I blew up my beloved JBL mpro 418s driver

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1

1hiep0

Member
2013-12-14 3:33 am
San Diego
  • #2
    I was planning to take the measurement outside, but the weather was not corporate. There was no bracing on the box but will see whether it's needed. I want to keep it light as possible.
     

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    starkeyg

    Member
    2002-01-02 4:24 pm
    Sourhern MI
  • #3
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    1hiep0

    Member
    2013-12-14 3:33 am
    San Diego
  • #6
    I did a measurement outside not ideal conditions but best as I can get.
    The outcome disappointed thought I could get to 40Hz for PA application.
    The new driver/recone 2241G is rather expensive for what it is.
    I want to modify the cab for better suit with the driver. It's one way to learn:)
    there is oscillating issue at 360Hz where it's also showed in imp sweep.
     

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    conanski

    Member
    2013-03-31 3:53 am
  • #7
    1hiep0 said:
    I did a measurement outside not ideal conditions but best as I can get.
    The outcome disappointed thought I could get to 40Hz for PA application.
    Click to expand...
    The box determines the tuning frequency of the system so it has to change if you want usable response to 40hz. Were you driving the 2241 at full power below the current box tuning? If so that may be why it failed. There are recone kits available for this driver both original and aftermarket that start at about $100, this can be a DIY project with the assembled version of the kit.

    If you bridge the Yamaha you should have plenty of voltage swing to drive the B&C, but you still need a different/modifed box to get reliable output at 40hz.
     
    1

    1hiep0

    Member
    2013-12-14 3:33 am
    San Diego
  • #8
    The speaker 2241g rated at 40V, amp rated at 66V so It's about 1.5Xcontinous. It was loud (to me) at the time as I was by the sub. I have the DBX DR260 setup cut off at 40Hz. The amp was clipping for sure. There were some music bass notes playing a little longer than I thought so it's maybe it don't know ?
    The JBL was spec 40Hz +-3dB. I wouldn't attempt to recone as I have no idea how to proceed and the chance of failure is rather high.
     
    weltersys

    weltersys

    Member
    2008-01-13 9:09 pm
    Florida
  • #9
    1hiep0 said:
    The amp was clipping for sure. There were some music bass notes playing a little longer than I thought so it's maybe it don't know ?
    The JBL was spec 40Hz +-3dB.
    Click to expand...
    The driver is rated for 600 watts, if a sustained bass line at 50Hz (box tuning, Fb, impedance minima) was clipped, the Yamaha P7000S could produce around double it's rated power until the magic smoke was released.
    A slow attack (200ms) limiter set to limit at or below 40v could have prevented the burnt coil, while still allowing peaks through.

    The "oscillating issue at 360Hz" is the port resonance, not really an issue as it would not be excited when crossed over in the 100Hz range as usual. The spec of 40Hz +/-3dB obviously is not true with a 50Hz Fb.

    Presently, the cabinet alignment is near "flat", tuning lower in the same small box will roll off the low end.
    Lowering the Fb to 40Hz by extending the port(s) would trade more 40Hz for less 50-60Hz.

    Art
     
    1

    1hiep0

    Member
    2013-12-14 3:33 am
    San Diego
  • #10
    I was not setting the Drive Rack correctly now I believe; Wish I could examine the voice coil it's long gone now.
    Isn't 200ms too fast for heating protection 1/2 (20V) of continuous power? I was thinking of 1 second.
    I guess I can leave the cab as is since it's fairly flat to 100Hz as I have been using.
    Thanks
     
    weltersys

    weltersys

    Member
    2008-01-13 9:09 pm
    Florida
  • #11
    1hiep0 said:
    Isn't 200ms too fast for heating protection 1/2 (20V) of continuous power? I was thinking of 1 second.
    Click to expand...
    My mistake, 200ms is only 4 cycles at 50Hz. Can the LF output limiter of the DBX DR260 be set to 1000ms attack time?
    20V would be only 100 watts at 4 ohms, the coil probably won't burn at that level even with signal with only 3dB crest factor..
     
    weltersys

    weltersys

    Member
    2008-01-13 9:09 pm
    Florida
  • #13
    1hiep0 said:
    It cannot the maximum is 200ms attack.
    Click to expand...
    1000ms/50 =20ms, 200ms is 10 cycles at 50Hz, not 4, oops.
    Still, 10 cycles attack time may limit peaks more than you want, but would clamp quick on sustained power.
    1hiep0 said:
    So with the b&c of 60V should be set at 3/4, 1/2 is 30V would be too light for 3dBb crest?
    Click to expand...
    Not sure what you are asking.
    Cutting voltage in half reduces power by 6dB (1/4 power), -3dB is half power.
     
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