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View Full Version : Reconing Alnico Magnet Speakers



wallstdrifter
08-01-2008, 01:40 PM
Alnico magnets cannot be re-charged or tested with cone on:banghead:. Their half life is 100 yrs giving many of them a 25% natural loss, I will send my speakers to Orange county speaker because they re-magnetize (re-gauss) at time of re-cone or new diaphram:applaud:. Thoughts?

Robh3606
08-01-2008, 01:43 PM
Do they meassure the gap flux before and after?? How do they know they have it right??

Rob:)

wallstdrifter
08-01-2008, 01:48 PM
They are factory authorized. It's all BS :barf: without the re-guass. The small shops talk their way out of it.


Do they meassure the gap flux before and after?? How do they know they have it right??

Rob:)

Robh3606
08-01-2008, 02:33 PM
Factory Authorized doesn't mean much. The question still is do they check the gap flux to see if they need it in the first place and do they check them after to make sure that the flux levels are in spec?? Because if they don't it's all BS

Rob:)

toddalin
08-01-2008, 02:58 PM
Do they meassure the gap flux before and after?? How do they know they have it right??

Rob:)

The concept is that the magnet will only hold so many gauss when it saturates. They "blast" the magnet with enough gauss to saturate it. No measurements are typically performed to determine "they got it right."

One can measure the BL factor as an indicator of the magnets strength.

That said, here is my experience.

I bought three Alnico 2205s on the 'Bay with the intent of having them reconed as 2235s and replacing the 130As in my L200 cabinets. I was using N1200/N7000 crossovers with a pad on the mid (makes a world of difference with the N1200).

OCS did the recone and recharge on the 2205s. I brought them home and installed them and I was extremely displeased with the loss of midrange and intelligability. :barf:

OK, I figured that 1200 Hz was too high to crossover the 2235s. New 800 Hz crossovers were designed and constructed based on the L200B circuit but to include an 075. Cost was about $150 each for three (~$450 total) using high quality components and by-pass caps. Things had to improve drastically!;)

Well, no, not much really. The mids were still soft in the male vocal range. :biting:

Grumpy suggested that the magnets (though supposedly just recharged) maybe weak acounting for the soft area. Grumpy came by with Woofer Tester 2 and we pulled a woofer and ran the tests. WT showed a BL of ~18.5 whereas JBL specs call for this value to be >20. For kicks, Grumpy also brought a 2235 and its BL was on the order of 21-22.

I called OCS and explained the situation and they said they didn't understand what could be going on, but bring them back and they'd recharge them again for free. :applaud:

I did and they did while I waited. :D

I reinstalled them, and still thought the lower mids were soft. Grumpy came by again and we again tested the woofer. This time the BL was >22.5, so the woofers are fine, at least in this respect. WT2 passed the woofer with the same specs as a factory 2235.

I changed the crossovers to let the woofers go a little higher by modifying the Zobal network and this did help some. Still, I feel that the male vocal is soft. (I miss the 130As in this respect.) Room compensation eq pretty much makes up for it, but it still bugs me.

Robh3606
08-01-2008, 03:27 PM
OCS did the recone and recharge on the 2205s. I brought them home and installed them and I was extremely displeased with the loss of midrange and intelligability. :barf:

Oh so in other words they zapped them the first time and Grumpy was able to confirm that they were not right. They took them back and redid them and then they were right. Is that correct??

So like I said, are they checking them before and then after?? Seems that they are not checking them after if I got the story straight and why should you pay to have them remagged if they don't need it??


The concept is that the magnet will only hold so many gauss when it saturates. They "blast" the magnet with enough gauss to saturate it. No measurements are typically performed to determine "they got it right."

They got yours right the second time. If you are not using some method to check to to see if it's right in the first place how do you know that the magnet structure was indeed saturated?? Seems to me that the problems you had proves my point that they should be checking either gap flux or BL to verify it's right.

Rob:)

Robh3606
08-01-2008, 04:45 PM
The concept is that the magnet will only hold so many gauss when it saturates. They "blast" the magnet with enough gauss to saturate it. No measurements are typically performed to determine "they got it right."

I for one don't know if that's the case. Especially with woofers. If you overcharge the magnetic assembly you will over damp the driver and loose low end response. I doubt they run them saturated unless the structure by design can only hit that magic number with a full charge. Not sure that's so. I can see that with a compression driver. It would be nice if a driver manufacturer like Steve Schell would jump into this.

Here take a look at this quote and you can see where I am comming from.

http://www.lansingheritage.org/images/jbl/specs/home-speakers/1974-l45/page3.jpg

It's from the Flair brochure. There is a statement about increasing the flux in the midrange driver to match the woofer efficiency. The driver would be an L100 midrange or and Le-5-2 with a new dash. Have to see if it's in the matrix.

Rob:)

toddalin
08-01-2008, 05:03 PM
Oh so in other words they zapped them the first time and Grumpy was able to confirm that they were not right. They took them back and redid them and then they were right. Is that correct??

So like I said, are they checking them before and then after?? Seems that they are not checking them after if I got the story straight and why should you pay to have them remagged if they don't need it??



They got yours right the second time. If you are not using some method to check to to see if it's right in the first place how do you know that the magnet structure was indeed saturated?? Seems to me that the problems you had proves my point that they should be checking either gap flux or BL to verify it's right.

Rob:)


That's the jist of it. My question was did it ever get done the first time or did someone think someone else did it? I was assured that it did. :hmm:

grumpy
08-01-2008, 05:06 PM
I think you stored them face up and some gauss leaked out... ;)

Robh3606
08-01-2008, 05:10 PM
I think you stored them face up and some gauss leaked out... ;)


LOL like the magic smoke??

Rob:)

wallstdrifter
08-01-2008, 06:06 PM
OT- Guys, got to fly, real quick , just got my K Citation 17 Pre-amp back from repair and clean, pulled my NIKKO GAMM30 preamp and VOILA...My L-65 speakers sound like new when I bought my first pr in WIESBADEN GERMANY back in 1978. Wundesrchoen, Ya Ya!

Looks like old pre-amps can sound stale and need a good service. My filters & such repair cost USD 200.00. Worth every penny. The HK Citation 16A Amp cost USD250.00 for new caps & such. SUCH SWEET SOUND! I AM FLOATING
ON AIR! NO MORE SPEAKER SURGERY! NO BASS AND TREBLE KNOBS DISTORTION (my HK 17 only has volume and balance knob controls.) THIS IS PURE!

John
08-01-2008, 08:52 PM
The concept is that the magnet will only hold so many gauss when it saturates. They "blast" the magnet with enough gauss to saturate it. No measurements are typically performed to determine "they got it right."


I will back Todd up on this, the magnet will only take as much as it can till it saturates. with the cone in place I do not believe the guass can be measured.:blah:

How to be sure it is fully saturated. Well if the magnetizer is working up to snuff, hit it twice and the woofer or driver is good to go.:bouncy:

This info was passed on to me by someone that has been doing this for about 30 years, so I think he knew what he was talking about. ;)

Robh3606
08-03-2008, 08:02 AM
How to be sure it is fully saturated. Well if the magnetizer is working up to snuff, hit it twice and the woofer or driver is good to go.:bouncy:


And if it's not?? Look at all the grief that Toddalin went through. He needed a friend with test equipment to figure out for sure what the problem was. All I am asking if they verify the job was done right. Some times people have a bad day or equipment malfunctions.


This info was passed on to me by someone that has been doing this for about 30 years, so I think he knew what he was talking about. ;)

Well that's great but from personal experience the devil is in the details. You don't know if JBL ran these full up or partially demaged them to get them into spec. Maybe your right, one of us is. I would like to know which one simply for posterity.

Anyone on the forum do the alnico magnet charging at JBL or know how they did it??

Rob:)