New member with Infinity IRS servo questions

[jacquesp]

Hi Infinity lovers,

Greetings from the Netherlands. I have been collecting some older Infinity loudspeakers for years now and like to use them in conjunction with Audio Research amplifiers.
Currently owning (amongst others)
IRS Beta
IRS Gamma
RS1b (very last version and in terms of natural sound completely unbeatable to my taste.)
ARC SP11 mkII
ARC SP8 mkII
ARC D79c
ARC Classic 150
ARC D70 MKII

I have been working on the IRS servo controller for some time now and although the official calibration method seems unavailable, I can say that with a microphone and a scope, it is quite well possible to adjust the internal potmeters in such a way that the woofers do produce a 50Hz square wave and that output is flat to below 20Hz.
Feel free to ask; I would be very happy to share what I have learned so far.

But I also do have questions regarding the used sensors.
In the old version of the Beta and Gamma control woofer, some sort of proprietary (rectangular, aluminium covered) sensor was used.
More and more of these are getting noisy by now and their sensitivity drifts.

Later on, Infinity used the measurements specialties ACH-01, which was connected to a small pcb. Also used in the IRS Epsilon. Seems to be more stable with the progress of time.
But the ACH-01 is not available anymore.
That's my first question: Does anyone have experience with a substitute for the ACH-01?

And then for something different. Out of pure curiosity, I am very interested to learn which sensor Infinity used on the IRS V. This seems to be a totally different thing than used in Gamma, Beta or Epsilon. Also in the sense that according to the IRS V schematic, there is no power source for the sensor. The Controllers for the Beta/Gamma and Epsilon all have power in the sensor connection.

Any input is greatly welcomed.

 

[Ervikingo]

Welcome Jacques!

I would love to hear what you have learned. I recently had one of my SCUs rebuilt and adjusted. I also had a friend from Germany send me some "tuned" control woofers. But, we are always looking for improvements.

Mine are IRS Beta with Threshold 12e on bass and Manley Snappers on mid/highs.

! Juan

 

[jacquesp]

Hello Juan,

Sounds like you have a lovely setup there! The Snappers are fantastic.

I have been looking at the output of the accelerometer from many control woofers to estimate the correct sensitivity.

And I have found that most aftermarket surrounds for our woofers are mostly too stiff or too flexible.
According to available data, the Fs should be 25Hz. But all I can source, are surrounds which will give a slightly too high resonance F (26 to 28 Hz) or make it far to low at around 21Hz.

I have surround that will make an Fs of 26Hz, as this is the best I can get.

Now when you get the output from the accelerometer within reasonable limits from the estimated "correct" output and you tune the LF Stab and Servo pots in the SCU (after offset has been adjusted) you can really get a fairly square 50Hz wave out of the speakers. And when that works, the system functions as intended.

Regarding the sensitivity of the sensors: I may describe the procedure in a next post. Maybe it is not the perfect way to do it, but it is reproducible.

 

[MFRD]

@jacquesp

In this thread, people discuss alternatives to the ACH-01 (starting pg 5). Hopefully some of that information will be useful.

Accelerometer Testing of Loudspeaker Drivers

I received a new batch of PCBs and Front Panels for the AP-2, the new version of the ACH-01 accelerometer amplifier. I also provide detailed documentation to build the amplifier. If someone is interested, send me a message.

www.diyaudio.com

 

[MFRD]

@jacquesp

If you don't mind my asking, do you consider the RS-Ib superior to the Beta? I am considering an upgrade to my RS-II and these two are at the top of my list.

RS1b (very last version and in terms of natural sound completely unbeatable to my taste.)

 

[jacquesp]

@jacquesp

In this thread, people discuss alternatives to the ACH-01 (starting pg 5). Hopefully some of that information will be useful.

Accelerometer Testing of Loudspeaker Drivers

I received a new batch of PCBs and Front Panels for the AP-2, the new version of the ACH-01 accelerometer amplifier. I also provide detailed documentation to build the amplifier. If someone is interested, send me a message.

www.diyaudio.com

Many thanks! This is great information.

 

[jacquesp]

@jacquesp

If you don't mind my asking, do you consider the RS-Ib superior to the Beta? I am considering an upgrade to my RS-II and these two are at the top of my list.

Hi mrfredo,

That is a good question and actually a very personal thing, I guess.
So what I will write below is solely my own opinion that might not be shared by everyone.

I listen a lot to acoustic music, in real life. Classical concerts, unamplified jazz gigs, folk, etc.
My goal is to reproduce the sound and soundstage of such events as closely as possible.

I consider the Beta's more "hi-fi" and the RS1b more "music."
The Beta's do give more Bass and certainly also more detail. Their bass has more impact than anything else I know of. But instruments sound much more real on the RS1b's. When listening to the Beta's, I never forget that it's a reproduction. But the RS1b's constantly fool me and make me think I am visiting a live gig.

The details and the bass may be a bit less impressive on the RS1b's, but to my ears they come closer to the sound of real instruments.

The same goes for dynamics. In my room (large 4mx10m attic; 4,5 meter high) the dynamics of the rs1b are more lifelike than either Beta or Gamma.

The size of voices and instruments are also most correct on the RS1b.
My feeling is that the setup (point source emulation) has a lot to do with it.

Both systems are in excellent condition and only the bipolar electrolytics in the filter are renewed. EMIM membranes all original and still very flat.

 

[MFRD]

@jacquesp

Thank you for sharing your experience, it is very much appreciated. Before we go back to the topic at hand (my apologies for the detour), I'll just add that since I listen mostly to electronic / ambient / sludge / dark jazz, usually at high spl, your feedback supports my hunch that the Beta might be the one best suited to my listening preferences.

To your question about the accelerometers in the IRS V, I recall reading somewhere that they were intended to prevent damage to the woofers by limiting cone excursion, which would be a fairly different use case. I can't guarantee this is accurate though.

Also, you may well already have a copy of the attached document; if not, I hope it is helpful.

 

[jacquesp]

Double post...

 

[jacquesp]

It's a very nice detour, so no apologies needed at all
I fully agree: With your choice of music, the Beta will win, hands down. (And it is exactly the reason I am not parting with my Beta's. I like it loud and spectacular sometimes. Plus the level of detail they can reproduce is simply stunning.

Thanks also for the document. I have it, but making it available again for a large group of people is always good.

Then for the accelerometer on the IRS story: Yup. A well constructed servo system will definitely prevent bottoming out of the woofers at the resonance frequency. But of course it's also there for bandwidth extension and distortion reduction.

 

[MFRD]

@jacquesp

This inspired me to take another look at the market for IRS Betas to see if I could find a set for myself, and I came across moderator removed link to eBay auction as AK rules prohibit such outside the Dollars & Sense forum that was modded by Bascom King, and the mods are described as follows:

They still use the IRS crossover and it’s still a servo system the upgrade was done to the actual accelerometer it uses the new one that was put in arnies next company genesis so the crossover was modified to accommodate it.

The listing includes pics of King's handwritten notes. I thought it might be useful.

 

[jacquesp]

Those are very interesting notes, @mrfredo .
Seems Bascom balanced the accelerometer input circuit on the servo.
Nice speakers anyway. The seller is trying to sell them for some time now. Will you be taking a chance on them?

 

[MFRD]

Betas don't fetch the kind of money he's asking, at least not in North America. And that's before even getting into tariffs, import logistics, etc. since he's in Canada.

 

[jacquesp]

You guys are so lucky. Here in western Europe, Beta's are hard to get and high in price. They are rare here.
On a different note: The seller mentions that the SCU is adjusted for the new Genesis accelerometer. Would anyone know what kind of sensor that is? Just like the IRS sensor, it seems to operate without an external power supply.

 

[nakmandan]

Thank you all for your contributions to this thread. As a fellow Infinity fan, I am dying to see what your listening space looks like. Any chance you could post some pics of your listening space?

 

[jacquesp]

Below some (messy) pictures with the Beta's and the RS1b's. It is an attic with a width of 4 meter, 10 meters length and 4.5 meters high.

 

[nakmandan]

Very nice. It must be great to have a dedicated listening space devoted exclusively to audio! Do you move the off line speakers to the back of the room while they are waiting their turn or do you have a separate storage area for the rest of your speakers?

 

[Ervikingo]

Very nice. It must be great to have a dedicated listening space devoted exclusively to audio! Do you move the off line speakers to the back of the room while they are waiting their turn or do you have a separate storage area for the rest of your speakers?

I used to have a swivel chair in my room with the Beta on one side and my Aerial 8b on the other. Now the Aerial are on a separate room with their own equipment

 

[jacquesp]

Very nice. It must be great to have a dedicated listening space devoted exclusively to audio! Do you move the off line speakers to the back of the room while they are waiting their turn or do you have a separate storage area for the rest of your speakers?

I swap from time to time. Just strong enough to lift the bass towers by myself.

 

[gizzyman47]

Very nice! I just recently became an Infinity fan. Picked up a pair of Kappa 8's a few weeks ago, and just today a buddy of mine gave me a pair of Kappa 5's which need a refoam.
Not at the level you guys are at, but loving it still!