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  1. #1

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    Default Passive radiators

    I have some Infinity SL50 speakers. It has the 3/4 inch tweeter and a 8 inch woofer. Below them are two passive radiators. My question is this. How effective are passive radiators? On these models, it seems like they don't really "kick in" until the volume is at a medium level. Is this common with all models with such a set up?

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    On Polk audio, Klipsch heritage and VMPS speakers, the PR's are tuned to reinforce the existing output of the active drivers. They kick in from low volume up. The Infinity Sl50's are not as well designed.

    A properly executed PR (like those I mentioned) will add response and performance without port noise. (PR is considered a port BTW). They are very effective when properly executed. problem is, many companies are clueless about them, much like phase plugs.

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    Yeah, I know the Infinity SL series was about at the bottom of there product line back then. But, thanks Litz! With the exception of the Polk SDA line, I don't think I will get anything else with them.

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    The deal with a passive radiator is it doesn't actually move my itself. It needs the air from the other speakers to move...I kinda reduces the sound of the bass and you feel more of a rumble with radiators than you feel a punch...
    So that could explain why it only happens when you turn it up is because maybe you speakers just don't move enough air?
    At least that what I was told anyway....

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    Quote Originally Posted by PerfectCreature View Post
    The deal with a passive radiator is it doesn't actually move my itself. It needs the air from the other speakers to move...I kinda reduces the sound of the bass and you feel more of a rumble with radiators than you feel a punch...
    So that could explain why it only happens when you turn it up is because maybe you speakers just don't move enough air?
    At least that what I was told anyway....
    That would be a fairly poorly designed one, but much like a turbocharger...it is dependant on the back motion (air) of the active woofer. Matthew Polk used to called them "Fluid coupled passive radiator" The fluid...is air.

    Polk and others made the PR such that it's not sluggish, and responds quite easily to small inputs. This also explains why some PR's don't do all that well when you crank the snot out of the system. I bought them just because Polks PR's work so well at a low to medium volume. that's why I get detail, body and bass from a Polk without having to play loudly.

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    Polk's PR's sound fantastic. Vintage Monitors and SDA's have some of the cleanest, tightest, authoritative sounding bass I've ever heard. My 2A's have enough bass output to rattle your teeth. I could only imagine the sheer output of some of the bigger SDA's.
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    Quote Originally Posted by comfortablycurt View Post
    Polk's PR's sound fantastic. Vintage Monitors and SDA's have some of the cleanest, tightest, authoritative sounding bass I've ever heard. My 2A's have enough bass output to rattle your teeth. I could only imagine the sheer output of some of the bigger SDA's.
    I have heard the SDA-SRS. They indeed produce bass in the 20-hz range. One of the first demos I heard was Enya: orinoco flow/longships. While other speakers of the day played, you'd hear cannon shots as a kind of flat "bang". With the SRS, you'd get a cannon shot that flapped your pants legs. The output there is between 21-28hz depending who you take measurements from. The bass was clean, without doubling. That 15" PR works like a champ!

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    Would replacing the PRs with real drivers be a bad idea?

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    A PR is an expensive port.

    Yes, replacing them with a real driver, since it isn't really a driver at all, would be a bad idea.

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    Quote Originally Posted by polkfan38 View Post
    Would replacing the PRs with real drivers be a bad idea?
    Very bad idea.
    1. An active driver has a voice coil and spider
    2. An active driver is not tuned to work like a PR.
    ( A PR can be mass weighted)

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    Was just a thought. I wont try it.

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    Quote Originally Posted by polkfan38 View Post
    Would replacing the PRs with real drivers be a bad idea?
    Terrible idea.

    Quote Originally Posted by polkfan38 View Post
    Was just a thought. I wont try it.
    Good call.
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    Here is a blurb about PR's: (VMPS AUDIO)
    The Passive Radiator (PR) located in the bottom of the cabinet already has a certain amount of mass attached to the center, by the factory. By adding or subtracting mass from the PR, it is possible to make system tonal balance warmer (higher Q) or tighter (lower Q).

    Moving mass of PR is very low. Since a PR is driven equally over its entire surface by the active woofer's backwave, the diaphragm will move pistonically even if it is not rigid.

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    I don't have first hand experience with your particular SL model, but a general rule of thumb, make sure everything is tightened down, active (mid)bass drivers, and pr's. If the pr's or active woofers have foam surrounds, they may need to be replaced, even if they aren't to the point of breaking up and falling away.

    Other than the things mentioned above, try to tweak placement in the room, different speakers respond differently, try to avoid equal or halved distances from the side / rear walls. You can move them around to avoid cancelling out the half or quarter wave (most common) due to room boundries.

    Cheers,
    Russ

    Litz, the general membership doesn't need to be schooled on everything, just a side note to make your time here easier. ;) Polk has been using PR's since it's inception with the Model 9, original Mini Monitor, and the one that 'put Polk on the map', the Monitor 7. At the end of the day, with all things equal, it's just that - an expensive port.
    Last edited by RuSsMaN; 05-06-2010 at 01:51 AM.
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    Quote Originally Posted by RuSsMaN View Post
    I
    Litz, the general membership doesn't need to be schooled on everything, just a side note to make your time here easier. ;) .
    Sounded like the poster had no knowledge of PR's...silly me for providing information cut and pasted from an authority to help clarify. My bad for being helpful, no good deed goes unpunished---or uncomplained about. Not all of us need schooling on polk history.
    Last edited by Litz; 05-06-2010 at 02:09 AM.

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    Quote Originally Posted by RuSsMaN View Post

    Litz, the general membership doesn't need to be schooled on everything, just a side note to make your time here easier. ;) Polk has been using PR's since it's inception with the Model 9, original Mini Monitor, and the one that 'put Polk on the map', the Monitor 7. At the end of the day, with all things equal, it's just that - an expensive port.

    I'm not trying to argue that, but I've seen Litz provide quite a bit of useful information since he joined up.

    He's taught me a thing or two that I didn't know...this in particular...

    "By adding or subtracting mass from the PR, it is possible to make system tonal balance warmer (higher Q) or tighter (lower Q). "

    Interesting stuff! I wonder if anyone's ever played around with adding/subtracting weight from the PR's in SDA's.
    The nirvana inducer-
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    Quote Originally Posted by comfortablycurt View Post
    I'm not trying to argue that, but I've seen Litz provide quite a bit of useful information since he joined up.

    He's taught me a thing or two that I didn't know...this in particular...

    "By adding or subtracting mass from the PR, it is possible to make system tonal balance warmer (higher Q) or tighter (lower Q). "

    Interesting stuff! I wonder if anyone's ever played around with adding/subtracting weight from the PR's in SDA's.
    Nothing that hasn;t been covered ad nauseum elsewhere multiple times. He should dial it down a bit. He comes off as a know it all name dropper.

    H9
    "Appreciation of audio is a completely subjective human experience. Measurements can provide a measure of insight, but are no substitute for human judgment. Why are we looking to reduce a subjective experience to objective criteria anyway? The subtleties of music and audio reproduction are for those who appreciate it. Differentiation by numbers is for those who do not".--Nelson Pass

    Pass Aleph 30; Eastern Electric Mini Max; Adcom GDA600; MIT S3/Z Pc; SDA 1C; Squeezebox; Tubes add soul!

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    Quote Originally Posted by heiney9 View Post
    Nothing that hasn;t been covered ad nauseum elsewhere multiple times. He should dial it down a bit. He comes off as a know it all name dropper.

    H9
    And you come off as a scolding , snobbish blowhard. What kind or idiot posts in a thead as if I am not able to read the post? Get over yourself windbag! You aren't exactly an audio God yourself.

  19. #19

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    Quote Originally Posted by Litz View Post
    And you come off as a scolding , snobbish blowhard. What kind or idiot posts in a thead as if I am not able to read the post? Get over yourself windbag! You aren't exactly an audio God yourself.

    I retract my previous statement.
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    PolkAudio SDA 2A's/PolkAudio Monitor 7A's
    Audioquest Type 4 speaker cables
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    Audioquest Black Mamba IC's
    Signal Cable Analog II IC's

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    Quote Originally Posted by comfortablycurt View Post
    I retract my previous statement.
    and I don't care...

  21. #21

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    Quote Originally Posted by Litz View Post
    and I don't care...

    Cool.

    I can already tell that you're not going to make many friends here. Better get in leagues with our resident trolls while you still can.
    The nirvana inducer-
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    DPA The Little Bit Three DAC
    Yamaha P-300 turntable/TCC TC-750 phono preamp
    Acurus L10 preamp
    Adcom GFA-545 power amp
    PolkAudio SDA 2A's/PolkAudio Monitor 7A's
    Audioquest Type 4 speaker cables
    Audioquest Sidewinder IC's
    Audioquest Black Mamba IC's
    Signal Cable Analog II IC's

  22. #22

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    So we are basically done here.

    Polkfan38 (and others), please feel free to start a new thread, same topic. Again, it's not always the information, as much as it is the delivery.

    This one is a wrap for obvious reasons, and will move to the Hall of Shame after Polk review tomorrow.

    Carry on...and thanks for your contributions to the board!

    Cheers,
    Russ
    Last edited by RuSsMaN; 05-06-2010 at 02:53 AM.
    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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