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Thread: 4628B curve for Zilch

  1. #16
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    Quote Originally Posted by Mr. Widget
    Kind of different... due to different speakers? ...due to different rooms? ...due to different measuring techniques? ... due to different measuring equipment?
    Yup. All that. John was gonna do his outside. Lemme read again to see if he actually did....

    Nope. Inside, on carpet. On their backs with mic suspended above. Mine are just stacked in garage, mic in front about 1M.

    I'm seein' them as similar, actually. Big climb at 1 kHz, peaks at 1.5, 4, and 10 kHz, linear rolloff above. Same animal, different playground....

    Though not as well defined in the lower frequencies, see also 80, 130, 250, and 500 Hz.

    [We don't have the quasi-anechoic measurement capabilities SOME good people here do.... ]

  2. #17
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    Has anyone verified crossover points of 4628B?

    Has anyone verified the crossover points of the 4628B? The cabaret brochure published 800hz and 3khz which is what was initially noted here.

    Jammin' Jersey has a pair of the crossovers they describe as being at ("approximately") 400hz and 4khz.

    The 4612B also uses the 2118 (a pair of Js) and 2404H (H-1) with a published cross likewise at 3khz. It was noted in another post that this is actually more like 4500 to 5khz. I have a pair of these crossovers and they do indeed seem to cross around 5khz.

    My question is has anyone checked the 4628B?

    Thanks in advance.

  3. #18
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    I have never determined the crossover points of 4628B, but I could, I suppose, if I knew how.
    Quote Originally Posted by hiQ
    The 4612B also uses the 2118 (a pair of Js) and 2404H (H-1) with a published cross likewise at 3khz. It was noted in another post that this is actually more like 4500 to 5khz. I have a pair of these crossovers and they do indeed seem to cross around 5khz.
    How did you determine the crossover point?

  4. #19
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    Quote Originally Posted by Zilch
    I have never determined the crossover points of 4628B, but I could, I suppose, if I knew how.How did you determine the crossover point?
    Hello - I used the word 'seemed' rather than 'determined' for my own action which is entirely subjective and empirical. I used a signal generator and simply tried to observe the equal point between two drivers. Certainly not perfect which is why I used the word 'seemed'. It does not 'seem' to be near 3khz (I am referring to the 4612B).

    The word I used for my query was 'verified', which I think suggests something more scientific, this inasmuch as I find myself in the good company of some with considerable expertise.

    I was hoping someone would tell me because of the discrepancy in the brochure vis a vis the report of the vendor I cited.

    Brochures have been known to be oblivious to engineering facts.

    My initiation to the thought that the crossover of the 4612 was something other than the published version is found at http://www.audioheritage.org/vbullet...over+impedance where GordonW brought the subject up. He was citing the numbers which certainly 'seems' more scientific than my approach.

    Mr. Zilch in his kind reply to a query in that thread suggested as one option the 4628 and that led me to the vendor who reported the variation.

    Everyone 'seems' to concur the 2404 needs to cross higher than 3khz (even though the brochure says 3K), and Mr. Zilch thought that the 2118 could cross lower than 800hz ('Might kick the 2118 in a little lower than the spec'd 800 Hz') although that might have been more a suggestion than an observation.

    I am still trying to work out something for a 2202H, 104H & 2404 combination and very much lower than 800hz would probably not be healthy for the 104H.

    There you have everything that I know. I used the words 'seemed' and 'verified'. The brochure says 800hz and 3Khz but a commercial vendor says 400hz and 4khz.

  5. #20
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    I've found JBL tech sheet info is usually good to two decimal places.

    800 Hz and 3 kHz looks like what it is.

    Nearfield measurements of the three drivers below (all playing).

    Port's next to 2118 and 2404. I stuffed it, but there's still leakage.

    Don't know why this 2118's dying at 2 kHz. Kinda looks like a phase hole.

    Indeed, the mid and tweeter are wired out-of-phase, but that shouldn't matter nearfield.

    Second unit, same deal, so nothing seems FUBAR here.

    http://www.jblpro.com/pub/obsolete/2118.pdf

    Anybody have the original that can tell us what the legend in the FR curve says?

    45° off-axis response shown falling off above 1+ kHz there?

    In any case, 13.5 uf into 8 Ohms translates to something just under 1 kHz, and 2.5 uF with 0.4 mH is up around 4.5 kHz, both depending upon the actual driver impedance, but it's the acoustic response what counts, shown in the measurements, i.e. how the filter performs with the particular drivers in the total design package.

    It's a little tough reading the values in the schematic, tho:

    http://www.jblproservice.com/pdf/Cab...ries/4628B.pdf

    Looks like 3.0 uF changed to 2.5 uF in the "B" version, raising the highpass frequency to the tweeter a bit.

    I wouldn't pay actual money for those crossovers; they barely qualify. Woofer plays full range, substantially overlapping the mid. ACK!

    [This has been a Zilchster stream-of-consciousness presentation.... ]
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    "Zilchster stream-of-consciousness presentation" appreciation response placeholder text.

    More later. Thank you!

  7. #22
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    For a nominal 8 ohm voice coil with 13.5 uf I get a 1472 hz high pass to the 2118, not 800 as the spec says.
    For a 5.5 ohm voice coil (= dc resistance of 2118h) I get a 2141 hz high pass.
    Am I doing something wrong?
    I am trying to calculate the inductor value to rolloff the E145 and 2118. Presumably the E145 rolloff should match the 2118 rollon. Similarly for the 2118/2404.
    Last edited by niconoise; 12-12-2006 at 12:10 PM. Reason: more info

  8. #23
    sa660
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    4328B E145

    The E145 was used in one of JBL statement loudspeaker.
    The Everest DD55000

  9. #24
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    The 4628 literature says the E145/2118 crossover is 800hz. The nominal impedance of the 2118h is 8 ohms, 5.5 ohms dc, and 6.2 ohms minimum. I cannot calculate a 800 hz crossover with a 13.5 uf capacitor. Is the literature wrong? Is the 2118r really not coming in until 2k?

  10. #25
    Senior Member martin_wu99's Avatar
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    Quote Originally Posted by Zilch View Post
    I've found JBL tech sheet info is usually good to two decimal places.

    800 Hz and 3 kHz looks like what it is.

    Nearfield measurements of the three drivers below (all playing).

    Port's next to 2118 and 2404. I stuffed it, but there's still leakage.

    Don't know why this 2118's dying at 2 kHz. Kinda looks like a phase hole.

    Indeed, the mid and tweeter are wired out-of-phase, but that shouldn't matter nearfield.

    Second unit, same deal, so nothing seems FUBAR here.

    http://www.jblpro.com/pub/obsolete/2118.pdf

    Anybody have the original that can tell us what the legend in the FR curve says?

    45° off-axis response shown falling off above 1+ kHz there?

    In any case, 13.5 uf into 8 Ohms translates to something just under 1 kHz, and 2.5 uF with 0.4 mH is up around 4.5 kHz, both depending upon the actual driver impedance, but it's the acoustic response what counts, shown in the measurements, i.e. how the filter performs with the particular drivers in the total design package.

    It's a little tough reading the values in the schematic, tho:

    http://www.jblproservice.com/pdf/Cab...ries/4628B.pdf

    Looks like 3.0 uF changed to 2.5 uF in the "B" version, raising the highpass frequency to the tweeter a bit.

    I wouldn't pay actual money for those crossovers; they barely qualify. Woofer plays full range, substantially overlapping the mid. ACK!

    [This has been a Zilchster stream-of-consciousness presentation.... ]
    Mr.Zilch,
    how to re-tool 4628B's crossover and make it more suitable for home HIFI use?

    Thanks so much
    Martin wu
    46 lover

  11. #26
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    Quote Originally Posted by Zilch View Post
    The originals go dirt cheap around $300 a pair here of late (not for very much longer, perhaps,) for a super nice combination of drivers. Hell, you can hardly buy the tweeters alone for that.
    These are/can be a steal.

    I sold three for $500 with professional road cases included (one needed the 8" and tweeter but all other components worked fine).

  12. #27
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    Quote Originally Posted by martin_wu99 View Post
    Mr.Zilch,
    how to re-tool 4628B's crossover and make it more suitable for home HIFI use?
    We never pursued it.

    Today, I'd start active with DCX2496, measurements, and listening to determine an appropriate transfer function, then passive crossover design software to implement it, and finally, voice the the outcome....

  13. #28
    Senior Member martin_wu99's Avatar
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    Quote Originally Posted by Zilch View Post
    We never pursued it.

    Today, I'd start active with DCX2496, measurements, and listening to determine an appropriate transfer function, then passive crossover design software to implement it, and finally, voice the the outcome....
    That sounds great! i'm looking forward to your big job.
    Learning a lot from your thread,i bought 4628B,l love it so much,it sound so pure\clean that no other JBL speakers can compare with when playing piano\guitar\saxphone and trumpet.you do a great found indeed!althoug lack of some low end. since then,i bought 4698B,it also sounds good as well. PRO SOUND AT HOME really!
    but i want to make my 4628B and 4698B more smooth and soft,what should do?re-tool the crossover?using active crossover?
    By the way,is there any other pro speakers can be used in home?which ones?somebody in CHINA using 4722\4725\4735\sp222 and 4719 at home!

    best regards

    Martin wu
    46 lover

  14. #29
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    That was actually a suggestion as to how YOU might proceed, as it is not likely I will further pursue this project anytime soon, my own more recent efforts being substantially committed to building 2-way designs....

  15. #30
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    Quote Originally Posted by Zilch View Post
    That was actually a suggestion as to how YOU might proceed, as it is not likely I will further pursue this project anytime soon, my own more recent efforts being substantially committed to building 2-way designs....
    Two way system?like 4691B?why?
    46 lover

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