Polk Crossover Question

dougy
dougy Posts: 182
edited April 2009 in Speakers
Most speaker makers seem to cross their mids and woofers over in the 200-500Hz range, but Polk (and some others) appear to favor lower x/o points (120Hz or so). I don't claim to be an expert, but I have seen some pretty ugly distortion graphs of the LSi-9 where distortion shoots up below 200Hz. So why the low x/o? I'm not trying to start a flame war here; just curious as to what the advantage of such low x/o points would be. Like I said, Polk isn't the only one who does this. The proof of the pudding is in the eating! (or something like that!)
THE MAN-CAVE 5.1 CHANNEL A/V RIG
Sony KDS-60A3000
a/d/s/ HT-400LCR (3)
a/d/s/ HT-300 (2)
Velodyne DLS-4000R (2)
Pioneer Elite VSX-55TXi
Pioneer Elite DV-47Ai
Sony BDP-S300
Sony SLV-779HF
DirecTV HD sat. receiver

MAN-CAVE 2-CHANNEL RIG (shares sources with a/v system)
Adcom GFA-5500
Bose 901 Series VI
NAD C-165BEE
Slim Devices Squeezebox Classic
TEAC CD-RW890
Technics SL-BD20D w/ Audio-Technica P34
Akai HX-A3X
Post edited by dougy on
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Comments

  • Face
    Face Posts: 14,340
    edited April 2009
    Do you realize the LSi9 is an cascaded tapered array, one mid plays from 40hz to the MT x-over point, the other plays from 40hz to 200hz... An issue in the 200hz area could be from the nasty 2ohm impedance dip and the associated amp not being able to keep up.
    "He who fights with monsters should look to it that he himself does not become a monster. And when you gaze long into an abyss the abyss also gazes into you." Friedrich Nietzsche
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  • dougy
    dougy Posts: 182
    edited April 2009
    Face wrote: »
    Do you realize the LSi9 is an cascaded tapered array, one mid plays from 40hz to the MT x-over point, the other plays from 40hz to 200hz... An issue in the 200hz area could be from the nasty 2ohm impedance dip and the associated amp not being able to keep up.

    I used to have a pair of Mobile Fidelity Sound Lab OML-2's that had a similar x/o. They had a pair of 6.5" mid-woofers. One worked all the way up to the tweeter x//o, while the other one only covered up to 300Hz.

    I was not aware of the impedence dip to 2 Ohms in the LSi9. That sounds rather brutal! I wonder how my little Onkyo would deal with that!

    Actually, the LSi9 wasn't the best example to illustrate my point, being a two-way (and a half!). It's just that it's the speaker I saw with the rising distortion measurement below 200Hz.

    I don't know about the amp issue you mentioned, but I suppose it's a possibility. The distortion did not spike at 200Hz, though. It just began to climb there, rising sharply all the way down to the measurement limit. That's what made me think it was just a case of pushing those small drivers too hard. I notice all Polk 3-ways seem to cross over from mid to woofer in the 120 -150Hz range. B&W and Canton cross their mids and woofers in the 300Hz area. Klipsch anywhere from 450 to 850 Hz. I guess I'm just curious as to what the advantage is of using a lowish crossover point, becaue I can understand the argument for the higher x/o -lower distortion and higher sensitivity.
    THE MAN-CAVE 5.1 CHANNEL A/V RIG
    Sony KDS-60A3000
    a/d/s/ HT-400LCR (3)
    a/d/s/ HT-300 (2)
    Velodyne DLS-4000R (2)
    Pioneer Elite VSX-55TXi
    Pioneer Elite DV-47Ai
    Sony BDP-S300
    Sony SLV-779HF
    DirecTV HD sat. receiver

    MAN-CAVE 2-CHANNEL RIG (shares sources with a/v system)
    Adcom GFA-5500
    Bose 901 Series VI
    NAD C-165BEE
    Slim Devices Squeezebox Classic
    TEAC CD-RW890
    Technics SL-BD20D w/ Audio-Technica P34
    Akai HX-A3X
    · Share on FacebookShare on Twitter