Speaker wire impedance? Speaker impedance?

I'll try to be that "guy in the corner nobody talks to" and shed a little light on the topics raised by the OP.

Impedance is somewhat like resistance conceptually, but for AC (as in Alternating Current like the power delivered to our homes or a music signal).  In fact, resistance is a component of impedance which also consists of inductive and capacitive reactance.  What's confusing is that impedance is often measured in ohms, like resistance.  It is helpful to see impedance denoted by a "Z" to differentiate.  

Another notable characteristic of impedance is that it varies with AC frequency.  Speakers can have a "nominal" impedance, such as 8 ohms, but that is an average value.  Speaker impedance varies greatly as you can see in the test results published in Stereophile, by manufacturers, and other places.  The impedance curve is a result of the drivers, cabinet configuration, and crossover.  Speaker impedance generally dips to half of the nominal value, so a nominal 8 ohm speaker will go as low as 4 ohms, and a nominal 4 ohm speaker will goes as low as 2 ohms at some frequencies.

Amplifiers also have an output impedance.  Some amplifiers have a very low output impedance of just fractions of an ohm.  These low-Z amps will often use a follower design or employ generous feedback.  Low-Z amps are often solid state, but tube amps can be built with low-Z as well.  Other amplifiers use very little, or no, feedback and can have an output impedance of several ohms.  High-Z amps are often tubed and can be SE and PP.  However, there are a few high-Z solid state amps such as some of Nelson Pass' designs.

Where it gets interesting is how an amplifier interacts with the speaker it is driving.  The ratio of speaker impedance to amplifier impedance is known as the "damping factor."  A high-Z amp such as no-feedback SE 300b with an output impedance of 2 ohms has a damping factor of 4 when connected to a nominal 8 ohm speaker.  At the other extreme, Benchmark publishes a damping factor of 254 into 8 ohms for the AHB2 at 1Khz.  That calculates to a very low-Z out of ~.03 ohms.

What this means is that a low-Z amp will output the same voltage regardless of the frequency and speaker impedance.  Whereas a high-Z amp will "sing along" with the speaker as the frequency and impedance varies.  Some speakers are design to work with a high-Z amplifier.  Most others are not.

Here are a few things that can contribute to a speaker being considered an "easy load":
 - High nominal impedance (results in a higher damping factor)
 - "Smooth" or flat impedance across frequencies (minimizes voltage variance with a high-Z amp)
 - High sensitivity (speakers can play loudly with little power from an amp)

The OP described Revel documentation warning against using speaker cable with more than 0.07 resistance.  This implies to me that the speaker was designed to be driven from a very low-Z amp and that even a small amount of output (or cable) impedance will affect the performance of the crossover and sound.

I hope this is helpful?

The reason a low impedance cable is "good" is that it will have less effect on the sound.  The amp will mainly "see" the speaker's actual impedance. Energy will not be reactivly stored or dissipated in the cable itself.

The reason low impedance speakers are tougher for an amp to drive is that the lower the load's impedance, the more it starts to resemble a short circuit, which means that current increases.  An amp driving such a load needs a stiff high current power supply.

Nobody understands this stuff, except for that guy sitting in the corner that nobody's talking to.

Can you imagine if cookbooks started using the word impedance in their recipes.

If you don’t understand what someone writes herein, its because they probably don’t know what they’re talking about

A little late on the ball , but get your self a dats v2 from dayton audio. It measures impedans. 

Plenty of information on you tube. 

Thanks for getting back to me @atmasphere ; oops, I see the typo I made.  No, two or three years ago my old Radioshack meter failed the drop test and bit the dust. I replaced it with a Southwire meter I bought at Lowes. It was that meter that I took the readings of 0.07 with and screwed around with adding my second run that I had used for bi-wiring and then read 0.05.

For now I think I can live with knowing that those readings were erroneously high (since Revel was listing 0.07 as the highest resistance for speaker wire; I would say that going by what you have told me I am below that)..

I guess I can add to my list relocating my gear to speakers relationship and either buying short runs of a high quality speaker wire or cutting my Kimber at least in half and then maybe just wrapping un-insulated strands of wire around the posts at one end or the other.

@immatthewj To the first question, yes.

If you were using a Radio Shack meter then you were seeing readings no lower than 0.1.

@atmasphere , after I read the replies I started thinking that the fact that I had always had at least the amp end of my cables connected when I was trying to measure made my readings to not be valid.

I would think that regardless of the length of the cable, the actual resistance was lower than what I thought I was reading?

As far as the meter, I didn't think it was anything special--when my old Radioshack meter that I used to bias my amp, I bought a Southwire at Lowes and that's what I was using.  

@immatthewj As a general rule of thumb, no matter what speaker cable you have, its good practice to keep it as short as possible. This is why monoblock amplifiers are common in high end audio as it allows the shortest cable length possible.

If the cable was connected to an amplifier and speaker, the reading you got isn't representative of anything. That's a pretty good meter that can read 0.05 Ohms BTW!

Your 8TC cables are 9AWG equivalent which is heavy enough for any run inside a listening room.  You have nothing to worry about.

Okay, thanks for getting back to me on that, @carlsbad2  , the reason I mentioned it is because in one of my earlier configurations, in a larger room, I bought cables that were made up to be long enough that my year was not situated between speakers but on a side wall.  Therefore they are longer.  

Your 8TC cables are 9AWG equivalent which is heavy enough for any run inside a listening room.  You have nothing to worry about.

Jerry

@atmasphere and ​​​​​@carlsbad2 and @everybody else who tried to dumb this down an explain it for me--thank you.

@atmasphere and ​​​​​@carlsbad2 I now know that on a couple of levels I wouldn’t get an accurate reading--for one the meter I was using,

and also: the fact that I was taking my reading from the amplifier post (with cables hooked up) to speaker wire post of speaker (with cables hooked up, and then again from amp post to the other end with cables NOT hooked up on speaker end).

Either way, that probably screwed up the measurement I was TRYING to take, right?

So last question: the actual resistance was probably way lower that the 0.07 and 0.05 that I THOUGHT that I was reading?

And as an aside, my speaker cables (Kimber, and I THINK I remember that they they are 8TC and 4TC) probably are longer than what would be considered ideal.

You really need a micro-ohmeter to measure such small resistances. best bet is to calculate it. if it is too high, then you need larger wire. the manual only mentioned "resistence" which is a funcion of wire gauge and length only, so the inductive portion of impedance apparently isn’t a problem for these speakers, still it should be minimized. Avoid loops, for example.

https://www.engineeringtoolbox.com/copper-wire-d_1429.html

Also avoid alloy wires for speakers. Surprisingly, alloys are always higher resistance--add silver to copper and you get an alloy that is a worse conductor than either silver or copper alone.

As for your question, the impedence of the speaker is the load where power is turned into sound, the resistance (lets equiate it to impedence) of the cable is the circuit that transmits the signal to the speaker. You don’t want any of the power being disipated there.

Jerry

Thank you.  I will no longer spend time trying to measure my speaker wire resistance.  

basically you are saying that measurements I took with my meter set to ohms are probably not accurate?

@immatthewj Yes. You need a really special Ohmmeter to read the actual resistance of most speaker cables! You were far more likely reading the contact resistance of your probes and probe wires than you were the speaker cables. To read a speaker cable you need an Ohmmeter that can read differences in resistance of only 0.0001 Ohms. That's an expensive and specialized Ohmmeter that can do that!

While on the subject of speaker cables.... Do not neatly coil excess speaker (or interconnects) wire, this is, in effect, making a coil, AKA "choke", and will definitely affect impedance. If you have excess wire it is better to have that extra wire "chaotic" crossing it self at close to right angles. Recent research is showing the life on the air side of the insulated wire is as interesting as what takes place in the "conductor".

Cheers, pup

it's an amazing place there in the Quantum Realm. Visit often. Take only pictures. Leave only footprints.......if you can

Impedance and resistance are not the same thing. Resistance is a fixed value, a 10 ohm resistor is a 10 ohm resistance a wire has a resistance value per foot.. Impedance, or conductance, is a value that changes in relation to AC circuit behavior., and since AC is ever changing, it is a measurement based on the Root Mean Square of the voltage. Rough impedance values can be calculated if you have the values of components and RMS V and I. Unless you have sophisticated test equipment, and the correct formulas you will not be able to "measure" impedance. There are basic electronic tutorials on you tube that actually explain the behavior of AC circuits MUCH BETTER than I can... yeah, I was surprised too.

@gs5556 , basically you are saying that measurements I took with my meter set to ohms are probably not accurate?

Open up your amp and have a look at the # 16 wire going from the board to the binding post, you will be disappointed. I was considering replacing that little assed wire with a #10 wire?

Keep in mind the test leads on the DMM are not resistance-free and the DMM itself has a tolerance at different ohm readings, but usually don’t state or promise any tolerances when measuring below 500 ohms. Measurements in the milliohm ranges should be done by more precise instruments or at least a 4-wire Kelvin test (plenty of info on Google how to do that).

@kijanki , they are actually longer than usual runs because of the way I had my system set up in the last room.  (The equipment was, and is, off to the side of the speakers as opposed to being in between the speakers.  I'll measure the length, hopefully, tomorrow.

I suspect you measured wrong. Kimber 8TC is gauge 9 that is 0.0008 ohm/ft. In order to get 0.05 ohm you would have to have 31 ft cables. For 0.07ohm it would be 44 ft. Revel is likely concerned that additional resistance in series with speaker’s crossover can affect (misalign) it. I’m sure Revel speakers work with tube amps that might have output DCR way higher than 0.07 ohm, so I wouldn’t worry about it.