Checking a 123A-1 woofer

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08-18-2009, 03:18 PM
Eaulive

Checking a 123A-1 woofer

Hello.

I'm new on this forum and I looked a lot for the answer but I would need some more advice.

I have 4 L100 with 123A-1 drivers, one of the drivers is noticeably weaker than the others, when I mean weaker, I mean with the four drivers on the test bench with a pink noise generator it's really obvious, I'd say 2-3dB.

Now the DC resistance of the coils are 5.2, 5.1, 4.9 ohms on the 3 "good drivers" and the suspect one is 4.5 ohms.

Question: I know the Alinco magnets are afraid of high power and they get demagnetized, before reconing (expensive C8R2212) I would like to know if the magnet is good, preferably without cracking the thing open :D

A driver that got overheated could have a lower resistance and in this case I could have two problems, bad coil and bad magnet... is there a way to know? I don't want to drop a new cone in it to find out my problem remains :(
08-19-2009, 09:29 PM
boputnam

Quote:

Originally Posted by Eaulive

... is there a way to know?

Excellent question. I've had this same concern a number of times. but no-one (to my memory) has posted this question.

I recently left a terribly trashed D130F for recone and expected it would need re-mag. The technician spot-tested it by-hand with attraction for a ferrous implement - nothing quantifiable. Odd...

So, how is a motor's "gauss" meaningfully measured (sorry - perhaps a pedestrian parlance) and what are the spec tolerance(s)? When does an AlNiCo motor need remag?
08-19-2009, 11:07 PM
Mr. Widget

Quote:

Originally Posted by boputnam

So, how is a motor's "gauss" meaningfully measured (sorry - perhaps a pedestrian parlance) and what are the spec tolerance(s)? When does an AlNiCo motor need remag?

Ping Edgewound he has a gauss meter and could tell you what the proper readings are for various drivers.

I believe the only way to accurately measure the magnet is by placing a probe from a gauss meter into the gap, so a recone would have to follow. On the other hand, recharging a magnet is cheap and can be done with complete drivers so you can always recharge one to feel good about it.

Widget
08-22-2009, 01:51 PM
Eaulive

Quote:

Originally Posted by Mr. Widget

I believe the only way to accurately measure the magnet is by placing a probe from a gauss meter into the gap, so a recone would have to follow.
Widget

Obviously, and that's my dilemma. To recone or not to recone.
For now the defectime woofer is part of one of the back channels on my 5.1 surround system and it works. Not the way it's supposed to but hey, it's only surround sound :)
The front L100s that I use for music listening are perfect... at least as perfect as an L100 can be.

The other thing is, being in the Dominican Republic I would have to ship the woofer to the states to remagnetize so right there it's not worth it, I rather put my hands on a good 123A-1 sometime and that's it.

Thanks for the help!
08-22-2009, 07:17 PM
boputnam

Quote:

Originally Posted by Eaulive

...to ship the woofer to the states to remagnetize so right there it's not worth it, I rather put my hands on a good 123A-1 sometime and that's it.

Er, I hesitate to suggest this, but you should trial a 128H in that same hole (invert the wiring) and reconsider your affection for the 123A's. The 128H is one hella fine woof.

(hint: There are some posts comparing the two in that exact box)

The shipping of 128H's is definately worth it. :)
08-23-2009, 06:34 AM
Eaulive

Quote:

Originally Posted by boputnam

Er, I hesitate to suggest this, but you should trial a 128H in that same hole (invert the wiring) and reconsider your affection for the 123A's. The 128H is one hella fine woof.

(hint: There are some posts comparing the two in that exact box)

The shipping of 128H's is definately worth it. :)

I was thinking 2213H to pair with another one that I have so I can do two boxes the same, what do you think?

Plus I'm allergic to foam surrounds :barf:
08-23-2009, 08:44 AM
Earl K

"Motor Health"

Quote:

Originally Posted by Bo

So, how is a motor's "gauss" meaningfully measured (sorry - perhaps a pedestrian parlance) and what are the spec tolerance(s)? When does an AlNiCo motor need remag?

- What matters is the BL product ( ie; "gauss level" in the gap times the "length" of coil found working in the gap ) .

- "BL" will tell one if the motor section of any driver is performing up to published spec .

- Measure the Bl ( with somethig like "Woofer Tester 2" and compare it to JBLs' published TS specs for the transducer ) .

>< cheers :)