Magnet question on Klipschorn

[jeffck]

Hello,

I recently acquire a pair of 76 Klipschorn. I read somewhere that magnet strength will deteriorate over time.

1) I wonder if anyone have them re-charge to full strength?
2) Where to re-charge?
3) How do I test the magnet strength on my own drivers?
4) What is the reading on full strength?

Please help.

[Coytee]

1) I wonder if anyone have them re-charge to full strength?

2) Where to re-charge?

3) How do I test the magnet strength on my own drivers?

4) What is the reading on full strength?

1. Don't know, I've heard myself about having them remagnetized. (at least, I think I did on Alnico's)

2. Don't know

3. Don't know

4. Don't know

I wanted to show you how much I didn't know before I tried to answer. When I was in Hope, we saw a driver being made AND the machine used to magnetize it!

At that point, I asked Trey about "refreshing" an old magnet and his answer was essentially they can't do it.

In the even they put the needy magnet in the machine and have it set for opposite polarity, they will kill the magnet. (seems to me if they do that, they now have a neutral item that can now be REmagnetized but he knows more than I do)

upshot of that conversation was, if a driver has a weak magnet, it is better to replace it than try to recharge it.

I don't know if that's much of an answer for you but it was the answer that was presented to me.

[Guest " "]

http://www.speakerrepair.com/services.html

[Coytee]

How about that!

Da man pulls through!

Oh, and welcome to the forum []

[jeffck]

Thanks for all info. The only reason I inquire about the magnet strength is because I like the "new" Klipschorn very very much and want to keep them for as long as I can. This 76 Klipschorn is actually my third pair of Klipsch speaker within the 1.5 year period. I believe all drivers in my Cornwall are interchangeable with the Klipschorn, I will try to swap them to see if there is any audible difference. So is there some way I can measure the strength of my magnets?

[jeffck]

Found this passage about magnet, http://www.magnetsales.com/Design/DesignG_2.htm

The effect of time on modern permanent magnets is minimal. Studies have shown that permanent magnets will see changes immediately after magnetization. These changes, known as "magnetic creep", occur as less stable domains are affected by fluctuations in thermal or magnetic energy, even in a thermally stable environment. This variation is reduced as the number of unstable domains decreases. Rare Earth magnets are not as likely to experience this effect because of their extremely high coercivities. Long-term time versus flux studies have shown that a newly magnetized magnet will lose a minor percent of its flux as a function of age. Over 100,000 hours, these losses are in the range of essentially zero for Samarium Cobalt materials to less than 3% for Alnico 5 materials at low permeance coefficients.

If the above is true, 3%@100,000 hours equal to 11.5 years of continuous playing time (24 hrs/day).

[DrWho]

I was just going to say I wouldn't worry about the magnet dying on you...even if you have a full 5% reduction you probably wouldn't be able to hear a difference anyway.

One thing I don't see included in that study is the effect of vibration. You can kill a magnet by dropping it hard on the floor enough times (it introduces new unstable domains).

But considering the speakers probably haven't been moved very much I wouldn't worry too much about it at all.

[D-MAN]

I would agree that the speaker magnet is the least of your worries, although there are those who would seemingly choose to die on this field, particularily with some full-range speaker fans of a particular brand that shall remain un-named here...

However, are the measurements above concerning permanent speaker magnets specifically were flux density measurements taken from inside the VC gap, the only place it actually matters in a dynamic speaker?

Who knows, but again, I wouldn't worry about the magnets themselves.

[steamer]

Here is an interesting article on the speaker motor and its various parts.Types of magnets are explained as well.

http://yu-ra.tripod.com/motor.htm

Greg

[WMcD]

The "I read someplace" are the toughest to prove or disprove. The origins are sometimes just suspicions or opinions, which are difficult to trace back to a measurement. Opinions are like bellybuttons, everybody has one. (To paraphrase Dirty Harry.)

There seems to be some reason to believe that alnicos can experience degradation. I have not seen any hard data of actual speakers suffering performance. There are 50 year old K-Horns which people report perform well. It is hardly scientific, but it is there.

OTOH, I read someplace (ahem) that there is a design aspect which addresses variations in magnet strenght.

The flux flows from the actual magnet flows though the iron pole pieces to the gap. These have a limited capacity based on cross section and can become saturated. That is to say they have a limit. So the flux in them, and in the gap, does not get any higher despite more magnet power.

So the technique is to use magnets which are so strong as to saturate the pole pieces by some percentage. As long as variation in magnet strenght does not get too low, the pole pieces stay saturated and the strenght in the gap is constant.

It is always fun to test, tinker, and hot-rod. But I think you have nothing to worry about.

Gil

[Trey Cannon]

Ok.

Let me re-phrase a bit.

After talking to our Magnet Engineer, I stand corrected. You can re-mag a alnico magnet.

There are chances you take when doing so, but it can be done.

What I mean to say is Klipsch does not re-mag dirvers.

[Deang]

Bill's crew at Great Plains does them.

http://www.greatplainsaudio.com/service.html

[John Warren]

Hello,

I3) How do I test the magnet strength on my own drivers?

4) What is the reading on full strength?

Please help.

The magnet strength of a loudspeaker can be derived from the "actual" T/S parameters measured from the actual driver of interest. In principle, this is a relatively straightfwd process requiring a minimum of test gear. It does however require "some" test gear and, for the vast majority of enthusiasts, it requires more gear than they are willing to purchase. It also requires some basic understanding of impedance and how it changes with frequency around cone resonance. Again, for the vast majority, these "details" are too overwhelming to consider. Once the T/S parameters are known however, everything about the electro-transduction behavior of the driver can be derived. A comparison with factory minimum values for the driver will determine if the magnet structure is distressed.

So, you need test gear, some understanding of the physics and the statistical spread of T/S values typical for that particular driver.

Regarding the required "strength" of the magnetic structure-The electrical damping (Qes) is inversely related to the square of the flux density in the gap so a small change in the field strength can result in a dramatic drop in electrical damping around the resonance frequency of the driver. Thus, by measuring the T/S parameters (i.e. Qes) as mentioned above, a detemination of the flux density in the gap can be derived and compared to the values quoted for that driver.

That said, unless the driver has been physically abused, oven baked or removed and stored with large random pieces of steel, iron or other magnets, it is unlikely that the feild strength in the gap has changed appreciably from the day it was energized 30 years ago.

The drivers used in the Klipschorn today are of modest cost and a new pair (last I looked) run about $250. If you are concerned that the drivers in your units are compromised I would recommend buying a new pair. It's the "easiest" way to solve your problem, perceived or otherwise.

[pauln]

The absolute magnetic strength measurement is secondary isn't it? A relative measure might be available to regular folks without test gear. Could one compare an unknown driver magnet to a known good strong one by using a nut tied to a string, hold it hanging a repeatable distance and position, and measure the relative angle of deflection toward the magnet? Not high tech, but one could tell if a magnet had lost strength, right?

[DrWho]

Flux in the gap is very different from the Flux outside of the cabinet. And due to the nature of magnetic fields you would need a very dead magnet to notice a visual change in the angle a nut on a string hangs.

[Trey Cannon]

Hello,

I3) How do I test the magnet strength on my own drivers?

4) What is the reading on full strength?

Please help.

The magnet strength of a loudspeaker can be derived from the "actual" T/S parameters measured from the actual driver of interest. In principle, this is a relatively straightfwd process requiring a minimum of test gear. It does however require "some" test gear and, for the vast majority of enthusiasts, it requires more gear than they are willing to purchase. It also requires some basic understanding of impedance and how it changes with frequency around cone resonance. Again, for the vast majority, these "details" are too overwhelming to consider. Once the T/S parameters are known however, everything about the electro-transduction behavior of the driver can be derived. A comparison with factory minimum values for the driver will determine if the magnet structure is distressed.

So, you need test gear, some understanding of the physics and the statistical spread of T/S values typical for that particular driver.

Regarding the required "strength" of the magnetic structure-The electrical damping (Qes) is inversely related to the square of the flux density in the gap so a small change in the field strength can result in a dramatic drop in electrical damping around the resonance frequency of the driver. Thus, by measuring the T/S parameters (i.e. Qes) as mentioned above, a detemination of the flux density in the gap can be derived and compared to the values quoted for that driver.

That said, unless the driver has been physically abused, oven baked or removed and stored with large random pieces of steel, iron or other magnets, it is unlikely that the feild strength in the gap has changed appreciably from the day it was energized 30 years ago.

The drivers used in the Klipschorn today are of modest cost and a new pair (last I looked) run about $250. If you are concerned that the drivers in your units are compromised I would recommend buying a new pair. It's the "easiest" way to solve your problem, perceived or otherwise.

John,

I was told that alnico can see a drastic change in temp and cause a loss in Qes. I know very little about this, so I am going on hear say.

[Guest " "]

"" I was told that alnico can see a drastic change in temp and cause a loss in Qes. I know very little about this, so I am going on hear say.""

Intresting. A few proceedures about removing magnets I read indicated not to use heat to losen the glue, use solvents or chisel/hammer.

[John Warren]

Hello Trey-

Alnico grades have good high temperature stability (i.e. high working temperature). They can be exposed to very high temps (~1000°F) and, upon cool down, retain their magnetism. They have low coercive strengths which mean they can easily demagnetized by other magnets or strong electric fields. Ceramics have much lower working temps but are not so easily demagnetized. The energy products are similar (Alnicos are somewhat higher). The raw material cost of ceramics makes them the choice for applications where high temperature stability isn't important (i.e. loudspeakers). Also, the volume of the magnet material in the circuit is critical (energy products are units of energy per cubic centimeter) and the low cost of ceramics means they can be made large without being prohibitively expensive.

jw