoV Auditioning

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    Actually tuning sub extremely low I didn't do

    to produce 13 Hz tunes, but I noticed

    that that kind of sub should have smaller group delays

    than sub with higher tuning. For example one with 19 Hz tuning has 26 ms group delay, If I add 2nd order HP tuning to 15 Hz I got nicer frequence respons, but that will raise group delay to 40 ms.

    Using Bass Boost at 7 Hz and 13 Hz tuned vented box I

    got -1.5db at 20 Hz and grop delay 12 ms. Bass Boost

    actually does not boost bass, but cuts higher frequencies, max -15 db.

    But If you think that it will be only used between 20-80 Hz is the design ok.

    Is there noticeable difference with subs that has group delay 10 ms and 40 ms at 20 Hz ?

    Marko
     
  11. Travis G

    Travis G Stunt Coordinator

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    One benifit of tuning your sub to a lower frequency then you need is that it makes it harder to bottom out. I blew the first sub I built tuned to 19 Hz via 1812 Overture.
     

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