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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
almarg's avatar
almarg
9,670 posts
 
Hi Duke,

I'm afraid I must offer another correction, this being a matter of considerable significance :-)

It was actually a different character, "Emily Litella," who concluded her commentary on Saturday Night Live with the words "never mind."  As I'm sure you realize, Emily Litella and Roseanne Rosannadanna were both characters portrayed by the amazingly talented Gilda Radner, who very sadly is no longer with us.

Best,
-- Al
    
audiokinesis
2,755 posts
 
"I’m afraid I must offer another correction, this being a matter of considerable significance... It was actually a different character, "Emily Litella," who concluded her commentary on Saturday Night Live with the words "never mind." " 

Well, it just goes to show you. It’s always something.

almarg's avatar
almarg
9,670 posts
 
:-)

Best,
-- Al

(For others who may not be aware, Duke's statement just above was made famous by "Roseanne Rosannadanna")

barnettk OP
410 posts
 
Ok thanks for all the great replies. However now that we have cleared up that I’m using SS amps. Has the consensus  changed any? Will I cause any damage to either the speaker or the amp by using them on the 8 ohm taps? I think this is my main question/concern.

Thanks
almarg's avatar
almarg
9,670 posts
 
No, you won’t hurt anything by using the 8 ohm taps.

In some other situations, involving amps that are much less powerful and/or speakers that are much less sensitive, the reduction in the maximum power capability of the amp that would presumably result from using a tap that does not correspond to the impedance of the speaker at most frequencies (especially in the bass and mid-bass regions, where lots of energy is typically required) might be conducive to driving the amp into clipping. Which in turn can be harmful to tweeters.

However, given the "conservatively rated" 600 watt capability of your amp (when load impedance corresponds to the designation of the tap that is used), and given the 88.3 db/2.83 volt/1 meter measured sensitivity of your speakers, and given the "Power Guard" function provided by your amp (which reduces its gain if and when necessary to keep the difference between output and input from exceeding 0.3%), that risk would appear to have zero chance of arising in your particular situation.

Regards,
-- Al

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