My Excellent RS1 Adventure

Discussion in 'Infinity Loudspeakers' started by pauljh, Mar 13, 2018.

  1. pauljh

    pauljh Active Member

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    I've been a fan of Infinity speakers since the time they only had one product: the Servo Static 1, which I heard at Woodland Stereo in 1968. My first pair of Infinity speakers was their second product, the original Infinity 2000, and I still have those speakers. I also have a pair of InfiniTesimals (0.3) which I use as front speakers in my home theater system.

    Recently, having regressed back to the interests of my youth, I've been trolling eBay and Craigslist ads for Infinity speakers. Just before Christmas 2017 I saw a pair of RS1s (not a or b) for sale locally on eBay for a what seemed a reasonable price. I ended up winning the auction, and the seller (a local sound reinforcement company) even delivered them, hauling them up four flights of stairs to my loft.

    They were mostly intact, but it was obvious they had led a hard life. The cabinets show water damage at the bottom, and not all of the drivers were pristine (or even working). I replaced two dead rear-firing tweeters with replacements from eBay, and replaced an oversized fuse or two (why is there a 3A fuse in this tweeter circuit?!?), and then started listening and adjusting.

    The system had a hum and ground loop buzz when using the Infinity servo-crossover. I tried various configurations and ground lifting schemes but never got things quiet. Since I had a Rane AC22B crossover lying around, I gave up for now and swapped the Infinity crossover out for the Rane, and set the (24db/octave) crossover point to 120Hz. (The Infinity crossover implements a passive second-order crossover point at 150Hz). Finally the system was dead silent when it should be.

    (I’ve worked on the Infinity crossover a bit since I put it on the shelf, and found that the ground shields on the RCA connectors weren’t all at ground potential, so I’ve ordered some gold-plated replacements from China and will install them when they arrive. I’m hoping that will quiet down the noise so I can use the Infinity crossover).

    After setting up the Rane crossover, I balanced the woofers with the midrange/tweeters by ear, but was disappointed in the low bass. Out came the laptop with Room EQ Wizard on it, and I got out my instrumentation microphone and looked at the room response. Without the Infinity servo crossover, the bass towers rolled off at 12db/octave starting at 60Hz or so. Since I was messing with REW anyway, I created some filters to smooth out the room response and a shelf filter to bring back the bass down to 30Hz. Since I no longer listen to vinyl (it's been about 20 years - is anyone interested in a SOTA Sapphire turntable, Dynavector Karat 23R cartridge and a Linn Ittok II tonearm?), and no longer listen directly to CDs, my only music source is digital from a PC running JRiver Media Center. JRiver has a very handy DSP module that will use convolution filter sets that you can generate with REW, so I installed my filters and things sounded much, much better. These speakers now go really low: for instance "Thanks to You" by Boz Scaggs is very impressive, as is the Chesky binaural demo recording of the Bach Toccata & Fugue.

    As I mentioned, there are some cosmetic issues with the enclosures, so I'll eventually be taking everything apart to refinish the cabinets. Also, though they work, the upper midrange EMIMs look pretty sad with some delamination of the traces from the diaphragms (presumably from playing Rock at sound reinforcement levels). Perhaps I'll invest in some replacement EMIMs and keep what I have as spares.

    Since, as far as I can tell, the only difference between the RS1, RS1a, and RS1b is the crossover, and since the crossover schematic to the RS1b is available, I’ve decided to upgrade my crossovers to RS1b specs. My next long post in this audio adventure thread will be about that work, and what I learn.

     
    Last edited: Mar 13, 2018
    Bahamayellow, 7.62, StimpyWan and 2 others like this.

     

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  2. Infinity!

    Infinity! Active Member

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    Congrats on your speakers! Since you are already opening up the crossover, you should replace the caps in it as well as they are 30-40 years old. I replaced the caps in my IIb EQ and it helped clean up the bass while taming some of the highs. Besides that, you'll have to let us know how they sound when you get the original Infinity crossover working and set up. Once again congrats and enjoy! :)
     
  3. okeeteekid

    okeeteekid Well-Known Member

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    Location:
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    Congrats! those crossovers come up on the bay every once in a while as do EMIM's, it's hard to see any water damage on the speakers from the pic, they look great.
     
  4. kurtgo

    kurtgo AK Subscriber Subscriber

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    Location:
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    Congrats on your speakers and your restoration efforts.
     
  5. geoff727

    geoff727 Well-Known Member

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    Location:
    Seattle, WA
    I love your story. Just one question....is your listening chair really right in between the two speakers? 'Cause, you know, these are dipoles, and they don't radiate too much to the sides.

    Sorry, I couldn't resist! :D
    G~
     
    pauljh and Infinity! like this.
  6. 7.62

    7.62 Gearhead Subscriber

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    Very nice, I believe I had seen those and showed them to the wife, just don't have the room. One thing I can say if I lived anywhere near Woodland, CA I'd be in a constant state of broke as I think I've seen every bucket list Infinity for sale at one time or another.

    Very informative post and I very much will be sifting thru some of the things you've said. Especially on the digital stuff. I very much want to go this route in my future audio room. I'm putting the brakes on here as I look into a dedicated 20 amp line to this room.

    And I also applaud you for diving into the restoration of those Beatiful Infinity's.
     

     

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  7. StimpyWan

    StimpyWan AK Subscriber Subscriber

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    A great story, and a nice save. It sounds as if your RS-1's went to the correct owner.

    Also, GRAZ, at Apogee Acoustics in Australia, was reproducing a new Infinity EMIM diaphragm. They were reported as being very well made, and better sounding than the originals. While not cheap, they seem a good investment. Especially, for the dedicated midrange EMIM.
     
  8. pauljh

    pauljh Active Member

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    132
    Location:
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    Chapter 2, the RS1 passive crossover.

    Before I got out the soldering iron and attacked the crossovers, I figured it would be good to know what I had. So, I opened up the crossover box on the bottom of one tower (see jpeg attached) and studied things so I could draw a circuit schematic, which I have attached below. I also hooked up a voltmeter to each of the five crossover channels in turn and measured the -3db points. I put those in a table, and made a jpeg copy thereof, which I have also attached below. For completeness, I have also attached the Infinity techsheet on the RS1b, as we will be comparing the RS1 crossover to the one in the RS1b. And finally, there is a frequency plot from CircuitLab which we will get to presently.
    RS1_Crossover.jpg
    My drawing of the RS1 crossover shows the labeled value of the component (if it was labeled) and also, between “[…]” the measured value if it was an unlabeled component, or if it measured different than it was labeled.

    The differences between the two crossovers are:
    1. The addition of a pot to control the output level of the upper-freq EMIM
    2. A change to the low-freq EMIMs low-pass crossover changing the 1.5mH inductor to 1.0mH which increases the Q and moves the theoretical crossover point from 800Hz to 1000Hz.
    3. A change to the upper-freq EMIM low-pass crossover changing the 0.28mH inductor to 0.4mH which decreases the Q and moves the theoretical crossover point from 3000Hz to 2200Hz.
    4. A big change to the mid-freq tweeters crossover changing the 2nd-order low-pass filter to a 1st-order one and replacing the attenuation pot with a variable band-stop filter.
    5. And finally, the values for the front high-freq tweeter high pass filter have been changed, increasing the Q and moving the crossover point from 9kHz to 8kHz.
    The polarity of the drivers is also different. On the RS1b techsheet, the low freq EMIMs are negative, the upper-freq EMIM is negative, front mid-freq tweeters are positive, the front high-freq tweeter is negative, and the rear tweeter is positive, which because it is facing rearward is really negative [- / - / + / - / + (-)]. Frankly, I’m not sure I believe this, as it doesn’t make a lot of sense. If anyone with an original pair of RS1b speakers would like to confirm or correct these polarities, I would be very interested to hear from you.
    RS1 Crossover Measurements.PNG
    The RS1 polarities for the same five groups of drivers are + / - / - / - / + (-). This is also weird, but it makes sense when you look at the measured -3db crossover points. Referring to my table, you will see that the -3db point for the mid-freq EMIM high-pass filter is 340Hz. This seems a bit low for a claimed 700Hz crossover point. And when you look at a model of the crossover (see the attached CircuitLab frequency plot) there is a gigantic Q. The combination of this filter resonance and overlapping crossover frequencies between the lower EMIMs and the upper EMIM would result in a whopping great increase in output at the crossover point, unless you did something about it. What could you do? You could reverse the phase of one of the drivers so instead of adding output at the overlap, you would be cancelling output. So, it does make a kind of sense. But it makes me wonder why Infinity didn’t just design a low-Q high pass filter at 700Hz and leave the polarities alone?
    CircuitLab RS1 Upper Midrange High Pass.PNG
    I’ve ordered a bunch of capacitors and inductors, and I’ll be rebuilding one crossover so I can A/B the towers and see if one crossover is clearly better than the other. I’ll also be trying out a correctly aligned 2nd-order Butterworth filter for the 700Hz crossover point, changing the polarities to match. Maybe I’ll learn something.
     

    Attached Files:

  9. windsor905

    windsor905 New Member

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    You don't see the couch positioned roughly where the photograph was taken from. :D
     
  10. windsor905

    windsor905 New Member

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    I just found a IIb bass EQ on Ebay and it should be here next week (my speakers--IIas I picked up recently, did not have one). I am curious to see how it affects the speakers vs. digital EQ filters. Do you have any experience with that?
     
  11. windsor905

    windsor905 New Member

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    Curious: What do you do to isolate the ventilation fan noise of your Hafler from disrupting your listening pleasure? I recently came into a pair of P500s, and I find them useless because of the noise in the background during quiet passages.
     

     

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  12. StimpyWan

    StimpyWan AK Subscriber Subscriber

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    I use a 14'x16' spare bedroom, for my listening room. I use that, instead of the larger Den that's upstairs, because the Den opens to the Living Room, due to a cathedral ceiling that's adjacent to the Den. So while my wife likes my toys, I like to be respectful to everyone else at home, and use the closed bedroom instead of the open Den, for my music and movies. As such, my gear is in the bedroom walk in closet. No noise pollution that way! :)
     
  13. windsor905

    windsor905 New Member

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    I tried inside the fireplace which has glass doors, but too much noise escapes even that way. You have a good solution, but I don't have the space to do that. The spare bedrooms in my little house are 10' x 10' - too small!
     
  14. StimpyWan

    StimpyWan AK Subscriber Subscriber

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    Which brand or brands of capacitors are you trying? NPE or polypropylene? I believe when Paul McGowan, of PS Audio, recapped his IRS-IVs, he had his engineer use Mundorf poly caps. This was at the recommendation of Arnie Nudell. Hence, my curiosity, as to which caps you'll use.
     
  15. StimpyWan

    StimpyWan AK Subscriber Subscriber

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    I have a 2 story house. Living Room, Master, and Library downstairs. Den, Attic, and spare bedrooms upstairs. My wife gets downstairs, and I get upstairs (no questions asked). While I'd love to use the Den, as it's much bigger, my stereo pollutes the downstairs, even at low levels, in there. So, spare bedroom it is!
     
  16. pauljh

    pauljh Active Member

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    I'm using Mundorf MKP polypropylene capacitors, as I asked Paul McGowen (via email) that very question and got the same answer you report. I'm going to leave the 250mF NPE in the low-midrange crossover alone, as it tests fine, and it is just too expensive to replace such a big value electrolytic cap with film caps ($110 per side), plus there isn't room.
     

     

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  17. StimpyWan

    StimpyWan AK Subscriber Subscriber

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    I had a 350uF cap to replace in my Acoustic Research AR90s. I didn't want to build up poly's for that either. So, I bought a Mundorf 330uF E-Cap NPE, and paralled it with a 20uF Axon poly. So far, so good. Parts Connextion sells both brands. Or, check out Sonic Craft. No Axon's, but they have the Mundorf NPE's and poly's. Cheaper than Parts Connexion too.
     
  18. pauljh

    pauljh Active Member

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    Location:
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    The 250uF NPE in my RS1s is bypassed with a 6.0mF polypropylene cap. So I think I'm okay in leaving things as they are.

    Since the RS1/a/b are bi-amped with an external electronic crossover, I have toyed with the idea of removing the lower-EMIM high pass filter altogether. I think its primary purpose is to protect the EMIMs from destruction from careless owners or misbehaving amplifiers (although there may be another reason I'm missing). Should I short across it and see what happens?
     
  19. StimpyWan

    StimpyWan AK Subscriber Subscriber

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    That 250uF cap is series capacitor. So, it's part of the high pass filter for the lower Emim's. I'd be hesitant to short it. While an external electronic crossover should sound better and offer more tweaking flexibility, it might not offer the driver protection that the cap also provides. The 250uF cap acts as a DC blocker, and would help protect against amp turn on thumps and transient spikes too. It's more than just a high pass component.
     
  20. pauljh

    pauljh Active Member

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    Location:
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    The RS1 ships with an external electronic crossover which (or some other external crossover) is required to run the system. The high pass section of the crossover, however, is passive. So it is possible that it was designed to work in conjunction with the high pass filter in the mid/tweeter towers. I think, though, that the major function of the speaker high pass low-EMIM filter is protection.
     
    Last edited: Mar 14, 2018
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