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  1. #1
    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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    Senior Member Hoerninger's Avatar
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    Zilch,

    be so kind and explain the difference between the orange and green graphs.
    ___________
    Peter

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    Glad you feel the 2245 (sorta) qualifies Zilch, as I'm playing with some in A-S mode.

    Another characteristic;

    Excursion at resonance is minimized. Therefore, unlike BR designs, you don't have to quit at Fs (yay). Naturally, there's a catch, small boxes raise the system resonance and introduce a parameter not used in BR design, Fb. Suddenly, your 20Hz Fs driver has an effective resonance of 40Hz or more (boo). No problem, just apply 12dB-sloped EQ, and take it back down, way down (yay), as long as you can supply enough juice and your driver can take it (boo). You also no longer have a port to integrate with its' chuffing, one-note bass (yay). Critical damping via stuffing density can be tricky to achieve, but when you get it, it's smooth as a baby's butt.

    My favorite A-S design was Roger Russell's (McIntosh) ML SYSTEM. I emphasized system, because it needed the active EQ unit to work as intended, something many owners never understood, so they didn't buy the EQ with the speakers (big mistake). The EQ gave 3, 6, or 12dB boost at 20Hz, which allowed one to compensate for placement and room gain, and run flat to 20Hz without blinking.

    Great thread topic, and something new to DIY. I know you had a big grin taking the sawzall to an AR box.

    And don't worry, we won't make you move to Boston.

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    Zilch - that's got to be the ultimate "bookshelf" system.

    John

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    RIP 2011 Zilch's Avatar
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    Quote Originally Posted by Hoerninger
    Zilch, be so kind and explain the difference between the orange and green graphs.
    Hi, Peter.

    The orange is the nearfield response of the woofer at 1" or less, running through the filter, showing what's happening at the very lowest frequencies, particularly the rolloff. I don't even bother turning off the tweeter for that measurement; you can see it still playing down 30 dB there. You can also see I've notched down ~400 - 1 kHz in the woofer response (perhaps too much for this one, actually,) to get rid of the hump in response common to several 8" drivers in this alignment.

    The green is the full system response at ~1 M. I've shown both RTA and non-windowed MLS, separately. There's boundary and room response effects inculded in those, of course. A purist would stitch groundplane or nearfield LF and windowed MLS HF response together to show a composite pseudo-anechoic response curve instead, but these separate curves pretty much show what's going on.

    Quote Originally Posted by moldyoldy
    Great thread topic, and something new to DIY. I know you had a big grin taking the sawzall to an AR box.
    Heh, heh. I jus' KNEW there were others out there, tho some members might desire I show less of the gore.

    I sure wish Giskard were here to participate. He likely knows the full skinny on this inside and out.

    A/S bass certainly has a different character from that of the vented systems we're used to, as much different as bass horns, I would imagine, though in an other way. Transients have something to do with it, and the tonality seems more "natural." Anyone running Sub1500 in a small closed box, for example, knows what it's like.

    I'm thinking there's a way to match the inherent power compression and system "Q" to equal loudness contours for an expanded SPL range without EQ. It's certainly easy to get sweet-sounding bass at moderate levels in a modest-size package with this.

    Quote Originally Posted by johnaec
    Zilch - that's got to be the ultimate "bookshelf" system.
    Well, there's precedents.

    In addition to the entire "other" industry, JBL themselves makes a couple of products configured this way:

    http://www.jblpro.com/pub/cspels/CSP18.pdf

    http://www.jblpro.com/ae/am4200_95.html

    Those're both vented, tho.

    Performance Series is closed box.

    I'm starting to consider more what the cone material is and how well it plays the mids, too. The woofer does the lion's share of the musical content work in these....

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    Cool idea Zilch. Even though the idea of a 2235H in a sealed box may not seem to make sense, I tried it with a 5cu.ft (4505 box) with medium fill and with EQ it was pretty darned good, somewhat along the lines of the old McIntosh ML/MQ systems from the 70's, someone mentioned above.

    The MAC's were damned good in their day if correctly set up.

    Even without EQ, the 2235H was impressive.

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    Senior Member duaneage's Avatar
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    My favorite box of all time is the sealed bandpass. I have built quite a few of them and always enjoyed the performance of any driver in this configuration. The transient response of a sealed system will usually be superior and accurate than a vented box because of the gradual rolloff and better phase characteristics. Amplifiers also prefer the impedance curve of a sealed system over a vented one.

    A/S bass certainly has a different character from that of the vented systems we're used to, as much different as bass horns, I would imagine, though in an other way. Transients have something to do with it, and the tonality seems more "natural." Anyone running Sub1500 in a small closed box, for example, knows what it's like.


    The difference is in the low end rolloff. As a transient signal, such as a bass drum, decays it's fundamentals are very low. The vented box cuts them off while the sealed box responds to the note. The vent in a ported system is a strict component in how it operates while the air in a sealed box offers variable damping in both frequency and amplitude. With big enough drivers and large boxes sealed systems are truly spectacular. The only drawbacks are lower efficiency ( -3 db less) and greater cone movement ( higher distortion compared to a vented box operating at the port frequency) although Qtc has a LOT to do with the cone movement, distortion and ringing performance. I prefer .707, others like .5 or even 1.2

    I have built more sealed systems than vented, although it was with non-jbl drivers that I worked with. JBL has always been a ported box company it seems.

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    RIP 2011 Zilch's Avatar
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    How about the "Plenty available from L100 partouts" 123A-1?

    How high do they play well? Clearly not 2 kHz, e.g., in L88, but if 1 kHz, that would open up a bunch of good DIY options for HF, maybe....

    Edit: L100 woofer only 1" nearfield, port closed. Fc = 56.19 Hz, Qtc (as Qts) 1.25. Still a boomer, just a little less so:

    [1 kHz looks "workable," at least insofar as it BEING there is concerned.... ]
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    Quote Originally Posted by Zilch View Post
    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.
    Hello Zilch,

    I have always liked sealed boxes, and although JBL is a true love I cant really suggest anything specific other than selecting one with good excursion and using low end eq and more juice to make up for some of the bass in going for a sealed over a ported box.

    I suppose one could try to doctor the driver by adding mass, damping (around the driver- as already suggested) or even electrically modifying its parameters by adding resistors to increase the effective Re of the driver and hence Qes and Qts. But I see this as wasteful and would prefer to choose one (probably and unfortunately non-JBL) for sealed box sub bass use.

    I can thoroughly recommend the NHT 1259 + eq. in this role. I have built subs with these (well the 4 Ohm version- not available any more) and I am very pleased with the results. That is not to say I dont love the 2245 subs I have waiting in the wings. Some info:

    http://www.madisound.com/nht1259.html
    Have Fun - >>> Nessun Dorma - 12 years old <<<
    Best, Joe Alesi

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    Quote Originally Posted by Joe Alesi View Post
    Hello Zilch,

    I suppose one could try to doctor the driver by adding mass, damping (around the driver- as already suggested) or even electrically modifying its parameters by adding resistors to increase the effective Re of the driver and hence Qes and Qts.
    As for modifying existing drivers- here is some info and an example which shows the way:

    http://www.birotechnology.com/articles/mass.html
    Have Fun - >>> Nessun Dorma - 12 years old <<<
    Best, Joe Alesi

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    Dang. Amateur speakerdave's Avatar
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    The LE15A was initially presented by JBL as a sealed box driver. Does anyone have any experience with it in that type of enclosure? I've read quite a lot about disappointing bass from this driver in bass reflex enclosures, but no one seems to look at the more gradual roll off of low bass in a sealed box which results sometimes in actual greater extension. That coupled with careful use of room rise might get a good result with this driver in a livingroom sized space. Since this driver was first offered for either closed box or bass reflex, I should think it would be an option to try sealed. I would think also that the big magnet would be an advantage for that.

    I think the real price of going sealed over bass reflex with that driver (and others) would be either remembering to stay within the decibel level it can produce safely that way (not a problem most of the time) or adding more cone area. The added cone area dictates a low crossover point for me. I find that even crossing over in the mid-hundreds there is definitely a sense of multiple sources that I don't care for (at my listening distance--10-12 feet). Even drivers side-by-side, following the most conservative view on when acoustic coupling occurs (acoustic centers a quarter wave length apart), pairs of 15 inch drivers must be crossed over at under 200 Hz.

    David

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    Administrator Robh3606's Avatar
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    The main issue I see with either one sealed Le-14 or 15 is the xmax. You may very well be able to get a good in room response but you will be SPL limited and won't really be able to add any significant boost if you are not happy with the inroom response with room gain. I will model them for you and post them. I am running a pair of 121A'a now in my second system in sealed enclosures and they sound really good. With room gain they are very nice. You have to watch the SPL though. I rarely ring the bell on the mass rings but it can happen depending on content. The LE-15 would give several db SPL advantage over the 121's.

    Rob
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    In 6 cuft Olympus, BB6P says LE15A closed-box F3 = 80.99 Hz, and F10 = 34.21 Hz. It'll handle 2.91 W down there, for 100.9 dB output.

    Vented looks like a WAY superior alignment with Fb = 27.86 Hz, F3 = 48.2 Hz, and F10 = 25.65 Hz, 15.7W, 108.3 dB output:
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    LE15A, 5.5 cubic ft., port vs closed box

    Quote Originally Posted by speakerdave View Post
    The LE15A was initially presented by JBL as a sealed box driver. Does anyone have any experience with it in that type of enclosure? I've read quite a lot about disappointing bass from this driver in bass reflex enclosures, but no one seems to look at the more gradual roll off of low bass in a sealed box which results sometimes in actual greater extension. That coupled with careful use of room rise might get a good result with this driver in a livingroom sized space. Since this driver was first offered for either closed box or bass reflex, I should think it would be an option to try sealed. I would think also that the big magnet would be an advantage for that.

    I think the real price of going sealed over bass reflex with that driver (and others) would be either remembering to stay within the decibel level it can produce safely that way (not a problem most of the time) or adding more cone area. The added cone area dictates a low crossover point for me. I find that even crossing over in the mid-hundreds there is definitely a sense of multiple sources that I don't care for (at my listening distance--10-12 feet). Even drivers side-by-side, following the most conservative view on when acoustic coupling occurs (acoustic centers a quarter wave length apart), pairs of 15 inch drivers must be crossed over at under 200 Hz.

    David
    Here you go - old fashioned data from a real oscillator (port tuned to 31-32 Hz):
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    Senior Member Loren42's Avatar
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    Quote Originally Posted by Mannermusic View Post
    Here you go - old fashioned data from a real oscillator (port tuned to 31-32 Hz):
    Could you elaborate as to how you conducted the test?

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