AR-2ax: Early Midrange

[ReliaBill Engineer]

If speakers can’t resolve differences in cartridges, then just how much “music” are you getting from your speakers? If the AR-2ax speakers present a Shure M44C (1964) the same as a Shure V15V-MR (1983), then there is a tragic loss of detail. Or an Empire 108 (1959) the same as an Empire EDR.9 (1980), there is something very amiss. Music? I can get that over my iPhone.

[Aadams]

I am not sure anyone here has an answer for you. Modifying your 2axs to sound like your Polks will not be considered an achievement on this site.  You could use a 15 band equalizer and nearly accomplish the same thing.

[ReliaBill Engineer]

My wife and I auditioned the new dome midrange driver last night. I won’t go into driver/fit detail here, as it’s not appropriate.  I left one speaker as-is, the other with the new midrange. Set my integrated amp to “mono” so I was sending an identical signal to both speakers, side by side.

The new dome didn’t change the sound “character”. But it sure did add the detail I was missing! SPL was dead on, and the crossover point was dead on with the original. Pot worked perfectly. Seamless with both the woofer and tweeter. Detail can’t be changed with an EQ; only relative SPLs can be altered. This dome has wide and smooth off-axis dispersion, and resolves massed strings and horns extremely well. The cone mid muffles those very articulate, delicate details. 
 

I’ll start a new thread in the mods and tweaks section. Doing a search, I see loads of info on replacing the tweeters in these and in 3/3a with new HiVi units. Seems to be accepted as a non-tweak. I see nothing about replacing these little paper midranges in the 2ax, and 4a/ax. So I think I can add some value to the discussion.
 

In a side by side comparison of the dome to the original paper cone mid, I could hear *why* AR put the fiberglass damping pad over the paper mid. And I can now see/hear why the 3a is heralded for its better mids using the AR dome mid. I will venture that this tweak/mod will bring the 2ax even closer to the 3a.

[RickB]

Bill what "dome midrange" did you use?

Thx!

[genek]

On 7/26/2023 at 10:30 AM, ReliaBill Engineer said:

I see nothing about replacing these little paper midranges in the 2ax, and 4a/ax. So I think I can add some value to the discussion.

Probably because unlike the dome tweeters, these drivers hardly ever seem to fail.

[ReliaBill Engineer]

Very reliable mid-tweets, for sure. Not much to fail, really. But once I removed one, I was underwhelmed by the quality. I know the 2ax had to meet a price point. The woofer is well made, tweeter the same as the 3, XO nearly the same as the 3, cabinet is well made. So the mid-tweet was a compromise. Keeping the (super)tweeter and woofer, the character of the AR is still there. 
 

Using the old Peerless dome mids. I first used these in 1982 and love their neutral, smooth sound and detail. Found a pair on eBay.

 

[RoyC]

On 7/26/2023 at 1:30 PM, ReliaBill Engineer said:

I see loads of info on replacing the tweeters in these and in 3/3a with new HiVi units. Seems to be accepted as a non-tweak.

This is because the HiVi tweeter (and associated inductor) is meant to emulate the original when it is not available or is damaged. It was never meant to be an "upgrade". (Bear in mind that this site is primarily oriented around restoration.)

I agree with Aadam's comments above, so I'll just add some of my own. Sensitivity, other electrical and (often overlooked) mechanical characteristics of individual drivers, crossover design/integration with other drivers, outboard enhancements such as equalizers and tone controls all significantly influence what you are generalizing as "detail".  Simply dropping a more expensive (or favorite) driver into the cabinet hole of an existing design and believing it to be perfect for that system's crossover seems a bit naive, imo. On the other hand, I'm sure it is understood that your own satisfaction is the only thing that matters.

Now, off to the mods and tweaks section with you!😁

 

[ReliaBill Engineer]

Naive?

Detail is the ability to resolve and reproduce complex integrated sine waves, without distorting or homogenizing the waveforms into something barely recognizable and foreign to the original waveform. In the world of phono cartridges, it’s well understood how one cartridge can resolve great detail from the grooves, but a lesser cartridge can’t. Speakers are transducers exactly like phono cartridges, only in reverse. An equalizer only emphasizes (or de-emphasizes) the power response across a relatively wide band, and has nothing to do with a driver’s ability to resolve complex waveforms.

It is widely recognized that the dome midrange of the 3a is more expensive and superior to the paper cone midrange of the 2ax. No?

But I’m not done. I’m not going to use the Peerless domes, while they do sound good. (I’ll use them in a pair of Wharfdales that need TLC, W70C.) I found a dome that “emulates” the 3a better. It “emulates” the 2ax better. For those with no midranges, or damaged midranges, they might find it useful to read about another’s attempts to try something else. Or even learn what not to do.

Nope. I didn’t just “drop” another driver into an empty hole in the baffle. The second set of dome midranges I’m working on are hard domes, not soft silk. The T/S parameters, sensitivity, resonant frequency, useable frequency band, impedance curve, Q (electrical, mechanical, total) are all similar to the AR hard dome mid. It has very smooth response characteristics and great off-axis response. It blends perfectly with the AR woofer and tweeter, in sound and appearance. So no, I’m not just dropping a driver into the hole in the baffle, not any more than using the HiVi unit. But if someone IS going to replace an AR driver, it needs to have complimentary and redeeming qualities. No? And I think everyone knows how to keep original AR drivers in the AR speaker. Basically, you do nothing. Not much of a challenge, really. And keeping (resurrecting?) the AR “sound” is a moving target; what was the sound when the speaker was first manufactured? Who really knows? How does one evaluate that, and conclusively, definitively, *know* and make a comparison? (I have nothing to “protect” here, I’m not in the business of selling my advice or services.) Appearance, yes. That’s a known quantity. Time and environment takes its toll on the appearance and performance of vintage speakers.

[Aadams]

The above post would be a good beginning post for your mods and tweaks thread.

[RoyC]

1 hour ago, ReliaBill Engineer said:

Naive?

Detail is the ability to resolve and reproduce complex integrated sine waves, without distorting or homogenizing the waveforms into something barely recognizable and foreign to the original waveform. In the world of phono cartridges, it’s well understood how one cartridge can resolve great detail from the grooves, but a lesser cartridge can’t. Speakers are transducers exactly like phono cartridges, only in reverse. An equalizer only emphasizes (or de-emphasizes) the power response across a relatively wide band, and has nothing to do with a driver’s ability to resolve complex waveforms.

It is widely recognized that the dome midrange of the 3a is more expensive and superior to the paper cone midrange of the 2ax. No?

I found a dome that “emulates” the 3a better. It “emulates” the 2ax better.

Based on what? Audio forums are full of subjective testimonials.

You are also not taking the crossover into account. Cartridges are not the integration of disparate drivers, which is why speakers are referred to as "systems".

The 3a was not known to have a more detailed midrange. In fact, in the early 70's Consumer Reports magazine subjectively rated the 2ax as "a better speaker at half the price" based on midrange response alone.  Dome drivers are considered to have better dispersion, not more detail. The 3a drivers could also handle much more power.

"And keeping (resurrecting?) the AR “sound” is a moving target; what was the sound when the speaker was first manufactured? Who really knows?"

Those of us who have worked with these speakers for 4+ decades do. You obviously have an idea as to how they should sound...so have at it. Just know that you are basically attempting to re-design them. You certainly would not be the first. It can be fun to discuss....in the mods and tweaks section.

 

[Aadams]

Looks like the pixie dust spreader has seen this thread.

[Jim Pearce]

I need to get those Heil ESS tweeters off of my pair of 2ax speakers and get those rebuilt 3/4 inch black domes in there.

Engineer Bill...

What is your opinion of the Polk RT16?

[ReliaBill Engineer]

On 7/30/2023 at 3:09 PM, RoyC said:

Based on what? Audio forums are full of subjective testimonials.

You are also not taking the crossover into account. Cartridges are not the integration of disparate drivers, which is why speakers are referred to as "systems".

The 3a was not known to have a more detailed midrange. In fact, in the early 70's Consumer Reports magazine subjectively rated the 2ax as "a better speaker at half the price" based on midrange response alone.  Dome drivers are considered to have better dispersion, not more detail. The 3a drivers could also handle much more power.

"And keeping (resurrecting?) the AR “sound” is a moving target; what was the sound when the speaker was first manufactured? Who really knows?"

Those of us who have worked with these speakers for 4+ decades do. You obviously have an idea as to how they should sound...so have at it. Just know that you are basically attempting to re-design them. You certainly would not be the first. It can be fun to discuss....in the mods and tweaks section.

 

Well RoyC, subjective testimony is all anyone ever has. Even showing frequency sweeps are subjective; they don’t tell anyone how a speaker or driver *sounds*.  T/S specs and plots don’t tell anyone how something *sounds* either. You rebuild original drivers, but I have no idea how they *sound*, only what they look like and the price. At least I’ve provided a chance at hearing how something sounds. I’ve tried to be informative. 
 

Everything in here re: speakers is subjective. The alternative is to be *definitive*. How do we do that? I’d like to know.

How *should* 50-60 year old speakers *sound*? Where is the definitive, non-subjective standard? Can we see it, hear it? Does anyone have a pair of *perfectly* preserved speakers, deemed perfectly preserved by a definitive authority?

I know the answer is “no.”

My “subjectivity” is no less valid than your “subjectivity”, or anyone else’s “subjectivity”. That’s all anyone has.

Measurements don’t tell a person how a speaker or driver *sounds*. They can assist with an intended design, or response. They can serve to stack the deck in one’s favor. That’s about it.

Where I work, all manner of measurements are done, models of stresses, pressures, forces and thermals are done, all to make predictions, assess and assign risks. But they in no way guarantee how Artemis will fly until it’s launched.

[ReliaBill Engineer]

I won’t be using the “approved” midrange replacements. I’ve selected and listened to my choice already. As for crossover, I’ve already designed it, and am waiting for parts. I will assemble it, then listen to it extensively and make any modifications needed. I’m going to leave the existing mid in place, positioning my replacement outside (on top) of the cabinet for comparing. Wire the replacement directly to the external terminals, and turn the pot for the existing mids to zero. This way I can do a very close comparison, A/B them. 
 

Ultimately, the new mid and XO will be a drop-in replacement without corrupting the cabinet, nor original XO circuit. 
 

It will be for those wanting to upgrade the sound, yet not be irreversible from original drivers or crossover. If later sold, both pairs of drivers can be included with the speaker pair; a choice of performance.

[ReliaBill Engineer]

So, I’ve started testing a new midrange dome for the 1965 AR-2ax pair I have. 
 

I have to say, I was underwhelmed at first. This dome sounded “thin”, but very clear. 
 

Then I drew out the schematic of what I had, and realized I had to remove the existing crossover’s influence; I had only turned down the mid pot, removing the original mid from the circuit, but NOT the influence of the cap and 16 ohm pot inside the cab! By connecting my circuit at the rear terminals, I was paralleling my circuit with the internal mid circuit.
 

But once I clipped the wire between the pot and 6 uF cap inside the cab,  disabling the mid circuit, and listened again, I was truly amazed!!

A very airy, smooth, neutral and detailed sound. But because the (super) tweeter and woofer are still in the cabs, playing with my dome mid, there is still that AR sound. 
 

Im still making adjustments to the crossover. I’ve added a 20 ohm pot. 
 

I made faceplates that match the existing hole and screw locations. In the end it will be a drop-in replacement. But for now, I’m listening to the dome placed on top of the cabs. Once placed into the cabs, I know it will sound a tad different. But not much.

 

 

 

 

[ReliaBill Engineer]

I’ve modified the crossover to get rid of the high frequency resonance of the dome, yet still keep the high frequency response. 
 

[ReliaBill Engineer]

So the next step….

I tied in to the original AR crossover network. Using the internal 6 uF capacitor and 16 ohm pot (rheostat). Plus my shaping network at the midrange dome. Added a foam ramp in front of the dome to deaden diffraction from the front edge of the cabinet top. But in alignment with the VC of the original midrange. Used foam weatherstrip to reseal the original mids and allow passing wires from behind the mids. Seal was good by using the “pressing the woofer cone” technique.
 

I played some Epic label Bobby Hackett trumpet music (playing Bert Kaempfert’s hits). These can sound hot or squawky on different speakers, especially so using the Shure V15V-MR cartridge. 
 

I think it sounds great! My wife actually noticed the difference, and began dancing in the living room! 
 

These sound very smooth, neutral, detailed, and very airy, with a huge spacious sound. Imaging is tremendously wide and deep, not 1-dimensional. 
 

I’ve found that these mid domes sound best at a 65% setting on the pots. Tweeter at 85%. And yet, still very much the AR sound. Just a whole lot less colored and squawky. And, now I can lose the toe-in position of the speakers. Just point them straight out. 
 

 

 

 

 

 

 

[ReliaBill Engineer]

Next, these will get the expanded aluminum grills, to keep with the AR midrange driver “motif.” 
 

And BTW, yes. I did remember to reverse the polarity of the midrange dome driver. 
 

I love the effortless, airy sound! I can listen for hours on end, with no irritation or fatigue. 
 

When complete, this will look the part of an AR driver, look right at home! But belie the squawky, numb sound these had. All my goals will have been met.

[ReliaBill Engineer]

Just some sound samples. Such a big, effortless sound!

Longer track. Linda Ronstadt:

 

Shorter track, also Linda Ronstadt:

 

 

And, for contrast, the squawky AR paper cone midrange:

 

 

 

Same track as above, 1965 Glenn Miller Chattanooga Choo Choo:

 

[ReliaBill Engineer]

Well, I went back and moved my original AR pots to their original positions. On my first speaker recap of the 2ax pair, after cleaning the pots, I moved them so the “dot” was exactly midway in the total rotation of the pot knob. As RoyC later advised, it wasn’t a good move. Agreed! So now both speakers have both pots in their original positions. 
 

And now I run both speakers with mid and tweeter pots in their “home” dot positions. 
 

I documented my midrange mod in the “Tweaks and Mods” section of the forum. Goal was to have the same sound as the original 2ax drivers, just cleaner, with more detail. That goal has been totally realized. But I did run into the same sort of issue that AR did with its paper cone midrange, namely that the top registers of sound were peaky and ragged. Same issue with the dome mid I selected. 
 

I chose an inductor to roll off that raggedness of the 2” dome. But regardless, I ran into the same issue that AR engineers did 58 years ago.

So, full circle, I ran into the same issues that AR did, and answered my original question of “why the FG pad over the midrange driver?”

Just a comparison. I chose a 1965 record of The Glenn Miller Orchestra on Columbia’s Epic label for jazz. My experience is that these records are recorded “hot.” They can be fatiguing over long listening sessions. 
 

But here, the pots are at their “dot positions” for mid and tweeter. Original crossover values, original pots, original internal rock wool damping. Not much difference in sound character between mids (domes vs paper cones) other than smoothness, dispersio,  and level of detail. 
 

(Domes are wired to the internal wires for the original mids, the yellow and green wires. Polarity of dome reversed the same as original mid and tweet. Using internal crossover and pot.)
 

 

 

[Aadams]

Why are there two videos presenting the same track from the record?

 

[genek]

My guess is that one is "before," and the other is "after." But since both videos sound identical, either the perceived improvement is too subtle for phone recordings on computers to capture or there isn't any actual improvement and the exercise has simply resulted in a method of reproducing original sound with a new driver and some crossover mods. 

[Aadams]

39 minutes ago, genek said:

But since both videos sound identical,

I thought the same thing until I listened on headphones and they clearly sound different.  While I was using the headphones I decided to stream a 256AAC version of the same music to get a good idea of how the track is supposed to sound. 

[genek]

I don't have headphones (not counting cellphone earbuds, which I have plenty of but don't consider worthy of being called "high fidelity"). Did you think one sounded better than the other, or were they just "different?"

[frankmarsi]

Testing speakers on floors while not observing correct room placement while playing sources of questionable fidelity without indicating equipment powering the whole shebang is hardly qualifying in appraising audio equipment.

 Out of numerous possibilities I sometimes use a vinyl album by “Super-Tramp” called, ‘Crime of the Century’. A forward-rock album which contains plenty of sound variations that can be easily used to judge sound quality of speakers and other components. Many older recordings on almost any format are not recommended as good sources due to advances made in audio recording since. 

FM

 

 

 

 

 

 

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