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MCM 55-5660

So perusing the new KB line from MCM got me interested in some of the smaller diameter models, the 5" in particular. It looks like it has an underhung coil which, with the copper cap, should provide a very nice distortion profile. 

On the other hand, advertised Qts is fairly high and the gap is fairly short, which might limit it to pure midrange or fairly limited extension usage - so...

When I read the ad-copy, I feel they are targeting Dayton's Reference series and what I see is an improved basket (the Dayton's lack under spider venting), copper in the motor (on the RS180 at least, there is no copper - the only shorting device is the phase plug itself), and of course the underhung voice coil - although I have heard compelling arguments in both directions for the benefits/drawbacks of such a thing. For now, I'll just ask this question:

"Do you think this driver has the potential to be a high end midrange in a large 3-way?" 

I love the Taiga tower speakers, listen to them every day in fact, but I feel the itch for a new set of towers building up - and a thread over at "the other place" started by someone who really has issues with understanding certain aspects of DIY and associated costing got me to thinking... 

This particular driver has an impressively flat impedance profile, and although at first blush the response curve looks goofy that broad depression between ~400 and ~1500 will actually be a benefit when installed in a cabinet. Within the expected pass band, the response is smooth - if not flat. 

Rumor has it that the KB series is showing up at MCM today - so sometime next week I will have a pair of the 3" and a pair of the 6.5" in-hand and will do some testing. The 6.5" are not mine to keep, but if the testing goes well I will purchase a pair of the 5" and test those. 

For the proposed (purely theoretical at the moment) high-end, ignore individual driver cost and focus on performance 3-way I think the best tweeter choice will be the Viawave ribbon, or if something cooler comes out in the meantime along the lines of ribbon drivers - I'll use those. I have been listening to the RS28A this week, and although it is a kickass tweeter - I guess I just prefer ribbons these days. There, I said it.

For shoring up the bottom end - I will wait for results on the 6.5". If the T/S indicate reasonable extension (under 45Hz F3) and the advertised 7.5mm Xmax holds up under scrutiny they should offer some serious bang for the buck performance as well. Bonus is that the overall footprint and aesthetics would probably end up very similar to Taiga (although Taiga has an F3 of 33Hz). 

Geoff, I would once again like to thank you for steering MCM in this direction. PE is a great company, but they have stood alone for too long in the world of in-house branded, high value drivers. I love having options in these price ranges.  
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Ge_off_meJasonPBryan@MAC

Comments

  • I'm excited to see what you think about the drivers once you receive them.

    Our goal was to design something that everyone would see and immediately have projects running through their mind. I personally have my eyes set on the 8" ;)

    We are trying to get our line to take off, and everything you guys are doing helps us. We want to make great drivers that are affordable to everyone, and we seem to be doing alright so far :)

    Thank your for the praise, and the topic starter.

    Best Regards,

    Geoff Schneider
  • The Kb series drivers were received in and should be ready to ship either today or Monday :)
  • Awesome! Very excited to run them through the ringer.
    I have a signature.
  • Looks neat as an extended mid. Not too sure how it would do as a woofer though with a gap height of 6mm, I find it hard to believe the Xmax is really 1mm, underhung or not.  Run it with a nice 10 or 12 from 200 to 3K crossed hard on top and I would bet it would be a hell of a winner. I agree with the reaponse, wonky, but curvy in all the right places. I would take no issue with it. 
  • Looking forward to some data on this driver!
    = Howard Stark: "This is the key to the future. I'm limited by the technology of my time, but one day you'll figure this out."
  • Just got a pair and did a little measuring. :)
    Here is a picture of the conditions. ARTA @ 4in.


    Next impedance and phase overlap

    DATS of #1.

    DATS of #2.

    #1 FR & distortion.

    #2 FR & distortion.

    Enjoy.
    Mzisserson
    ............. could you hum a few bars.
  • Sorry for resurrecting an older thread...

    I bought a pair of these MCM 55-5660 drivers from Johnny this past weekend in Iowa.  Thanks JR for the smokin deal!!!

    Anyway I had a chance today to do a thorough inspection of these drivers and measure them with DATS.  So after that I fully agree with Johnny:

    - the frame is very nice, much more elegant than the RS150P's clean but simplistic frame.  Under spider venting takes it to another level IMHO.

    - the kevlar/paper mix cone is every bit as nice as the Dayton RS paper series.  Same conical profile, almost the same Mms.  The RS has a higher Mms probably due to its longer voice coil (over-hung design).

    - flexing the suspension exposes a copper ring on the pole piece!

    - the glue lines are very clean and consistant.

    - polished phase plug (extended pole piece).  It looks nice but I will probably knock it out and anodize it black, then reinstall it.

    - DATs measured T/S parameters are spot on.

    - the biggest difference between this driver and the RS series is the under-hung design.  This yields a very limited Xmax but I suspect better distortion performance.  This driver would be a huge disappointment if you were expecting any bass performance.  But if you deploy this driver as a dedicated mid it should perform stellar.  I will be trying this driver as an OB mid in a 3 way, crossed over at 200 Hz or higher.

    JasonPjr@macBryan@MACS7910
  • PWRRYD said:

    - the biggest difference between this driver and the RS series is the under-hung design.  This yields a very limited Xmax but I suspect better distortion performance.  This driver would be a huge disappointment if you were expecting any bass performance.  But if you deploy this driver as a dedicated mid it should perform stellar.  I will be trying this driver as an OB mid in a 3 way, crossed over at 200 Hz or higher.

    One thing I don't see talked about anymore is the way theoretical xmax is calculated. In years gone by, xmax used to be extended by one-third the height of the magnetic gap. In the modern era this has been taken away. I believe this was meant to simulate the extension of the field beyond the gap, as it isn't like the field just stops instantly outside it. I'd be interested in other peoples knowledge of this calculation method.

    I mention this here because it would radically change the calculated xmax of a lot of under-hung drivers. I'm not sure if it would generate a realistic number though, I suppose klippel studies would be needed to confirm.
    = Howard Stark: "This is the key to the future. I'm limited by the technology of my time, but one day you'll figure this out."
  • I wish I would have bought up a bunch of these when MCM folded - they look really nice even at full price.  Then again, they would probably just be chillin' on the shelf with everything else that hasn't found its way into a project.

    Jason, I've seen some Klippel reports that reveal Bl and Kms induced distortion well before Xmax and some that look good well after Xmax.  Some underhung and some overhung and some stark differences even within a line of drivers (i.e. the 5" driver will underperform its Xmax while the 7" driver outperforms it).  I don't know what all the variables are that produce these differences, but generally, the underhung coils have pretty broad, flat Bl curves that fall off rapidly after some point.  It wouldn't surprise me if these KB drivers have a good 4-5mm of low distortion excursion before hitting a wall.

    Dan
  • Thanks for bumping this up Craig.

    I pulled some measurements from the pair I got from JR at DIY Iowa (how many pairs did he bring, lol). I agree with Craig and JR on their assessments of the driver. I measured about 3mm peak xmax before the suspension ran out of flex FWIW.

    Very solid midrange driver in a three way. I'm planning on using mine with a Gradient tweeter (thanks JR!) as a sealed top end over a pair of dipole 12" woofers.
  • That sounds like an interesting project Matt.
  • And if those 12" woofers are the ones I think they are...  pm me...  I have two more with your name all over them ;)
  • PWRRYD said:
    That sounds like an interesting project Matt.
    It'll be a learning experience for sure. You planted the seed with the twelves ;) , Tajanes' dipoles gave it the final push to fruition.
  • I have two more of those woofers that you can have.
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