How loud can I play an Alnico driver?

[otenmsa]

I have read on this forum that the Alnico drivers demagnetize due to large voice coil currents. This means that I could possibly demagnetize the driver if playing too loud.

However, I haven't found on the topics how much would be loud enough? What are the large currents for these drivers to demagnetize?

Can I drive a JBL L300 (with 2231A) with a McIntosh MC402 at loud levels? I like to play loud and usually the power meter goes to the 40-400W range.

How long for can I drive these speakers at very loud levels without ruining anything?

[Cyclotronguy]

It's all about heat, not necessarily about loud. If the voice coil heats the pole piece and thus the magnet till it's hot, then you have an issue.

Loud peaks on wide dynamic range material may very well result in less average wattage dumped on the magnet than moderately loud highly compressed material.

Back in the day a simple Altec A-7 pair would cover a 400 seat movie house and last for decades before the magnets had to be charged.

Kent

[Lee in Montreal]

A small amp that clips continuously will send DC. Then DC will turn the coil into a toaster wire. That will heat up the Alnico magnet, which will lose its charge over time.

[otenmsa]

If I use 400 watt clean power there would be no DC sent, but could still heat up the Alnico?

The L300 brochure states 300W power handling for the Alnico 136A and 400W for the Ferrite 136H. This means I could use 300 watt continously without heating up?


A small amp that peaks continuously will send DC. Then DC will turn the coil into a toaster wire. That will heat up the Alnico magnet, which will lose its charge over time.

[hjames]

If I use 400 watt clean power there would be no DC sent, but could still heat up the Alnico?

The L300 brochure states 300W power handling for the Alnico 136A and 400W for the Ferrite 136H. This means I could use 300 watt continously without heating up?

You would soon have hearing issues running 300 watt continuous power (at serious volume) on those speakers.

[Horn Fanatic]

I have read on this forum that the Alnico drivers demagnetize due to large voice coil currents. This means that I could possibly demagnetize the driver if playing too loud.

However, I haven't found on the topics how much would be loud enough? What are the large currents for these drivers to demagnetize?

Can I drive a JBL L300 (with 2231A) with a McIntosh MC402 at loud levels? I like to play loud and usually the power meter goes to the 40-400W range.

How long for can I drive these speakers at very loud levels without ruining anything?

This is a trick question, right?

You can play a loudspeaker with an AlNiCo magnet as loud as one with a mud magnet. The question is, why would anyone play a loudspeaker so loud as to worry about degaussing the magnet? Before that happens your voice coil would suffer a melt down if not disassociate itself from the gap.

I have never heard of completely degaussing a magnet structure due to excessively high levels, and I don't believe it's possible to do so. AlNiCo magnets do get warm, and over time under abuse they would lose a bit of their flux density, but not completely. I'd say, over a span of forty years under normal use a decrease might be measured on a Gauss meter, but nothing the human ear would detect.

I used to own four L300's that I rescued from a Disco, and the most chronic problem they had were the load resistor leads in the networks breaking off at the circuit board due to vibration because they cranked the speakers up to the threshold of pain, and the occasional blown 136A. Frankly, I wouldn't want to be in a situation where four L300's were focused six feet from my head loud enough to part my hair. They ran them without the slant plate lens.

My advise, use the L300's for what they were intended, for the living room, not a forth of July block party. The last thing you want to do is force a 136A or 2231A, or any loud speaker past it's excursion limit. That would be just silly!

Good luck, H.F.

[ratitifb]

How long for can I drive these speakers at very loud levels without ruining anything?including your ears or not :crying:

FYI a level of over 100 dBA is loud enough to begin causing permanent damage after just 5 minutes per day!

:screwy:

[martin2395]

This.

I bet that you would go deaf before you reach 300W's on the L300's :D (i guess you'd also toast the networks way before reaching 300W)
But again, we are talking about 300W continuous power, a 300W peak for a short period can't be a problem.

[rdgrimes]

^^^
Ditto, I'd like to see anyone tolerate continuous 300W with ANY speaker. 100W maybe.

[Horn Fanatic]

^^^
Ditto, I'd like to see anyone tolerate continuous 300W with ANY speaker. 100W maybe.

Heck. Putting a single ended 300B on a set of horn speakers is enough to part the Red Sea!

[otenmsa]

In the Great Alnico / Ferrite Debate, there's a quote on Greg Timbers saying that a peak of current could instantly drop 3dB on a 2231A response and that these drivers were designed for tube amps. He says: "With the advent of big solid state amps, the current levels went up and the problems started to surface."

This means I could demag the Alnico with only peaks of high power/current?

Say, listening to a 40W continuously and having dynamic peaks of 200W or maybe 300W on certain passages.

http://www.audioheritage.org/vbulletin/showthread.php?4031-The-Great-Alnico-Ferrite-Debate

[otenmsa]

I didn't say I would listen to the L300 driven by 300 watts continuous power. I asked if the driver would be capable of handling this amount of power/current, since it is on official JBL L300 specifications/brochure. If that is correct, would be some sort of guarantee from JBL that the Alnico wouldn't demagnetize if kept driven under this rated power.


You would soon have hearing issues running 300 watt continuous power (at serious volume) on those speakers.

[Robh3606]

This means I could demag the Alnico with only peaks of high power/current?

Yes that's what he said.

Rob:)

[Lee in Montreal]

If the peak exceeds the amp's capacity, it will output a flat line, which is DC. It occures during clipping.
http://www.st-andrews.ac.uk/~www_pa/Scots_Guide/audio/clipping/fig1.gif

[otenmsa]

Lee, thanks for the explanation, but I'm talking about a peak that is under amp's capacity, it is a MC402 able to provide 400W/channel of clean power. In this case there would be no DC sent, could still heat the magnet?


If the peak exceeds the amp's capacity, it will output a flat line, which is DC. It occures during clipping.
http://www.st-andrews.ac.uk/~www_pa/Scots_Guide/audio/clipping/fig1.gif

[Robh3606]

The demag has nothing to do with clipping. It's the intensity of the back EMF field that causes the problem. The higher power the amp the more powerful the EMF field can be. Read Gregs post that is already linked.

DC and heat are not the issue.

Rob:)

[ds23man]

I think this an over exaggerated issue.

I have been working in the PA business all my life and had aprox 150 K140/E140 and 100 K120/E120 drivers in our systems. First driven by Crown DC300 and later Carver PM1.5. They where abused in power terms and we never discovered problems with the alnico types.

[dezmond]

^^^
Ditto, I'd like to see anyone tolerate continuous 300W with ANY speaker. 100W maybe.

You should ear the jbl 4731x , I am hitting 117db 12 ft away. 100 db is loud ? Maybe for old farts , lol .

[Robh3606]

I think this an over exaggerated issue.

In your setting with multiple boxes and drivers in the dozens yeah it would be. At home definately more noticeable with single driver pairs. It's a fact it happens. Only the K's count the E's would be fine.


Rob:)

[jblwolf]

" loudspeaker handbook "chapter 4-principles of magnetics"

[Audiobeer]

I have read on this forum that the Alnico drivers demagnetize due to large voice coil currents. This means that I could possibly demagnetize the driver if playing too loud.

However, I haven't found on the topics how much would be loud enough? What are the large currents for these drivers to demagnetize?

Can I drive a JBL L300 (with 2231A) with a McIntosh MC402 at loud levels? I like to play loud and usually the power meter goes to the 40-400W range.

How long for can I drive these speakers at very loud levels without ruining anything?


The only way your gonna hurt an Alnico is dropping it. Driving a pair of L-300s with the Mcintosh MC402 is going to destroy your ears before it has any effect on the magnets of the Alnico.

[ds23man]

In your setting with multiple boxes and drivers in the dozens yeah it would be. At home definately more noticeable with single driver pairs. It's a fact it happens. Only the K's count the E's would be fine.


Rob:) If this was a problem we should have noticed it with our stage monitors. A 2 or 3db drop in output level is very noticable, certainly if you have two side by side with one E140 and the other with a K140. Most of them had been reconed twice, the surrounds where tearing......

[Allanvh5150]

I would have to say your ears will be well and truly done in before an ALNICO magnet starts to demagnetise. Also, the driver voice coil will be having serious issues as well.

Allan.

[ivica]

I have read on this forum that the Alnico drivers demagnetize due to large voice coil currents. This means that I could possibly demagnetize the driver if playing too loud.

However, I haven't found on the topics how much would be loud enough? What are the large currents for these drivers to demagnetize?

Can I drive a JBL L300 (with 2231A) with a McIntosh MC402 at loud levels? I like to play loud and usually the power meter goes to the 40-400W range.

How long for can I drive these speakers at very loud levels without ruining anything?

Hi otenmsa,

If we take JBL nominal driver impedance value to be 8 Ohms, and for 2231A driver max.nominal power to be 100W, that would give us that effective voltage value to be 28.23V, or about 40V maximal voltage amplitude. On the other side lowest applicable frequency of such amplitude would be about 25Hz (in order not to overcome Xmax).
From some simulation program minimal impedance of the driver 2231A in L300-box would be about 6.7 Ohms around 150Hz), what would reduce the maximal voltage about 10%, So I believe if You limit the voltage to 36V max value and use frequency range over 25Hz, your driver would operate under JBL declared operating conditions, and demagnetization would not have to become a dangerous threat.

But "hard" limiting the power amplifier voltage to the mentioned value,( if such limitation have happened ) can destroy compression on UHF drivers, so a kind of "soft" limiting has to be applied.

I have seen one K120 with the reduced magnet "strength" ( about 2~3 dB lower output), and one Altec VHF driver that had reduced sensitivity too, so demagnetization can happen to AlNiCo drivers.

Regards
Ivica

[Retroman]

I think the question is a good one and probably best answered by an transducer engineer. As mentioned, its not a heat-related problem as the Curie temperature for Alnico 5 is far beyond the operating temperatures geneated by a JBL woofer in a typical residential sound system.

My understanding (limited) is the problem stems from the overall size of the motor system and the whether the coil assembly is underhung or overhung. For example, the LE15a with its relatively deep motor and underhung voice coil is not generally susceptible to de-magging. However, the overhung/short magnet 123a could loose 3-6 dB (maybe more)when driven by a Phase Linear 400 and playing the Sheffield Drum record. Put a powerful enough amp on a pair of L100s and watch what happens. (Happened to me in the 80s').

So the question remains, how to determine the amount of safe power that can be used with a given JBL woofer with an Alnico magnet. Take the example of the L100. What could be considered safe? 100 watts, 125 watts (unclipped).

[audiomagnate]

I finally got one of the soft clipping lights on my Nak PA7 (around 200WPC) to flicker the other day driving my L300s. That was loud! Keeping it at that level for any amount of time would have been crazy.

[jblwolf]

some old info I once read

[ivica]

I think the question is a good one and probably best answered by an transducer engineer. As mentioned, its not a heat-related problem as the Curie temperature for Alnico 5 is far beyond the operating temperatures geneated by a JBL woofer in a typical residential sound system. ....



Hi,

You are right, temperature is not the main reason for AlNiCo 'demagnetization'. An "inverse magnetic field" ( produced by current pulse) can partially demagnetize the magnet. As seen for Alnico Hc is less then Ceramic, not to mention Samarium or Neodymium.

For Alnico-V Hc is about Three TIMES LESS then Alnico-8. I have added some graphs.

As driver Re and Le are almost constant, only the value of the applied peak voltage and its duration can define the current peak value...

Regards Ivica

[ratitifb]

some old info I once readmany thanks for sharing that old JBL's info but the second graph doesn't concern alnico demag issue but only shows the failure mode of the 1" comp dia. vs the material and surround design of the dia. along the time at different power levels applied ;)

and as mentioned above the material (alnico) isn't the only parameter that affects the degauss issue but the magnet circuit design itself and voice coil geometry also do (Eddy's currents) ...