Speaker Impedance: Resistance and Phase Question

Almarg,

Great expansion on the subject; I tried for a simpler answer, but, it is good to see a complete explanation.

For practical application of such information, the tests you mention that Stereophile publishes are helpful. They plot the imdedance of the speaker against frequency and also plot the phase angle against frequency. The most meaningful use of that data is to look at the low points of impedance and then look to see how far off the phase angle at that same frequency is from zero. A low impedance and high phase angle (positive or negative) represents a difficult load. If that point is also in a frequency range where there is a lot of musical energy, that makes the speaker even more demanding.

A lot of speakers have deceptive nominal ratings; for example, the manufacturer may claim 8 ohms because over much of the frequency range the impedance is close to 8 ohms but at some crucial point (e.g., 80 hz) the impedance drops closer to 2 ohms and the phase angle is more than 30 degrees. That would be a demanding impedance characteristic.

I run tube amplifiers so my experience is mainly with matching speakers with such amps. A lot of people look at efficiency numbers when trying to decide whether a low-powered tube amp will work with a particular speaker. To me, the impedance characteristics is much more telling than nominal efficiency. I have heard a 15 ohm speaker which, I believe, has a 83 db/w efficiency rating that played loudly in a large room with an 8 watt amp. I have heard supposedly 95 db/w speakers that could not play well with even 50 watt amps because of their difficult impedance characteristics.

Thanks very much Larryi and Al. When I stated speaker phase shift I meant to say phase angle. Given the relative 'lameness' of my question, I was provided exceptional feedback. It came as no surprise given the authors.

I wish to provide a little feedback on myself and my equipment given the the kind responses I have garnished. I have been involved in this hobby since I was 20, some 44 years ago. In that time I have developed only 3 systems, all on the budget end. My current system: Esoteric MG10s, Bel 1001MK5, Jolida Fusion 3000, Arcan DV137, PS Digital Link III w/Hiface USBtoSPDIF, Sonographe turntable (bought in 1983), Bluepoint N0. 2, Lounge phonostage, Kimber and Audioquest cables. Looking to replace the DAC and USB converter as evident from some of my other posts.

I only became involved in this forum this year and have enjoyed it immensely.
Thanks to all.

I should add to my previous post that I first became aware of the importance of speaker reactance via John Atkinson's writings and that aspect of Stereophile,s speaker evaluation I find most informative. I have long known that reactance =resistance+inductance+capacitance however am gaining a far better understanding. Would it be fair to say that capacitance becomes a most critical issue over inductance or resistance in regards to speaker and speaker cable interaction with cables having adequate isolation between the = and - strands and of an adequate gauge?

Just one clarification. The voltage is fixed with zero phase angle. It is the current that either lags or leads the voltage. Depending on whether there exits a capacitive, inductive or combination of the two load.

enjoy

Thanks for the nice words, Mesch. Yes, JA's measurements, and the interpretations he provides in the associated text, certainly represent major contributions to the hobby. I couldn't begin to count the number of times I and many others have referred to them in threads here, in identifying potential mismatches when components are being considered for purchase, and in diagnosing problems. And it has been extremely rare that I've ever sensed that his measurement-related comments might be in error in some way.

Good follow-up by Larry in his above post.

Regarding your question:

Would it be fair to say that capacitance becomes a most critical issue over inductance or resistance in regards to speaker and speaker cable interaction with cables having adequate isolation between the = and - strands and of an adequate gauge?

I think that the following comments address the intent of your question, but let me know if I'm misinterpreting your post.

Generally speaker cable capacitance is not a significant concern, except in those few cases where it is extremely high. A few cables, such as Goertz, achieve ultra-low inductance at the expense of having ultra-high capacitance. Those kinds of cables should, especially if driven by solid state amplifiers, generally be used with a Zobel network, or otherwise their extremely high capacitance can adversely affect the sonic performance of the amplifier, or even cause it to oscillate and self-destruct.

In typical situations, though, speaker cable capacitance is a non-issue. It can, however, be a quite significant consideration in the cases of line level interconnects and phono cables.

Given adequate gauge, and correspondingly low resistance, speaker cable inductance can be the one of the three parameters that is particularly important. But its criticality will depend on the impedance characteristics of the speaker at high frequencies. Inductive reactance (the inductive form of impedance, which is measured in ohms) is directly proportional to frequency, and will be negligible for any reasonably designed cable at low and mid audio frequencies. It can become significant at high frequencies, though, especially if speaker impedance is low at those frequencies. The impedance of many box-type dynamic speakers tends to increase in the upper treble region, fortunately. But many electrostatic speakers have impedances which descend to 1 ohm or thereabouts at 20 kHz, which will make cable inductance particularly critical. Once again, JA's measurements can help to sort things like that out.

Best,
-- Al