What is a "passive radiator"?

Discussion in 'Archived Threads 2001-2004' started by Richard Harvey, Feb 26, 2002.

  1. Richard Harvey

    Richard Harvey Stunt Coordinator

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    I demoed center channel speakers last week, and walked away with a Boston VR-910 center. The basic specs of this speaker are solid, and match my system very well. However, I'm confused on one aspect of this speaker I haven't run into before. Boston describes this as having:

    1" aluminum tweeter

    5.25" active woofer

    5.25" passive radiator

    Just how in the heck does a passive radiator differ from an active woofer?

    Rich
     
  2. John Doran

    John Doran Screenwriter

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    richard,

    here's a definition for you - A passive radiator is a

     
  3. John Royster

    John Royster Screenwriter

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    An active woofer has a magnet and voice coil. You receiver/amplifier uses this to move the speaker. That's active.

    Passive has no magnet and uses the air pressure inside the speaker cabinet created by the active driver to move.
     
  4. Vince Maskeeper

    Vince Maskeeper Producer

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    In the old days, they were sometimes called a "sympathetic radiator".

    Basicially it is an alternate to a ported speaker design- in theory giving a "split the difference" performance between Ported and sealed enclosures (bass volume equal to ported with quickness and tightness almost equal to a sealed box- without the size needed for a full port).

    So basically you have a speaker cone that isn't getting power and has no magnet or voicecoil- and that passive speaker just flops with the pressure in the box created by the powered drivers, doing the job of a port.

    -V
     
  5. Richard Harvey

    Richard Harvey Stunt Coordinator

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    Very interesting. So, basically, you get some advantages like smaller enclosure (since a port isn't necessary), better bass extension, and possibly lower power draw. What are the disadvantages to this design?

    I'm amazed how much new stuff I learn every day in this forum!

    Rich
     
  6. John Doran

    John Doran Screenwriter

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    at least one disadvantage of the design is that you get the full benefits of neither vented nor sealed enclosure - the bass won't go down as deep as a sealed enclosure, nor as loud as a vented enclosure.

    similarly, one of the architectural advantages of the design is that it allows for smaller drivers to be used, which further compromises bass depth, volume, and accuracy at the limits of both.

    in the end, though, what counts as disadvantageous will in some measure depend on your priorities in bass reproduction as between (at least) aesthetics, volume, depth, and accuracy.
     
  7. Patrick Sun

    Patrick Sun Studio Mogul

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    The drawback is the added expense of the passive radiator, and tuning it correctly (you add bits of mass to the passive radiator to tune to a specific frequency of the enclosure).
     
  8. ThomasW

    ThomasW Cinematographer

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  9. John Doran

    John Doran Screenwriter

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    thomas,

    do you know if a PR can attain the same db-level as a vented enclosure of the same dimensions?

    also, do you know how close the active driver of a PR comes to its excursion-limit?

    my understanding of PR's is that, though they are functionally equivalent to vented designs, there are nonetheless practical differences between the two.

    though i am well aware that i could well be wrong.

    however, if a PR's db-limit on average falls between that of a vented and a sealed enclosure, and if its proximity to its excusrion limit at that point (i.e. max-db) also falls somewhere between the sealed- amnd vented enclosure, than i would call that a compromise.

    also, what i was trying to get at when i made the claim that PR's allow for smaller drivers, was that that PR-designs allowed for smaller drivers to be used relative to sealed-enclosures with larger drivers, while at the same time achieving some of the same bass-benefits of those larger-driver sealed enclosures.

    i was also implying that PR's allowed for smaller enclosures, as well.

    but i should have been clearer, to be sure.

    thanks for the correction, thomas.
     
  10. ThomasW

    ThomasW Cinematographer

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  11. Richard Harvey

    Richard Harvey Stunt Coordinator

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    This thread has answered so many questions. Besides the sound quality of the speaker, one of the reasons I really liked the Boston design is that the other centers I was seriously considering (like the Klipsch RC-3 II) were absolutely HUGE compared to the Boston. I have a Toshiba TW40F80 16:9 set, which has a very shallow ridge for placing a center. I needed a quality speaker, but one that could firmly sit on this shallow ledge (my wife wasn't too keen on a wall mounted center). I was amazed at how well the VR-910 could crank out clear sound with such a shallow enclosure, but now I understand the mechanics behind it.

    Rich
     
  12. John Doran

    John Doran Screenwriter

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    thomas,
    i guess i'm still not being clear.
    i understand the xmax thing.
    what i was actually wondering was, for instance, how close to it's xmax each of the drivers would be in each of 3 subs (vented, sealed, and passive radiator, all of relevantly similar design) at some arbitrary db-level. let's say 105db.
    i know that one of the advantages of a vented enclosure is that it allows the sub to put out more volume with less driver excursion than a sealed sub.
    what i don't know is how a PR and a vented sub compare in this respect. i know you keep saying there's no difference, but i've never been sure that you've understood my question. which is my fault.
    so. at 105db, which of a vented sub's and a passive-radiating sub's driver would be closer to its xmax?
    and, as for the the PR driver acting like a bigger driver, that's not exactly what i was trying to suggest, either. not really.
    what i meant was only that a PR sub would be able to achieve, for instance, the volume of a sealed sub with a larger driver, and it would be able to do so because of the passive-radiation design.
    which, i suppose, may still be wrong...
     
  13. Larry B

    Larry B Screenwriter

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  14. Larry B

    Larry B Screenwriter

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  15. ThomasW

    ThomasW Cinematographer

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    John

    First start using proper terms. 'Volume' is not SPLs (sound pressure levels/loudness/output). Volume is the amount of area, cu. ft/liters etc inside an enclosure. In other words volume is the size of the box

    So if you're going to refer to loud something will play use SPL's/output level/loudness not 'volume'.

     
  16. BruceD

    BruceD Screenwriter

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    My Dynaudio Contour 2.8 towers have a woofer and a PR with a -3dB spec of 32Hz and I really liked their sound much better than the ported Contour 1.8 towers with 2 woofers and a -3dB of 30Hz.

    I found the bass and mid-bass to be cleaner on the 2.8 with the PR. I never heard it "chuff" on the Dynaudio 1.8, but some people have commented on port "chuffing" of other ported speakers.
     
  17. Patrick Sun

    Patrick Sun Studio Mogul

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    One of the other positives of using a PR over a port is that you won't get chuffing sounds if you seriously underport the enclosure with a port that's too narrow.

    So, if you have money to burn, and size restrictions for the total volume of the enclosure, PRs are probably the way to go, but you need to mate it to the right driver for a good design.

    And if you're cheap, and can handle a larger enclosure, then ports are probably a better option. (That would be me).
     
  18. Doug Drake

    Doug Drake Stunt Coordinator

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    Richard - I may have missed this in my quick scan of this thread, but what main speakers are you trying to match with your center speaker? You mentioned you also listened to a Klipsch RC-3 (which would only match the Klipsch Reference series). Size notwithstanding, you will want a center that is correctly matched (timbre-wise) to your existing mains (or your planned upgrade) so as to create the smoothest possible front soundstage.
    Doug
     
  19. Jack Gilvey

    Jack Gilvey Producer

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    Yikes, lots o' misconceptions.
    Try here first.
     
  20. Brian Bunge

    Brian Bunge Producer

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