thebes Posted March 4, 2009 Share Posted March 4, 2009 ...give a rat's bumkess. I keep running across references to "Z" in audio parlance. Either it's got some sort of meaning or purpose, or it's one of those clever little things tech-heads conjure to confuse the body politic and increase their funding. I see it used in reference to amps, and a fellow I'm in communication with just asked me what the "Z" of my Cornwalls is, are(?). Once again dazed and confused. Quote Link to comment Share on other sites More sharing options...
mark1101 Posted March 4, 2009 Share Posted March 4, 2009 impedance. Quote Link to comment Share on other sites More sharing options...
thebes Posted March 4, 2009 Author Share Posted March 4, 2009 Ok, and impedance is what: A couple of bruisers standing in your way when your skipping town over gambling debts? Not being flipant, despite all my time here, I'm still very much clueless about some of this technical stuff. Quote Link to comment Share on other sites More sharing options...
mark1101 Posted March 4, 2009 Share Posted March 4, 2009 Impedance is basically opposition to current flow and is made up of resistance, capacitance, and inductance. Quote Link to comment Share on other sites More sharing options...
WMcD Posted March 4, 2009 Share Posted March 4, 2009 The easiest situation is where Z is a pure resistance R. That means the device is always consuming power. Resistance is not a thing, like I was telling Larry once (that it is not a thing). It is a ratio. R = V/I or voltage divided by current intensity. If R = 100, then the current is 1/100th of the applied voltage at all times. If R = 10. then the current is 1/10th of the applied voltage at all times. It is like R = 1/(0.01) or R = 1/(0.1) As you can see from the math, this means that a higher R means more "resistance" to current flow. You can image the voltage being a sine wave of 1 volt. The current is a sine wave scaled down by 1/100 and 1/10. They are the same shape, exactly. This is very handy to tech heads because we can know the current resulting from an applied voltage. You might consider a set of light bulbs in you home. You can buy a 10 watt light bulb. And you can buy a 100 watt light bulb. When screwed in to a 120 volt service, each takes the power wattage as advertized. But this brings up the age-old engineering question, "How do it know?" (As we said in the Bronx.) We know that Power = Volts x Current. One way of decribing that is the R of the respective lightbulbs. The 10 watt lightbulb has a higher resistance. Less current. Less I means less power. That is how it know - - - Things get very complicated when we want to examine the impedance of a device which does not consume power, but stores it and can return the stored up power. This is going to be complicated. But it could be helpful to others pondering the issue. Suppose you want to charge up a capacitor (which is like a rechargable battery). Think of a dead car battery, and you have a voltmeter and amp meter on the dashboard. This used to be the case. But no more. When we start the processes, the generator/alternator is putting out 12 volts but the battery is very dead. (We've just pushed the car down a hill and popped the clutch to get the electrical system going). [**** see FN for funny story.] So the voltage across the battery is going from 0.0 volts to about 0.0001 volt. The ammeter pegs to very high. So the voltage across the battery is very low but the current is very high. That is unlike the resistor when the voltage and current are in lock step. Also. consider when the battery is all charged up. Now the generator/alternator is applying 12 volts, but the ammeter shows no current going in (because it is charged). Now voltage is high but current is very low. This is again unlike the resistor. - - - Going further. Suppose we only had a voltmeter across the rechargable battery and what to figure the current through it. If the voltage is increasing, we know the current is going into the battery. If the voltage is falling, we know the current is coming out of the battery. So the rate of change of voltage (slope) tells us the current. Suppose we only had a current meter and wonder about our auto battery. We could look at how long current has been going into the battery and infer the condition of the battery. Gee, I've had the battery charging up for 10 minutes so voltage available from the battery must be somewhat high. Then, I'm going to turn on the headlights for a while, say 5 minutes, and the voltage must be getting lower because the ammeter is showing negative. But then we'll charge up for 15 minutes (ammeter positive). And then turn on the lights for 8 minutes discharging the battery. Here, in the second example, we see that the voltage on the battery (capacitor) is related to the sum of all the current vs. time we've put into it. We were looking at how long current was going in and out. This is called "integration". - - - - The bottom line here is that when we have a device capable of storing power and then returning it, our appled voltage and current are not really exact scaled versions of each other. They are out of phase in a general sense. - - - - - We can go a bit further. With a pure R, we could apply a squggly music voltage V to the resistor and we'd know the I current going in is the same squiggly waveform, just scaled. But with our cap, we know the current is the slope (time a scaling function) of the squiggly applied voltage waveform. This is horrid math problem with trying to figure the slope of the squiggly music.waveform. Also, if we know the current, we know the voltage at a given time is related to the sum of all the current in and out due to the squiggle current waveform. We could be really SCREWED figuring out the slopes and integration of signal waveforms . . . assuming they are squiggly music. The slope and integration is called . . .ugg . . . calculus. Math and brilliant mathematicians come to the rescue. The math guys are named LaPlace, Heavyside, and Steinmetz. Newton and Leibnitz too. They all described that you can take the slope of a function (which may give you something horrid). But then if you integrate the slope, you get back the original function. Well that's a relief, we can get back to the original squiggly liine. It means that in the functions we're dealing with, taking the slope, and taking the integral are inverse functions. This is similar to putting any value into a calculator. Multiply it by X. You get something. If you divide the something by X, you get back the original number. Division by X will undo multiplication by X. They are inverse function. X and 1/X. Note that on some calculators there is a 1/X which is called, "invert". - - - - Now this is okay but we've still got the issue of dealing with squiggly waveforms. The math that comes to the rescue is the sine wave. You might have wondered why testing of systems is done with sine waves, which have a single frequency. The Z is such and such at THIS frequency. (Or we put the many freqs on a graph.) The reason is a very peculiar characteristic of the sine wave. If we take its slope, we get a cosine wave. That is the same shape as the sine, but the shape is shifted by 90 degrees, left. So we have the same shape shifted in phase. More amazing is that if we sum up a sine wave (integrate) we get a negative cosine, and this is the sine shifted 90 degrees to the right. The immediate above is a very, very, very big deal. It seems very complicated with this shift by degrees. (Is anyone still awake out there?) But it means that if we look at a single freq at a time (the sine), we don't have to worry about slopes and integrals of wiggly music (which would have multiple freqs). All we have to look at is how much the current and voltage of a sine have shifted in phase with a sine.. = = = = Again we might look at the current into and out of a cap. At zero degrees on the voltage of a sine is zero (and increasing), but the cap it is pulling high current in, like in our car battery, and the cosine is 1 (or high).. When the voltage is max there is no current, and cosine value is zero (or low). With cap and AC going negative, we get into more trouble and the car battery analogy breaks down. The concept is the same, though. The rest of the story can't be told without diagrams. But we see that the R concept is not enough. We have to call the relationship between voltage and current = Z. The Z is more more complicated because, like in the speaker load, things which can store up power and returns it L and C. and some which only consume it R. In the speaker there are many of these things which store up power and then release it, and some resistance which only consumes it. We have the electrical caps and inductors and resistors, the mechanical masses and springs and mechanical resisistance, and the acoustic items which do the same. - - - - Keeping track of the shifting of phase of the voltage and current realtionship is made more simple with the use of the imaginary number "j" (or "i") which is the square root of -1 in addition to a "real" number R in vectors at a given freq of sine waves. That is Steinmetz talking. It is hard to believe that this is "simple" yet it is more simple than real calculus with squiggly waveforms. - - - - - **** I got in a jam one time with the college car. After fixing a flat with the flashers on, the battery was low. I was on a slight up-hill. I pushed it up the slight incline a couple of times and almost jumped it. My date was saying, "Do you want me to call my father to help?" (Grrrr.) Then I realized that I could let it roll backwards down the slight hill and jump it in reverse. Which worked. The realationship didn't work out. Wm McD . - - - - Quote Link to comment Share on other sites More sharing options...
Don Richard Posted March 5, 2009 Share Posted March 5, 2009 Super simple explanation of impedance: AC resistance that changes with frequency. It is important when connecting the components of a sound system to pay attention to the impedance, especially when hooking up speakers. Too low impedance speakers can cause the amp to overheat, shut down, or be damaged. Quote Link to comment Share on other sites More sharing options...
thebes Posted March 5, 2009 Author Share Posted March 5, 2009 My reply seems wholly inadequate to the kind responses posted here. WOW! Very informative, and something I'll be re-reading quite a few times. Is this a great forum or what! Quote Link to comment Share on other sites More sharing options...
richinlr Posted March 5, 2009 Share Posted March 5, 2009 Impedance is basically opposition to current flow and is made up of resistance, capacitance, and inductance. And varies with frequency. Quote Link to comment Share on other sites More sharing options...
richinlr Posted March 5, 2009 Share Posted March 5, 2009 Excellent! You should be a teacher! Thanks for an explanation that will carry me a long way. After I read it about a dozen times... Quote Link to comment Share on other sites More sharing options...
efzauner Posted March 15, 2009 Share Posted March 15, 2009 what you got was a load of crap from a bunch of propeller heads. I can see their beenie hats right now. All WRONG. *Z* is the last letter of the alphabet. It is used to denote the *ACME* *LATEST AND BEST* Product made. Be it Cars, Audio gear, Computers ... Add a Z to the end and it becomes your flagship product. Quote Link to comment Share on other sites More sharing options...
richinlr Posted March 16, 2009 Share Posted March 16, 2009 OK. I guess it is time to ask the question again... What is "Z" and Why should I... Hint: Z is an electrical engineering quantity and not simply a letter on the end of my "flagship" product. Sooooooooo....... Gotta a better explanation of Z? Quote Link to comment Share on other sites More sharing options...
artto Posted March 16, 2009 Share Posted March 16, 2009 Z = Impedance: Example #1: I get mad at Thebes and take a swing at your head. Your head is impedance to my fist. Example #2: You eat to much tonight. I mean a lot! You wake up tomorrow morning and have to take a big dump. The toilet gets plugged up. Impedance. Example #3: Z = the square root of R squared + X squared where R = resistance and X = reactance. Reactance (X) = XL -Xc where XL is inductive reactance and Xc is capactive reactance. For all practical purposes the term "impedance" is often used for simple circuits which have little or no inductance or capacitance. In these simple circuits its safe to assume its just another word for resistance. Quote Link to comment Share on other sites More sharing options...
thebes Posted March 16, 2009 Author Share Posted March 16, 2009 Z = Impedance: Example #1: I get mad at Thebes and take a swing at your head. Your head is impedance to my fist. Well now that you mention it, in my youth I encountered imepdance on a regular basis. Then I got married and it only increased. Then I joined a certain unamed forum and it really increased.[] Good thing somebody invented aspirin. Quote Link to comment Share on other sites More sharing options...
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