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jwgorman

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    1985 Cornwall issue

    in Technical/Restorations

    Posted

    Are those Cornwall IIs?

    I acquired a pair of Cornwall IIs last year (circa 1986) and rebuilt the crossovers as a matter of maintenance. I found a solder joint that was pretty questionable, so I’m glad I did. I guess you could start troubleshooting and pull a lead from every driver except the squawker, and with a pink noise signal  at a constant spl and an spl meter at s fixed close distance, see what you find. If you keep the variables as close to the same as possible and one squwaker is louder you can then troubleshoot further to see if it’s a diaphragm issue or a crossover issue. 

    There are a lot of smart guys on this board who will probably chime in with a better test but that’s one way. 

    Here are what my crossovers looked like after I rebuilt them

    2D050EB2-4BFE-4BE9-A5A1-C5400AC37A4A.jpeg

    Heil Air motion transformer for Cornwalls

    in Technical/Restorations

    Posted

    On 12/29/2018 at 8:53 AM, Chris A said:

    I believe that it's worthwhile to list the downside to using AMT drivers on top of Cornwalls:

     

    1) The AMTs really aren't as capable in very high SPL as the original Klipsch drivers.  If you find yourself regularly listening at 105+ dB at your listening position (for instance, daily or perhaps more than once a week), I'd rethink using AMTs because their measured distortion levels will probably be higher than the Klipsch drivers/horns at those SPLs.  This isn't really that significant a factor, but it is one that you should consider for your application.

     

    2) The AMTs have a real problem in the vertical direction coverage.  I'm working on dealing with this using horn closures/extensions, but so far, it's pretty complicated.  I'd strongly recommend listening on-axis or within ±10-15 degrees.  I'd be careful of putting anything acoustically reflective just above these drivers, since they will reflect a tonally imbalanced off-axis acoustic energy which could affect your listening pleasure.  I'd be in favor of adding absorption to low ceilings and/or furnishings that are in the near field of these tweeters in the vertical direction.

     

    3) Setting up your DSP crossover to balance the PEQs vs. frequency will likely be a much more difficult task than your basic Cornwall due to the dipole radiation pattern of these drivers.

     

    4) I would seriously think about completely absorbing the backwave if you place the AMTs within 2 feet of a wall or another acoustically reflective surface immediate to the rear of the driver.  Otherwise what you're going to hear isn't going to be nearly as pleasant to listen to in terms of overall tonal balance and/or soundstage imaging.

     

    5) Remember to keep the closest crossover driver as close as possible to your AMTs.  That means the midrange horn mouth or woofer.  Do not separate the AMT far from its closest driver unless you're ready to hear issues with lobing and separation of higher frequency sources.  If using a Cornwall woofer only in a two way configuration (they way I use mine), I recommend flipping the Cornwall bass bin over 180 degrees to keep the woofer as close as possible to the AMT.

     

    6) I'd also recommend keeping the AMT centered on top of the Cornwall cabinet (and moved to the back of the cabinet if using crossovers without channel delay capability) with soft absorption material on top of its top surface to acoustically absorb the nearfield reflections.  I'd recommend making sure that you use soft absorption material on top before trying to set the delay values for the AMT channels is using a DSP crossover.  Look especially at the off-axis performance of the driver with the crossing drivers (horizontally at 20-45 degrees angle from the centerline of the driver).  You might be surprised. 

     

    Chris

    Chris, is the distortion issue mitigated by say a second order filter on the AMT, crossed at say 3k? Every once in a blue moon I’ll briefly play music that loud. 

    Crites titanium diaphragms for K79 tweeters

    in Technical/Restorations

    Posted

    As some of you know, I’m very sensitive to tweeters :)  Even as an old guy who can’t hear much beyond 12k, for some reason an otherwise great speaker sounds bad to my ear if the tweeter is mediocre. 

    I’m putting my Cornwalls back together from ESS experimentation and decided to try the Crites Titanium replacement diaphragms for the K79s in my CWII. Wow!

    They totally transformed my tweeters and made the sound very, very good.  

    My original diaphragms measured fine but the Crites are so much more detailed and smooth at the same time. Don’t hesitate if you’re sitting on the fence. 

    70E03F82-21BA-482D-852D-19E6BF34499E.jpeg

    • Like 1

    Heil Air motion transformer for Cornwalls

    in Technical/Restorations

    Posted

    4 hours ago, Chris A said:

    Anyone that doesn't believe in drivers breaking themselves in within the first few hours of operation, here is a comparison of the step response of the AMT-1 plus Cornwall combination new out-of-the-box (green trace) and after perhaps 12-24 hours of operation (red trace):

     

    883555950_AMT-1plusCornwallnewandbrokeninstepresponse.thumb.jpg.554deb47bedfaae9e176d960484c4428.jpg

     

    That's about as much difference in response as I have ever measured from one driver.  Bottom line: get a few hours on your AMTs then recheck them to rebalance their DSP settings.  They apparently went from 1.5 ms delay (relative to the Cornwall bass bin) to zero delay.  The required EQ changed fairly extensively, too.

     

    Chris

    Good to know. That explains a lot. Thanks Chris. 

    Heil Air motion transformer for Cornwalls

    in Technical/Restorations

    Posted

    15 minutes ago, pzannucci said:

    Sadly, can't leave well enough alone.  Just as jwgorman gets convinced to go two way.

    Well.  Maybe. I’m going to go passive. And, I already have the mids. Dang it. I’m trying to model bessel 2nd orders at 400 and 1500 and compare them to 300 and 1200. I mean, on paper, it looks good. 

    But my cabinet maker can’t get to my project for another month. So I have plenty of sleepless nights ahead. :)

    Heil Air motion transformer for Cornwalls

    in Technical/Restorations

    Posted

    2 hours ago, Chris A said:

    Comments:

     

    1) I recommend flipping your Cornwall upside down in order to get the woofer much closer to the AMT on top of the cabinet to reduce polar lobing and to get the midrange of the woofer much closer to the highs of the AMT.  This audibly coalesces the vertical soundstage image further.  If you have risers, just take the screws out and reuse the risers free-standing under what was the top of the Cornwall.  A little wood filler will hide the screw holes from the riser on what was the bottom of the Cornwall box. 

     

    2) The electrical leads on the AMTs seem to be color coded opposite of the polarity that I'd guess.  The reddish-purple lead is actually the negative lead according to the SPL vs. frequency near the crossover region that I ran switching polarity.

     

    3) The phase plot for the AMT-1 is almost unbelievably flat--less than 45 degrees of phase wander (measured in-room) until you get to below 2 kHz.  The harmonic distortion numbers are also amazingly low (all are less than -55 dB ref. a 90+ dBC on-axis). 

     

    4) These are really dipole drivers--believe it.  The rear-wave shows up almost perfectly in the spectrogram plots. Recommend moving them out a little bit from reflective walls if you can.  It helps the spaciousness greatly (but basically decreases deep bass response...bummer).  I found that I needed about 1.5 ms of delay using Bessel 12 dB/octave filters if you reference the AMTs flush to the front of the Cornwall cabinet.  They're also much less sensitive than the Cornwall midrange and tweeter, so you'll likely need to bi-amp them (as I'm doing) in order to avoid having to pad down the bass bins further.

     

    5) This is, on balance, a fairly spectacular upgrade to a Cornwall--or any Klipsch Heritage loudspeaker (JMTC).  $280USD for two.  They're stayin'...

     

    Chris

    Thank you sir, I never would have thought to turn the Cornwalls upside down! And thanks for measuring them. I do enjoy them much more with a couple of feet between the AMT and the wall. 

    I have contacted a cabinet maker to build a Cornwall with a M5N8 Faital Pro essentially where the tweeter is now on my stock Cornwalls.  I will have enough room to accommodate an LTH142 (or similar large horn) if I do not like the experiment with the M5N8.

    Last weekend I actually ordered another pair of the ESS AMT1s. 

    I really think this is a worthwhile experiment. 

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