Should I use Impedance 4 or 8?

No risk of damage. Use the taps that sound the best to you.

use the ones that sound the best.

Try them both for a day or so, whichever one you like best. There is no right or wrong way.

There is no damage that will happen in using an output transformer into an unmatched load, however the amount of power available will be greatest into a matched load. Ie 8 ohm tap, 8 ohm speaker.

That said, the damping factor of the 4 ohm taps should be almost double that of the 8 ohm taps. That may be the source of your reduced dynamics issue; overdamping of the woofer. The damping factor (output impedance) will interact with the design of the woofer differently, and since there is no clear guidance, as others have suggested, it seems best to pick the sound that you prefer.

Any chance you contacted Raven Audio to just see what they say ??

I have had Raven Audio since 2019 and have been a very happy customer with them responding to every question I have asked..

Hope you enjoy the Black Hawk , I started with that for month then ended up with Osprey for 5 years now have Reflection with Corvus Speakers and luv the sound.

As you know, that lower-imp. tap is reserved for A+B, speakers connected in parallel or the speaker with lower nominal impedance. A good, issue-free amplifier should not deliver drastically different performance between two taps. When connected to 8 ohm rated speakers, the 2-3 ohm tap on my Parasound NC2125 actually generates less heat and performs more effortlessly than the 4-8 ohm tap.

Maybe this answers it but I'm still very confused about four versus eight ohms.

@viridian  does a great job in his second paragraph and the second paragraph has a lot of information in it.  Maybe some further clarification on this important paragraph. Thank you.

i Use the four ohm from my amplifier because I hear things may sound better when those ranges are explored by my speakers. Speakers tend to very quite a bit in the four and eight areas and this adds to the confusion in my tiny mind.

Yep... Try both...Please let us know if you hear any difference. I have done this and could not tell any difference. 

Yeah. In my experience, disregard the advice some give to go with the tap that sounds loudest. I'm not informed on the science but I suspect more is going on than matching average impedance. My Audion 845 valve monos sound better on the 4 ohm tap into Coincidence Super Eclipses (92dB, nominal 14 Ohm) than they do using the 8 Ohm tap.

The tap that's loudest is the best impedance match.

The tap that sounds best is the tap that sounds best.

The two are usually, but not always, the same.

While I don't use tube amps, the Stereophile impedance curve shown from the review dated Mar 17, 2023 shows what some consider to be an older design when people used tube amps versus more modern designs where impedance curves are both flatter and closer to the 4 ohm mark and can fall under 4 ohms but which may be too demanding for tube designs and even solid state amps regarding heat, clipping, etc.

Personally I think its just a preferred design where low impedance speakers are meant to maximize power output capabilities of well designed amps.  A well designed amp with sufficient heat dissipation will likely have no issues.

Your speakers, along with many modern speakers have widely fluctuating impedance values throughout the frequency range with peaks in the lows, mids and highs but also dips to 4 ohms at various points before peaking upwards.  So the range can vary from 4 ohms up towards 30 ohms or higher. 

Solid state amps are said to be able to output the necessary power for widely fluctuating frequency curves better than tube amps which may like a flatter, less fluctuating curve but the Klipsch are still highly sensitive and easy to drive.  I would think the 8 ohm tap will be less restrictive of power output and the few points at 4 ohms isn't enough to over stress the amp.  If it sounds better, use it.   

The hum might be able to be addressed separately if its an issue.  Definitely would call the manufacturer to discuss how to handle.

If your speakers were an 85dB sensitivity speaker then the curve could be more troublesome and the 4 ohm tap a better choice. 

As to current output requirements, I think the Raven are pretty good at providing current perhaps from something I read awhile back but the fluctuating impedance might also impact.

Ideally for a tube amp, the impedance curve should be flatter say somewhere between 6 ohms to say 12 ohms as an "example" but few speakers have been designed that way with some still being hard to drive too regarding sensitivity and/or current requirements.   

My own speakers, small Audel standmounts have a widely fluctuating impedance reaching a low of 7 ohms in the mids and 5 ohms at the highest frequencies, but reaching a high of around 35 ohms in the mids, probably averaging around 9 to 10 ohms compared to those stated to be 8 ohms.  So, while an easy load for an amp, my smallest integrated which had previously played every  speaker well, sounded flat, duller on these. I was surprised.

My other two amps with more power and capacitance, more current output too made them come to life with my middle power amp sounding preferred to me. Plenty of power for my needs but it won't compete with the LaScalas as to output. 

I drove myself nuts researching impedance curves and no longer worry about it if the system sounds good.  Its still important to know what it does to the power output of an amp (lowering output wattage) but it doesn't mean it won't be sufficient for your needs.  Perhaps the lowing of power output is too much and you might need a more powerful amp, as in my case but that seems to be about it.

Other views might differ on the engineering design and state a flatter impedance is a better target for a designer to achieve and they wouldn't be wrong, but alot of speakers old or modern still have widely fluctuating impedance along the frequency curve. 

You could probably redesign and pay more for a better crossover network resulting in a flatter impedance curve and perhaps a flatter, more linear frequency curve but whether that results in a better sound or not isn't clear, but perhaps it should or at least be truer to the source.  Whether you can do this and how much it would cost is a consideration.  Any speaker can be tweaked I suppose.

There's also a formula where a speaker shouldn't fall below say 0.8 of the nominal rating, for example an 8 ohm rating shouldn't fall below .8 X 8 ohms or 6.4 ohms even if most nominal ratings don't strictly adhere.  So "technically" your Klipsch would be deemed a nominal 5 ohm load accordingly. 

Hope this helps or at least explain some things. 

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.

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.

sorry about the multiple posts : I thought it didn't work and pressed several times...

Ok....my comparison experiment went pretty well. And don't get me wrong. When I say 'hum' I am talking about OCD hum here. The 4 ohm taps have almost 0 hum. I mean quiet quiet quiet BUT the snap and 3-D quality goes too. At 8 ops the music is more lively somehow. The 4 ohm speaker connections present a more two dimensional sound stage. Either one could be a livable sound but I'd rather hear that ever so slight hum presence than lose even an ounce of the dynamics of the music. So my conclusion is: for me my Klipsch Lascalas II sound best at 8 ohms which is exactly what the manufacturer recommends after all is said and done. According to my DB meter neither registers any significant difference in volume. My speakers rate a 104 or 105 db sensitivity rating so power is never an issue. My amp produces 20+ watts which will blow me out if I even think about using a full WATT! Thanks everyone for the feedback