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best aplication for two Tempest's

Discussion in 'Archived Threads 2001-2004' started by Kevin Beck, Jun 13, 2002.

  1. Kevin Beck

    Kevin Beck Stunt Coordinator

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    Well,.. not sure what I will end up doing, but I may build new enclosures for the Tempests. Theater is in the basement, 15 X 20 room, 7ft. plus ceiling. More than likely, will be feeding them quite a bit of power,..over the 250 normally used. Any experienced oppinions. The Sono I have doesn't sound like its going to work out. A little more testing, but it doen't seem to have the output it should.
    Thanks >>>--->
     
  2. Greg Monfort

    Greg Monfort Supporting Actor

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    What did you build and how much output did you measure? What's your goal?

    Using high power/driver is a waste of $$ since thermal power compression eats up to 3dB of it.

    Two Tempests with 250W total is good for ~115dB/m peaks. A bit shy for reference levels. With 350W/driver, ~119dB/m, so still a little short unless you sit close. Four, with 250W each gets the job done, but do you have the space/budget?

    GM
     
  3. Rick Guynn

    Rick Guynn Second Unit

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    Do you have any open spaces behind any of your basement walls? (closet or something akin to it?) Twin Tempests have been used quite a bit for IB installations.

    You might also do some more measuring around your room for a better place to put your sonosub. I have been doing soooo much reading on this lately I have placement concepts coming out of my ears.

    RG
     
  4. Kevin Beck

    Kevin Beck Stunt Coordinator

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    Guys,..I built a big sono. 24" dia, X 72" long, One Tempest and 20" port on each end. Mike Strassburg built the same system, and has been having a ball with it. He is on a first floor though, as where I am in the basement. I think its tuned too low for my room.
    >>>--->
     
  5. Greg Monfort

    Greg Monfort Supporting Actor

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    Not based on this info. 115dB/m/30Hz peak capability isn't exactly quiet. [​IMG] It's only been in the last ~5yrs that this level of performance has been available to all but the ones who had plenty of space/disposable audio income.
    Are you absolutely sure you've got everything wired right, with the electronics set correctly? Both driver's VCs working?
    GM
     
  6. Rick Guynn

    Rick Guynn Second Unit

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    Aside from an equipment problem, the only thing that would really explain the problem is you may be sitting in a null (or multiple wall(s)/ceiling nulls).

    Just for grins, have you tried putting it right next to your listening position?

    RG
     
  7. Chris Tsutsui

    Chris Tsutsui Screenwriter

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    -Greg Monfort

    "Two Tempests with 250W total is good for ~115dB/m peaks. A bit shy for reference levels."

    I am confused as to what reference level you are talking about. If someone calibrates their subwoofer to say 75db using a test DVD, then isn't that set to reference level?

    So people can't achieve reference level unless their subwoofer can produce like 122 decibels at each seat? That's insane. Or does that mean a sub needs to Peak over 115db in order to make reference level...
     
  8. Rick Guynn

    Rick Guynn Second Unit

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    Chris, my understanding is that reference level is 105dB. I believe that a few sources call for the sub to run hot a few dBs at reference. Then you subtract a few on the output for distance, and you would need over 115dB output to reach 'true' reference.

    The tones used by most calibration materials (VE, Avia) outputs a signal at ref -30 or -20. So while you are calibrating to 75dB (or 85, depending on which one you use), if you left the volume at that level, you would potentially be seeing the 105dB reference peaks.

    RG
     
  9. Greg Monfort

    Greg Monfort Supporting Actor

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    Right, the DD reference is 105dB peaks at the *listening position* for each channel, with the LFE channel being 115dB. Since they spec 20dB and 30dB of headroom this means a reference level of 85dB from all channels at the listening position is required.
    Yes, it's loud, especially when you consider that if all channels are reproducing signals at the same amplitude it's 10*log(6) = ~7.8dB louder than just one channel, and of course can be louder still if one or more channels has something like an explosion going on. This is why they came out with a lower, 75dB reference for TV and smaller HT rooms (can't remember what they call it), but I always use the original reference and leave it up to the individual to decide if that's where they want to be, many don't for one reason or another.
    If you use the 75dB reference, then design around 95dB/105dB peaks at the listening position.
    Now about that listening position part, in free space sound rolls off at 6dB/square of distance, though in typical HTs it's usually closer to 3-4dB, so indeed, the sub will need to be capable of more than 115dB to meet reference without clipping the amp.
    Something I didn't mention is the possible room and/or boundary gain that increases the sub's output due to better acoustic efficiency, but again, I ignore these figuring that the additional headroom lowers distortion levels, a big deal with me, so take my info as a worst case baseline to work from.
    For example, if you're sitting 16ft from the sub in a large room so there's a 6dB roll off due to minimal room interaction, then:
    dB(peak) = [20*log(D2/D1)] + reference = 128.76dB required as a baseline for the 115dB reference, 118.76dB/105dB reference.
    Where:
    D2 = distance from the sub to the listening position
    D1 = speaker rating distance, usually 1m (3.2808ft).
    (Note: for 3dB, use [10*log(D2/D1)] + reference)
    Let's say it's in a well constructed (stiff/massive) corner of a basement and get the full +6dB of corner loading (2-4db is typical for most stick built rooms), then it drops to 122.76dB (112.76dB) to reach reference at the listening position in this example.
    Still think it's insane? [​IMG]
    GM
     
  10. Brian Bunge

    Brian Bunge Producer

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    Greg,

    With all channels set to small, isn't the LFE supposed to be capable of 121dB at all seating positions?

    Brian
     
  11. Greg Monfort

    Greg Monfort Supporting Actor

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    Ooh, good question, I keep forgetting about this in my responses on this subject. [​IMG] Thanks for bringing it up.
    It would be the reference plus 10*log(5) = ~7dB, or ~122dB/listening position for the 115dB reference and ~112dB for the 105dB reference. This pumps up the previous numbers in my example to 129.76dB (119.76dB) to get the same perceived loudness of fullrange mains/surrounds plus the LFE channel.
    My kind of performance! [​IMG] Really though, these SPL levels are limited to high Q peaks that only add a bit of perceived spaciousness to the sonic event, with actual loud passages being much lower in amplitude. Still, if you want to 'hear' all the director meant for you to, then this is where you need to be performance wise.
    GM
     
  12. Kevin Beck

    Kevin Beck Stunt Coordinator

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    Well guys,..All wires and settings have been checked about 15 times. The JBL performs very well in this room. It didn't in the old room. Very different type sub, but just to compare, it does perform prety well for what it is.
    I'm stumped. I am building an Adire unit right now, just to see how things compare. Much smaller in size, but it will tell me a bunch when I fire it up. Its the 194L ported enclosure. Should have it up and running tomorrow. Any more info would be greatly appreciated.
    >>>--->
     
  13. Greg Monfort

    Greg Monfort Supporting Actor

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    Not familiar with the JBL per se, but all the consumer sub response curves I've seen show an underdamped alignment, i.e. a hump in the midbass, with the attendant rolled off bottom octave.

    Your Tempest sub OTOH reproduces the signal much more accurately and goes lower, but doesn't have the 'punch' of the typical consumer sub. You would need a much smaller cab tuned higher to get similar performance from the Tempests. Or just EQ the 'hump' in, centered around ~60Hz.

    GM
     
  14. Michael R Price

    Michael R Price Screenwriter

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    Kevin,

    By 'doesn't seem to have the output it should' what do you mean? Is the amp clipping, driver bottoming/distorting, what? I don't see any reason why a JBL consumer sub would be better than a twin EBS Tempest. Even if the JBL has more midbass punch, the Tempest should blow its output away unless it's one of the huge pro models.
     
  15. Mike Strassburg

    Mike Strassburg Second Unit

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    Kevin,

    Just to clarify: I'm on the lower level of a Tri-level, so the sub's on a concrete slab covered with Pergo. It's also in a corner along the same wall as the listening position (couch). I couldn't imagine this thing on the first floor, house would probably crumble apart!

    Perhaps the tune is lower that what you're used to and this is why you're not happy with it. My AudioSource 12" did hit pretty hard in a VERY narrow range, but could do NOTHING down low and not near the SPL of my sono. Mine will hit you in the chest pretty hard, but on low stuff the WHOLE house starts shaking/rattling and your pant legs will move from the air.

    I've measured max SPL's of over 127 with test tones, and that's more than enough to provide a satisfying listening experience, but I will build a second or an IB when I move to a bigger house/HT room.

    I still think something must be wrong for you not to be happy with it. I've had friends of my teenage son over who have "killer" car systems and they're impressed! "Damn your house pounds as hard as my car" is the response I usually get. The offer's still open if you want to head up for a listen/comparison. Take care...Mike
     
  16. Mike Strassburg

    Mike Strassburg Second Unit

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    Kevin,

    One more thing: have you had a chance to actually measure max SPL's?? I'd be interested to see what your readings are as we've got the same sub in basically the same size room: mine's 16x22 with an 8' ceiling.
     
  17. Kevin Beck

    Kevin Beck Stunt Coordinator

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    Mike,..
    One way or another,..I do want to have a listen,...Just don't know when. I have so much going on right now,..its just nuts. If I get a chance, I will give you a buzz ahead, and seeif we can conect,...
    >>>--->
     

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