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"New" '78 La Scala's in the Garage


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This is a continuation of a thread started in the Alerts section.



His La Scala's are currently stored in my garage, and I thought I'd post measurements.  These appear to be completely original, except for what appears to be caked drywall dust everywhere.




My first measurement was puzzling, as there were deep notches around 300hz, 700hz, and 3600hz (RED plot).  Everything seemed to be wired correctly, but I decided to reverse the polarity of the woofer.  I think that was the first time in 44 years that the spade connectors had been touched, as they were really stuck to the barrier strip.


The Green plot is with the woofer polarity reversed.  To my surprise, all the dips vanished.  




I did find an FR plot, and the RED plot does seem similar to the solid plot.  Why the 3600hz dip vanished is even more puzzling.  Thoughts?  



I plan on measuring individual drivers next.  I'll be out of town all day so these will have to wait.  I also plan on checking the woofer itself to make sure it was wired properly.



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20 hours ago, Bacek said:

I would place something thick and soft (blanket, pillows) on the floor between mic and La Scala, some of those could be reflection effects.


I wondered the same thing.  Last night I placed a moving blanket on the floor and got the same results.  Today I'm going to place a capacitor across the woofer output just see "see" what happens.


20 hours ago, Deang said:

I used to pay Mike to measure things for me, now I have to pay to make him stop.


Your tab will be going up a little today 😎


I've always wanted to listen to La Scala's, and man they sound good.  This is also the first time I can measure single phase plug K-55-V's.  I did discover that one speaker was missing it's squawker gasket.  Either it's always been missing or they are not as "untouched" as I had thought 😞

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12 minutes ago, mboxler said:


I wondered the same thing.  Last night I placed a moving blanket on the floor and got the same results.  Today I'm going to place a capacitor across the woofer output just see "see" what happens.

 did you check to see if the  woofers are  the  Original  K-33    the lascala  have either a bottom woofer access panel  or an upper panel  

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  • 2 weeks later...

Here are the rest of my findings...


One squawker gasket was missing, the other pretty compressed.  New gaskets installed.


Both AA tweeter inductors were secured with ferrous screws and measured 315uh.  Replaced with non-ferrous and now both measure 265uh.


One AA's woofer inductor measured 2mh, the other 2.5mh.


Removed doghouse from one speaker.  Woofer is K-33-E Square Magnet.


Plots were made on just one speaker, as I wanted to see the how the crossovers measured.


First, I was surprised how little the inductor difference made.  White is 2.0mh crossover, green is 2.5mh crossover.



Next I reversed the polarity of the squawker.  Green is normal polarity, orange is reversed polarity.



Next is a mod that I had to try out.  I've always thought the AA tweeter filter peaked too soon, resulting in the SPL bump between 5khz and 6khz.  I added a 4uf capacitor across the second 2uf of the tweeter filter and remeasured.  It did decrease the bump by 4db, but it also extended the tweeter response (much flatter).  Orange is 2uf, red is 6uf.




Last is a comparison between the stock AA (Green) and the modded AA (Red).




I plan on adding the notch filter to tame the 160hz bump, then I think I'm done! 



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  • mboxler changed the title to "New" '78 La Scala's in the Garage

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