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Thread: Acoustic (Air) Suspension

  1. #31
    RIP 2011 Zilch's Avatar
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    By coincidence, Audivex had a 2213 recone on the bench today illustrating a failure mode from overexcursion. I snagged the old cone from the trash.

    Theory: flexure occurs in the cone itself where it "rounds over" to meet the accordian surround, which creates an annular weak spot over time:
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  2. #32
    RIP 2011 Zilch's Avatar
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    Quote Originally Posted by duaneage
    Zilch has proven that using a driver different than what it's T/S parameters suggest may be a good marketing trick but in the end it's better to do it right.
    It's been mentioned several times in the past in these forums; I can't claim credit for anything other than not ignoring the good advice previously posted here.

    [And maybe having an "easy fix" available.... ]

    Calculation update: 2213 (123A-1) in L88. Blk = port closed, heavy fill (yet to be determined). F3 = 48 Hz, Qtc = 0.838. Usable bass (-10 dB) to 30.41 Hz (cursor).
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  3. #33
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    Thumbs up

    I know the plumbers plug would probly work better, but I was looking at the other plug on ebay for its aesthetic quality of being black versus the look of shiny metal. While I could paint the fancy one up all pretty and throw an acorn nut on it instead of the wing nut I think the black plug might just dissappear better. That and I don't want to have to prep prime and paint something........

    Oh and Zilch even though you may not be able to take credit for coming up with the idea to use a driver as it is intended, plugging the ports with a plumbers test plug will from this day forward be known as the "Zilch mod" . Congratulations on your new legacy!

  4. #34
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    Hi Zilch,

    Great thread. I'm getting too much bass from my L222 in my small room. For a while, I've been thinking of removing the passive radiator and sealing up the opening to make the L222 into a A-S design. Is that recommended for the L14A?

    Thanks

  5. #35
    RIP 2011 Zilch's Avatar
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    LE14A isn't on the "closed box" list, but you might explore what would happen with WinISD.

    I think I'd try tuning the passive radiator per L220 first. There's info in some threads here. L222 has the boomy "Disco" tuning, as I recall....

  6. #36
    Senior Member edgewound's Avatar
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    Quote Originally Posted by Zilch
    LE14A isn't on the "closed box" list, but you might explore what would happen with WinISD.

    I think I'd try tuning the passive radiator per L220 first. There's info in some threads here. L222 has the boomy "Disco" tuning, as I recall....
    That's an easy one. The PR300 has a number of mass-loading discs that are attached to the backside under the dustcap via a 10-32 machine screw. Simply take out the PR300 and remove one disc at a time, remount and listen. The factory did that by design so the user could adjust the bass response.....pretty cool feature. Just make sure the screw isn't too long to break through the dust cap when only one disc is used. Some versions used paper discs, some used metal discs.
    Edgewound...JBL Pro Authorized...since 1988
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  7. #37
    Senior Member grumpy's Avatar
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    While you're experimenting...

    might also consider -adding- weight.
    (swap fiber disc out, metal disc in, if bolt-length limited)

    -grumpy

  8. #38
    Senior Member edgewound's Avatar
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    Quote Originally Posted by Zilch
    It's been mentioned several times in the past in these forums; I can't claim credit for anything other than not ignoring the good advice previously posted here.

    [And maybe having an "easy fix" available.... ]

    Calculation update: 2213 (123A-1) in L88. Blk = port closed, heavy fill (yet to be determined). F3 = 48 Hz, Qtc = 0.838. Usable bass (-10 dB) to 30.41 Hz (cursor).
    Just to keep the facts straight and not embarrass anyone...the 2213 is the same a 123A-3

    123A-1 is the same as 2212.

    ....and as grumpy pointed out...adding a little mass could also be a cure for boominess...depends on your room.
    Edgewound...JBL Pro Authorized...since 1988
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  9. #39
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    Stuck some poly fill inside my l100 cabinet today after installing my 104hs and I wasn't too impressed. Perhaps I'll have to start experimenting later, but in this application (where the woofer half of the midrange) i think you've got to pick either blocking the port or stuffin the box with insulation. Polyfill was just too much and all i had left was HF and upper MF, so for right now I'm gonna leave em be and enjoy my new amplifier and midranges. Which if you have an l100 i strongly advise and upgrade to 104h's

  10. #40
    RIP 2011 Zilch's Avatar
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    Quote Originally Posted by edgewound
    123A-1 is the same as 2212.
    Well, HELL.

    Now I gotta make more plots....

  11. #41
    Senior Member edgewound's Avatar
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    Quote Originally Posted by Zilch
    Well, HELL.

    Now I gotta make more plots....
    Just wanted to keep you off the streets Zilchster!
    Edgewound...JBL Pro Authorized...since 1988
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  12. #42
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    Hi Edgewound and Grumpy,

    Can I clarify - more heavy weights equal less bass? or vice versa?

    Thanks

  13. #43
    Senior Member Rudy Kleimann's Avatar
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    Unhappy or demagnetization...

    Quote Originally Posted by moldyoldy
    The reduced excursions you note can have a big effect on driver longevity, not to mention reduced distortion by keeping things within their range of linear response. Excursion becomes less of a factor for max response, as coil burnout takes its place as the limiting factor.
    In defense of A-S designs, the nicest thing about sealed boxes is the lack of delay in output near resonance, not to mention the lack of wild swings in output delay depending on what frequency the sealed box woofer is reproducing. It is, simply put, "faster" and more integrated time-wise with the other frequencies being produced at the same instant. "Time aligned" comes to mind right now...

    However...

    Don't forget the AlNiCo's are bad about suffering demagnetization from over powering... so watch it with your vintage AlNiCo woofers, or you'll end up with a driver that needs reconing so it can first be re-magnetized. Output goes down across the board from box resonance all the way up to where the midrange or HF finally takes over. All the while you're thinking how "safe" your drivers are in their new sealed box home.
    Add to this the loss of LF output of an A-S system compared to a ported driver system, and you'll be wanting to put more power to them automatically. We all know JBL coils can handle power... pretty soon you could be asking yourself "what happened to the lows and mids?":dont-know

    Regarding distortion vs. excursion, any ported system should be rolled off sharply below the tuned frequency of the ported box anyway. I never run a ported system without a steep cut-off high-pass filter set about 7% below tuned frequency of the box. See the user manuals on the BX63 bass filter or the dipswitch settings inside the 5234,5235 crossovers for more info. While you're at it, note that you can tune a ported box 1/2 octave lower than normal and add a 6 dB narrow-band peak at the new frequency and extend the output of the ported system 1/2-octave lower if you have the power and the speaker can handle it... that is the purpose of the BX63 and the other dipswitch settings in the 523x crossovers.

    Notice also that most of the DBX PRO (another Harman brand) crossovers, EQ's and signal processors are equipped with switchable 40Hz high-pass filters to protect the 40Hz tuned JBL PRO cabinets (virtually all JBL PRO cabs are tune to 40Hz). Other electronics MFG.s also provide this function in their gear. Makes a world of difference in the sound quality, whether it's on a 25,000 watt FOH stack, a 500-watt stage monitor system, or a 100-watt amp at home.

    If you don't eliminate the signals below box frequency, you'll:

    A: beat the woofer to death, since the ported box basically "unloads", letting the woofer flop uncontrollably while at the same time the port delivers out-of-phase output that cancels the woofer output and even helps push the woofer even farther. Suspension components get stretched out of shape permanently. Even with a modest amount of power, the coil can bottom out in the magnet, quickly destroying the coil.

    B:waste a lot of Amplifier power, to the point of creating amplifier clipping while it delivers signal that the speaker system can't even reproduce.

    C: create a lot of harmonic and intermodulation distortion from extreme cone travel. And power compression from heated-up voice coils...

    If you do roll off these frequencies, all of these "disadvantages" relative to a sealed box are virtually eliminated. In a ported cabinet, there are a narrow range of frequencies somewhat above the box tuned frequency that excursion is slightly higher (for the same SPL level produced) than would be in a closed box, but not by much. OTOH, the increased loading by and acoustic output generated by the port in a tuned box system dramatically lowers cone movement (and distortion generated by long excursions) is a benefit over a broad range of frequencies. As the frequency goes down near resonance in a ported cabinet, cone motion reduces to the point that the woofer barely moves at all near resonance, where the A-S woofer moves farther and farther as you go down in frequency toward resonance.

  14. #44
    Senior Member Rudy Kleimann's Avatar
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    Quote Originally Posted by ngccglp
    Hi Edgewound and Grumpy,

    Can I clarify - more heavy weights equal less bass? or vice versa?

    Thanks
    More weight lowers the tuning frequency which also lowers the output above the tuned frequency. If there is a peak in output above resonance before adding weight, the peak will be reduced while at the same time the heavier weight will yield deeper bass.

    The same is true of ported cabinets with a port longer than stock, a la L100...

    The problem with the L88/L100 is the cabinet is too small for flat, deep response anyway, esp.for ported use with that 123A woofer...

  15. #45
    RIP 2011 Zilch's Avatar
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    Quote Originally Posted by Rudy Kleimann
    However...

    Don't forget the AlNiCo's are bad about suffering demagnetization from over powering... so watch it with your vintage AlNiCo woofers, or you'll end up with a driver that needs reconing so it can first be re-magnetized. Output goes down across the board from box resonance all the way up to where the midrange or HF finally takes over. All the while you're thinking how "safe" your drivers are in their new sealed box home.

    Add to this the loss of LF output of an A-S system compared to a ported driver system, and you'll be wanting to put more power to them automatically. We all know JBL coils can handle power... pretty soon you could be asking yourself "what happened to the lows and mids?":dont-know .
    Speaking specifically of the L88/L100 alignment, I was surprised to discover that the 123Ax is already operating with quasi-2nd-order rolloff ported in that too-small box.

    If the BB6P analyses are correct (and I do wish some others would run them to be certain,) closing off the port merely strips off the LF bump (e.g., #32, above,) the overall efficiency throughout the range remaining the same, while a bit of LF extension is picked up concurrently.

    I'm hearing "too much bass" as the primary complaint, so "wanting to put more power to them" doesn't seem to be concomitant with removal of the "boom" in this case.

    For my own part, working with L88, there's still too much bloom, even freefield, which I'm addressing with additional damping to further lower the Qtc. BB6P says heavy vs. typical fill should lower it by 0.1, i.e., from 0.948 to 0.838, with one driver variant in particular, a substantial improvement.

    I'm not getting those kinds of numbers here in my own measurements, but just now pursuing it more precisely in a controlled manner to report here....

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