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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.

[Dave Barnett]

Dave, what kind of venue is this?

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.

Believe me I'd love to replace the lot.  Getting the boss to spend the money is quite another issue though.

Venue is a small room, 300 capacity, live music from multiple genres.  Mix of local, regional and national "talent", and the occasional DJ show.  In a 48'x64' room you'd think eight "1000W" woofers would be enough?

Anyway thanks for another data point re: recones not seeming to hold up.

[Elliot Thompson]

Venue is a small room, 300 capacity, live music from multiple genres.  Mix of local, regional and national "talent", and the occasional DJ show.  In a 48'x64' room you'd think eight "1000W" woofers would be enough?

Eight 18-inch drivers will not be enough if the cabinet they are residing in is not capable of offering the right frequencies at high sound pressure levels.

Keep in mind the EV Manifold series is only good to around 55 Hz. That may be fine for Rock but not nearly enough for DJ requirements in this day and age.

Once you are constantly burning up voice coils that is an indication of asking too much from your woofers. This stems from the following:

1. The Continuous Average Levels is too high for the voice coil to manage under long-term conditions. This can occur from heavy limiting when the goal is to prevent the amplifier from clipping. Since cone movement is minimised under these conditions, the voice coil is not cooled properly.

Matters will be worse if you push the amplifier harder with the assumption the limiter will prevent loudspeaker damage, due to a non-clipped output signal from the amplifier.

2. The cabinet is not efficient to reproduce the lower notes with enough SPL. Generally for DJ requirements, 40 Hz is needed. Manifolds, offer a  –3 dB point @ 55 Hz. So the drivers need to work very hard to reproduce 45 – 35 Hz, which is common in the majority of music, DJs play.

Possibly you should contact Electrovoice and ask if it is possible to purchase their new 18-inch model (DVX 3180) used in the Pheonix Line. If you prefer to use the Manifold cabinets this may be the only way to remedy the problem providing the TS Parameters are similar to the EVX 180B.

Another option is to explore Faital Pro. They offer a woofer that is very close to the EVX 180B that should work in the Manifold series.

Best Regards, 

Elliot

[thorsten bolvig]

Eight 18-inch drivers will not be enough if the cabinet they are residing in is not capable of offering the right frequencies at high sound pressure levels.

Keep in mind the EV Manifold series is only good to around 55 Hz. That may be fine for Rock but not nearly enough for DJ requirements in this day and age.

Once you are constantly burning up voice coils that is an indication of asking too much from your woofers. This stems from the following:
----
Best Regards, 

Elliot

Not knowing the actual cabinets i  agree on the 55Hz manifold problem.
Another solution could be to change cabinets to the Xi1191 or similar.
Maybe use a combination of the two types which would give you the best performance for the frequency range in design.
The 180B is capable of performing good down to well below 40 Hz given the cabinet design supports it.

From memory i recall something like using Xds from 34 to 80 Hz and Xb from 50 to 125 Hz give and take...

Thorsten

[paul bell]

I'm with Mr. Thompson here. I've replaced quite a few EVX woofers with Faital Pro woofers with very good success.

Regardless of woofer, the EV manifold bass cabinets the OP has will not support bass below 50 Hz.  If they (his venue) is happy with the sound but wish to eliminate the nuisance of blown woofers and downtime, a better modern woofer will make everyone happy again.

[Dave Barnett]

Matters will be worse if you push the amplifier harder with the assumption the limiter will prevent loudspeaker damage, due to a non-clipped output signal from the amplifier.

This is something I've long suspected, that smashing the signal into the limiters will just give the amps and speakers a signal with a really ugly duty cycle.

[ProSoundWeb Community]