Should I use Impedance 4 or 8?

Many questions posted on this site are things I came across yrs ago so sometimes I wonder why people don’t know this stuff but the again I have to realize some people haven’t been in this hobby as long as others.   If someone tells you to match the impedance tap on the back of your amplifier to the correct impedance of your amplifier, they’re wrong!   Use the tap on the amplifier that sounds best to your ears and your system.  I’ve asked this question throughout the yrs to many tube manufacturers and the consensus is to go with whatever sounds best. One example, in my home, one of my setups is a pair of very large Martin Logan speakers that are 4 ohm load speakers. My VTL tube mono block amplifiers have only one tap, 4 ohm.  Sounds ok on the VTL’s but I get better results on my Conrad Johnson Premier 1b with the 8ohm tap. Some tube amplifiers come with various speaker taps. I’ve found that to be very useful in helping to get things to sound right. I’ve found in my experimenting throughout the years that 8 ohm tap usually sounds more open, airier, and detailed than the 4 ohm tap and 16 ohm sounds even more airier and open over the 8 ohm tap on my amplifiers.  On myML speakers, I have a perfect sound using the 8 ohm tap on my amp.  Go with whatever sounds best to your ears, you will not be damaging any of your components. Been in this hobby for 35 yrs and I have well over 20 tube amplifiers and a few speakers and never experience any form of issues of concerns. 

@allears4u 

You have received good advice to try both and pick what sounds best.  I don't understand the electrical principles but as an example, I have Audio Research tube amps and 4 ohm speakers.  ARC told me directly to use the 8 ohm taps and that's what I do with great results.

Considering the purchase of a CJ ART 150 amp, I realized that there is only one tap for 4 ohms - and my speakers are rated 8. I tried to find an answer online and I've seen a range of answers from "no problem at all" to "risky for amp and/or speakers" - all with a good degree of certainty. Unfortunately that kind of distribution makes it very hard to actually answer the question. Some suggested calling the manufacturer, so that's what I did last week. The following is what I heard from CJ (I think I understood correctly - don't shoot if details are not fully accurate - but the conclusion remains the same):

A "nominal" 8 ohm speaker is based on a measurement at a given fixed frequency (I believe 1kz but don't quote me on that) and as agwca above was saying, the impedance varies quite a bit with the frequency. For many speakers it dips below 8 esp. in the lower frequencies where it is closer to 4. Therefore they picked 4 as a better match, and according to CJ it works for 98% of the speakers. Only those speakers rated higher than 8 ohms may be a problem, in that case they can reconfigure the amp to a 16 ohm tap but otherwise 4 ohm is the preferred choice (and the only choice on ART 150). 

When I read the technical review of my speakers (Paradigm 9H), the reviewer stated that the "real" impedance (measured) was lower than 8 ohm (less than 4) given the frequency changes and related fluctuations. This is consistent with the above.

One thing to keep in mind is that it is not only about impedance: one needs to also consider amp power (which also changes with impedance) vs. speaker sensitivity. Therefore I assume switching taps on a 25 watt amp paired to low-sensitivity speakers may have more of an impact than a 150 watt amp paired to same speakers. If the amp has to work harder this could explain a less happy sound. In my case, my speakers are 93db sensitivity which is reassuring on the power-matching standpoint.

Anyway, I think I answered the question for my specific case and learned something along the way. Your results may vary due to amp and speaker specs, so your best option may not be same as mine, but based on the comments from a reliable source, 8 ohm speakers should be able to be plugged in 4 ohm taps without blowing up the system. I hope this was helpful.

Considering the purchase of a CJ ART 150 amp, I realized that there is only one tap for 4 ohms - and my speakers are rated 8. I tried to find an answer online and I've seen a range of answers from "no problem at all" to "risky for amp and/or speakers" - all with a good degree of certainty. Unfortunately that kind of distribution makes it very hard to actually answer the question. Some suggested calling the manufacturer, so that's what I did last week. The following is what I heard from CJ (I think I understood correctly - don't shoot if details are not fully accurate - but the conclusion remains the same):

A "nominal" 8 ohm speaker is based on a measurement at a given fixed frequency (I believe 1kz but don't quote me on that) and as agwca above was saying, the impedance varies quite a bit with the frequency. For many speakers it dips below 8 esp. in the lower frequencies where it is closer to 4. Therefore they picked 4 as a better match, and according to CJ it works for 98% of the speakers. Only those speakers rated higher than 8 ohms may be a problem, in that case they can reconfigure the amp to a 16 ohm tap but otherwise 4 ohm is the preferred choice (and the only choice on ART 150). 

When I read the technical review of my speakers (Paradigm 9H), the reviewer stated that the "real" impedance (measured) was lower than 8 ohm (less than 4) given the frequency changes and related fluctuations. This is consistent with the above.

One thing to keep in mind is that it is not only about impedance: one needs to also consider amp power (which also changes with impedance) vs. speaker sensitivity. Therefore I assume switching taps on a 25 watt amp paired to low-sensitivity speakers may have more of an impact than a 150 watt amp paired to same speakers. If the amp has to work harder this could explain a less happy sound. In my case, my speakers are 93db sensitivity which is reassuring on the power-matching standpoint.

Anyway, I think I answered the question for my specific case and learned something along the way. Your results may vary due to amp and speaker specs, so your best option may not be same as mine, but based on the comments from a reliable source, 8 ohm speakers should be able to be plugged in 4 ohm taps without blowing up the system. I hope this was helpful.

Considering the purchase of a CJ ART 150 amp, I realized that there is only one tap for 4 ohms - and my speakers are rated 8. I tried to find an answer online and I've seen a range of answers from "no problem at all" to "risky for amp and/or speakers" - all with a good degree of certainty. Unfortunately that kind of distribution makes it very hard to actually answer the question. Some suggested calling the manufacturer, so that's what I did last week. The following is what I heard from CJ (I think I understood correctly - don't shoot if details are not fully accurate - but the conclusion remains the same):

A "nominal" 8 ohm speaker is based on a measurement at a given fixed frequency (I believe 1kz but don't quote me on that) and as agwca above was saying, the impedance varies quite a bit with the frequency. For many speakers it dips below 8 esp. in the lower frequencies where it is closer to 4. Therefore they picked 4 as a better match, and according to CJ it works for 98% of the speakers. Only those speakers rated higher than 8 ohms may be a problem, in that case they can reconfigure the amp to a 16 ohm tap but otherwise 4 ohm is the preferred choice (and the only choice on ART 150). 

When I read the technical review of my speakers (Paradigm 9H), the reviewer stated that the "real" impedance (measured) was lower than 8 ohm (less than 4) given the frequency changes and related fluctuations. This is consistent with the above.

One thing to keep in mind is that it is not only about impedance: one needs to also consider amp power (which also changes with impedance) vs. speaker sensitivity. Therefore I assume switching taps on a 25 watt amp paired to low-sensitivity speakers may have more of an impact than a 150 watt amp paired to same speakers. If the amp has to work harder this could explain a less happy sound. In my case, my speakers are 93db sensitivity which is reassuring on the power-matching standpoint.

Anyway, I think I answered the question for my specific case and learned something along the way. Your results may vary due to amp and speaker specs, so your best option may not be same as mine, but based on the comments from a reliable source, 8 ohm speakers should be able to be plugged in 4 ohm taps without blowing up the system. I hope this was helpful.