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    RIP 2011 Zilch's Avatar
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    Acoustic (Air) Suspension

    It's been a very long time since I've worked with or listened to small closed-box speakers, a design approach pioneered by "East Coast Sound" proponents of the '60's - AR, Advent, KLH, etc.. Building DIY Minis recently led me to trying that approach with JBL drivers, with good result.

    A little research in Dickason's Loudspeaker Design Cookbook serves as a refresher on the essentials:

    1) A good starting DIY project - easy to build and easy to succeed; the alignments are not critical.

    2) Excellent extended bass, as the rolloff is just 12 dB/octave.


    3) Driver parameters:
    EBP = Fs/Qes < 50
    Qts > .3
    Low Fs
    High Xmax
    High MMS
    High Vas


    4) Box size - for true air suspension, < 1/3 Vas.

    5) Easy to measure (test) and understand.

    There's not many JBL drivers that qualify, but BB6P EBP meter identifies these potential candidates:

    116A, H, H-1
    123A
    125A
    127A, H
    2145A
    2213

    Another group, more intermediate between closed and vented designs includes:

    2245
    508G
    LE10A
    LE8T-8
    Sub1500



    [Lists subject to change without notice.... ]


    I have been using a $15 yard sale pair of AR4x as test boxes (18.45 l, 0.652 cuft gross internal volume,) but recently discovered that the OASR "Dr. Seuss" horn would just fit. Ut-oh:

    3" hole saw and small Sawzall make the "clover-leaf" cutout for the OASR horn with 2407H neodymium tweeter.

    708G-1 8" woofer fits perfectly. I'm trying others, too.

    Control 128W crossover (2.5 kHz) plus notch filter on the woofer and L-pad + compensation cap on the tweeter gives immediately satisfying results, bottom.

    Off to critical listening tests, soon....
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