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Thread: The purpose of JBL E145

  1. #76
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    Quote Originally Posted by gibber View Post
    That two-port 28Hz tuning you like less is very similar to the 30Hz i have here. Instead of changes on the ports my cabs have, i just tried using a beefy transistor amp and gave it a 10ohm resistor in series to my (early version) K145's ca 9ohm coil dc resistance. New Qes' equals (Rg + Re) / Re * Qes, so Qes goes up to 0.52 or so and hence new Qts is around .49 (see Qms in tables earlier in this thread).
    Result is a more "normal" bass sound, the mid is similar as before, and subjective speed is slightly less, imho not too much so to offset advantages in the deeper register. Mid output subjectively is down by 2dB (should be 3 dB but the higher Qts with series-R maybe reinstates some of the premature-but-gradual rolloff that a driver of Qts=0.23 w/o series-R has).
    Possibly another work around is to explore DB Keele 6th order paper on his web page and run the numbers.

    My estimate is that depending on the QTS' (between 0.26/0.29 with some Rx from crossover L) an F3 in the high 30's is possible. Add a modest room gain and you are in business.

    I consider adding significant Rx un suitable as you trade un warranted losses in driver efficiencies for extension when electrical boost of 6 db and Q equal 2 with Keeles formulae can offer extension in a WaF friendly box.

  2. #77
    Senior Member frank23's Avatar
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    Quote Originally Posted by Earl K View Post
    Here's a ( very ) handy online calculator for ( decibel > THD distortion conversions ) .

    I was actually looking for the rising distortion with a rising level. The distortion figures for the E145 are at 10W, and I wondered about the figures for 1W. But looking at this graph, I think one can assume the difference between the distortion for 1W and 10W to be roughly 10dB:



    So that would mean the 150Hz distortion for the E145 at 1W would be about -55dB if every horizontal line represents 1dB for a full graph scale of 40dB. And -45dB at 10W.

    The 1501AL does -65dB at 10W which is significantly lower. I still wonder whether the scale of the E145 graph is not 2dB/division so the E145 would come at -70dB. Wishfull thinking perhaps...

  3. #78
    Senior Member gibber's Avatar
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    Resistor for changing Qts?

    Quote Originally Posted by frank23 View Post
    I finally tried this today, after having tinkered with it on and off over the past few weeks.

    I could see no improvement in lf extension when inserting a resistor. in fact extension suffered a little. The E145 was in a 4507 5cu 150l cabinet. I think I had it with all 4 ports open, but I was tinkering with that also, so I can't recall that exactly, might even have been closed :-)
    Hi Frank, the change in Qts requires a re-alignment of the box for the new Q.

    Assuming your measurement frequency is at (or a least near) the minimum impedance between those two reflex "humps", then the added series resistance will take away more power at that very point than it would anywhere else below 150 Hz or so (i.e. where impedance has its natural minimum before rising due to coil inductance).


    Quote Originally Posted by Ian Mackenzie View Post
    Possibly another work around is to explore DB Keele 6th order paper on his web page and run the numbers.

    My estimate is that depending on the QTS' (between 0.26/0.29 with some Rx from crossover L) an F3 in the high 30's is possible. Add a modest room gain and you are in business.
    Hi Ian, Yes -- very good way to move forward, but requires your system to be active. Or stay passive as in the '70's EV implementation (also by Keele). But staying passive means to loop the complete signal through the (analog or digital) bass-EQ. EV recommended to use the tape monitor loop for their Interface XX series, but problem was the supplied analog equalizer killed mid/treble sound quality while doing that 6th-order bass EQ


    Quote Originally Posted by Ian Mackenzie View Post
    I consider adding significant Rx un suitable as you trade un warranted losses in driver efficiencies for extension
    May sound like the baby/bathwater thing, but that's perhaps the price when going passive. The series-R method is good for small changes only and makes a speaker less over-damped, optimizing step response a wee bit. A 2nd more powerful passive alternative would be to bend down the mid response early to "gain" bass extension. This comes with a penalty in phase response if passive/analog. For an E145 this would kill something like 10dB of its rated efficiency. In fact, Frank went a third and similarly powerful route by using an early X/O to his 2123 10" cones. But if passive, i wonder if sensitivity below 100 Hz still is on the good side of 90 dB that way?


    Quote Originally Posted by 4313B View Post
    One of the hallmarks of the traditional JBL transducers was their low Qts. Arguably the 124 and 136 went a tad overboard.
    Giskard, the E145 maybe, too. Market pressure must have been significant for E145, as Yamaha entered the musical instrument sound market with their brand-new JA3882 "K14x-killer" and claimed higher sensitivity than K140/145 had. Wording in the K- and E-series brochures you linked to at the beginning of this thread shows JBL's pride rgd that aspect at the turn from '70s to the '80s. E140/E145 have improved magnetic energy compared to the models they replaced. Hence Qts went down. The 3882B has an average of 0.14 on 8 samples taken from a US forces (must have hurt to see them buy Japanese) cinema here in Germany.

    Ralph
    Last edited by gibber; 01-04-2015 at 09:30 AM. Reason: JA3882B Qts data

  4. #79
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    Regarding E145 VAS

    WinISD can be used for calculating VAS. Which I did.

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  5. #80
    Senior Member gibber's Avatar
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    Quote Originally Posted by more10 View Post
    WinISD can be used for calculating VAS. Which I did.
    The Vas you get is in line with what Giskard expected.
    Maybe you took K145-8 values into WinISD?

    K145 has Re of ca 9 ohms. It is a “12 Ohm“ driver.

    But I would expect Vas results to be the same, also for K145-16 and the ultrarare K145-4

    The wear of the doped paper surround has a much bigger effect than the coil mass differences between 4/8/12/16 ohms. I get values from below 30 to mid 40’s for Fs on the samples i measured over time

    All the best, Ralph

  6. #81
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    Straight from the table. I see I forgot le, but le doesn't affect VAS. Green in WinISD is entered. Blue is calculated.
    Attached Images Attached Images  

  7. #82
    Senior Member gibber's Avatar
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    Quote Originally Posted by more10 View Post
    Straight from the table. I see I forgot le, but le doesn't affect VAS. Green in WinISD is entered. Blue is calculated.
    Sorry, my bad. You worked on E145, which only exists in 4/8/16 ohm versions to my knowledge. The Mmd shown in the table for the unit was taken over from K145. But E145 have a fabric double roll glued to a thicker paper than used in E145.

    The wide range of Fs i noted for K145 may well have been the reason to go for fabric surround in E-series

    Ralph

  8. #83
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    K145 frame clips

    By the way is it still possible to find those clips for front mount? I would need for four k145...

  9. #84
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    E145 messurement

    I can put in some messurement of used E145 wich a friend, Oliver hoschibill, did last year.
    The units where old and used but in good working condition.

    Fs: 29
    Re: 6
    Qts: 0,2
    Qes: 0,21
    Qms: 3,34
    MMs: 73g
    Rms: 4,23
    Cms: 0,000406m/N
    Vas: 452
    Bl: 19,9
    ETA: 5,36
    Lp@ 2,83V: 100,65

    Maybe that is helpfull for someone.

    I just purchased a pair of nearly new E145,
    going to put them in a sealed 40 Liter enclosure.
    Should give them a rolloff at about 100Hz with Qtc 0,7.
    Trying to let them play up to 800-1kHz and fit my diy Ribbon for highs.
    If that does not work I 'm in need for something else to play on top.
    How far low can I tweak the 2425 with the 2344?

    Liked the crispy detailed sound of the E145, but bass is not much like stated before.
    So I will try them as a punchy lowmid driver and luckily I have some decent units to fit the lower end.

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    Cabasse 55 for those who wonder.
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    looking for a JBL 2346 horn

  10. #85
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    E145 for 2231A

    How would the E145 work in place of a 2231A in the 4343?

  11. #86
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    Quote Originally Posted by rwwear View Post
    How would the E145 work in place of a 2231A in the 4343?
    Poorly ( no matter if you EQed in the bass > you'd be left with a sense of loss ( no bass > no impact > no weight > no anchor to the sound ).


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    Quote Originally Posted by Earl K View Post
    Poorly ( no matter if you EQed in the bass > you'd be left with a sense of loss ( no bass > no impact > no weight > no anchor to the sound ).

    Thanks Earl. Is there a substitute that works well without the Alnico magnets?

  13. #88
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    Quote Originally Posted by rwwear View Post
    Is there a substitute that works well without the Alnico magnets?
    The recommended alternative is the 2235H. It was the driver that was developed after the 2231H ferrite replacement for the 2231A alnico driver.

    The 2235H is a drop in replacement for the 2231A.


    Widget

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    Quote Originally Posted by Mr. Widget View Post
    The recommended alternative is the 2235H. It was the driver that was developed after the 2231H ferrite replacement for the 2231A alnico driver.

    The 2235H is a drop in replacement for the 2231A.


    Widget
    In your opinion, does the 2235H sound better? Do you think Alnicos are a detriment? with modern amps.

    Here's a quote from Great Plains Audio.

    "Alnico magnets, by their nature, are easy to degauss (demagnetize) with drive. They will not change with time and their dependence on temperature is really small – maybe 1% at 100 degrees Fahrenheit. Alnico stability and resistance to back EMF is really good. This is why they make very good sounding magnetic structures. Unfortunately, given a big enough pulse of magnetic energy, they will degauss by up to 3 dB. The sensitivity to degaussing is dependent on the specifics of the magnetic circuit and the length of the coil providing the field. Underhung woofers, midranges, tweeters, and compression drivers do not have sufficient back EMF fields to push the operating point of the structure below the knee. They are essentially stable regardless of input signal. The short-gap, long-coil speakers are the ones that have a problem. A woofer can take a hit of up to 3 dB, if a big enough hit of current takes place. 1.5 dB to 2 dB is more common. The effect does not get better or worse with time, it solely depends on how much current is driven through the coil. The more current, the more field. Once the field is bigger than a certain number, some amount of degaussing occurs. It is permanent (until externally recharged) and will only increase if a larger sustained current hit occurs. Therefore, if you have a qualifying alnico woofer and you have played it loudly, you have some degaussing. You can have the unit recharged, and it will be fine until you play it again. Exceed the critical level, and it will start degaussing again. If you never do, it won’t ever degauss. Most of these designs trace back to the 50’s and 60’s where 15 – 30 watt tube amps were the rule. They didn’t have the current capability to hurt anything. With the advent of big solid state amps, the current levels went up and the problem started to surface.
    Most of the qualifying motors will lose 1 – 1.5 dB, unless they are pummeled. Some of the older 3″ motors with really short magnets will typically be around -3 dB down. They go really easily.
    Great Plains Audio can regauss your alnico magnets, if they need it. Regaussing is included free when we replace diaphragms and cones." https://greatplainsaudio.com/great-p...agnetic-field/

  15. #90
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    Without commenting on the drivers themselves, here's a little piece (two, actually) on the magnets

    http://www.audioheritage.org/vbullet...Ferrite-Debate

    The Great Plains piece is copied from the second one, written by Greg Timbers. Not sure if Great Plains gave attribution.

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