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ML-2C PROJECT COMPLETED: Custom mid-tweeter arrangement

Discussion in 'McIntosh Audio' started by Johnny_Law, Aug 14, 2016.

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  1. Johnny_Law

    Johnny_Law AK Member Subscriber

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    Last night I was listening with my Fisher X100B and without the MQ102 - just to make sure everything worked.

    This morning I checked my midrange polarities (had one backwards, oops), and put the MQ102 between my C32 and MC7300.

    They sounded great last night, without the MQ102, driven by ~25 watts of Fisher tubes. BUT. With the MQ102 and the MC7300 ... my goodness. The bass is deep, strong, and tight kind of a-la AR3a, but turned up to 11. The mids have fantastic depth. I'm not sure how these dome tweeters compare to the original cones, but they give excellent sparkle without being too forward.

    (Just a quick note on the cabinet construction - the inner volume is split horizontally. So, each 12" woofer has its entire sealed volume one on top of the other. It's almost like two ML-1Cs stacked horizontally. I mention this because in my ML-2C searching on here, some people think the 12" woofers share cabinet volume - they don't.)

    I have to say I'm totally, completely impressed and to be honest pretty surprised by how good these sound.
     
    Last edited: Oct 15, 2018

     

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  2. damacman

    damacman Blown and Injected Subscriber

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    You should hear the 4Cs ...
     
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  3. Johnny_Law

    Johnny_Law AK Member Subscriber

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    I can't even imagine. Those must be insane. I've now realized, Roger Russel is a maniac, in the best way possible.
     
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  4. Johnny_Law

    Johnny_Law AK Member Subscriber

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    The sun was making the veneer shimmer earlier, couldn't resist taking a picture, although the picture hardly does it justice.

    [​IMG]
     
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  5. c_dk

    c_dk Addicted Member

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    With the ML2c jammed into a corner it is obvious you two have a serious bass deprived childhood.

    From past room measurements I would expect the RH speaker to see a + 12 dB peak in the bass between 50 and 100 Hz. with a -12 dB drop at 10k. Rock on.....
     
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  6. Johnny_Law

    Johnny_Law AK Member Subscriber

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    Well, I measured the room and placed them as ideally as I could - and likewise with my seating position. But I couldn't hear them very well, sitting on top of them in the middle of the room. So back to a rational location they went. :rflmao:

    Edit: You've got me curious about room measurements now ... all my speakers have always gone where the ML-2Cs are sitting now. There certainly doesn't seem to be a +12dB bass hump from my listening position. But maybe there is? The engineer in me is dying to verify that and/or disprove the hypothesis with measurements. How should I go about that?
     
    Last edited: Oct 15, 2018

     

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  7. damacman

    damacman Blown and Injected Subscriber

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    Look at you .., I was just discussing Scientific Method in another thread. If you don't have access to an RTA, then a simple SPL meter, graph paper, and test tones spaced 1/3 octave apart from 20-200hz would get you started.
     
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  8. Johnny_Law

    Johnny_Law AK Member Subscriber

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    Ooh sounds fun. I have an SPL meter app on my phone. And can play test tones via youtube / tonegen app. So what, just play the test tone at a given volume then record measured SPL around the room?
     
  9. captouch

    captouch AK Subscriber Subscriber

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    I admire all the work you did to get these up and running and sounding as good as possible. :trebon: I bet they sound great.

    An all-Mac setup has appeal to me - just seems right. It's too bad we don't have infinite room or a Jarvis type robotic butlers that would move all our speakers for us and find a magical storage place to store all our excess gear.
     
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  10. damacman

    damacman Blown and Injected Subscriber

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    At the listening spot sir. Then plot it on graph paper to view the response.
     
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  11. Johnny_Law

    Johnny_Law AK Member Subscriber

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    Ah I get it, SPL in one location at one frequency relative to other frequencies at that location, instead of SPL in one location at one frequency relative to SPL in other locations at that same frequency.
     

     

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  12. c_dk

    c_dk Addicted Member

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    The first room voicing I participated in was in Oct. 1978 for a pair of ML2s. They were set up in a typical setup for the day, on either side of a couch in the room corners. As such thy had a pair of table lamps on them and the Mrs.' display of "Precious Moments" figurines. The client's listening chair was across the room, in a mother corner a Forslunds " Rip van Lee" recliner.......so a very typical American living room of the time......No TV, that was for the family room.

    My employer, his client, and RR being bass fans, made use of the Roger's MQ104 design to pull down the room node resonant peaks caused by the corner loading.

    It was a year or so later in solving a 1 dB issue in the critical vocal range that the importance of matching the curves between L&R speakers became apparent, and much more applicable with the MQ107. This really propelled GG's and my ongoing room voicing discussions.

    Reading through Roger's site under the eq heading he highlites other EQ systems but does not mention KEF's or Theil's. I found Stereophile's review of Vandersteen's model 7 and JA's analysis of it's integral 7 band EQ interesting........makes me try to remember back 25 years ago or so when during a surprise visit Richard stopped by while I was doing a voicing on the sales floor.

    Then there was a 1 1/2 year long voicing project......with a pair of ML2s but that tale is best told at another time.
     
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  13. Johnny_Law

    Johnny_Law AK Member Subscriber

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    OK here we go. Sitting in my listening position. (This is a maybe 12 x 16 foot room with 10 foot ceiling?) Background noise present but not loud (fan on elsewhere in house, occasional car driving by outside w/ window open).

    I ran a frequency sweep video on YouTube, and set my app to hold. That's the yellow line.

    This is with the MQ-102 on position 1 on both channels.

    Science!

    [​IMG]
     
    Last edited: Oct 18, 2018
  14. c_dk

    c_dk Addicted Member

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    Interesting snapshot, does not appear to have much if any resolution below 100 hz. What microphone/ measuring app are you using?

    As it is I see plus 12dB, minus 20 dB with -80 as a baseline.

    EQ at 1 adds no bass boost as per RR and would be correct for a corner location.

    I would expect a major node at 50 hz if the measurement system had the resolution. I would guess the room would physically measure odd dimensions that would affect 50, 100, 150, & 300 Hz.

    Did you ever play with wave tanks in Highschool physics?
     
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  15. Johnny_Law

    Johnny_Law AK Member Subscriber

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    I may have noticed something alarming after comparing a picture I took of the crossover against the crossover diagram in the service manual. Someone earlier in the thread suggested the crossovers may have been mucked with ... it looks like that's true, although I didn't notice it before. C3 looks to have been completely removed from the circuit. There's a yellow wire looped to a blue wire. And a red wire that doesn't exist in the manual. So I will need to see what the heck is going on.

    Re: wave tanks in highschool physics, no, but in a past life I was a mechanical engineer. In college I did research into engine intake manifold design which involves a lot of pressure wave physics. It's been a while but I've got some of the basics in my noggin somewhere! Didja know that Helmholtz resonance and "organ pipe" standing wave theory is used to design engine manifolds ... :p
     
  16. c_dk

    c_dk Addicted Member

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    Yes I do, I also remember a article about resizing the intake ports of the old small block ford canted vale heads to improve cylinder filling and flow......mimicking the old tunnel port concepts proved to be too big allowing standing waves to cut the flow rate.......I want to say it was published by Falconer.......

    If each curve is of a individual speaker you can see a number of issues that could be either crossover or room issues.

    If each is of a individual speaker ole' blue eyes would literally jump across the stage each time he hit C5 because of the level difference between each speaker at 500 Hz. If both speakers would have that major dip it would sound like he was singing that note from behind the accompanying band.

    Attacking these speaker pairing aberrations became a big part of the ongoing McIntosh voicing program, especially when the MQ107 became available. I have in the past spoke of my 4 way conversation with Gow, Coderman, and Russell, to solve a 1.5 dB aberration for a especially well trained client.

    This special in house service became a near and dear project for Gow to continue the special services Mac dealers could offer their clients. It was a part of every presentation for Mac owners and those for dealers that I heard after 1980 that he delivered.
     
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  17. Johnny_Law

    Johnny_Law AK Member Subscriber

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    Ok here's a question - I'm worried about blowing the mid domes. I suppose maybe not an issue with my MC7300. But does anyone recommend taking measures to protect them, like wiring fuses into the crossover?
     
  18. c_dk

    c_dk Addicted Member

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    In my experimental Franklin a pair upgrade I used a thermistor type protector from parts express.

    I sent them off to Omaha with my son and a Tandberg TR2060 and he has not had any issues that I am aware of.
     
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  19. mcdmgb

    mcdmgb AK Subscriber Subscriber

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    I am in the same situation as Johnny_Law except the speakers are ML-1Cs. What thermistor would you recommend to protect the mid-domes?

    Thanks
     
  20. c_dk

    c_dk Addicted Member

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    2/3s of the time when I would get invited to voice a pair of ML speakers which were driven by a non power guard amp a mid dome was malfunctioning. Finally needing to schedule a 2nd visit became tiresome so I would keep a replacement dome in my voicing kit.

    Mac was going to fuse the last generation of MLs but decided to introduce the XR series along with the MQ104. They also upgraded the dome design.

    If I remember correctly I replicated what they did but instead of using a fuse I used a resetting 1 1/4 amp thermistor.
     

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