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Thread: Jbl 1200fe-8

  1. #16
    Senior Member pos's Avatar
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    I traced the active low pass curve and got pretty close using a combination of:
    • 2nd order low pass filter at 240Hz, Q=0.68
    • 2nd order low pass filter at 650Hz, Q=1.58

  2. #17
    Senior Member RMC's Avatar
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    Hi Grumpy and Pos,

    Re my "Will sound bass shy vs the rest of the spectrum?"

    @ Grumpy:

    Thanks for the info on the 1200FE listening test. Its informative.

    After making the 1200 modeling in Winspeakerz, I did another quick one this time with Win ISD Pro thinking my first one may be incorrect (wrong entry from me or something). But results were the same the 2nd time.

    "My recollection is that only the passive crossover was at work. No active signal shaping or tone controls, DSP, electronic delay, etc"

    I just wanted to rule out this possibility of signal processing impact. Your listening test is in not being challenged here.

    In fact I'm testing the following statement, made in the help files, by the makers of Win ISD Pro with regards to the frequency response curve generated by their software, i.e. the green plot they refer to below:

    "The green plot is the actual representation of how this speaker will sound in a completed box." They assume the usual half-space driver radiation as they mention.

    The listening test doesn't support their statement (according to which it should have sounded bass shy but it did not), moreover they seem to forget other important aspects of room acoustics effect on speakers with such statement... Therefore, Grumpy 1, Win ISD 0.

    @ Pos:

    RE: "It depends on how you look at it: this dropping response down low can be seen as a rising response in the higher range, and addressed in the electrical LP filter to get the proper acoustical response with a lower final sensitivity."

    You're absolutely right, I agree with you. I keep forgetting about this. Similar to the glass that can be seen as half-full or half-empty, depending on how you look at it... Regards,

    Richard

  3. #18
    Administrator Robh3606's Avatar
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    I couldnt find any infos about the linear xmax as well, propably because these drivers where never meant to be sold seperatly...
    You have a 1" coil with a .5" gap so figure about 12.5mm PP maybe a little less.

    Rob
    "I could be arguing in my spare time"

  4. #19
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    Thanks a lot for all this great input and support!

    My assumption is, that JBL used a small enclosure (1,8 cu ft) within the 4428 modell to justify it as a bookshelf speaker. With the S5800 being a big floorstand-speaker, they aimed for a more appropriate enclosure volume... Just my guess...

    @Rob: That sounds logical and is much better than the Audax-woofer which I was going to use in the first place.

  5. #20
    Senior Member JuniorJBL's Avatar
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    I would add to Grumpy's statement of the sound of these 12" 2 ways. It was probably the best sounding 12" 2-way I have ever heard. We both listened to them in the same spaces two different locations.
    Always fun learning more.......

  6. #21
    Senior Member Ian Mackenzie's Avatar
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    I agree with Grumpys comments.

    If you look at the voltage drive on the woofer the signal to the woofer is shaved off or contoured above 100 hertz.
    Its a passive EQ if you like.

    The woofer tuning is what is referred to as a shelf alignment which is a tuning used in LEAP software.

    The actual acoustic response sums flat when the HF level adjusted to match the EQd response of the woofer.

    The loss of 2 dB or so mid band sensitivity is an acceptable compromise.

    Jbl do do this elsewhere in other systems and you can see it in the voltage drive on the woofers.

    As Richard points out it would otherwise be unbalanced subjectively.

  7. #22
    Senior Member RMC's Avatar
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    RE post # 21

    Certainly the best post here to align logically the different views mentioned (not necessarily contradictory ones) about sound heard (Grumpy and Junior), modelings done (me), crossover details and way of looking at response curve (Pos), etc. That reconciliation of the info does make sense to me! Not afraid to say it, a good shot is a good shot.

    Since I didn't hear/don't own the Array, 1200FE nor LEAP I can't really comment on actual sound heard for example.

    GT and many others at JBL are quite smart Engineers. They can make almost any speaker system and still make it sound proper, with the number of "tricks" they have up their sleeve.

    The alignment chosen is not the first go to or must have type of LF alignment I would jump on normally for a few reasons, but the Design Engineer has his reasons, tricks and constraints to go that way, which I respect, and these are certainly as good or better than mine.

    It seems to me one of the objectives may be to extract some deeper bass than usual from a relatively small box Vb, even if that means losing a couple of DBs on sensitivity. Its a purposely made design choice, as others are.

    Richard

  8. #23
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    Indeed, very well thought answers!

    If Im not mistaken, this passive-eq or high-shelving of the woofer occurs in the 4428/4429 circuit as well. There are two inductors in series with the woofer...
    My plan was to use these with a JBL M553, so Im stuck with a simple 4th order filter. I guess I should rather aim for a more conventional (linear) tuning than. This means smaller box with higher tuning...

  9. #24
    Senior Member Ian Mackenzie's Avatar
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    What l would do is acquire a dsp amp with some EQ and level the shelved bass alignment with a simple shelf filter below 100 hertz with +2-3 dB lift.

    If your signal path is pure digital you can do this in a variety of ways.

  10. #25
    Senior Member RMC's Avatar
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    Hi Olaf,

    In case you don't want to add another amp or if DSP ones are too expensive, you may want to consider another option, Parametric EQ boost to deal with the shelf issue. Though the example shown below is a single channel unit, XLR, 1/4" and RCA, two of them cost $320.US ($160. each) and the Euro is worth about 12% more than USD... Made in the USA shown! I don't know if they are available directly in Germany though, you would need to verify that. Regards,

    Richard


    ROLLS DATA SHEET _RPQ160b[1].pdf

  11. #26
    Senior Member pos's Avatar
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    The required LP filter is easy to achieve with an analog crossover using Sallen-Key topology: you simply need to chain two LP sections with the proper freq and Qs measured in post #16.

  12. #27
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    Quote Originally Posted by Ian Mackenzie View Post
    What l would do is acquire a dsp amp with some EQ and level the shelved bass alignment with a simple shelf filter below 100 hertz with +2-3 dB lift.
    Guess what, my NAD C165 Preamp has a 100hz shelving-filter (Tone-controls...).

    @RMC: PEQ are great, I can borrow a Klark Teknik DN405 to try...

    @Pos: It might be easy, but I want to keep the JBL M553 untouched.

  13. #28
    Senior Member RMC's Avatar
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    Hi Olaf,

    The important part I'm glad about is the outcome here. At least now you have different options to consider/try: tone controls, DSP amp, Parametric EQ, custom built filter (Pos). Having worthwhile options to choose from, based on your specifics, is a lot better than having none and your back to the wall... Regards,

    Richard

  14. #29
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    Well summarized Richard, now its up to me

    I will have an Audax PR330M0 12"-woofer for comparison, but I suppose the JBL will produce a better low-end.

  15. #30
    Senior Member RMC's Avatar
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    Hi Olaf,

    RE: "I will have an Audax PR330M0 12"-woofer for comparison, but I suppose the JBL will produce a better low-end."

    Your Audax PR330MO remind me I did use a pair of Audax 10" woofers in boxes years ago, but can't remember the model number, it may have been an OEM model. Unfortunately, at one point the foam surrounds were really done and I couldn't find the right replacement for these. The foam roll on that model was notably wider than usual for driver size, and I didn't want to spend time and money on making Frankenstein woofers with these... So I gave them away.

    I kept the good boxes (Vb about 1.5 cu.ft.) and with some minor modifications I made a pair of small sound reinforcement boxes using Britain's Fane Pro 10" woofers with special cone and Vifa dome/horn tweeters. I bi-amp these enclosures with the 2205H bass cabinets I have (not subwoofers). Nice SR Sound. I've been using some European drivers from various manufacturers (Fane, Vifa, Peerless, Audax) for a while, most of which I still have.

    As for your JBL/Audax comparison, on paper, I note the following: Fs 27/28 hz, Qts .26/.27 so these two items are pretty much the same; Vas 125/264 L. The Audax has more than double the JBL here. Based on the principle that optimum box volume is proportional to Vas (Bill Mc Fadden) there's a possibility, depending on box size used, that the box may be a little small for Audax optimum LF potential, therefore creating a small LF bump, though this may not be a big deal in practice.

    With regards to Xmax 6.25/4 mm the JBL is a little more generous on this aspect for low-bass reproduction, as well as on power input capability, however on sensitivity 91/98 db if real the Audax would be far more sensitive which can make-up for its lesser power capacity of 150W. I say "if real" because one graph seen shows closer to 94 db and the other graph seen is closer to 98 db. I tend to think the former number makes more sense than the latter for a few reasons, but I may be wrong.

    In any case, when comparing sounds with same input power, don't forget that a more sensitive and louder speaker usually seems more impressive, but its not necessarily better sounding than a less sensitive one. You'll decide which one pleases you most. Regards,

    Richard

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