Finding (calculating?) speaker and amp impedance

Thank God for John Atkinson.  From my long experience in reading Stereophile technical reports it's very rare that some part of a speaker's impedance curve isn't below 4 ohms.  And vanishingly rare at 6 ohms.  Accordingly most valve amps should almost always be set to their 4 ohm tap.  If they have one.  Atkinson nearly always recommends this.  Flea power examples should really only be run into 'full' range horns with sensitivity in the high 90s and above.

@hleeid 

Surprisingly (to me) was finding out that my old 80 db sensitive little monitors are known to be great with tube amps. These are Rogers LS3/5a from the early 70s

This represents the significance of the speaker impedance load and curve characteristics. Yes, these were very low sensitivity speakers, however they were 15 ohm impedance, so very easy to drive.

The sensitivity measurement of a speaker has more to do with limits of volume/SPL for a given amount of amplifier power. How easy a speaker is to drive has more relationship and effect due to the impedance load/characteristics.People could drive the Rogers monitor speakers (82 db sensitivity) easily with low power tube amplifiers due to the very friendly 15 ohm impedance it has.

Charles

Good timing for this topic. Using a pair of Focal Aria 936’s with a PL HP Integrated and all is good. But…I just had my 45 year old Sansui AU-717 fully restored and it’s in transit as I type this. Per Stereophile’s review, these speakers drop to about 2.7 ohms in the mid/bass region, yet publish as 8 ohms nominal. The PL tube amp handles it just fine in either mode (70 wpc in ultralinear, about 40 wpc in triode).

Im eager to try the vintage Sansui in this system upon its arrival. Bad idea?

@chocaholic 

I have a Sansui AU-20000 that will not come out of protection mode.  I've been told it is essentially a boat anchor.  Used it for many years and really liked it, put it in a closet when the ARC amps appeared out of nowhere (wink).

Would you please share the repair shop who did your 717.  Thanks.

Regards,

barts

@barts I was referred to a gentleman on AudioKarma that specializes in vintage Sansui. He stripped boards, removed all old corrosive glue, completely recapped in addition to countless other parts, extensively tested, adjusted bias, burn-in, more measurements, etc…and kept me updated with details and photo’s throughout the process. He’s in a small town in Mississippi and prefers not to ship equipment. So, a 10 hour round trip for drop off and retrieval from here. 
 

Bottom line, it’s more of a hobby for him than a business. I’d want to check with him before passing his name along.