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speaker impeadance question

Hi everyone, 

Out of curiosity I was playing around with the 4 and 8 ohm taps on my Mcintosh MC601 mono blocks last night. I currently use Sonus Faber Olympica iii speakers which have a nominal impedance of 4 ohms. I have run them on 4 ohm from day one (non bi-wired), but I was quite surprised to hear that there is a very distinct difference in SQ (positive) moving from the 4 ohm taps to the 8 ohm. So after doing a little digging I was able to find the impedance plot for the speaker and according to the plot I can see why they are rated at 4 ohm but what I don't understand is why they sound so much better at 8 ohm. What I am concerned about is the huge spike at 3khz ..see link below:

https://www.soundstagenetwork.com/index.php?option=com_content&view=article&id=1285:nrc-meas...

So I thought I would throw this out on the forum to see what you guys think in regards to using the 8 ohm taps based on this plot. 

Thanks in advance

-Keith
barnettk
mijostyn's avatar
mijostyn
8,570 posts
 
Keith, yes it is likely that the speakers will sound brighter on the 8 ohm tap and it might also be more sibilant. Depends of your room. But you are not going to hurt anything running them on the 8 ohm tap. It is all about what sounds most natural to you. But, if female voices and violins hurt too much you might go back to the 4 ohm tap.
It is not unusual at all for speakers to have wide impedance swings. Going too low bothers amps the most in term of stability. Higher and the amp just has less work to do.

Mike
barnettk OP
410 posts
 
Thanks. I plan to keep it on the 8 ohm connections for about a week and further evaluate which of the two I like the best but from what I heard last night I think I like the way they sound on the 8 ohm tap. I was a little concerned about the possibility of damaging the speaker. I don’t really drive them that hard so it should be fine. 

Thanks again
atmasphere's avatar
atmasphere
11,778 posts
 
You won't damage the speaker. The feedback in the Mac will handle that impedance spike just fine.
audiokinesis
2,735 posts
 
" What I am concerned about is the huge [impedance] spike at 3khz..." 

Notice that this impedance spike (which is closer to 2.5 kHz) corresponds with a frequency response dip, when driven by whatever voltage-paradigm amp the NRC uses. So an amp like your McIntosh, which is more of a power-paradigm amp (outputs constant wattage rather than constant voltage) fills in that frequency response dip somewhat. This is a really nice synergy.

Duke
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