Amp problems?!!? over excursion?..

Is the speaker grill metal? Is that rattling?

 

Is there a contour feature on that amp? If so, turn it off. It sounds less like over excursion and more like a mechanical vibrational problem, like internal bracing vibrating, some other panel not being firmly attached, the speaker being loose in the baffle, handles being loose, or the grill. Over excursion sounds like speaker distortion not a rattle.

 

Hard to say, but if it sounds like something is vibrating/rattling, then it probably is an issue with the cabinet - either the speakers are bottoming out and you're hearing the voice coil hitting the back plate, or something is rattling in the cab like handles, grille, jack plate, etc.

It may just be that you have found the cab or heads limit and everything is functioning exactly as designed. You do seem to be pushing your gear to the max. Maybe you need another cab.

Robby

 

What's funny is he said it happens with 2 different cabs...

 

The voice coils are part of the speaker, not the amp.

Also, manufacturers wattage ratings mean next to nothing. I would take the 700w rating with a grain of salt. Generally speaking, use your ears. If it sounds like something bad is happening, it probably is.

 

Your cab's rating of 700w is the thermal rating, not the excursion limit. That means that its entirely possible to make the voice coil hit the back plate with less than the full thermal limit. Its also why speaker cabinets tend to distort and 'fart' out well before you're anywhere near the thermal rating of a cab.

 

This assumption is not how it really works. The cab is rated @ 700 watts RMS, but what does that really mean? It's the point at which the voice coil will melt. NOT how many watts it can actually make use of. The actual wattage limit for the mechanical excursion of the spkr is usually around HALF the rating, so around 350 watts in this case. This is also dependent on the actual frequencies being reproduced, lower freq's eating up much more power than higher freq's. So, not as simple as looking at an amps wattage rating vs a speakers wattage rating.

 

Is the amp head sitting on top of the cab? See if the same issue happens with the head off the cab...

Just wondering about vibrations, and not the good ones...

=wr=

 

The voice coil is the part of the speaker that is behind the cone and causes the cone to move back and forth. There is a metal plate behind it that if it is driven too far, it will hit. Just based on what you said, this sounds like a very likely culprit.

Don't think that just cause you are using a '700 Watt RMS' cab with a '500 Watt RMS' head that you can't cause over excursion. Every time you go one octave lower, you need to move the cones 4x farther to reach the same level. Add in that your cab unloads below tuning, which I think is about 40 Hz. Your low B has a fundamental of 31 Hz, so you are creating a perfect storm for bottoming out your woofer and causing permanent damage.

Robby

 

The wattage rating of the drivers has no relationship with how much power they can make use of before exceeding excursion limits. Your options are to dial back the volume and/or the low end EQ and/or double your cab count to deliver what you're demanding of your rig.

 

Voice coils hitting the magnets back plate on the back stroke = over excursion/mechanical damage. Keep it up and you'll be in the market for new speakers. If you have to run that loud, pull down some low bass at the amp and use more mids instead, or add more speakers. Having the rest of the band not run that loud is another option.