Can someone explain to me IMPEDENCE ? (1 Viewer)

[Jim Carr]

Keep in mind I'm a HT newb
Learning as fast as I can.. but there is alot to take in! lol. I don't understand impedence.. can someone explain it using the smallest words possible? Ok maybe not the smallest words.. but keep it simple for a novice like myself can understand
thanks alot!
Jim

 

[Tom D]

in simplest terms, impedence = resistance. Typically used when stating speaker impedence (resistance). The average speaker is rated at 8 ohms for example, now this is an average rating, because the impedence changes with frequency or the load that you are trying to reproduce. The lower the resistance the closer you are to a short cct. So in terms of amplifiers, the power ratings are averaged to 8 ohm loads, but the important number to look at is the 4 ohm loadpower rating because that gives you a good idea about the power supply. If you half the load, you should be able to double the power. If you familiarize yourself with ohms law then it becomes a little clearer on what the specs are trying to tell you.
Ohms Law: Voltage = Resistance x Current, Wattage = Voltage x Current
In a nut shell, hope this helps.

 

[ThomasW]

IMPEDANCE IN AUDIO TECHNOLOGY
by Marty McCann
Several years ago I wrote four separate articles on Loudspeaker Impedance that were published in various Peavey Monitor Magazines. Realizing that many people may not have read each of the articles, I have decided to address the subject of Impedance in audio once again. This will be a detailed technical paper that will start out with the basics so that sound system operators and technicians may have an opportunity to establish a thorough understanding of the fundamental concepts of loudspeaker impedance and their applications. I will also continue to address the subject of impedance as it applies to the interfacing of those electronic components ahead of the power amplifier. In order to completely understand the workings of impedance, one must grasp the mathematical aspects of impedance and Ohm's Law. Ohm's Law is actually quite simple. However, some people get glassy eyed when it comes to any kind of mathematics. If you want be just a roadie in the music industry, you may not need to understand Ohm's Law. However, if you want to be the best sound system engineer, you must fully appreciate the principles set forth in this paper. You don't have to understand this to operate a system, but if you are connecting sound system components together and you ignore Ohm's Law, you are destined to literally pay for your ignorance with your pocketbook. So don't let impedance be an impediment to your success.
LOUDSPEAKER IMPEDANCE
A simple definition of impedance is "the opposition of one thing to another." For an analogy: you are in a room and you would like to leave that room, but if there were a 365-pound wrestler standing in the doorway and he didn't want you to go through the door, he would represent a significantly high impedance. He could easily impede or prevent you from going out of the room. If, one the other hand, some person much smaller and lighter than you were standing in the doorway, he would not offer much opposition to you if you truly desired to go through that doorway.
A loudspeaker's impedance is its opposition to current flow from the power amplifier. It is the current flow from the power amplifier that actually performs the work, or causes the voice coil attached to the paper cone to move back and forth in the magnetic field, which causes the loudspeaker cone to start the air molecules bumping in to each other to produce what we hear as sound. The more current that flows in the voice coil, the greater the cone's motion and the higher the sound pressure level, i.e., the louder the sound that is produced. The loudspeaker is a transducer, or a device that changes energy from one form into another.

This is taken from
http://www.peavey.com/technotes/20.html

 

[John Miles]

Briefly, impedance (Z) is resistance to the flow of an AC current. It is measured in ohms, just like conventional DC resistance.

A pure resistor has the same effect on current of any frequency, from DC on up. But in the real world, there's no such thing as a "pure" resistance. Speakers, in particular, are a complex combination of resistance, capacitance, and inductance. The latter two properties mean that a given value of impedance is dependent on the frequency at which you measure it -- something that's not true of DC resistance.

A given impedance value always has both resistive (power-consuming) and reactive (phase-shifting, but not power-consuming) components. It's a vector (R+jX) quantity, where R is the plain old ordinary DC resistance component and X is either capacitive (Xc) or inductive (Xl).

As if all this weren't complicated enough, it's not even possible to state the precise impedance of a component such as a loudspeaker, because it will vary dramatically depending on the frequencies and amplitude levels the speaker is reproducing at any moment. Because the figures you generally see in print ("8 ohms" and "4 ohms") are derived under particular conditions involving a pure test tone at a standardized frequency, all they really tell you about the real-life characteristics of different speakers is that one has roughly half the impedance of the other.

Any good-quality power amplifier should have no problems driving either 8- or 4-ohm speakers, regardless of whether it has a speaker impedance switch. It takes less voltage (but more current) to get the same sound pressure level from a 4-ohm speaker, all other things being equal, but because speakers are strongly dynamic loads to begin with, any amp that can't safely drive a 4-ohm speaker is a hopeless POS anyway.

In terms of sound quality, a vacuum-tube amp with a transformer output is likely to be more particular about working into its specified speaker impedance than a solid-state amp that acts more like a "stiff" voltage source. At the end of the day, though, as long as your speakers sound good with your amp and you don't hear any distortion or smell any smoke, don't sweat the impedance thing too much.