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[Jared Payne]

Howdy!

So suddenly one of my subs is quieter than the other.

System:
M32
Driverack pa2 (set stereo tops, mono sub)
2x JBL prx715
2x JBL prx718xlf

Tested direct from M32 to subs and from pa2 to subs.
Tested many different cables.
Swapped cables so I was passed audio through the louder sub to the quieter one, and then reversed to pass audio from quieter sub to louder. Did this from the mixer and from the driverack.

I notice it being a bit quieter myself at home. However, when we were out at a gig Saturday with enough ambient noise around us and only the kick drum going we simply thought it wasn't working at all... that much of a volume difference.

The input indicator light is flashing, though doesn't seem to be quite as active as the other sub.

Ideas?

[Christian Ekren]

Howdy!

So suddenly one of my subs is quieter than the other.

System:
M32
Driverack pa2 (set stereo tops, mono sub)
2x JBL prx715
2x JBL prx718xlf

Tested direct from M32 to subs and from pa2 to subs.
Tested many different cables.
Swapped cables so I was passed audio through the louder sub to the quieter one, and then reversed to pass audio from quieter sub to louder. Did this from the mixer and from the driverack.

I notice it being a bit quieter myself at home. However, when we were out at a gig Saturday with enough ambient noise around us and only the kick drum going we simply thought it wasn't working at all... that much of a volume difference.

The input indicator light is flashing, though doesn't seem to be quite as active as the other sub.

Ideas?

Looks like you've managed to narrow it down to the cab itself pretty well.

First make sure the input sensitivities are set identically between the two subs (and the knobs are still accurate - try turning them both full up or full down and ensure the "marks" line up around the same locations!)

I believe that cab uses a DVC (dual voice-coil) driver. The amplifier actually feeds two channels of identical program material to the driver. If it is truly just a reduced output level - that is, there is not audible distortion, etc. - it is possible that one of the VC's has been disconnected. This would net a -6dB reduction in output (roughly half as loud.) To confirm, if you take one of the handles off you should be able to peer in and see if all 4 wires are connected to the driver and amplifier. The connection to the amp is a 4-pin Molex connector I believe, ensure it is fully seated and not sitting at an angle!

If they are connected and issue persists, the amplifier may have a bad channel - this can be confirmed by swapping pairs of wires to check each channel independently.

[Chuck Simon]

 Check the polarity button on the back of each sub.  It’s happened to me.

[Tim Padrick]

One leg of the input is likely kaput.

[Jared Payne]

Okay, sorry about the long response time. Life and stuff.

Anyways. I just pulled the whole sub apart. Everything looks good, tight, clean.

Hmmmmmm.... And it's not like I can say it blew out.... because it still works. Just at a much lower level.

Leg of the input? You mean the xlr pins.

@polarity.... Yeah I always ALWAYS start with the stupid stuff.

Is it plugged in, take dbx out of the equation, reverse everything to other sub, etc, etc.

[Scott Holtzman]

Leg of the input? You mean the xlr pins.

Or the circuitry connected to it. 

[Jared Payne]

If it is the pins on the xlr connections you're referring to. Everything looks clean, and it has two "channels"

I can plug into either channel and the subwoofer exhibits the same lower volume than the other sub.

The sub only has one voice coil, 2 wires running to input on the back of the driver. Other wire coming from the back of and amp assembly run to the LED indicator.

[Christian Ekren]

The sub only has one voice coil, 2 wires running to input on the back of the driver. Other wire coming from the back of and amp assembly run to the LED indicator.

That is odd, the spec sheet lists the 718XLF as having a 2278G Differential Drive dual voice-coil driver, however the technical manual lists a 2278H single voice-coil driver..

[Tim McCulloch]

That is odd, the spec sheet lists the 718XLF as having a 2278G Differential Drive dual voice-coil driver, however the technical manual lists a 2278H single voice-coil driver..

Description notwithstanding, the designators "G" and "H" refer to the nominal voice coil impedance (unless JBL changed something).

The number refers to the physical model, so both the G and H flavors should be either single or dual coil, but not both.

[Will Knight]

That is odd, the spec sheet lists the 718XLF as having a 2278G Differential Drive dual voice-coil driver, however the technical manual lists a 2278H single voice-coil driver..

I suspect a marketing dept error. JBl has been using Dual VC drivers in most of their passive and active subs going back to the Eon 518 then the current SRX8 with the MRX and STX series as the only exceptions. The material I’ve seen still refers to a dual VC even though the picture is incorrect.

[ProSoundWeb Community]