AR4x replacement tweeter recomendations?

[tourmax]

So, I had a set of AR4x's hooked up to my Sansui 8080DB. I have  small listening room (10'x10') so the AR's fill it quite nicely and I enjoy their sound.

A buddy of mine plugged a mic into the Sansui while it was playing, intending to sing along. Big feedback squeal and everything went really bad after that.

The 8080DB dropped the left channel and everything went very muddy and muted. I have fixed the 8080DB (Full tear-down and lots of o-scope work) but upon reconnecting the AR4x's, it still sounded "muddy". 

Ear up to the woofers revealed they were doing their job but the tweeters were......silent. Seems my buddy's "mic spike" is the gift that just keeps on giving......

I have a second pair of AR4x's (waiting for a resto, they've lived a harder life than my "cherry" set) so I pulled them out of storage. Upon hooking them up to the Sansui, the right speaker tweeter was working fine but the left was dead. At least I now knew that the tone issue isn't still a problem in the 8080DB.

I pulled the tweeters out of the cabinets, figuring if I meter them they should return 8 ohms. Meter them and they're both open, so I figure the voice coil is burnt.

Finding a vintage pair is unlikely (I don't think there's a way to repair the originals, please let me know if there is) so I'm looking for a recommendation for modern replacement.

I would like to keep the AR4x's sound as close as possible to original. I found a post on AK about some "Tang Band" tweeters that were close to the AR4x's originals sonic-ly, but it seems they're no longer made either. 

I'm not worried about the size as long as they are smaller than the original cab holes. Making an adapter plate out of anything from wood to aluminum to steel isn't an issue for me. I have all I need out in the metal shop for that.

 

On a more positive note: I pulled the tweeter on the second set that wasn't working and it metered at 8 ohms, so it's likely the dirty/corroded pot issue. So at least I can continue enjoying that smooth AR sound on my second set, even if the cabs aren't as "cosmetically" nice as my first set.

[AR55]

Midwest Speaker is selling a Chinese made tweeter that they say is a replacement for the 4X tweeter on eBay.  See link below:

Acoustic Research Replacement Tweeter for AR-4x Speaker - MT-4107-4 | eBay

[JKent]

That's a standard phenolic ring tweeter (PRT). Parts Express also sells them, for a lower price.

Our RoyC did extensive research to find a replacement for the 4x tweeter and found the classic PRT to be the best, albeit not perfect replacement. Ebay seller Vintage-AR sells these, mildly modified by Roy with his sealant. Those would be your best choice IMHO. His ebay store is closed until March 11. https://www.ebay.com/itm/194443157067

 

[RoyC]

2 hours ago, JKent said:

That's a standard phenolic ring tweeter (PRT). Parts Express also sells them, for a lower price.

the classic PRT to be the best, albeit not perfect replacement.

This tweeter is certainly not a perfect replacement, especially when used in a pair next to an original. Unfortunately, there are really no other "drop-in" options. There was some experimentation with crossover changes for this tweeter mentioned in the forum quite a few years ago, but I'm not aware of anyone who implemented any of the suggestions.

Midwest is selling a 4 ohm version as well as the 8 ohm version sold by PE and Vintage_AR, and I'm more inclined to recommend that one if given a choice. https://www.midwestspeakerrepair.com/product/mw-audio-mt-4107-phenolic-cone-tweeter-2/

(Btw, VAR's addition of the sealant is just an attempt to calm the harsher nature of this tweeter...with very limited success.)

Roy

[RickB]

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

[tourmax]

23 hours ago, RickB said:

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

I’m in Canada, which means exchange, taxes and duties and international shipping charges. 

They quite a bit get more expensive, frighteningly fast.

 

Believe me, if I could get a pair here for 50 bucks, I’d be all over it. Maybe later in the summer when funds are a little bit more freed up. Tax time here and that is always a tight time…

[tourmax]

Well, I’m not admitting defeat on the original tweeter rebuilds/repairs, but decided I needed a “backup plan” just in case.

ordered a pair of the phenolic ring tweeters off an eBay seller. Still came out to just under 100 bucks CAD all said and done. 
 
Tried parts express and others and they only ship here by fedex/ups/etc and that means high shipping charges and a nasty “brokerage” surprise when they do arrive. Figuring in exchange rates, they all came to a fair bit more than 100 CAD.

Hopes are still to rehab the original tweeters, but if it doesn’t work out at least I have a viable alternative.

[tourmax]

Hmmm, the tweeters I just ordered are 8 ohm but I’m reading various threads on the forum that 4x’s are anywhere between 4 and 6 ohms.

Did I order the wrong impedance tweeters and if I did, can I bring them closer to the proper values with some resitors?

[RoyC]

21 hours ago, tourmax said:

Hmmm, the tweeters I just ordered are 8 ohm but I’m reading various threads on the forum that 4x’s are anywhere between 4 and 6 ohms.

Did I order the wrong impedance tweeters and if I did, can I bring them closer to the proper values with some resitors?

As I mentioned above, the 4 ohm version is a better bet.

If the mid range seems too forward, you can experiment by placing parallel resistance with the higher impedance replacement tweeter, starting at 8 ohms.

 

[tourmax]

3 hours ago, RoyC said:

As I mentioned above, the 4 ohm version is a better bet.

If the mid range seems too forward, you can experiment by placing parallel resistance with the higher impedance replacement tweeter, starting at 8 ohms.

 

You know, I read that and it went right out of my head when I ordered. Oh well. 

I guess a little "fine tuning" headroom with some resistors isn't that bad a thing either.

 

Any recommendation on a min wattage for resistors in the tweeter path? 5W sound appropriate or can/should I got a bit lower?

[RoyC]

8 hours ago, tourmax said:

Any recommendation on a min wattage for resistors in the tweeter path? 5W sound appropriate or can/should I got a bit lower?

5w would be the minimum. 10w or higher would be better.

[tourmax]

13 hours ago, RoyC said:

5w would be the minimum. 10w or higher would be better.

Noted. Thanks.

[ReliaBill Engineer]

Decided it’s a better fit here. 
 

This modified PRT sounds much smoother than stock. 
 

Below, stock PRT. The clear dope constrains movement of the tweeter cone.

Surround removed (below):

 

Below, after internal damping was added, and a new (very thin) butyl rubber surround was added:

[frankmarsi]

@ ReliaBill Engineer , Wow that's quite a noble effort and evidently an excellent physical feat that was accomplished with that tweeter.

I obviously don't have it in my hands to see or hear but from what I can see, a wonderful effort in forming the surround, what's it made of?

I admire your patience and skill. At this moment it looks so good, I would bet you'll get members inquiries of performing that same operation

at a price. Keep us posted, I'm very curious how they sound. I venture a guess RoyC. would be pleased also.

I don't use my 4ax's as I purchased them several years ago(2005), when I was more collector driven and just had to have a pair.

I was actually inspired by their sound quality back in 1965-66 as my dentist had a pair in his office area.

I was so thrilled they sounded so good* to my 16 year old ears I made a promise to myself that a good sounding personal playback system was in my future.

That notion was correct because that year in 1966/7, I started building home-made speakers from street found drivers, cabinets and I made a few cabinets myself, all of which my father felt had no room in the house or basement to occupy.,

Though I camouflaged one cabinet behind stuff, and dismantled the rest when I entered the service 2 yrs. later and came home on leave, it had mysteriously disappeared. To be fair, I was taking up room with my new at the time silver-face, Fender Bassman amp and bass guitar. Though, I guess he redeemed himself by building for me a four-wheel dolly out of angle-iron with heavy-duty 3 inch swivel wheels and that saved my back tremendously later on. You lose some, you gain some.

FM

P.S. * at that time, 1966, I was already seeking any and all information I could find about the hobby that was on my to-do-list of future hobbies.I was tinkering with found raw speakers, discarded radios, it didn't satisfy enough. Even though I worked at part-time jobs, that small amount of money was only enough to take my girl to the movies, certainly not enough to buy a quality music play-back system. Forgot to mention in later 1967 I built my first electronic kit the Dynaco PAS-3x and ST-35.

Evidently, I wasn't kidding myself as decades later I find myself ensconced with vintage turntables, pre-amps, amps, expensive phono-cartridges, and  many, many AR speakers.  

Good-Luck to you ReliaBill Engineer as I've been impressed by your motivation and willingness since you arrived here. A positive virtual shot in the arm for this site.

FM

 

 

 

 

 

 

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[ReliaBill Engineer]

Butyl rubber surround. Not fully cured until tomorrow. I did fire it up for a few minutes, to check it out. But the process for making the surround is too labor intensive. I’m going to try a different method.

[tourmax]

 Now thats interesting!
 

Probably beyond what I would do with a brand new set, but I’m interested in what the results are.

I’m an old “greasy paw” and also can’t leave much alone “as is”, so I totally get the need to tinker and see what you get.

 

Carry on!

[ReliaBill Engineer]

I’ve got materials coming to me via Amazon. If all goes well, I may buy 2 of the 4 ohm units and work on those. 
 

What I failed to effectively communicate to RoyC is that if these sound good in my Polks, they’ll also sound good in the 4X, or in any speaker, regardless of the crossover. Speaker designers and mfrs always start with a good sounding driver. Even they can’t make a silk purse from a sow’s ear. If they try, they will wind up spending lots of R&D time and increase the parts count in the crossover trying to tame a so-so driver. I think of the extra steps AR used to form the metal grill, add a fiberglass pad, then glue the grills onto the 2ax midrange cone driver, just to attempt taming its squawky nature from using a low cost driver.

[tourmax]

3 hours ago, ReliaBill Engineer said:

I’ve got materials coming to me via Amazon. If all goes well, I may buy 2 of the 4 ohm units and work on those. 
 

What I failed to effectively communicate to RoyC is that if these sound good in my Polks, they’ll also sound good in the 4X, or in any speaker, regardless of the crossover. Speaker designers and mfrs always start with a good sounding driver. Even they can’t make a silk purse from a sow’s ear. If they try, they will wind up spending lots of R&D time and increase the parts count in the crossover trying to tame a so-so driver. I think of the extra steps AR used to form the metal grill, add a fiberglass pad, then glue the grills onto the 2ax midrange cone driver, just to attempt taming its squawky nature from using a low cost driver.

I get that.

 

but I’m also just starting to absorb more details about crossovers (new to the details of them) and it seems the crossover network is just as important as matching tweeter and woofer so they compliment one another vice one “shouldering” the other to the side a bit. 
 

gotta start with good drivers but it seems you still have to do the work to match them in the crossover. 
 

seems theres a whole tone of math in it too. Thankfully, I’ve run across a couple “freeware” programs that lets you play around with impedance and resistance to see how the curves move. Reading it on a page or working out the math is one thing, watching how the charted curve moves is another. I’ve had more than one “aha!” moments playing with the values. 
 

like I said, I’m just starting to learn crossover networks, but it seems that you need to work it all as a system to me so far.

 

cheers

[ReliaBill Engineer]

I’ve been working (designing, building, testing) crossovers since 1981. I wrote my EE thesis on the crossover I built in 1983 for my dad’s Wharfdale W70C speakers (1966). 
 

If you start with a driver with a smooth, well-behaved impedance and response curve, watch where your crossover frequencies and fundamental resonance are, it’s relatively easy. Back in 1983 I had to plot those curves by hand. Since the Linkwitz-Riley wasn’t out yet, I used a combined Butterworth-Chebyshev 2nd order 3-way response curve. 
 

But truthfully, these early ARs had/have very fundamental crossovers. Inductor on the woofer for low pass, high pass capacitor on the tweeter. The only more simple crossover than these is no crossover. 
 

Forgot to include these pics of the PRT tweeter. Installing the wool felt inside the cone, to absorb/damp any sound from the back wave. Also just a small amount of loose wool fiber.

 

Below, the wool felt installed:

 

 

 

 

[tourmax]

This might just be my inexperience showing, but I'm not really understanding how the "PRT" tweeter is a lot different from the AR cone tweeters, other than the obvious response differences, which I'm guessing is as much down to the size of the cone as much as anything else.

It just looks like a cone tweeter that is attached to the phenolic ring instead of the top/front of metal basket itself and the phenolic ring looks like it's bonded to the metal basket. Would not that make the phenolic essentially "rigid" like the metal basket would be anyways?

Unless it's something like the phenolic changes the response (resonance I'm guessing maybe?) as opposed to the metal basket. ....

[Pete B]

I wonder how this Visaton paper cone tweeter with a smooth response would do as a replacement,

with a parallel resistor to match the impedance:

https://www.mouser.com/ProductDetail/Visaton/TW-70-8-Ohm?qs=VWNNG7jHlrLkQoY0VZlmUA%3D%3D

Mounting would have to be worked out, perhaps 3D printed.

[ReliaBill Engineer]

15 hours ago, tourmax said:

This might just be my inexperience showing, but I'm not really understanding how the "PRT" tweeter is a lot different from the AR cone tweeters, other than the obvious response differences, which I'm guessing is as much down to the size of the cone as much as anything else.

It just looks like a cone tweeter that is attached to the phenolic ring instead of the top/front of metal basket itself and the phenolic ring looks like it's bonded to the metal basket. Would not that make the phenolic essentially "rigid" like the metal basket would be anyways?

Unless it's something like the phenolic changes the response (resonance I'm guessing maybe?) as opposed to the metal basket. ....

There’s more going on in this tweeter than you realize. 
 

First, RoyC said this PRT has a sound similar to the 4x AR tweeter, but some find it more harsh. That’s where I started. I also read through every post, every page in Tweaks And Mods of the 4X crossover efforts by Speaker Dave. That gave me some background.

Other background I have is repairing and modifying countless tweeters over the last 40+ years, so I’ve seen many of the best out there. Also, I’ve taken apart, repaired, improved many phono cartridges; they are merely the reverse of a speaker driver. A driver converts an electrical signal into mechanical sound energy; a phono cartridge converts mechanical energy into an electrical signal faithful to the mechanical movements of the stylus. One is the reverse of the other, yet all the same principles apply. 

Also, I have dual degrees in mechanical and electrical engineering.

After examining the PRT I see why it has distortion, sounds harsh. The cone is rigid-mounted. (The same problem an aged phenolic dome tweeter has in the 3a and 2ax speakers!) The clear dope on the outer edge of the PRT is way too stiff; the cone fights itself to move. It has a powerful motor (magnet and voice coil) so the voice coil is going to move while the outer edge of the cone cannot. That’s a recipe for distortion! It also has no damping for the back wave produced when the cone center moves. 
 

A tweeter is like any other driver or a phono cartridge; it’s a tuned motor system. The PRT has a motor (VC and magnetic gap) and a spring. The motor moves the cone. It moves the cone against a spring; the spring is the accordion spyder, a flat sheet of phenolic-treated gauze in the case of this tweeter. To get proper motion, the cone surround provides damping that resists bouncing of the spring-loaded VC. In this case, the surround of the PRT is STIFF and WAY over damped, to the point that the cone can’t move properly. 
 

The phenolic ring is an insulator for the VC wires. It allows running the VC wires on the surface of the mounting plate without electrically shorting the wires. AR used black electrical tape to achieve this on the early 3a and 2ax front-wired tweeters (and mids on the 3a).

What I’m going to do is retune the surround on the PRT cone. Allow it to move, but match the damping of the surround to the spring force of the spider. It’s exactly the same as matching a shock absorber to the spring of a car’s suspension. In that case, a car will bounce uncontrollably on its springs when it rides over a bump in the road; the shock absorber allows one bounce, then return to neutral position. Same for a properly tuned speaker driver’s cone suspension.

Thats why RoyC’s attempt to tame this PRT failed. He added his dope to the existing dope. Adding dope to a surround that is already too stiff won’t accomplish anything.

 

 

[Aadams]

I thought for a while this thread was hijacked.  Now I am not sure.  What you are doing is interesting but unless you actually get something done, its like listening to grandpa Simpson stories that don't go anywhere.   You don't have the name recognition of Allison or Kantor, so even if you put this in a 4x for instance and tell us it is better we will need an easy and inexpensive way to verify your claim.  We don't all possess your skills or inclination to invest the time to replicate your efforts so where is this project going?  The crossover mods in the M&T thread you mentioned are easily replicable, your surgery and techniques are not. How will this serve the interests of AR4 owners in general after you finish?  Otherwise, this thread should be a in Mods and Tweaks.

I am still waiting for you to restore 3a dome mids? 

[ReliaBill Engineer]

My Amazon order arrived today. So tonight I hope to finish work on the tweeter. I removed my butyl roll edge. Looked great, but not the damping I needed. 
 

Didn’t Speaker Dave make his theory, progress and calculations before he published his schematic and “How To”, and even his listening observations?  Pretty sure he did. 
 

This thread is about a replacement tweeter, not an original AR tweeter. So I’m not blaspheming an original AR component here. 

In a previous post I offered to send RoyC these modified PRTs for evaluation. 
 

And RoyC’s modified PRT was linked to previously in this thread. So I’m hardly doing anything or saying anything without precedent. 
 

So far what I’ve said/shown is what I’m doing, why I’m doing it, and final product is in progress. Testing will come later. That’s why I’m leaving one PRT untouched. 
 

While I don’t have a full suite of test equipment, I do know someone across town who does. 
 

Im a bit surprised at the hypersensitivity. I’m not in the market for selling my services or products, as others in here are.

Once I’m done and satisfied with the results, I’ll freely pay to send these to RoyC for his observations and critique. It won’t hurt my feelings if he gives me a “👎”. Like you said, my saying they sound great carries no weight or credibility.

As for the 2 midrange drivers, that’s a longer term project. They are both missing the original “guts”. No VC, no domes. So it’s more than just a restore; it’s a new fabrication. But according to you, when I’m done, it will be fruitless, since I don’t have the “street cred” to say they sound good and are viable repairs/replacements.

 

[Aadams]

46 minutes ago, ReliaBill Engineer said:

While I don’t have a full suite of test equipment, I do know someone across town who does. 

This would be helpful

 

46 minutes ago, ReliaBill Engineer said:

Im a bit surprised at the hypersensitivity. I’m not in the market for selling my services or products, as others in here are.

No reason to be shy.  If you can credibly restore failed AR5/AR3a/11 midranges for a reasonable fee you will get interest. 

46 minutes ago, ReliaBill Engineer said:

But according to you, when I’m done, it will be fruitless, since I don’t have the “street cred” to say they sound good and are viable repairs/replacements.

I am saying what you are doing to the PRT is not practicable for almost all of us, so unless you bring it to market or show us how it is simple to do,  this is an academic exercise that should be in Mods and Tweaks. We would pay you for the modified part in the expectation that it would meet expectations.  You would build cred as the number of successful transactions increased and through supportive reports of success on this and other sites.