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  • Failed driver question...

    I lost a woofer in a Yorkville NX20 that was out on a rental last week. The driver tests open circuit on an ohmeter. How can I find out what killed it? I'm worrying that my amp (Behringer powered mixer) may be putting out speaker-killing signals since it has also started acting squirrelly in other ways. The system was rented out so I don't have a good way of knowing what may have happened at the event.

  • #2
    The first thing I would check is if Yorkville's no fault warranty will cover it BEFORE doing anything to the driver.

    Cutting the driver apart may give an indication as to the type of failure. In general, the following descriptions indicate to the corresponding problem for cone type drivers.

    SYMPTOM:Burned voice coil, shows strong discoloration throughout it's height but maybe darker at the top and bottom. There may be swelling along the inside of the bobbin as well with Kapton, and blistering with aluminum.

    FAULT: The voice coil suffered thermal failure due to excessive power. This could be from reproduction of highly compressed, exceeding the RMS (thermal) capability of the speaker, excessive clipping or limiting (thermally the same as compression except that clipping will increase the area under the power curve to as much as 2X the undistorted RMS rating of the amp. Another possibility is high frequency oscillation, too high to be audible but low enough that the VC inductance doesn't increase the impedance to where no damage would result.

    SYMPTOM: Open VC, (very) slight discoloration at the ends of the coil only and the open is visable at the last turn's bend (or bond) to the lead-out wire.

    FAULT: This is classic damage due to excessive short term power overload, exceeding the current handling capacity of the crossectional area, which decreases slightly at the bend. Also, work-hardening at the bend plays a small factor in creatingthis weak point. It's the weakest point for transient power overloads, where Xmech does not come into play.

    SYMPTOM: Damage to the end of the bobbin, wire loose on bobbin, loss of wire from end of bobbin, damage to cone neck bond, tinsel wire, bobbin buckling, torn or cracked surround at the edge of cone or basket, ripple in cone around the dust cap or below.

    FAULT: This is due to exceeding Xmech, fatiguing the mechanical suspension components of the speaker and is most definately from driving the speaker beyond the limits of the speaker AND enclosure tuning. Many speaker's power handling capacity decreases significantly below the cut-off frequency of the enclosure. The derating can be as much as 400%, hence the need to really pay attention to high pass filtering (both freq and slope).

    SYMPTOM: Darkening/burned as only one end or the other. Speaker may also be pushed out and "stuck"

    FAULT: Possible amplifier failure causing massive DC offset, protection circuit in amplifier inoperative. If the amp fails DC positive, the top of the VC will be burned and the cone will push out. If the amp fails DC negative, the bottom of the VC will be burned and the cone will have pulled in (on conventional polarity drivers). The reason for darkening is that the offset causes the VC to travel to it's extreme and the wire outside the gap does not get any additional cooling by conduction to the pole and return piece.
    -------------------------------------------------------------------------------------------------------------------------------------------------------------------
    Former product development engineer: Genz Benz, a KMC Music/FMIC/JAM Industries Company, continuing factory level product support and service for Genz Benz

    Currently product development engineer: Mesa Boogie

    Comment


    • #3
      [QUOTE=agedhorse;21104901]The first thing I would check is if Yorkville's no fault warranty will cover it BEFORE doing anything to the driver.

      Cutting the driver apart may give an indication as to the type of failure. In general, the following descriptions indicate to the corresponding problem for cone type drivers.

      I wish... These are several years old (discontinued model now) and Yorkville's warranty is 2 years on components. It won't cost a fortune to replace the driver; I just want to know what went wrong.

      So, to check it out I'd just cut the spider out carefully and clip the tinsel leads so I could inspect the voice coil? The driver is a neodymium 12" made by B&C; is there any advantage to reconing vs. replacing the driver?

      Comment


      • #4
        I'm worrying that my amp (Behringer powered mixer) may be putting out speaker-killing signals since it has also started acting squirrelly in other ways.


        What ways? Do you think it's putting out DC? If you're gonna cut into the speaker ... DC burns are usually limited to the very top of the windings.

        Whatever you do ... don't go plugging your suspect amp into good speakers til you're sure.
        Don Boomer

        Comment


        • #5
          What ways? Do you think it's putting out DC? If you're gonna cut into the speaker ... DC burns are usually limited to the very top of the windings.

          Whatever you do ... don't go plugging your suspect amp into good speakers til you're sure.


          The mixer has started acting funny: no signal on one side on 1 channel and sporadically I'll get clip lights on channels with no inputs. Can I check for DC by just using a meter set to DC on the speaker outputs? Is this kind of failure likely to be intermittent or would it be easier to find? The obvious answer is to get rid of the B** mixer, but I'd like to know what's going on with it for sure.
          BTW, the speaker has a light-bulb type current limiting device. The bulb isn't blown and the HF driver is fine. The renter was using a CD player into the mixer with some pretty serious low-end stuff.

          Comment


          • #6
            Note that I didn't include the following on my original post:

            SYMPTOM: Darkening/burned as only one end or the other. Speaker may also be pushed out and "stuck"

            FAULT: Possible amplifier failure causing massive DC offset, protection circuit in amplifier inoperative. If the amp fails DC positive, the top of the VC will be burned and the cone will push out. If the amp fails DC negative, the bottom of the VC will be burned and the cone will have pulled in (on conventional polarity drivers). The reason for darkening is that the offset causes the VC to travel to it's extreme and the wire outside the gap does not get any additional cooling by conduction to the pole and return piece.
            -------------------------------------------------------------------------------------------------------------------------------------------------------------------
            Former product development engineer: Genz Benz, a KMC Music/FMIC/JAM Industries Company, continuing factory level product support and service for Genz Benz

            Currently product development engineer: Mesa Boogie

            Comment

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