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[Dave Barnett]

Question about the Crown MA-5000 and MA-5002 amps -- do the back panel compression and "Loudspeaker Offset Compensation" controls actually help anything?

I've got one each of the 5000 and 5002, driving four 2x18 bass cabinets in a 300-cap venue.  The bass cabs are EV MTL-2B boxes loaded with EVX-18B drivers.  I went about ten years without ever blowing a woofer, but in the last year I've started having failures. 

You'd think that the MA-5002 would be a good match for two 8-ohm cones/channel, each cone rated at 1000W power handling capacity.  I'm using an XTA processor, and I'm reluctant do dial back the limiter on the woofers much more, and was wondering if the gadgets built into the Crown amps might help anything? 

[Jason Phair]

Question about the Crown MA-5000 and MA-5002 amps -- do the back panel compression and "Loudspeaker Offset Compensation" controls actually help anything?

I've got one each of the 5000 and 5002, driving four 2x18 bass cabinets in a 300-cap venue.  The bass cabs are EV MTL-2B boxes loaded with EVX-18B drivers.  I went about ten years without ever blowing a woofer, but in the last year I've started having failures. 

You'd think that the MA-5002 would be a good match for two 8-ohm cones/channel, each cone rated at 1000W power handling capacity.  I'm using an XTA processor, and I'm reluctant do dial back the limiter on the woofers much more, and was wondering if the gadgets built into the Crown amps might help anything?

MA5K is a fine choice for that setup.   Offset Compensation is DC protection, so you'll definitely want to have that turned on.  Also by all means use the amps' limiters as well as your processors.  I'm guessing your failures have all involved cone tears?  Paper gets old, loses its stiffness and fails.  I've had similar things with EAW subs that lasted forever, and then had a rash of failures with no changes to the rig...just dying of old age, as it were.

[Jim McKeveny]

Offset Compensation is DC protection..

Only in that there is a high -pass filter in circuit. The Loudspeaker Offset Integration circuit uses an algorithm that centers disparate near-synchronous LF waveforms on a loudspeakers excursion "swing". A loudspeaker already at 75% positive excursion doesn't benefit from an input signal requiring 50% more.

We found that unconventional magnet structures: i.e. AURA's radial , confused the system, but on conventional structures was indeed a woofer saver.

Keep in mind that the MTL2 isn't exactly a "sub" sub. It tends to be happiest above 50hz. Modern music stretches down more, and more often. This will also affect cone life.

[Dave Barnett]

Offset Compensation is DC protection..

Only in that there is a high -pass filter in circuit. The Loudspeaker Offset Integration circuit uses an algorithm that centers disparate near-synchronous LF waveforms on a loudspeakers excursion "swing". A loudspeaker already at 75% positive excursion doesn't benefit from an input signal requiring 50% more.

We found that unconventional magnet structures: i.e. AURA's radial , confused the system, but on conventional structures was indeed a woofer saver.

Keep in mind that the MTL2 isn't exactly a "sub" sub. It tends to be happiest above 50hz. Modern music stretches down more, and more often. This will also affect cone life.

You'll note that I never used the word "sub" in the original post... 

Thanks for the information, I'll give it a shot.

My failures have been voice coils cooking, not cone tears.  Well, I had one voice coil separate from the cone after cooking...  Another thing, it seems to always be the same three baskets that I'm sending back.  I wonder if the recone kits just aren't up to snuff?  All my recone work has been done at the EV factory in Morrilton AR, just a short hop up I-40 from here.  You'd think they'd know how to do it.  I've tried moving them to different amp channels to eliminate the possibility that the problem is upstream, and the faults seem to follow the cones, not the amp channels.

Another thing I've noticed is that in the MTL2 boxes, one woofer faces up and one faces down.  At the end of a show, the top ones will often be hot to the touch, and the bottom ones still cool.  But I'm not necessarily losing more woofers from the "top" location.

[Elliot Thompson]

Hi.

If the voice coil is burning up, the continuous average level of the amplifier is exceeding the thermal capacity of the driver. With the amount of compression offered in music these days such an occurrence is possible. Matters will be worse if you are limiting the amplifier in hopes to prevent clipping.

If you find the problem is occurring only to the drivers you are repairing, chances are the replacement materials are not as robust as the original voice coil of the EVX 180B.

The Crown Offset Integration switch is a sub-low-roll-off filter, which triggers around 35 Hz. If I remember correctly, the compressors affect the input signal of the amplifier.

 If you are using the old 1980’s MTL cabinets, it may not offer enough convection cooling why the top drivers are heating up opposed the woofers residing below.

Although I am using Crown Macro-Tech 5000vz amplifiers in addition to Electrovoice EVX 180 B woofers, I am not using MTL cabinets and, haven’t had any of my 180 B’s repaired.

Best Regards,

[Art Welter]

Offset Compensation is DC protection..

Only in that there is a high -pass filter in circuit. The Loudspeaker Offset Integration circuit uses an algorithm that centers disparate near-synchronous LF waveforms on a loudspeakers excursion "swing". A loudspeaker already at 75% positive excursion doesn't benefit from an input signal requiring 50% more.

We found that unconventional magnet structures: i.e. AURA's radial , confused the system, but on conventional structures was indeed a woofer saver.

Keep in mind that the MTL2 isn't exactly a "sub" sub. It tends to be happiest above 50hz. Modern music stretches down more, and more often. This will also affect cone life.

You'll note that I never used the word "sub" in the original post... 

Thanks for the information, I'll give it a shot.

My failures have been voice coils cooking, not cone tears.  Well, I had one voice coil separate from the cone after cooking...  Another thing, it seems to always be the same three baskets that I'm sending back.  I wonder if the recone kits just aren't up to snuff?  All my recone work has been done at the EV factory in Morrilton AR, just a short hop up I-40 from here.  You'd think they'd know how to do it.  I've tried moving them to different amp channels to eliminate the possibility that the problem is upstream, and the faults seem to follow the cones, not the amp channels.

Another thing I've noticed is that in the MTL2 boxes, one woofer faces up and one faces down.  At the end of a show, the top ones will often be hot to the touch, and the bottom ones still cool.  But I'm not necessarily losing more woofers from the "top" location.

Have you measured the DC resistance of all the drivers? might be the new batch is lower and getting more power. Other small changes in materials could possibly make the new cones a lower impedance when loaded in the cabinets.

The top speaker, getting hotter, may actually be safer due to the voice coil heating and raising in impedance more than the lower unit, drawing less power.

That said, my money is on slightly different parts and slightly more average power lately has put them over the edge.
It sucks when the new parts don't last.

On a semi-related issue, when I had a diaphragm failure several years ago I ordered a pair of replacement diaphragms, I did not know there were series 1 and series 2 of the  Eminence PSD2002 driver diaphragm. Yesterday, cleaned and tested the four drivers, the one (series 1) diaphragm that I had replaced with a series 2 still played, but "whistled" at certain frequencies. It had developed a crack along the edge, but had no sign of over excursion.

I expect the replacement of the same vintage may develop the same malady..

[Bob Lee]

Only in that there is a high -pass filter in circuit. The Loudspeaker Offset Integration circuit uses an algorithm that centers disparate near-synchronous LF waveforms on a loudspeakers excursion "swing".

That's essentially what a high-pass filter in a power amp will do; call it an "algorithm" if you want but I think that suggests more complexity than actually exists.

I agree with Elliott that burning up voice coils is an indicator of average power that exceeds their thermal dissipation capabilities.

[Bruce Burke]

Only in that there is a high -pass filter in circuit. The Loudspeaker Offset Integration circuit uses an algorithm that centers disparate near-synchronous LF waveforms on a loudspeakers excursion "swing".

That's essentially what a high-pass filter in a power amp will do; call it an "algorithm" if you want but I think that suggests more complexity than actually exists.

I agree with Elliott that burning up voice coils is an indicator of average power that exceeds their thermal dissipation capabilities.

That or a DC offset problem at the output of the amp.

[Dave Barnett]

I agree with Elliott that burning up voice coils is an indicator of average power that exceeds their thermal dissipation capabilities.

That or a DC offset problem at the output of the amp.

What if I've got two woofers in the same box, driven from the same amp channel, and one has gone open circuit multiple times, but its partner continues to function normally?

The amps have both been back to the factory within the past year.  Also, wouldn't Crown MA amps with DC show some kind of IOC error on the front panel?  Also, wouldn't DC show as a turn-on thump?

In my previous post the term "cooked the voice coil" may be a bit of an overstatement.  I think I've only ever had one EVX-180B failure where the coil seized, usually what I see is they just go open circuit with no other symptoms, no feeling of "roughness" when you push on the cone.

[paul bell]

Dave, what kind of venue is this?

I'll agree that today's music is becoming more bass heavy. I'll also agree those cabinets won't do much below 50 but they do have some pretty good "kick".

I think it's time to move onto newer/more modern bass cabinets or consider replacing the EV woofers with a more modern design that will handle more power electrically and physically.

I've also run into this. The re-cone kits from EV don't hold up like the original drivers did when they were still a relatively new and current driver. Ultimately, the long term fix was a driver upgrade. I've had shattered surrounds, broken leads, spiders that came undone from the coil former and of course, roasted voice coils.

[ProSoundWeb Community]