A 416 dilemma. What to do?

**Todd W. White** · May 19th, 2010, 12:14 PM

OK - I talked with Jerry Hubbard, who was Head of Acoustic Research at Altec for over ten years, and here's what he says:

He says we first need to find out if the magnet is charged with the proper polarity. It is possible that it could have been charged in reverse. This happened, he said, at Altec all the time. There were instances when they had to go back and remagnetize entire production runs because they were charged with the wrong polarity.

The type of magnet recharger that Altec used (and Bill has) has the ability to reverse the polarity of the charge given to the magnet. When recharging an Alnico magnet, Jerry says, you set the remagnetizer one way, and you REVERSE it for Ceramic speakers. This is done because of the difference in the magnetic structures between Alnico and Ceramic. When you're done, the performance will be the same, but the procedure for getting there is different.

That said, he suggests you perform a simple test to see if the magnet is charged with the proper polarity:

1. Take the offending speaker and place it face up on a table.

2. Take a 9-volt (or 1.5-volt - whatever you have) battery, and touch the negative terminal of the battery to the negative terminal on the woofer, and the positive terminal on the battery to the positive terminal on the speaker for just an instant.

3. Observe the movement of the cone. Tell us which way it moves.

Once we know this, we can proceed.

**Panomaniac** · May 19th, 2010, 03:05 PM

Great info Todd. Thanks.

I tested. Both mine appeared reversed.
(positive voltage on red post = diaphragm moving toward rear of driver)

**Todd W. White** · May 19th, 2010, 05:19 PM

OK - Jerry said that if the cone moves away from the listener (in this case, toward the magnet), then they've been recharged with the polarity reversed and will need to be demagnetized, then recharged with the correct polarity.

With regard to remagnetization, Jerry said that any Alnico magnet that has partially lost it's charge can be successfully remagnetized without being discharged to zero first. In fact, he was adamant that discharging one while there was still some magnetism left in it was totally unnecessary.

Further, he said that if, after remagnetization, the flux density in the gap should be measured to see if it is within specification tolerances, then it should be reconed and the T/S's should be carefully measured to see if they are within spec as well.

My suggestion is to:

1. Send the woofers back to GPA.
2. Tell Bill what you've found and ask him to recharge them with the correct polarity and measure the flux density once he's done.
3. Recone them and measure the T/S's to make sure they are within specifications.
4. Include a record of the above measurements when they are returned to you.

I might add that this could have easily been a simple mistake that wasn't really anyone's fault - it just happened - and that the sooner it's cleared up, the better.

I hope this helps!

**Panomaniac** · May 19th, 2010, 06:33 PM

Hey Todd. Looks like we are making progress, thanks.

I'm not sure that I want to pay for another recone of these drivers plus all the shipping. =(
Having already done that. Will have to think about it. It's a chunk of change.

**Todd W. White** · May 19th, 2010, 07:51 PM

Let me see what I can do about that - just send them on in...

**robertbartsch** · May 19th, 2010, 08:32 PM

How would the proper polarity in a pair, not just one, of woofers get reversed?

If the polarity is reversed, why would another re-cone be necessary? Is this because a polarity reversal requires dis-assembly of the motor?

Is there a way to test the motor polarity before re-coning?

Thx...

**Altec Best** · May 20th, 2010, 10:01 AM

Originally Posted by Panomaniac

Hey Todd. Looks like we are making progress, thanks.

I'm not sure that I want to pay for another recone of these drivers plus all the shipping. =(
Having already done that. Will have to think about it. It's a chunk of change.

Well having said that I think the responsibility lies on Bill's shoulders.After all you sent them in for a re-cone and remag wouldn't that be Bill's responsibility to make sure they were re-charged correctly.Bill's good people I think you will be OK Pano

**Panomaniac** · May 20th, 2010, 12:30 PM

Yes, I'm sure we will get this all sorted out just fine. Todd has found us some very useful information. A learning experience for all!

Now I just gotta see if I still have the boxes....

**Todd W. White** · May 20th, 2010, 02:24 PM

They have to be un-coned, then magnetized correctly, then re-coned.

What happened at Altec, Jerry Hubbard says, is that the capacitor-based remagnification unit has the ability to be switched from polarizing the magnet one way to the other. With Ceramic, you charge it with the polarity set one way, and the reverse for Alnico.