AR3a/LST tweeter repair claim

[Mexicomike]

I ran across this message in the audio karma archives:

I have owned a pair of LSTs since the 70's and blew out all the tweeters twice (both times due to an ultrasonic amp oscillation I did not know about). I've gotton pretty good at rewinding the voicecoils and remounting the domes after doing it twice with (8) tweeters each time = 16 tweeters.

I don't need any tweeters repaired but I was wondering about this statement since info here indicates it is not a fixable item. I am NOT trying to set up an argument with folks here who know orders of magnitude more than I do about this subject. But I'm wondering about this gentleman's statement.

The thread containing the above is at: http://www.audiokarma.org/forums/archive/i...p/t-112200.html

[RoyC]

I ran across this message in the audio karma archives:

I have owned a pair of LSTs since the 70's and blew out all the tweeters twice (both times due to an ultrasonic amp oscillation I did not know about). I've gotton pretty good at rewinding the voicecoils and remounting the domes after doing it twice with (8) tweeters each time = 16 tweeters.

I don't need any tweeters repaired but I was wondering about this statement since info here indicates it is not a fixable item. I am NOT trying to set up an argument with folks here who know orders of magnitude more than I do about this subject. But I'm wondering about this gentleman's statement.

The thread containing the above is at: http://www.audiokarma.org/forums/archive/i...p/t-112200.html

This is a very old discussion, and scratching below the surface of such claims has never produced a re-built 3a tweeter. It is the "remounting the dome" part that would be very interesting to witness.

Roy

[Pete B]

This is a very old discussion, and scratching below the surface of such claims has never produced a re-built 3a tweeter. It is the "remounting the dome" part that would be very interesting to witness.

Roy

You probably remember that I repaired an AR 3/4" tweeter from an AR-11,

however this dome has a more conventional suspension as compared to

the "globs of foam" suspension on the earlier 3/4" tweeter.

I commented about the foam when I was checking out a pair of AR-2ax's

in one of my first threads on this forum. What I didn't notice is that there is

also a clear, cellophane looking layer where a normal tweeter's suspension

would be. It seems to me that this layer is probably there to keep foreign

matter out of the magnetic gap as I doubt that it provides much restoring

force. I seem to remember the solid lead in wires being routed through the

globs of foam which would help to keep the flex evenly distributed across the

wire to reduce breakage. What do you think Roy? Does this sound reasonable

from your experience and research as to the intent of the design?

[RoyC]

You probably remember that I repaired an AR 3/4" tweeter from an AR-11,

however this dome has a more conventional suspension as compared to

the "globs of foam" suspension on the earlier 3/4" tweeter.

I commented about the foam when I was checking out a pair of AR-2ax's

in one of my first threads on this forum. What I didn't notice is that there is

also a clear, cellophane looking layer where a normal tweeter's suspension

would be. It seems to me that this layer is probably there to keep foreign

matter out of the magnetic gap as I doubt that it provides much restoring

force. I seem to remember the solid lead in wires being routed through the

globs of foam which would help to keep the flex evenly distributed across the

wire to reduce breakage. What do you think Roy? Does this sound reasonable

from your experience and research as to the intent of the design?

I agree with your take, Pete. According to Tom Tyson, the clear coating is a butyl rubber compound meant to protect the gap, and the foam is the suspension. It was manufactured using jigs, and there were many rejects! I believe that the clear coating is acting more like the suspension these days, as that hasn't degraded as much as the foam has . I imagine power handling, as well as frequency response, varies quite a bit from tweeter to tweeter today, and that the original specifications are mostly compromised.

Roy

[Pete B]

I agree with your take, Pete. According to Tom Tyson, the clear coating is a butyl rubber compound meant to protect the gap, and the foam is the suspension. It was manufactured using jigs, and there were many rejects! I believe that the clear coating is acting more like the suspension these days, as that hasn't degraded as much as the foam has . I imagine power handling, as well as frequency response, varies quite a bit from tweeter to tweeter today, and that the original specifications are mostly compromised.

Roy

Thanks for confirming Roy. I have to wonder how they came up with this method

for construction?

Pete B.

[KlausDK]

According to Tom Tyson, the clear coating is a butyl rubber compound meant to protect the gap, and the foam is the suspension.

I have had a set of backwired AR-3a tweeters repaired by the loudspeaker magician Sinisa Rankov in Belgrade (Sinevoice.com). He has previously repaired a set of AR-11/10Pi tweeters to my great satisfaction.

I have had one of the repaired tweeters mounted in my AR-3a Improved, and it worked fine, couldn't detect a difference in level and sound on a brief listenning session. I took the out again, since he has not sealed the gap around the dome/coil. I wonder if anybody knows of a liquid transparent butyl rubber substance, that could be used for the purpose of sealing the gap?

I have enclosed a picture, my camera does not allow me to get real close, but I hope you can see some details anyway.

BRgds Klaus

[genek]

I don't need any tweeters repaired but I was wondering about this statement since info here indicates it is not a fixable item.

In 30 years as an engineer I learned that most any task that is "impossible" for most people can be done by someone, somewhere. I've known a welder who could repair pot metal castings, and seen an entire line of chormatography instruments depend upon a lightpipe made by repeatedly hand-dipping a single strand of optical fiber in liquid plastic, a feat that could be performed by exactly two people in the entire world. So I would say that yes, it is conceivable that somewhere in the world there is someone who has through a combination of skill, practice and genetically-inherited dexterity managed to develop the ability to rebuild one of these. Does that mean that you or I could ever hope to do it as well? Probably not a snowball's chance in Hell.

[Mexicomike]

Though totally unrelated to speakers but related to the above, I once saw a welder take an oxy-acetylene cutting torch and blow a seized, broken off head-bolt out of a Mopar 426 Hemi cylinder casting without damaging the threads in the casting. A quick run of a thread chaser and it was ready for the new head bolt. I would have (and did) call that impossible before actually seeing it done.

There are true "artists" in just about any field. As you pointed out, FINDING them can be difficult; DUPLICATING their skill is nearly impossible.