Speaker wire impedance? Speaker impedance?


I finally got into the owner’s manual for the speakers I bought last May (Revel M126Be) and under "SPEAKER CABLE" Revel is saying that, "High loop resistances that exceed 0.07 Ohms (for each wire run) will cause the loudspeaker’s filter network to be mis-terminated, resulting in considerable degradation of sound quality."

I ohmed out my (longer than I think is optimal) single run (the Revels are not bi-wireable) of (what I think I remember being) Kimber 8TC and I read 0.07. My B&Ws were shotgun bi-wired, so today I also doubled up my single runs with the other bi-wire cable (so two wires are terminating on one speaker post for + and - for both speakers) and rechecked the impedance and read 0.05 ohms which I assume is a variance going in the proper direction.

But I have a probably stupid and probably very basic question (as I make NO claims of having a tight grasp on this stuff). If a lower impedance run of speaker cable makes for an easier load for an amp to drive, why is it that a speaker with higher impedance is a easier load to drive? Can this be dumbed down for me?

I apologize because I am sure this has been asked before, but I cannot find the right combination of words for a search engine that is yielding an answer.

 

immatthewj

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.

 

 

 

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. 

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

 

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.

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?