Blown AR4x tweeters and a repair attempt…

[tourmax]

I've recently had a set of AR4x's blow their tweeters. They meter as an open circuit.

So now I’ve got to replace those tweeters if I want this particular set of AR4x's to sing again. Finding AR anything around here is as hard as finding a 2lb gold nugget and its probably going to be a while until I will run across 2 more on ebay or the like.

New style replacements are an option, but I've got time to wait for originals to show up. I just pressed a second set of AR4x's (that were waiting a restoration) into service.

So, I figure I’ve got not much to loose to try and pull these apart. Can’t make them any more “dead” than they already are. They'll either get stronger after the operation or die on the operating table. Not much to loose other than a bit of my time.

Out on to the desk they go.

First thing is to lift the glued edge. But I need to be very gentle so as to not destroy those cones and their integrated surrounds.

About 2 hrs of gentle work with a fine, thin hobby blade and dabbing IPA with a cotton bud lifted the edge.

Talk about slow and nerve racking! Fraction of an inch at a time!

But the edge is now lifted. Interestingly enough, its not open space behind the tweeter cone but a fibrous like insulating material.

I guess AR thought they needed more control over the cone movement than just a closed back. To be honest, these are the first tweeters I've ever opened so this may be a common practice.

There's no “tinsel wire” like you would see on larger speakers so I’m guessing it comes out the side through the middle of the terminals. Seems to make sense as the middle on the terminal blocks have solder down in the middle “holes” and there's no other evidence of the wires on any other part. 

I actually gave re-flowing the solder a try in case it's a cold solder joint causing continuity loss, but no dice. They stay dead open. Looking more and more like it's the voice coil shorted internally. I may have to take a try at rewinding it and see what I get. I sometimes rebuild motors by rewinding the coil, so it's not a new thing to me. It's just going to be much finer wire. OR maybe it won't be "do-able". At least I'll find out one way or the other.....

And that's where I left them for the day. My nerves are just shot from lifting the first surround. Tomorrow, I’ll see about removing that solder and if I can get the cones/coils out.

This is not a place to be “rushed”. These parts are small, fiddly, old and easily broken.

And my nerves really need a break right now…

[Anthonyv62]

After being unable to save the original tweeters from a pair of AR4X or find a decent pair of original replacements, I gave up and settled on Parts Express replacements. Except for my son recently telling me that they sometimes sounded overly bright (introducing him to the rear adjustment knob helped tame that problem) I actually like the Parts Express replacements. Still wish I could find a nice pair of original 4X tweeters though...😉

[tourmax]

Well well.

I didn’t get to do a lot with the tweeters today. Busy busy.

But sitting in the music room at the end of the day enjoying a tea and the one tweet I’ve lifted the cone on is right in front of me. 

I grab a small thin probe and work the yellow insulating material back so I can see the terminals inside. One has the voice coil wire right to the inside part of the terminal. I gently move the material around a bit and find the other terminal and its plain to see the voice coil wire has detached from the terminal. Either broken or perhaps it “burnt back” a bit.

At least that gives a little hope the coil on the tube is still serviceable. Perhaps I’ll be able to reconnect the broken voice coil wire back to the terminal.

Will be quite a bit of fiddly work to do that if I don’t completely remove the cone. I may make an attempt, but am wary of getting even a fine tip on the soldering iron that close to the cone (even on low heat).

I might be able to save these tweeters after all….
 

 

 

[ReliaBill Engineer]

Last pair of 4x tweeters I worked on had the same issue. I used an Exacto knife, new blade, to cut the glue holding the paper cone edge. Then removed the solder from both terminals. Desoldering braid worked for me. Then I cut one remaining lead. Lifted out the cone+ voice coil. Checked coil condition and continuity. Both were good. I soldered extension wires onto the originals. Threaded the extensions into the terminals. No solder yet. I then ran a small bead of thinned black RTV under the edge of the cone, centered it. While still moveable, I used a 1.2 volt battery cell to energize the leads, to center the VC. Then pressed the cone edge into the glue all around. I rechecked the centering by using the battery cell.  No scraping sound. I let the glue cure. Then soldered the wires to the terminals. 
 

Pretty much what I do for repairing dome tweeters also. 
 

I like using thinned RTV because it’s reversible. If I find that I goofed, an Exacto blade can be used to cut the glue and start over. 
 

AR was fond of using fiberglass batting to damp mids and tweeters.

[tourmax]

Thank you. Thats very helpful.

[RickB]

Parts Express latest catalog has the replacement tweeters on sale for $17.98 each.

[ReliaBill Engineer]

I’m thinking of buying a pair to play around with. Harshness comes from distortion. So have to reduce the distortion.

[RoyC]

1 hour ago, ReliaBill Engineer said:

Harshness comes from distortion.

Not necessarily. In this case it probably has more to do with its inherent frequency response and behavior with the existing crossover.

[ReliaBill Engineer]

Duplicate post…

[ReliaBill Engineer]

On 3/7/2024 at 5:16 PM, RoyC said:

Not necessarily. In this case it probably has more to do with its inherent frequency response and behavior with the existing crossover.

Inherent frequency response and behavior *is* the distortion, if it’s in the pass band. A crossover can limit distortion if it occurs below or above the XO frequencies.

Even with the crossover, there shouldn’t be distortion. Rather, it should have a smooth roll off at both ends of the FR. And an inherently smooth pass band.
 

The AR-2ax mids are harsh. AR really liked using fiberglass batting to damp distortion.

I bought 2 of the 8 ohm PRTs to play around with. I don’t know if I’ll have any more luck than you did smoothing them out. But it will be a fun learning experience.

I’ll test them using my Polk speakers, since it’ll be easy to adjust the mounting, and I have impedance adjusting resisters, and I’m very familiar with the original sound of these Polks. Also, the efficiency matches as well as useable FR.

[RoyC]

7 hours ago, ReliaBill Engineer said:

Inherent frequency response and behavior *is* the distortion, if it’s in the pass band. A crossover can limit distortion if it occurs below or above the XO frequencies.

Even with the crossover, there shouldn’t be distortion. Rather, it should have a smooth roll off at both ends of the FR. And an inherently smooth pass band.
 

I disagree. No speaker system (or individual driver) has ruler flat frequency response...so are those departures considered to be "distortion"?  The 4x replacement tweeter referred to as "harsh" by some people has been found to be satisfactory others. Earlier in this thread a forum member stated "I actually like the Parts Express replacements". Are you going to tell him he prefers "distortion"? If so, based on what?

"Distortion" is usually considered to be something that should not be present such as noise, static, rattles. clipping, etc. I think you are actually referring to frequency response and tonal balance, not distortion. The crossover integrates presumably properly functioning drivers to produce a desired response. There will always be variations and preferences on the part of the designer and the listener.

[ReliaBill Engineer]

14 hours ago, RoyC said:

I disagree. No speaker system (or individual driver) has ruler flat frequency response...so are those departures considered to be "distortion"?  The 4x replacement tweeter referred to as "harsh" by some people has been found to be satisfactory others. Earlier in this thread a forum member stated "I actually like the Parts Express replacements". Are you going to tell him he prefers "distortion"? If so, based on what?

"Distortion" is usually considered to be something that should not be present such as noise, static, rattles. clipping, etc. I think you are actually referring to frequency response and tonal balance, not distortion. The crossover integrates presumably properly functioning drivers to produce a desired response. There will always be variations and preferences on the part of the designer and the listener.

I disagree.

Distortion usually arises from lack of pistonic motion from the driver. It can be coloration, or most often from resonance(s) in the cone or dome. It’s a lack of faithfulness of the driver’s output compared to input. 2nd and 3rd harmonics produced in addition to the fundamental signal.
 

Cone breakup is common from paper cone tweets. The outer edge of the cone can’t keep up with the center motion driven by the VC. Out of phase output from the outer edge compared to the center of the cone often results.

That’s why AR used dome tweeters in its upper line speakers, so the outer edge IS the driven part where the VC is mounted. The PRT has an outer edge restrained and a center free to move by the VC.

Can you imagine a woofer with a secured outer edge instead of a surround, trying to reproduce low frequencies? Or lower mids? Or upper bass?

I remember the paper cone tweeter used on the ‘66 Wharfdale W70C. It had similar issues of harshness and beaming. It was a paper cone mounted on its outer edge to a grey felt ring. I wound up replacing it with a dome tweeter back in 1982 on my father’s speakers. I couldn’t get that Wharfdale tweeter to sound good.

 

 

[RoyC]

23 hours ago, ReliaBill Engineer said:

That’s why AR used dome tweeters in its upper line speakers, so the outer edge IS the driven part where the VC is mounted. The PRT has an outer edge restrained and a center free to move by the VC.

First of all, we are talking about subjective impressions of a 4x replacement tweeter based on feedback from users, not your opinion of the original AR tweeter. It should be noted that the replacement PRT type tweeter does not have the same construction as the original 4x tweeter...which has a more compliant suspension. The PRT replacement is not as capable in the mid frequencies primarily due to excursion differences. Despite this, a great many users are satisfied with it. It is the difference between this tweeter and the original AR-4x tweeter under discussion, not any flaws (or "distortion") associated with the overall use of this type of tweeter.

Secondly, your conjecture as to why AR used dome tweeters is not accurate. It is not uncommon for speaker manufacturers to successfully use cone tweeters in 2-way designs. AR used dome tweeters for the highest frequencies in 3-way models to enhance dispersion and power handling, not because their cone drivers were distorting. Dome tweeters were used only in their more robust 3-way designs, never in their 2-way models. The cone tweeter used in 2-way models such as the AR-6, 7, 8, and 18 is still highly regarded.

Obviously any driver used outside of its design parameters can "distort". In the end, we are probably talking about the same thing. We just have a different definition of "distortion".

[ReliaBill Engineer]

There were extensive tests done in the early ‘80s on tweeter pistonic motion. Laser interferometry was used to analyze various cone and dome tweeters, design and materials. Cone tweeters tended to have the highest distortion caused by vibration nodes; different velocities and phase from center to outer edge. Domes had much less; even less depending on material and surround used.

Paper cone tweeters just cost less than well designed domes. Paper cone tweeters tend to be used on the bottom tier speakers of any given mfr, 1950 to now. (The paper cone mid on the 2ax is another example of price point compromise.) There are exceptions, of course. The paper cone tweeter I showed above in the wharfdale W70C was replaced with a modified dome in the W70D, but the W70C was an expensive iteration of the paper cone tweet. Even that didn’t work well. Poor dispersion and a harsh character to its sound. 

The 4X was not AR’s flagship model. Not by a long stretch. 
 

The below tweeter, while not paper, is a very good design for a cone tweeter. It’s actually smooth and well behaved. 
 

[RoyC]

15 hours ago, ReliaBill Engineer said:

The 4X was not AR’s flagship model. Not by a long stretch. 

The below tweeter, while not paper, is a very good design for a cone tweeter. It’s actually smooth and well behaved.

So you have experience using this tweeter in the 4x? What crossover and cabinet changes did you make to accommodate this tweeter?

[ReliaBill Engineer]

Just got these in. Hopefully I’ll have time tonight to make a few changes. I bought 2. One will remain unmolested.
 

 

[RoyC]

44 minutes ago, ReliaBill Engineer said:

Just got these in. Hopefully I’ll have time tonight to make a few changes. I bought 2. One will remain unmolested.

4 or 8 ohm. Are you installing them in 4x's? What kind of changes do you have in mind?

[ReliaBill Engineer]

4 hours ago, RoyC said:

4 or 8 ohm. Are you installing them in 4x's? What kind of changes do you have in mind?

I said this in an earlier post:

“I bought 2 of the 8 ohm PRTs to play around with. I don’t know if I’ll have any more luck than you did smoothing them out. But it will be a fun learning experience.

I’ll test them using my Polk speakers, since it’ll be easy to adjust the mounting, and I have impedance adjusting resisters, and I’m very familiar with the original sound of these Polks. Also, the efficiency matches as well as useable FR.”

[RoyC]

Hmmm, I'm sure it will be interesting, but it is hard to see how it will be relevant to the 4x. Impedance is only one parameter. You are proposing using it with a different woofer, different cabinet, different crossover...and conclusions reached based on your listening impressions?

[ReliaBill Engineer]

6 hours ago, RoyC said:

So you have experience using this tweeter in the 4x? What crossover and cabinet changes did you make to accommodate this tweeter?

Not in the 4X. 1988 I restored a pair of McIntosh XR7 speakers.

 

 

 

 

 

[ReliaBill Engineer]

37 minutes ago, RoyC said:

Hmmm, I'm sure it will be interesting, but it is hard to see how it will be relevant to the 4x. Impedance is only one parameter. You are proposing using it with a different woofer, different cabinet, different crossover...and conclusions reached based on your listening impressions?

Relevant to the 4X? Aren’t these PRTs being used to replace original AR tweeters in the 4X? Haven’t you yourself, and others tried to make them more suitable as a replacement? Or did I misunderstand?

Listening is always the final test. Test equipment has its place, but the final test is in the listening. Right?

The Polk RTA-8T speakers I’ll be auditioning these tweets in are also 2-ways. They’ll make for a good test case for these tweeters.  Sink or swim. 
 

[RoyC]

7 minutes ago, ReliaBill Engineer said:

Relevant to the 4X? Aren’t these PRTs being used to replace original AR tweeters in the 4X? Haven’t you yourself, and others tried to make them more suitable as a replacement? Or did I misunderstand?

Listening is always the final test. Test equipment has its place, but the final test is in the listening. Right?

Suitable as a replacement in the 4x, not pair of Polks. No relevance.

[ReliaBill Engineer]

Really? Are you just trying to be difficult and defensive? Or am I misunderstanding you?

So….I guess after I get these sounding smooth, I’ll have to buy a pair of 4X speakers in which to install them. But even then you’ll be skeptical, regardless of what I say, show, or even record.

Likely I’ll have to send them to you for auditioning. But I’m very hesitant to do that. 

[ReliaBill Engineer]

19 minutes ago, RoyC said:

Suitable as a replacement in the 4x, not pair of Polks. No relevance.

 

“I bought 2 of the 8 ohm PRTs to play around with. I don’t know if I’ll have any more luck than you did smoothing them out. But it will be a fun learning experience.

I’ll test them using my Polk speakers, since it’ll be easy to adjust the mounting, and I have impedance adjusting resisters, and I’m very familiar with the original sound of these Polks. Also, the efficiency matches as well as useable FR.”

[RoyC]

1 hour ago, ReliaBill Engineer said:

 

“I bought 2 of the 8 ohm PRTs to play around with. I don’t know if I’ll have any more luck than you did smoothing them out. But it will be a fun learning experience.

I’ll test them using my Polk speakers, since it’ll be easy to adjust the mounting, and I have impedance adjusting resisters, and I’m very familiar with the original sound of these Polks. Also, the efficiency matches as well as useable FR.”

Not being defensive or difficult, just thinking that believing impedance matching resistors and your ears are all you need to make the tweeter compatible with two completely different speakers is naive. If nothing else it will be interesting.

I think this thread has been sufficiently hijacked with this conversation at this point.