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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
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
12,168 posts
 
You won't damage the speaker. The feedback in the Mac will handle that impedance spike just fine.
audiokinesis
2,772 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
erik_squires
16,892 posts
 
What huge spike??

That's very typical for a speaker with a 2 way crossover. What I'm impressed with is how flat the rest of the speaker impedance curve is.
barnettk OP
410 posts
 
Thanks for the response Duke and Erik. Right I am aware that speakers change impedance at different frequencies. I was only concerned because I changed from the 4 ohm to 8 ohm outputs. Which is why I looked for the data in the first place before changing it permanently.  I too was quite surprised to see how flat the impedance curve was. the amps run very cool, but I guess that’s not unusual for McIntosh Amps, but I’m sure the rather consistent impedance helps also.

Anyway. Listened most of the day today to various samples of music and so far I do like these speakers on the 8 ohm taps. I think that is where they will stay for a while at least.

Thanks again

-Keith
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