K77 alnico. Just out of curiosity I want to test if remagnetization works.

[KT88]

Or I should better say whether this method of remagnetization works. Because according to the provider, it is quite uncomplicated and rich in results.. So I.have found a reputable company that remagnetizes Alnico drivers among all other speaker restore measures. I have read a lot about complications e.g. that you have to disassemble the parts of the magnet and other stories e.g. that the drivers are shot across the room. I talked to the owner of this company on the phone. He says that it is not witchcraft. These photos below are from a documentary that was broadcast on German TV about his work restoring old speakers. I bought K77M yesterday through ebay. They will be delivered in about two weeks. It's just plan B in case the alnicos don't improve.  But I will have my 1977 K77 alnico remagnetized at this store. I also ordered diaphragms from Michael Crites for my K55V. I will have these drivers remagentized as well.
Measuring the magnet strength in the air gap is quite expensive as you would have to take everything apart, the voice coil has to be removed. But the company makes an input measurement of the frequency response and after remagnetization an output measurement. I will report back to you. I do this out of interest and curiosity. Although I get K77M delivered but I like the K77 alnico very much. They are just a bit too dull. Maybe they will radiate higher frequencies again. Costs are 25€ per driver which sounds reasonable.

 

 

[billybob]

Not said but implied, that the process should improve the Alnico's, else what would be the

point.

Pretty sure if the 77M's are up to snuff, you will be pleased.

[Langston]

Full bandwidth impedance measurements are the best way to verify driver motor health. Of course you'll need curves of known good drivers for comparison. A defective diaphragm will mask the results of an otherwise good motor (magnet). Acoustic measurements are not as reliable an indicator of driver health, but I'd do that too and compare to known good curves. Measurements will need to be done well (at as low a drive level as possible while maintaining reasonable S/N). Otherwise GIGO. Good luck!

 

God bless you and your precious family - Langston

Edited June 1, 2021 by Langston

[KT88]

This is the original text on remagnetizing from the company that will be getting my 44 year old K55V and my K77 in the next few days:

 

Magnetizing and re-magnetizing

As has long been suspected, magnets made of ALNiCo can indeed lose some of their magnetic force over time. 

This is particularly noticeable in a lack of brilliance, impulse and sound pressure as well as spongy and imprecise bass reproduction.

In other words, the speaker no longer sounds lively and lively.

The only remedy is to magnetize the speaker with a pulse magnetizer. In this process, the magnet is subjected to an extremely strong magnetic pulse lasting only a few milliseconds, during which the particles of the material are realigned and parallel on an atomic level. 

 

MAGNETIZING

However, a simple pulse is not sufficient for an optimal magnetizing result, which is why we put the magnets through a specific mode of re-magnetizing and de-magnetizing with different switching stages in order to reach their set point at the end with a targeted pulse.

For magnetizing, the chassis is clamped into the magnetizing coil and specially braced to absorb the repulsion of the magnetic fields caused by the magnetic pulse. Failure to do this can result in damage to the chassis and personnel (danger to life). For this purpose, special holders must be made to ensure the optimum fit of the magnet. Also covers, protective caps and diaphragms must be removed, since these can be damaged by the developing forces. 

Due to our special process, chassis with built-in voice coils (except diaphragms) can also be magnetized.

 

MAGNETECH

Manufacturer MAGNETECH (UK)

Impulse voltage 0-1000V (infinitely variable, electronically controlled)

Pulse current ca 1300A

Energy storage 48.000uF @1000V (Stepless switchable)

 

Possible magnetizing coils 165mm / 195mm / 240mm

 

Source:

https://www.lautsprecher-manufaktur.de/index.php/werkstatt/reconing-sp-1327173451

Since I have exchanged the diaphragms of the K55V last week against new ones, the company gets only the magnets. Otherwise they would have to disassemble the driver anyway.
The company was a support dealer and repair center for Electrovoice from 1981 until a few years ago. For that reason, they still have some of the good diaphragms for my Alnico K77. I'll let new diaphragms installed right there after they magnetize the Alnicos....

 

The company has a very good reputation in Germany among connoisseurs. The reason why they are no longer Electrovoice service center: Bosch had bought EV and kicked the company out because they are „too small“. These are the principles nowadays... 
But small almost always means good, and not bad, because otherwise "small" can't compete in the market. Similarly small and good like Crites, for example.

 

The reason for new diaphragms in the K77 is the same as in the K55V, pure curiosity, which has already been greatly rewarded in the K55V. For the same reason I let them magnetize the drivers.
I will report back in about three weeks when I get the parts back.

 

[AndreG.]

I´m looking forward to Your findings. Very interesting.