Impendance - Resistance & the story of "Z"

I want to thank all who took the time to respond and educate the non-EE’s (me) on this complex topic. I now have a better understanding of things. The reason I asked in the first place was because the manufacturer of the pre-amp I just purchased suggested that a long interconnect to the amp would be OK if I used and IC that kept the resistance low. I will now go back and ask if he meant resistance or impedance. (Does anyone know what he may have meant? He does not publish an output impedance spec for the pre-amp).

Sean, in particular, thanks for explaining the concept of an impedance transformer as related to interconnects. I see now how the electrical parameters of the components connected along with IC’s have a big impact on the “complex impedances” of the system. Understanding that the impact of a cables “Z” (nominal impedance) depends on its application (amp-speaker or source-pre-amp) wouldn’t one now question the cable manufacture that say’s that a lower “Z” for both IC's and SC's is always better? Perhaps I missed something.

Regards,

Joperfi: As i mentioned, most amplifiers have a very low output impedance and most speakers have a relatively low ( several ohms ) input impedance. Using a cable that is somewhere between these two figures will typically provide the best results. If one is trying to alter the sonics of a poorly matched system, introducing some type of colouration via series resistance ( makes the cable sound leaner due to less current flow / reduced bass output ) and / or high inductance ( makes the cable sound warmer and smoother due to high frequency roll-off ) can do that. Using a cable that offers both high series resistance and is inductive would act somewhat like a band-pass filter i.e. reduced bass and soft highs with "reasonable" mids. This might be okay for a system or speaker that was very boomy and bright. Having said that, it would be better t fix the system than to have to band-aid it though.

As far as interconnects go, the source output impedance may be anywhere from a very low impedance ( 20 - 50 ohms ) up to several hundred ohms. The input impedance of most preamps or amps is quite high i.e. several thousand ohms up to 100 - 200 thousand ohms. You have to remember though that we are talking about complex impedances here, not just straight resistance. This complex impedance can consist of XXX ohms of resistane combined with XXX values of capacitance and / or inductance. As such, it is possible to find a cable that "cancels" or minimizes the reactive part of the complex impedance found on the input of the device, allowing the source component to see what effectively looks like "pure" resistance. Since reactance is equivalent to "active resistance" or the load "fighting back" against the source, minimizing this encourages power transfer and can improve linearity via reduced ringing / improved phase & transient response. Obviously, this can get phenomenally tricky and for most folks, becomes a matter of trial and error. As such, due to the differences in voltage to current ratios and the impedances that we are dealing with, the electrical characteristics for a speaker cable and an interconnect are different. As a side note, something that works well as a low impedance speaker cable will typically work pretty well as a power cord too. That is, so long as it can pass enough voltage / current without potential safety hazards coming into play. Sean
>

I am intrigued by Sean's observation that complex crossovers, designed to flatten impedance curves, tend to suck the life out of the music. The man is always loathe to name names, but would anyone care to identify some speakers with very simple crossovers or no crossovers at all? In addition to single-driver designs, of course.

I know that some of Israel Bloom's past efforts used very simple "crossovers" ( if you want to call them that ). They are the first that came to mind. This is not to say that i agree with all of the design strategies used in those products, because i surely don't. I'm sure that others can fill in some of the blanks here. Sean
>

Sen - good job, however mentioning characteristic impedance is also useful. For low-frequency analog signals, impedance is important, because is represents AC resistance. For high-frequency signals, a phenomenon know as characteristic impedance comes into play. It is defined as SQRT(L/C). Characterisitic impedance is a single number that represents the resistance and matching property of a transmission-line to a system, including a terminator, connectors, line drivers and cables. If such a system is matched impedance, no high-frequency reflections will occur anywhere in the system.