2ax woofer thunking

[Guest filedog]

I was finishing my repair to the voice-coil wire on one of my woofers, when I remembered to test it. I used the battery method described here, and it works fine. So, I figured I'd test the other one. When I apply voltage to push the cone out, it works, but when I disconnect from the battery, it returns with a thunk, sounds like the VC is bottoming out. Gently pushing by hand reveals plenty of travel, and no thunk, not even close to bottoming out. It moves smoothly, with no sign of rubbing. No loose parts when shaken, no sign of what's making the noise. Any ideas?

BTW, these are cloth surround, 6 bolt, round magnet woofers, they look all original, both are exactly the same.

[dynaco_dan]

>I was finishing my repair to the voice-coil wire on one of my

>woofers, when I remembered to test it. I used the battery

>method described here, and it works fine. So, I figured I'd

>test the other one. When I apply voltage to push the cone out,

>it works, but when I disconnect from the battery, it returns

>with a thunk, sounds like the VC is bottoming out. Gently

>pushing by hand reveals plenty of travel, and no thunk, not

>even close to bottoming out. It moves smoothly, with no sign

>of rubbing. No loose parts when shaken, no sign of what's

>making the noise. Any ideas?

>BTW, these are cloth surround, 6 bolt, round magnet woofers,

>they look all original, both are exactly the same.

Hi Gordon;

If you have the aluminum framed alnico magnet woofer.

I might suggest checking out the spider attachment to the frame.

Also check out the surround attachment to the frame.

I have seen numerous semi and mostly complete detachments from the frames as the original adhesive let's go.

You may try gently lifting the cone, evenly, from underneath the cone to better see if there is any detachment.

Just a thought.

[Guest filedog]

Vern, damn dude, you're GOOD! Yup, spider COMPLETELY detached, and there was a loose spot where the frame attaches to the masonite surround ring.

The pair has pretty close serials, but the other woofer was fine. Pulled the screens and epoxied 'em back, no more thunking : ) I'm REALLY glad I got that sorted before putting everything back together. Speaking of which, when you are working on a project like this, do you do a "dry run" with all drivers connected and installed, but no stuffing or caulk, and test, before final assembly? Thanks very much!

[dynaco_dan]

>Vern, damn dude, you're GOOD! Yup, spider COMPLETELY

>detached, and there was a loose spot where the frame attaches

>to the masonite surround ring.

>The pair has pretty close serials, but the other woofer was

>fine. Pulled the screens and epoxied 'em back, no more

>thunking : ) I'm REALLY glad I got that sorted before putting

>everything back together. Speaking of which, when you are

>working on a project like this, do you do a "dry

>run" with all drivers connected and installed, but no

>stuffing or caulk, and test, before final assembly? Thanks

>very much!

Hi again Gordon;

Care must be taken with this type speaker system, Gordon.

Being acoustic supspension, the woofer can be damaged or destroyed real easy, when not loaded down with the sealed enclosure.

I would have used the same technique as installing a new surround, with the spider.

The woofer of course should be sitting on the front of the enclosure being careful not to sit it on the mid or tweeter.

Knowing that the surround edge is soldly mounted still, I would have glued the loose portion first.

I would have left that to set for a day at least.

With the woofer facing upwards, I would have used a very, very low level Stereophile CD test tone, or signal generator, of around 100 Hz, on repeat, and tried to see how the spider centers itself freehand first.

A battery is not adequate for this type of operation at all.

You'll hear a growl as you touch the side of the voice coil.

When you have a feel of where it is to be centered, you can glue it down.

As the glue is setting, at first, try to slide it ever so gently back and forth from the center pole, in both directions, listening for this gentle growl.

As the glue is setting up be mindful of the setting up time, 5 - 15 minutes is all usually, and check that the spider lays flat, as best as possible.

When you are certain the the spider is centered, turn off the test signal and let the glue setup, about 24 hours again.

Check the tightness of the tweeter and mid range driver screws, the next night, re-seal the drivers if they appear poorly sealed or not at all.

You might just give a very low level music test, very, very low though.

Do not be tempted to play regular music, just yet.

Now re-seal the woofer opening, re-bolt the woofer in the opening, tightening enough that you can feel and maybe even see some putty oozing slightly from around the rim, if it is still soft.

You should be able to stand the speaker up and play music with it now.

[Guest filedog]

Vern,

thanks for the info. All drivers are out at this time. Well, it doesn't seem to rub, so hopefully it's ok, I'm learning as I go : )