Speaker magnets; do they lose power over time?

[Bobby1Note]

I was having a conversation yesterday, with a very nice young fellow who's operating an up-and-coming sound company, and he said that speaker-magnets lose roughly 5% of their power per year. Whaddaya think?

[Coaster]

where does the power go?

[Miko Man]

Maybe, if you fail to properly protect your speakers by using "Monster" brand power conditioners, cables, and paranoia shields to fight the silent efforts of evil Dr. DeGauss? Mark C.

[soul-x]

Magnets do lose strength over time. But, under normal conditions with modern devices its more like fractional percentages over decades.

[dboomer]

They do but it's not that simplistic.

[W. M. Hellinger]

 

They do but it's not that simplistic.

 

hoakey...

 

I'm under the impression that alnico magnets gauss-fad slower than ceraminc. I'm also under the impression that generally heat is an enemy of magnet gauss strength.

 

So what's the real scoop?

[agedhorse]

Magnets will lose a little strength over an initial period of time and then fractions of a percent over their lifespan. It's part of the hysteresis cycle of the magnetization curve of the magnetic material.

 

There are other things that can cause demagnitization but some of this is governed by the Curie curve for the particular material.

[Mutha Goose]

Quoting

"Sintered Nd-Fe-B magnets will remain magnetized indefinitely. They experience a miniscule reduction in flux density over time. As long as their physical properties remain intact, neodymium magnets will likely loose less than1% of their flux density over 100 years. Generally the magnet will experience a degradation in its physical properties, such as corrosion, prior to it demagnetizing because of age. However, heat and high magnetic fields can demagnetize these magnets. If you heat them beyond 170 degrees Fahrenheit (80 degrees Celsius) the magnets will begin to loose their magnetic properties. Sustaining these temperatures for a length of time or heating the magnet significantly higher than this will permanently demagnetize it. Other types of magnets such as Samarium-Cobalt have higher heat resistance. There are also other types of Nd-Fe-B magnets that are not as susceptible to heat induced flux degradation. "

 

[tlbonehead]

Magnets will lose a little strength over an initial period of time and then fractions of a percent over their lifespan. It's part of the hysteresis cycle of the magnetization curve of the magnetic material. There are other things that can cause demagnitization but some of this is governed by the Curie curve for the particular material.

isn't this the main theory/hearsay for the old PAFs, etc sounding so sweet? (pickups) Also, who was it here that commented about actually receiving drivers where the magnet was mistakenly not charged?

[agedhorse]

 

Also, who was it here that commented about actually receiving drivers where the magnet was mistakenly not charged?

 

 

That was me, the magnet was never charged, that of course was not degredation but an initial condition.

[tlbonehead]

One of the "theories" I'm sure... That was me, the magnet was never charged, that of course was not degredation but an initial condition.

correct. Can't you also "discharge" the magnets and recharge them to your own desired strength?

[mrcpro]

OK another question I've always wondered about: In cabnets where there are magnets within inches of each other, is the process of demagnetization accelerated?

[agedhorse]

 

correct. Can't you also "discharge" the magnets and recharge them to your own desired strength?

 

 

Yes, they can be discharged (electrically generated inverse mag field) and recharged BUT not to your own desired strength, you will be limited by the magnetic permeability and hysteresis curve of the magnetic material itself.

[tlbonehead]

Yes, they can be discharged (electrically generated inverse mag field) and recharged BUT not to your own desired strength, you will be limited by the magnetic permeability and hysteresis curve of the magnetic material itself.

meaning there is a maximum strength I would assume? Would they always be charged to the full capability of the material?

[Dogoth]

Here's an interesting way to look at it. If a speaker looses 1% of it's gauss each year (possibly a high estimate but for our purposes, it'll do), what does that equate in real SPL output? If in 50 years it looses 50% of it's gauss, then the SPL out put would be down by only 3 db (an approximation on my part - there's probably other factors involved). If the average life of a driver is 10 to 20 years (if it's treated well for it's whole life), then the actual loss of SPL over it's life is pretty much neglible.

 

In other words the spider & surround will probably die well before there is any real performance loss due to lost magnetism.

 

Just a thought.

[agedhorse]

 

meaning there is a maximum strength I would assume? Would they always be charged to the full capability of the material?

 

 

Yes, and generally yes.

[tlbonehead]

Here's an interesting way to look at it. If a speaker looses 1% of it's gauss each year (possibly a high estimate but for our purposes, it'll do), what does that equate in real SPL output? If in 50 years it looses 50% of it's gauss, then the SPL out put would be down by only 3 db (an approximation on my part - there's probably other factors involved). If the average life of a driver is 10 to 20 years (if it's treated well for it's whole life), then the actual loss of SPL over it's life is pretty much neglible. In other words the spider & surround will probably die well before there is any real performance loss due to lost magnetism. Just a thought.

I wonder if the T/S parameters wander noticeably along with the magnet losing strength. I guess they would also change as the suspension got looser, etc as well.

[agedhorse]

 

I wonder if the T/S parameters wander noticeably along with the magnet losing strength. I guess they would also change as the suspension got looser, etc as well.

 

 

Correct on all accounts.