Isobaric and Tempest Questions:

Discussion in 'Archived Threads 2001-2004' started by Chris Popovich, Mar 1, 2001.

  1. Chris Popovich

    Chris Popovich Stunt Coordinator

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    Hello All,
    I have two questions here. The first concerns the isobaric design; in a push-pull design where the drivers are mounted like this , does the effective sd decrease due to the voice coil taking up moving space on the outside of the box? If so, what would be the expected decrease in SPL? Does the transducer frame cause air turbulence that effect sound quality?
    The second question is about using passive radiators with a Tempest; would 2 of the Adire PR's be adequate? Anyone around here build a smallish (well.... under say 6 cubic feet) Tempest PR design?
    Your input is, as always, appreciated.
    Thanks,
    Chris
     
  2. Jack Gilvey

    Jack Gilvey Producer

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    I'm not really sure of the question,but...
    You don't really have to worry about that stuff. The VC doesn't take up "moving space". The design allows air to flow freely either way,as is needed even in a conventional mounting scheme. When mounted in a clamshell-style isobaric (like this ), the drivers are wired out-of-phase electrically,so as to be in-phase acoustically. So, they'll be moving in the same direction,when one is moving out of its frame,the other is moving in.
    In iso designs in general,the only advantage is an enclosure about half the size as would be needed for the same alignment for one driver. To look at it another way,you lose 3 db compared to the potential output from 2 drivers.
    The Tempest apps are posted on the Adire site, but only the sealed ones. I expect the PR and ported (very similar alignments/sizes) to show up soon.
    ------------------
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    I prefer to listen to my music in its Original Aspect Ratio: Stereo.
     
  3. Chris Popovich

    Chris Popovich Stunt Coordinator

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    Thanks for the reply, let me clarify what i was asking a bit:
    Doing the clamshell isobaric design, you have a woofer behind a wall, and another firing backwards into the room:
    I---I
    I < >
    I---I
    The woofer that is firing backwards into the room has less cone that 'sees' the air it's trying to move. This is so due to the area within the voicecoil diameter not being cone surface area, and not directly contributing to driver output. Does this decrease in surface area of the cone effect the maximum output characteristics, and if not then why not? Spyder movement?
    I guess what I'm saying is that if you have two cyclinders of equal outer dimensions, one solid the other with a hole in the middle, how can they displace the same amount?
    Dan, any input here?
    Thanks again,
    Chris
     
  4. John E Janowitz

    John E Janowitz Second Unit

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    Chris, the Sd of the cone is so much greater than that taken up by the VC that it should not effect anything. Example, with a typical 15" driver has Sd of aroudn 132 sq inches. The Sd taken up by a 3" VC would be only 7 sq inches. This would be only 5% of the total surface area and is really insignificant.
    John
     
  5. DanWiggins

    DanWiggins Second Unit

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    Chris,
    There is a slight loss in Sd, as John points out. It's really not much at all, though; Sd of Tempest is 779 cm^2, but the voice coil is 6.35" in diameter, so you "lose" 30 cm. Or less than 4% of the area. Will this affect peak SPL? Yep - by about 0.17 dB. Basically a non-issue difference.
    Jack,
    The Sealed Tempest apps are up; likewise the vented and PR ones are up, too.
    John,
    Excellent clarification! Well put!
    Dan Wiggins
    Adire Audio
     
  6. Jack Gilvey

    Jack Gilvey Producer

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  7. DanWiggins

    DanWiggins Second Unit

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    Nope. You'll need to open the file, then edit to add your own room dimensions and layout. We used the IEC standard sized room, with corner placement of the sub.
    Dan Wiggins
    Adire Audio
     
  8. Chris Popovich

    Chris Popovich Stunt Coordinator

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    Thanks John, Jack and Dan, that clarifies things quite a bit. Dan, the Tempest Apps. papers are really helpful, thanks!
    Chris
     
  9. John Joosten

    John Joosten Auditioning

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    I did a design for a tempest in a 160 litre box (6cuFt) with two pr15's with an extra 375 grams mass on each Pr. The box should be flat responce down to about 20 hz in room.Put the tempest on the front panel and load one pr on each opposing side . This will be an awesome sub.
    John
     

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