Neodymium Speakers and Heat Issues

You could easily be pumping 500+ watts into that 210. Volume controls are not "wattage" controls. You most likely are overheating the speakers. The MB500 is a class D output amp and class D does not usually "throttle" the output level, usually the cut off the output (cut out).
The MB500 is a very capable amp, go for an 8 ohm cab, Chasing the last watt of output never gets volume, just damages speakers.

 

Power Rating Avatar 210: 500 Watt
Power Rating mb500: 500 Watt

It seems like the power ratings are of the same size. It looks like the same but I'm pretty sure it is not.

Even if the amp is cranked to it's "audible non distorted" maximum output potential. It's nearly impossibel to get more then 1/3 rms of rated power unless the sound becomes messy distorted.

I'd assume the cab consumes not more then 150 Watt rms even in full power mode!
But a heavily cranked power amp with lots of (very audible) distortion is a very different animal of course!

btw I have got no idea how much loudness level do you need to feel happy and I have got no idea how your effect board looks like. The side effects of distortion pedals are unpredictable if boundary conditions are unknon.

 

It sounds like you were sending too much power to the speakers as B-String mentioned. If that's the case then it really doesn't matter what kind of magnets are in there. A hot voice coil is a hot voice coil.

 

Ah guys - a voice coil's resistance INCREASES as it get hotter, not the other way 'round .

 

You should find new techs. When voice coils heat the impedance goes up, not down. That causes the volume to drop. Its called thermal power compression. If you turn up more to compensate the impedance goes higher and the volume goes lower. You need more speakers to play at the volume you want so they won't heat.

 

A hot voice coil is a hot voice coil but copper remains copper and a voice coil remains a voice coil even in neodymium loudspeakers.

 

I'd suggest the power compression around -3dB unless the voice coil is already melting.
If the power compression loss makes the loudspeaker unusable my crystal bowle tells me this loudspeaker is already dead!

 

OP, you should consider a new tech that know at least fundamental electro/physics. As a normal wire/resistor/voice coil heats up, the impedance will RISE, not fall. A speaker at maximum operating temperature will pull LESS current/power from the amp (for a given output voltage), not more.

*edit*
RoadRanger, Rick James and ThisBass were quicker on the keyboard...

 

Someone who uses the term 'ohmload' is not a tech.

 

However we don't know if the tec really used the term "ohmload" unless the OP swears on the Bible!

 

The whole myth of Neodymium failing when getting (speaker driven super hard) hot needs to die. along with underpowering blowing up speakers, and light amps can't reproduce bass. Grrrr

The Curie temperature of modern Neo compounds is well above the operating temprature of a speaker, even driven to within an inch of it's life.

 

Sure but what happens to impedance(in any type of speaker) with a hot voice coil? Just curieous. : D In theory it should rise but is it a real factor? 'Thermal compression?'

 

Yes, VC DCR increases with temperature, but by the time this happens with any consequence there are other more electro-mechanical factors (specifically in a LF driver) that come into play that also factor into power compression. They include factors that impact the magnetic field interactions between the static field generated by the magnet and the dynamic field generated by the voice coil which varies according to the position of the voice coil relative to the static magnetic field. You have to remember that when driven hard, there is nothing symmetric about the resulting system... this is a big factor in how a speaker sounds when overdriven. It's a decidely non-linear set of mechanisms that generate additional harmonics as well as "power compression" in addition to the thermal component. Total "power compression" is made up of the sum of a variety of factors.

 

Get an 8 ohm cab, then get a second one.

 

Thanks Agedhorse for the reply. It's mostly mechanical in nature as the coil leaves the gap and can push no more if I understand. To the OP: if you have a SUDDEN volume drop there is something wrong with either your amp or cab. Regarding a 410…I use an MB500 as well, with a 4 ohm SWR Golight 410 with excellent results. It's very, very loud. Have not tried with 8 ohm cab, which I also have. Will try tomorrow and see if there's much difference.

 

It's not just the VC "leaving the gap" (which they don't really do anymore as most bobbins have enough depth as to make this unlikely except under severe abuse scenarios) but the interactions of the two magnetic fields (which are not uniform but varying in strength and shape) that are responsible ALONG WITH non-linearities at the driver reaches Xmax (which is one way Xmax is defined).

 

There are some old wives tales here. Neodymium when it is fully magnetized is as good and stable a material as any ferric-based one.

When a speaker heats up, the impedance doesn't go down --- it goes up! That is what's referred to in audio terminology as power compression. The amp can't deliver anywhere near

This is CORRECT. When a speaker is driven hard, the increase in temperature in the voice coil causes its impedance to rise. The rise in impedance can be very significant - and cause the amp to deliver as much as 80% less power. This has nothing to do with the magnetic material - just the voice coil.

 

Neo speakers have less heat issues in general, because the small powerful magnet means a lot more space for a heatsink, hence the vaned backs on neo speakers.