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Actual impedance (over entire freq range) of Cornwall Is?

Bob Gardner

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I recently saw a very positive and very informative review of the Heresy IV.  The review noted that, while the nominal impedance of that speaker is 8 ohms, they used advanced instruments to test the actual impedance at multiple frequencies and over all frequencies, and the actual impedance was closer to 4 Ohms than it was to 8 Ohms (according to the article).


I ask because I recently acquired a McIntosh amp (an MC-2120) with four sets of output terminals, for 2, 4, 8 or 16 Ohm impedance speakers, and if my Cornwall Is are actually closer to 4 Ohm impedance, the amp may respond with more dynamic output or lower distortion on the 4 Ohm terminals.




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4Ω Is the probably the closest answer if you don't want to experiment.


Your amp can dissipate much more power than the Cornwall will ever need, thus I'd suspect that the 2Ω output terminals will sound best because it will result in the least frequency response variation due to the amp having the least output impedance. Then again, the frequency response variation may sound nice, thus I'd consider the 8Ω output terminals as well.


You can measure it yourself very accurately using the Dayton Audio DATS.


God bless you and your precious family - Langston

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Hi Bob Gardner, when I first read your post I assumed that your amp must be tube because of the presence of different ohm value speaker taps. Imagine my surprise when I looked it up and found it to be SS. I had no idea that multi-tap SS amps existed!


And a 2ohm tap; now that's gotta be rare. I think the existence of the 2ohm tap speaks volumes about the low impedance ability of that amp.


I read the same thing regarding the true impedance of those speakers; might've been the same review. The guy said the true impedance was 5ohm so should be rounded to 4ohm since he said designers don't like using odd numbers (for some odd reason - pun intended 😉).


I agree with Langston and jcn3; conduct a listening experiment using multiple taps and then use that DATS test mentioned above and see what it reveals.


The picture I saw of the MC-2120 reveals a nice looking piece of gear. Is it vintage? It looks so. Prob no longer made huh?

Btw, when was it made?

I've recently been bit by the vintage bug, acquiring a couple of Japan-made pieces [Sony preamp/Marantz amp], probably made around late '90s or 2000-ish and they sound great. I'm almost tempted to never buy new again.


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