passive woofer

beefy
beefy Posts: 5
edited August 2001 in Technical/Setup
Could someone explain how the passive woofer works
Post edited by beefy on
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  • RuSsMaN
    RuSsMaN Posts: 17,987
    edited August 2001
    Audio definition:
    Passive Radiator - A device that functions as a Helmholtz resonator, typically used in place of a port in a speaker cabinet.

    So what does that mean? Helmwhat? Imagine a woofer, without a magnet or voice coil......

    A passive radiator does not have the pipe resonance, air turbulence, and escaping internal box noises that the simple port has. They are also easier to implement than a port when the tuning frequency is very low, and most importantly will not compress the output until they reach the limits of their suspension travel (excursion).

    HOWEVER, the cabinet will need more attention to the placement as they are effectively another driver cutout. The mass of the passive is capable of shaking the cabinet if care is not taken in the design.

    An extreme example of Pr's might be dual 15" 1400gram passive radiator cabinets (talking a sub here). A port equivalent to these would be over 18" in diameter and 46 FEET in length! This is where the passive radiator works best, in situations that ports cannot be used under any circumstances. The example 18" port mentioned would have incredible output compared to a standard, say 4" port if it could be made to work, however the port size is not feasible while the passive radiator is.

    More in-depth if you so desire:
    PR's in depth

    Cheers,
    Russ
    Check your lips at the door woman. Shake your hips like battleships. Yeah, all the white girls trip when I sing at Sunday service.
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  • beefy
    beefy Posts: 5
    edited August 2001
    Russ.dude.Iam a simple guy,could you dumb it down a bit for me thnx
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  • RuSsMaN
    RuSsMaN Posts: 17,987
    edited August 2001
    The passive radiator acts in place of a port, especially when the optimal port length would exceed a reasonable size for the speaker cabinet.

    The passive radiator shares the acoustical 'load' of the woofer. This reduces the woofers excursion (movement), thus increasing its power handling capabilities. Passive radiator cabinets usually require a little more thought put into the design of the cabinet, but almost always can be tuned to a lower frequency....

    Cheers,
    Russ
    Check your lips at the door woman. Shake your hips like battleships. Yeah, all the white girls trip when I sing at Sunday service.
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  • George Grand
    George Grand Posts: 12,258
    edited August 2001
    Damn Russ! He said dumb!

    Beef,
    The passive radiator has no electricity running to it. It is not "driven" by the amplifiers output the way the OTHER speakers in the cabinet are. As the woofer that HAS electricity going to it moves back and forth, it forces air into the speaker cabinet as well as out into the room. The active woofers "back stroke" pressurizes the INSIDE of the cabinet, causing the PASSIVE woofer to move back and forth.

    George Grand (of the Jersey Grand's)
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  • Aaron
    Aaron Posts: 1,853
    edited August 2001
    My only question is if the passive radiator is the "port", then how does ANY air get in or out? Sounds like a sealed box to me.

    Aaron
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  • RuSsMaN
    RuSsMaN Posts: 17,987
    edited August 2001
    It is sealed.....

    Cheers,
    Russ
    Check your lips at the door woman. Shake your hips like battleships. Yeah, all the white girls trip when I sing at Sunday service.
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  • Aaron
    Aaron Posts: 1,853
    edited August 2001
    Originally posted by George Grand
    As the woofer that HAS electricity going to it moves back and forth, it forces air into the speaker cabinet as well as out into the room.

    ...that's not what George is saying.

    Aaron
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  • RuSsMaN
    RuSsMaN Posts: 17,987
    edited August 2001
    Forget ported/sealed...all that for a sec.

    When the woofer moves out, it moves air into the room, the air in front of it. When the woofer moves in, it moves air in the cabinet, the air behind it.

    When the the woofer makes its inward and outward motions, it changes the pressure inside the cab, thus making the PR move.....

    Think SDA, ever seen a port on one?

    Cheers,
    Russ
    Check your lips at the door woman. Shake your hips like battleships. Yeah, all the white girls trip when I sing at Sunday service.
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  • George Grand
    George Grand Posts: 12,258
    edited August 2001
    A poor choice of words on my part. The active woofer compresses the air ALREADY IN the room and the cabinet. There you go Aaron. Thank you.

    George Grand (of the Jersey Grand's)
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  • Aaron
    Aaron Posts: 1,853
    edited August 2001
    Originally posted by RuSsMaN
    When the woofer moves out, it moves air into the room, the air in front of it. When the woofer moves in, it moves air in the cabinet, the air behind it.

    When the the woofer makes its inward and outward motions, it changes the pressure inside the cab, thus making the PR move.....

    Russ:
    When the woofer moves out it's moving are IN the room, not moving are INTO the room. That's implying that there is a flow of air from the cabinent into the room. Anyway, those little words can be confusing. Pressure is what we're talking about. I know you know what you're talking about, Russ, I just got hung up on your wording.

    George:
    Score one for "the kid". :)

    Aaron
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  • RuSsMaN
    RuSsMaN Posts: 17,987
    edited August 2001
    Sorry bout that there, barrel ****.

    Cheers,
    Russ
    Check your lips at the door woman. Shake your hips like battleships. Yeah, all the white girls trip when I sing at Sunday service.
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  • Aaron
    Aaron Posts: 1,853
    edited August 2001
    What's a "barrell ****"? I know what "****" means, but "barrell" doesn't show up in my dictionary. Perhaps you meant "barrel". :p

    Aaron
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  • RuSsMaN
    RuSsMaN Posts: 17,987
    edited August 2001
    Thats what I said, didn't I bottle nose?

    Cheers,
    Russ
    Check your lips at the door woman. Shake your hips like battleships. Yeah, all the white girls trip when I sing at Sunday service.
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  • Aaron
    Aaron Posts: 1,853
    edited August 2001
    Nice try, Russ! You had me do a double take, though. :D

    Aaron
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  • beefy
    beefy Posts: 5
    edited August 2001
    russman,me beefy understand now thankayou somucha!!!!
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  • beefy
    beefy Posts: 5
    edited August 2001
    aaron you live in PA areyou near Pittsburgh
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  • Aaron
    Aaron Posts: 1,853
    edited August 2001
    I live in Hershey, PA and go to school in Bethlehem, PA. Pittburgh is a good 5 hours from here.

    Aaron
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