Dynaco A25 Rubbing

[M. Ackermann]

Recently purchased a pair of Dynaco A25 speakers from the original owner.
Great price, came with all the original paperwork and receipt of purchase, and are about as clean as can be for 50 year old speakers. Owner never even took the grills off.

After inspection, they have been well cared for, but...there is a little rubbing when I flex one speaker, and after tapping the woofer, it is flat about a third of the way around. It does not ring flat all around, just on one side of a single woofer.

This does not seem to make a difference in sound. And maybe, this isn't even a problem. I do not listen to music very loud so maybe I shouldn't even fuss with them. I am just concerned it may get worse.

Advice is appreciated, thanks.

 

[Dadbar]

Unscrew the woofers and rotate them 180 degrees then screw them back on. See if it still rubs.

 

[elitopus]

So can you hear the rubbing when playing music, or just feel it when pushing the woofer with your hand? If it’s the latter, stop pushing the woofer with your hand

 

[M. Ackermann]

So can you hear the rubbing when playing music, or just feel it when pushing the woofer with your hand? If it’s the latter, stop pushing the woofer with your hand

Oh, I was easy on it. Played with it some after tapping the woofer and heard a thud. Definitely not messing with it. But, I do plan on recapping them, and when I do, just thinking I’d be proactive.

 

[elitopus]

I’ve had speakers where the clearance around the voice coil was so tight that it would rub if pushed by hand, but wouldn’t rub with music. I think you can never really push the cone In evenly by hand.

Just curiously, what are you listening for with the cone tap, and what does it mean? Like if you tap it and it sounds flat or dull in one spot, what does that tell you?
I have an uncle who taps the cone of a speaker to tell if its “good”. I don’t know why, and I should probably ask him what he knows that I don’t

 

[Jereostereo]

I know this is an old thread, but just in case someone happens upon it with a rubbing voice coil on an A25 woofer, this was my solution. First I carefully peeled the outer edge of the rubber surround from the basket. If you take it slow and carefully pry up around the edge of the rubber with a small screwdriver to get it started, you can get underneath the surround and gently peel it up all the way around the basket. The glue is still holding but it’s getting weaker, so that makes this possible. At that point you can re-center the cone to eliminate the rubbing. When I did this, it required trimming away a little bit of the outer edge of the surround to make room for it to move slightly in the direction it needed to to re-center the cone. After that, I just re-glued the surround with rubber cement and two hours later it was ready to use. Hope this helps.

 

[kwayde]

I know this is an old thread, but just in case someone happens upon it with a rubbing voice coil on an A25 woofer, this was my solution. First I carefully peeled the outer edge of the rubber surround from the basket. If you take it slow and carefully pry up around the edge of the rubber with a small screwdriver to get it started, you can get underneath the surround and gently peel it up all the way around the basket. The glue is still holding but it’s getting weaker, so that makes this possible. At that point you can re-center the cone to eliminate the rubbing. When I did this, it required trimming away a little bit of the outer edge of the surround to make room for it to move slightly in the direction it needed to to re-center the cone. After that, I just re-glued the surround with rubber cement and two hours later it was ready to use. Hope this helps.

I have one that's similar to this. Was thinking about listing it along with a few tweeters to anyone who wanted to see if they could get them working. After reading your reply I think I'll give it a shot to see if I have success as well.

 

[wmgwizard]

It's not uncommon for a driver to "sag" after so many years. Gravity is a constant force and after a while old stuff tends to sag.

The more common remedy is to rotate the woofer 180° every 10 years or so.

Separating the surround from the frame, trimming and re gluing just opens the door to potential damage / destruction and should only be used as a last resort.

 

[kwayde]

It's not uncommon for a driver to "sag" after so many years. Gravity is a constant force and after a while old stuff tends to sag.

The more common remedy is to rotate the woofer 180° every 10 years or so.

Separating the surround from the frame, trimming and re gluing just opens the door to potential damage / destruction and should only be used as a last resort.

Rotating the driver 180 degrees as prevention would be ideal but I think the majority don't do this. Then folks like me end up with a driver that needs attention.
Either an attempt to repair is done or it gets thrown away. It's unusable as it sits so it's time to see if it can be salvaged.

Your last sentence applies to drivers with foam surrounds that decay as well. They are repaired quite often with great results.

 

[wmgwizard]

Replacing rotted foam is a common repair as usually the only other option is replacement of the entire driver.

A-25's have rubber surrounds that typically do not deteriorate like foam. Risking damaging a driver when other proven methods are available is not advisable.

 

[elitopus]

So what are the other options? Let’s say you buy a pair of A25 and the woofers have never been rotated. Let’s say one of the woofers rubs, and even if you filp it 180 it still rubs. What’s the fix?

If you rotate the woofer and let it sit for (what like a few years?) the woofer will sag back the other way. Or you could do the surgery mentioned above and have (probably) a working woofer right away.

Besides replacing the woofer I don’t see any other options. Obviously prevention is the best option. But that’s not always possible.

 

[wmgwizard]

If after rotating the woofer the rubbing does not resolve, then more drastic measures would be justified; they just shouldnt be the first resort.

 

[kwayde]

The woofer from the A25 isn't very heavy to begin with so I don't see the weight of the cone being much of a factor in it's failure.

 

[elitopus]

I agree you should rotate it first to see if that fixes it. @Jereostereo didn’t mention if he did that.

 

[wmgwizard]

Rotating the cone is not usually an instant fix, it could take a few days or weeks to begin to offset years of gravity.

I am not suggesting this is an absolute cure, nor is it the only possible cure. Rotating the driver is free, easy and non destructive; that's why it was recommended.

The weight is irrelevant for the most part. There is still the constant "pull" of gravity, lighter weight just means it will take longer for gravity to take affect. The spider that supports the rear of the cone and voice coil can weaken over time and allow misalignment of the voice coil.

 

[kwayde]

Rotating the cone is not usually an instant fix, it could take a few days or weeks to begin to offset years of gravity.

I am not suggesting this is an absolute cure, nor is it the only possible cure. Rotating the driver is free, easy and non destructive; that's why it was recommended.

The weight is irrelevant for the most part. There is still the constant "pull" of gravity, lighter weight just means it will take longer for gravity to take affect. The spider that supports the rear of the cone and voice coil can weaken over time and allow misalignment of the voice coil.

Why doesn't that happen with foam surrounds on heavier coned drivers?

 

[wmgwizard]

It can but the foam usually rots away first and part of the re foam process is re centering the voice coil.

 

[kwayde]

It can but the foam usually rots away first and part of the re foam process is re centering the voice coil.

Foam will last for forty years before it fails yet will still hold the cone in the correct position. I guess it all depends on the weight of the cone material.

The A25 driver I have doesn't rub at it's most inward position. When I pull it towards it's most outward position is when it rubs. It seems to be centered good yet, no sag.

Edit: Decided to operate on the patient. Turns out the coil wasn't glued well enough to the bobbin and it just fell off into the bottom of the gap making a bird's nest.