A 416 dilemma. What to do?

[Todd W. White]

I'm working on this issue, as I think I mentioned, and plan to get a complete answer out shortly.

Thanks for your patience.

[Panomaniac]

Thanks Todd.

Just back from Lone Star Audio Fest in Dallas where I had a lovely pair of 605A drivers that were reconed and recharged by GPA. More on that tomorrow.

This thread has bifurcated into "what to do with them?" and "why didn't this work?"
The second is actually more interesting. Who knows how many folks actually test their drivers after rework? So we have no idea how common - or not - this problem may be.

[Altec Best]

Welcome Back Pano, Please tell me you have some pictures Like to hear all about the fest. :thankU: Regards ~ AB

[Todd W. White]

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]

Great info Todd. Thanks.

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

[Todd W. White]

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]

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.