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Thread: JBL 2245H with crazy TS specs measured with Dayton DATS 3

  1. #16
    Senior Member grumpy's Avatar
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    Wanna hear my wild ass guess? Someone reused a cone/voicecoil/spider assembly (the latter looking a bit torn up in one of the pics), then refoamed it.
    Would explain a worn/sloppy suspension (low Fs). I don't really think the DATS-3 is the problem; the high Re just --appears-- to be function of their algorithm that made some assumptions about how low (and how high a Q) the resonance of a driver would be. The curve shapes and 6 ohm minima between 100-200 Hz isn't crazy ... even cone resonance wiggles look kinda right. I hope I'm wrong about the driver.

  2. #17
    Senior Member Ian Mackenzie's Avatar
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    Thatís a possibility.

    I think putting it is a test box would disclose the true parameters.

  3. #18
    Senior Member Ian Mackenzie's Avatar
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    My DATSv3 arrived and l have started some testing on several Jbl drivers. I am using a Windows Lap top and it installed without a hitch. There are to calibration routines. That is fool proof that itís working correctly.

    With the actual testing with a 2235H sitting on my desk l got an FS very close to the factory spec.

    My 2245 all measured with an FS of between 26 and 30 hertz.

    The Vas value was about half the factory spec using added mass of 145 grams. I suspect that because the drivers have been re foamed that has impacted on the Fs and the VAS.

    l dare say this is the case with most 2245 currently in use where the driver has been re foamed (Edgewound will be shaking his head...told you soooooo).

    I will plug all the values into a simulator to compare to the factory spec drivers.

    Intuitively l realised that the Piston Diameter measurement is sensitive to the VAS measurements. The measurement of the piston diameter should be at the mid point of the surround (according to a pop up error message l got).

    I am going to build a clamp to support the drivers in free air and do more tests.

    In the case of Mortonís drivers l think the driver measurements of the FS are most likely accurate.
    Lowering the FS with added mass does increase the Qts. The question is why the drivers have a lower FS than spec.

    Why also the higher than spec RE?

    At a guess the surround has been over stretched beyond the useable limit.
    Obviously something is not right.

    My suggestion is to have them looked at by a technician. They may be able to re build the drivers.

    Holding the driver firmly alters the figures a bit. I am going to make a clamp jig to support the drivers firmly with space under them.

  4. #19
    Administrator Robh3606's Avatar
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    My 2245 all measured with an FS of between 26 and 30 hertz.
    l dare say this is the case with most 2245 currently in use where the driver has been re foamed (Edgewound will be shaking his head...told you soooooo).
    Hello Ian

    Wow that's something to remember. I have re-foamed a decent amount of drivers over the years including 2 pairs of 2235 and Fs were within a hertz or 2. Same with 2122's 2108 125 2214 LE-14 128's the only common was all foams from Rick Cobb. Guess it does matter who you get them from!

    Rob
    "I could be arguing in my spare time"

  5. #20
    Senior Member Ian Mackenzie's Avatar
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    Quote Originally Posted by Robh3606 View Post
    Hello Ian

    Wow that's something to remember. I have re-foamed a decent amount of drivers over the years including 2 pairs of 2235 and Fs were within a hertz or 2. Same with 2122's 2108 125 2214 LE-14 128's the only common was all foams from Rick Cobb. Guess it does matter who you get them from!

    Rob
    Well thats right.

    Mind you they work all the same.

    I will model the parameters once I do the Vas in a test enclosure.

    Ian

  6. #21
    Senior Member Ian Mackenzie's Avatar
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    Quote Originally Posted by Earl K View Post
    Morten,

    You posted a pdf indicating the measured Re values were/are in the neighborhood of 22 ohms ( post 3 ) .

    This should be a MAJOR red flag that either; those 2245H woofers Voice-Coils are toast ( and you've made a bad purchase ) or your measurement system or methodology are faulty.

    Normally when presented with a figure so far from official spec. ( someone more experienced in these matters ) would simply go get their MultiMeter ( then set it to measure DC resistances > DCR ) to get a second opinion ( before posting their doubts to social medfia ).

    Your failure to make ( or mention making ) a dedicated DCR test using an alternate method ( has me shaking my head ).

    Hi Earl,

    I was re reading this thread before my last post.

    This is a person who has come here for help and itís only his third post.

    Most LHS member were helpful and considerate with their posts.

    Isnít your notion that a visiting person looking for help should be familiar with testing a loudspeaker rhetorical? Why else would they visit this site?

    How could you have done this better?

  7. #22
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    This 2245H was measured with a S&L Woofertester 2
    At the time measurement was done the driver was just reconed with one of the last oem kits sold in Norway by me.

    Meaasured with the driver in horisontal position, screved too woden blocks positioning it 4" above the floor.
    Test mass was a roll of duct tape weigthed on a kitchen scale.

    As seen there are some parametres that are suspicious. MMS are very high (More than tvice the real weigth of the cone Assembly), Vas are low, BL are very high, and Qms are high.

    I vaguely remember somone claimed that the 2245H are very difficult too get dependable measurements of.
    so i use factory specs for my simulations rather than trusting DATS or WT2.

    The driver are currently in use in a 8cuft cabinet ported too 26hz, 6db boost at 26hz Q=2
    20Hz 24db/oct HP. 50hz 18db/oct LP. Performs great.



    Buffer[1] Vas Ver 7.01
    Completed: Sat Jul 16 20:11:52 2016
    Drive level 100.000% [3.417 mA]
    Sine,LoZP(LV/LA)->Vas,19 pts
    ;------------------------------------------------------------------
    Re = 5.0568 ohms
    Fs = 19.2550 Hz
    Zmax = 158.7390 ohms
    Qes = 0.2330
    Qms = 7.0824
    Qts = 0.2256
    Le = 1.3190 mH (at 1 kHz)
    Diam = 400.0000 mm ( 15.7480 in )
    Sd = 125663.7126 mm^2(194.7791 in^2)
    Vas = 507.3981 L ( 17.9186 ft^3)
    BL = 28.1596 N/A
    Mms = 302.0576 g
    Cms = 226.1853 uM/N
    Kms = 4421.1528 N/M
    Rms = 5.1598 R mechanical
    Efficiency = 1.4605 %
    Sensitivity= 93.6630 dB @1W/1m
    Sensitivity= 95.6551 dB @2.83Vrms/1m
    Krm = 9.195E-03 ohms Freq dependent resistance
    Erm = 702.906E-03 Rem=Krm*(2*pi*f)^Erm
    Kxm = 16.504E-03 Henries Freq dependent reactance
    Exm = 711.469E-03 Xem=Kxm*(2*pi*f)^Exm
    ;------------------------------------------------------------------
    Ftest = 12.005 Hz
    Ftest/Fms = 0.6235
    Test Mass used = 475.0000 g (Equal to 95.0 nickels)
    Test Mass (Ft=Fms*0.90) = 70.853 g (Add -404.147g for Ft=17.329)
    Test Mass (Ft=Fms*0.75) = 234.934 g (Add -240.066g for Ft=14.441)

  8. #23
    Senior Member RMC's Avatar
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    Hi FE3T,

    Thanks for posting your actual results.

    RE "At the time measurement was done the driver was just reconed with one of the last oem kits sold in Norway by me."

    Was there a good driver break-in period before measurements?

    RE "so i use factory specs for my simulations rather than trusting DATS or WT2."

    Why not use your actual ones, not confident? Have you tried it? I wonder if there would have been major box modeling differences had you used your actual measured parameters instead of those from JBL's table. Might have been interesting to see.

    Recently, you're the second member I see posting actual data measured following original recones, and some of their numbers showing notable parameter differences compared to JBL T/S table, pic below.

    This is NOT an evaluation of your work nor of your driver. I simply find this puzzling for the second time considering its ORIGINAL recones, not aftermarket stuff... Plus you indicate "Performs great."

    Some TS shown are pretty much on par, while others are off. I had noted quickly Qts, Vas, BL, Mms, No. The most intriguing one being Mms since this one should not vary much...

    The reason for my post is that recently I've been looking into this TS parameters shift issue and its possible impact or not in real life use, plus to what extent.

    I found from credible sources interesting things that may explain why drivers having some shifted parameters can nevertheless perform acceptably. Hopefully I'll be able to report that soon, though its income tax return time here now, I'm loaded, it may have to wait a little. Best Regards,

    Richard

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  9. #24
    Senior Member Ian Mackenzie's Avatar
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    Quote Originally Posted by FE3T View Post
    This 2245H was measured with a S&L Woofertester 2
    At the time measurement was done the driver was just reconed with one of the last oem kits sold in Norway by me.

    Meaasured with the driver in horisontal position, screved too woden blocks positioning it 4" above the floor.
    Test mass was a roll of duct tape weigthed on a kitchen scale.

    As seen there are some parametres that are suspicious. MMS are very high (More than tvice the real weigth of the cone Assembly), Vas are low, BL are very high, and Qms are high.

    I vaguely remember somone claimed that the 2245H are very difficult too get dependable measurements of.
    so i use factory specs for my simulations rather than trusting DATS or WT2.

    The driver are currently in use in a 8cuft cabinet ported too 26hz, 6db boost at 26hz Q=2
    20Hz 24db/oct HP. 50hz 18db/oct LP. Performs great.



    Buffer[1] Vas Ver 7.01
    Completed: Sat Jul 16 20:11:52 2016
    Drive level 100.000% [3.417 mA]
    Sine,LoZP(LV/LA)->Vas,19 pts
    ;------------------------------------------------------------------
    Re = 5.0568 ohms
    Fs = 19.2550 Hz
    Zmax = 158.7390 ohms
    Qes = 0.2330
    Qms = 7.0824
    Qts = 0.2256
    Le = 1.3190 mH (at 1 kHz)
    Diam = 400.0000 mm ( 15.7480 in )
    Sd = 125663.7126 mm^2(194.7791 in^2)
    Vas = 507.3981 L ( 17.9186 ft^3)
    BL = 28.1596 N/A
    Mms = 302.0576 g
    Cms = 226.1853 uM/N
    Kms = 4421.1528 N/M
    Rms = 5.1598 R mechanical
    Efficiency = 1.4605 %
    Sensitivity= 93.6630 dB @1W/1m
    Sensitivity= 95.6551 dB @2.83Vrms/1m
    Krm = 9.195E-03 ohms Freq dependent resistance
    Erm = 702.906E-03 Rem=Krm*(2*pi*f)^Erm
    Kxm = 16.504E-03 Henries Freq dependent reactance
    Exm = 711.469E-03 Xem=Kxm*(2*pi*f)^Exm
    ;------------------------------------------------------------------
    Ftest = 12.005 Hz
    Ftest/Fms = 0.6235
    Test Mass used = 475.0000 g (Equal to 95.0 nickels)
    Test Mass (Ft=Fms*0.90) = 70.853 g (Add -404.147g for Ft=17.329)
    Test Mass (Ft=Fms*0.75) = 234.934 g (Add -240.066g for Ft=14.441)
    Thank you for posting your data.

    You raise from good points about testing of these drivers and when to rely on DATSV3 data?

    The question then is how and when can the DATSv3 be reliably used?
    The problem its there are unknown unknowns like is the driver at fault, the measurement method or the measurement device?

    I am told those big speakers are tough to measure, particularly with the added mass method. The resonance peak should be high and sharp. If it looks heavily damped, the coil could have a shorted turn. A shorted turn wonít change the DC much but it will screw up the parameters big time.










    I plan to look into this further

  10. #25
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    I have the suspicion that there's something very bad with the software or the measurement setup Morton has been using. Look at his graphs and results in #11. Both drivers show a minimum impedance at some frequency between 100 and 200 Hz with a value of about 6 ohms in both cases, which appears to be reasonable for an 8 ohms speaker. As we know that a speaker's impedance never can fall below it's Re value, I'm heavily scratching my head how the software had calculated it to about 22 ohms? And if the software - or setup - fails in calculating such an easily to determine parameter, how can one trust it's other results?

    Keep your head up, Morton!

    Best regards!

  11. #26
    Member ds23man's Avatar
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    The only way to measure T&S accurate on drivers with a low FS is the added volume method. With added mass you will reach the limits of the measurement setup ( soundcard). We know that the provided T&S parameters by JBL are pretty accurate. To check the condition of a JBL driver only two parameters are needed: Dc resistance and Fs. To check the Fs you only need a sine generator and observe the max cone exursion at which frequency it occurs in free air.

  12. #27
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    Another possibility (how it is done by me): Arrange a flying lead lab bench setup: Sinusoidal signal generator - power amplifier - lab bench power supply. Tune frequency and watch the amplifier's power consumption. The frequency that results in the amplifier's lowest power consumption is fs.

    Best regards!

  13. #28
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    Some more thoughts on the possibility of a blocked back vent: I don't follow the argument that a blocked vent only will affect Q, but not fs. As this adds some more stiffness due to the locked air between the - hopefully air tight - dust cap and the obstruction, I'd expect a major influence on fs - it will raise (not fall!) dramatically, as well as Vas will dramatically be decreased.

    Best regards!

  14. #29
    Member ds23man's Avatar
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    Quote Originally Posted by Kay Pirinha View Post
    Another possibility (how it is done by me): Arrange a flying lead lab bench setup: Sinusoidal signal generator - power amplifier - lab bench power supply. Tune frequency and watch the amplifier's power consumption. The frequency that results in the amplifier's lowest power consumption is fs.

    Best regards!
    Nice method! I call my test the dribble test, with some power the driver won't stay put at Fs.

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