Blown 18" sub

[jonwhittaker]

Hi everyone.

 

We have a bar PA system which contains a single Celestion Substation 18" bass bin. This is powered from a JBL MPX1200 amplifier, at 8 ohms, off one channel.

 

The source is through a Denon dnx500 mixer from the rear "sub out" socket which acts as a crossover.

 

The bass bin blew last night, at least I assume that is what happened, there was suddenly no output from the unit, we have tried replacing cables and the amp is fine. I assume the amp clipped, is there anything we can do to avoid this happening again?

 

We are considering running two new Celestion Substation 18s that we have in storage off the same amp channel (however at 4 ohms) with a Cloud Compressor in the chain to limit the signal. Would this be a suitable option?

 

Many thanks in advance.

[KevinE]

All PA systems subject to a DJ should be limited by some device to prevent either intentional or accidental overdriving or clipping. You cannot rely on a DJ or performer to constantly monitor levels and ensure they stay in the green, a LMS or AVC is the best way and is de rigeur on installed rental or hire systems to prevent risk to a company's assets.

[tinnitus_man]

Coil gone O/C - check the braids going up to the speaker connections on the chassis - could have gone OC or come off the speaker connection. The coil may have started to rub on the former causing it to go O/C - push against the cone you will hear it rubbing - if so the speaker it duff.

 

I would suggest a signal processor unit - one with a limiter on - perhaps DBX DRIVERACK PA+ - SPEAKER MANAGEMENT SYSTEM there are many others.

[cameroncoats]

^

I'm not going to count the number of threads about driverack PA's blowing up speakers.

 

OP - I remember seeing a product that when volume levels were turned up, it would make the speakers sound overdriven, but at a safe level, then actually reduce the volume going to the speakers if it was turned up further. Details to come, unless anyone knows anything about this.

[widowgobo]

I thought the driveracks problem has been ironed out, also the Ultra drive is supposed to be one of uli's finest creations if money is a prob.

[csg]

the ultra-drive is widely regarded to sound significantly better than the dbx driverack pa, ive done A/B tests myself and would agree.

 

The MPX1200 is a very beefy amp, capable of delivering sustained power far higher than the thermal capacity of the substation, which uses a relatively lightweight driver. Not a great match in my opinion.

 

Using 2 substations, parallel sharing one channel of the mpx1200 will improve matters somewhat, as the amp will not deliver twice the power into half the load impedance, but it is still possible tht damage will occur, particularly if clipping is taken into account

 

so, a limiter would be a very good idea. I would recommend a drawmer / formula sound unit such as an avc-2, which will limit levels and maintain dynamic range ( to a degree), or a good LMS unit with decent limiters - the berry ultradrive is a good starting point.

[david.elsbury]

I thought the driveracks problem has been ironed out

Correct, in the driverack PA+ (note the "+" on the end)

[jonwhittaker]

the ultra-drive is widely regarded to sound significantly better than the dbx driverack pa, ive done A/B tests myself and would agree.

 

The MPX1200 is a very beefy amp, capable of delivering sustained power far higher than the thermal capacity of the substation, which uses a relatively lightweight driver. Not a great match in my opinion.

 

Using 2 substations, parallel sharing one channel of the mpx1200 will improve matters somewhat, as the amp will not deliver twice the power into half the load impedance, but it is still possible tht damage will occur, particularly if clipping is taken into account

 

so, a limiter would be a very good idea. I would recommend a drawmer / formula sound unit such as an avc-2, which will limit levels and maintain dynamic range ( to a degree), or a good LMS unit with decent limiters - the berry ultradrive is a good starting point.

 

Thats a great help thanks very much.

 

Incidentally, we have a redundant MPX600, would that be a better match for a single substation bin? Please forgive my lack of expert technical knowledge in this field

 

With regards to limiting, we have a Cloud Compressor unit in our rack which is currently not connected. Any thoughts?