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Took a Peek at Trashed S15-D

Discussion in 'Amps and Cabs [BG]' started by bgavin, Jan 18, 2003.

  1. A bud of mine has a smoked Bag End S15-D cabinet that I got to examine at a gig. The DCR of the voice coil is still intact, but the cone won't move by hand. Hooking it up to my rig at low power demontrated how trashed it is... awful buzzing and grinding.

    The Bag End tech support figures the driver was over driven and melted the voice coil in the gap, hence the inability to move the cone by hand.

    A cursory calculation of the cabinet and port dimensions leads me to believe the cab is tuned around 70 Hz for a net internal volume of 1.79 cubic feet. The T/S data for the driver indicates it is suited for 3.5 cubic feet or larger. The squished cabinet will give it the classic Carvin/Eden hump around 100 Hz, and the resulting rapid rolloff in bottom end. I'm hoping to get the cabinet on the test bench after it is repaired.

    If the cab is actually tuned this high, I suspect the driver was munched by over powering the cab below 70 Hz. My buddy has numerous 5-string basses, so I suspect this is the cause of the destruction.
  2. ESP-LTD


    Sep 9, 2001
    From what little I know of cabinet design, I wonder why more cabs don't fry.
  3. ThunderStik

    ThunderStik Guest

    Jun 25, 2001
    Claremore OK.
    Me too.
  4. Brad Johnson

    Brad Johnson Supporting Member

    Mar 8, 2000
    Gaithersburg, Md
    DR Strings
    OTOH I can't understand how people blow as many speakers as they do. I used mine again on a gig last night and as usual it sounded great. My two cab setup sounds great with my five strings:D
  5. Flat Bass

    Flat Bass

    Dec 8, 2002
    I have played the **** out of mine and they have never even asked me once to turn down. Those are some awesome cabs and speakers. Maybe that one was just defective. I also played 5 string and trust me it pumps alot lower than 70 hertz. These damn thing put out some serious round low end with a 5 and still are able to get the Jaco bite and surprisingly enough high end with a 75 Jazz.:rolleyes:
  6. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    Bruce, I'm not sure I understand why that would happen. If the cab is tuned to 70 Hz, its output drops off dramatically below that frequency. It drops off because the impedance of the system rises dramatically. Why would a driver fry faster if the system impedance is way up and its power draw way down?
  7. Not exactly.

    Vented boxes have an impedance trough. The low point in the trough is the tuning frequency. There is an impedance peak both higher and lower than the tuning frequency.

    When the driver is at the tuning frequency, cone movement is virtuall nil. This is coincident with maximum current draw, due to the impedance minima at tuning. If the driver is designed for motion cooling and it isn't moving at all, yet drawing full power... melt.

    The chances of the player staying at a steady 70 Hz long enough to melt the driver from the above conditions is pretty slim. I know there are a lot of one-note bass lines, but one at 70 Hz, dum-dum-dum would be boring as hell.


    The more serious problem is the lack of acoustic loading below 70 Hz. This gets worse at the rate of 24 ~ 36 dB per octave, depending on the cab configuration. At 31 Hz, this driver has very little, if any, acoustic loading.

    This driver appears to have melted and welded its voice coil into the gap, rather than jumped out of the gap and become physically misaligned. I pushed on the cone gently and it wouldn't move, so I did not push harder.

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