pics of AR3A voice coil Help

[roundhome]

Hello got this woofer and it pops when I play it new foam and its centered no rub 2.9 ohm reading?

Any ideas?

Thank you

Jim

[Carlspeak]

Is the spider flat or sagging when the woofer is laying on its back? A sag could cause it to bottom out making the pop sound.

Sagging spiders are usually associated with a very floppy suspension. If so, you'll need a recone job.

[johnieo]

Hello Jim:

I obtained a pair of AR-3 cloth-surround woofers last year to use in reconstructing a pair of AR-3a Limiteds. They measured well, in fact their Fs was very low, around 11 Hz. (That should have been a clue that something was wrong!) When played at low levels they sounded fine, but when fed organ music from an instrument with 32' pipes, they hit the back plate. After recognizing the clicks, the amp was quickly silenced. We laid the woofers flat, and set a straght edge across the top of the basket frame so that it was raised on small blocks above but not touching the surround. Using a small scale, we measured the distance to the dust cover, then depressed the cone to the back plate and measured it again. the difference was 3/8". It should have been 1/2". That's an easy way to diagnose sagging spiders.

Since I wanted to preserve the cloth surrounds, I asked Bill LeGall to retain the surrounds, cone and voice coil and replace only the spiders. Of course there are none available today as compliant as the originals, but he had a pair of spiders that were quite soft. The units now perform beautifully.

Hope this helps,

Cheers,

[Carlspeak]

Here are two pictures of an AR3a woofer with a badly sagging spider and the resultant collapsed VC in the second pic from bottoming out. The picture of the whole woofer shows the sagging by the pulling down of the surround, which in this case was not attached to the frame at the time of the picture. The AR3a restoration document on pg. 5 shows other examples of collapsed VC's caused by back plate bumping.

I believe spider sag is caused by a deterioration of the spider's phenolic binder system over time. The 3a woofer cone is quite heavy. When the foam surround fails, the spider is then the only thing left to support the cone's weight. 3a woofer spiders were relatively loosely bonded to start with by design in order to meet the low Fs requirements. I have also seen similar collapsed spiders on Advent woofers.

Roundhome's pictures show the beginning of VC failure by the faint white line on plane with the VC vent holes. That is the weak area of the VC in the plane it travels in. My pictures show the eventual collapse if music is played at too high a volume with a sagging spider.

So, a warning to those out there who have scored some 3a's or 3a woofers. Before you power them up, be sure to check the spider to ensure it's relatively flat.

[Pete B]

Hello got this woofer and it pops when I play it new foam and its centered no rub 2.9 ohm reading?

Any ideas?

Thank you

Jim

Hi Jim,

Just thought I'd mention that the VC windings are clearly visible through the

gap in the former in your second photo on the right. It is easy to compute

how much of the coil should be above the top plate, at least from a theoretical

point of view. Perhaps some of the refoamers who remove the cap could also

measure known good drivers to determine how they were actually constructed.

This is an easy way to check the VC centering, however, we have to remember

that the suspension will deflect due to the weight of the cone, and more so with

a weak spider. It may be best to measure cone up and cone down and take

the average, or do it in the actual operating position.

Setting the VC slightly offset can help reduce distortion due to the asymmetry

in the motor, I don't know if AR did this in the 3a woofer.

[Carlspeak]

The voice coils I use to recone 3a woofers with ceramic magnets have windings that are 1 1/8 inches long. Centering the windings on the 1/2 inch thick front pole plate is normal procedure. It puts the top of the windings about 5/16 ths of an inch above the pole piece (assuming it is flat with the pole plate). That looks to be about what's shown in roundhome's second pic.

[roundhome]

The voice coils I use to recone 3a woofers with ceramic magnets have windings that are 1 1/8 inches long. Centering the windings on the 1/2 inch thick front pole plate is normal procedure. It puts the top of the windings about 5/16 ths of an inch above the pole piece (assuming it is flat with the pole plate). That looks to be about what's shown in roundhome's second pic.

You know what is funny about this bad woofer bought off ebay. is that my children could tell it was bad and the guy tried to buy a pos feedback .said I will send you 20 but only after I gave the pos feedback first .he had also sent a AR 5 mid in place of a AR 3A mid I had paid 75 for the both his buy now price and he gave me a neg feedback. because he could not do things correctly and can't admit he screwed up. that is fine with me makes other look to see why someone with such a good record gets a neg. I'm proud of the three negs I have:) any way just venting about ebay it takes all kinds to run this world.buy th way he even hung up on me twice why trying to solve this. it really is a buyer be ware world. I did get a new voice coil and will get it fixed some times you have to eat someone mistakes

any if you buy off ebay take your chances

have a good day all and remember this is just a hobby