Deang Posted September 22, 2005 Share Posted September 22, 2005 A good read: http://www.peavey.com/support/technotes/concepts/impedance.cfm Quote Link to comment Share on other sites More sharing options...
jacksonbart Posted September 23, 2005 Share Posted September 23, 2005 No luck on the link. Quote Link to comment Share on other sites More sharing options...
Speedball Posted September 23, 2005 Share Posted September 23, 2005 The person who wrote it broke it down so even I can understand some/a lot of it. Quote Link to comment Share on other sites More sharing options...
Colin Posted September 23, 2005 Share Posted September 23, 2005 very good: Here is an analogy for impedance in the physical world. You have loaded a wheel barrow with dirt, and now you must move the payload. When you pick up on the handles of the wheel barrow, the weight offers a resistance. However, because the handles operate with the wheel and the axle to form a kind of inclined plane (lever), the resistance is less than the actual weight. In order to get the wheel barrow moving, you must apply even more force, but the mass (real weight of the dirt) offers inertia or opposition to the force applied (Inductive reactance). Now imagine you have moved the payload to its intended location, and must now stop the wheel barrow's forward motion. But now the opposition to the deceleration is in the form of momentum or stored energy in the actual motion of the wheel barrow (Capacitive reactance). In the case of our loudspeakers, their opposition to current flow from the power amplifier is their impedance. Audio electrical signals are electrical analogues or representations of the positive and negative fluctuations of air pressure that have been converted to positive and negative fluctuations of voltage. This fluctuating electrical signal that represents the vibrations of air or sound is by its very nature Alternating Current or AC (i.e., the direction of current flow changes directly with the number of audio cycles per second being reproduced). Loudspeakers actually involve three forms of impedance. The first is the electrical impedance offered to the power amplifier discussed above. The second is the mechanical impedance of the loudspeaker, which is taken into account in the design of the loudspeaker enclosure. Third is the impedance of the air or the acoustic impedance that the combination loudspeaker/enclosure encounters. Quote Link to comment Share on other sites More sharing options...
sunburnwilly Posted September 23, 2005 Share Posted September 23, 2005 Viagra ? Cialis ? Consult your physician . [W] Please continue Colin ... Quote Link to comment Share on other sites More sharing options...
Colin Posted September 23, 2005 Share Posted September 23, 2005 even ends with table showing the difference for high power amps on long cable runs for average effciency speakers: Copper Wire Guage AWG# Diamils Diamm Cirmils Squareinches Sqmm Meter/ohm Feet/ohm Audioamps Maxpwr LengthDF<50 22 25.35 0.6438 642.4 0.000504 0.33 18.52 60.75 3 18 40.30 1.024 1624 0.001276 0.82 46.8 153.6 5 150W 10 Ft 16 50.82 1.291 2583 0.002028 1.31 74.47 244.26 7 280W 15 Ft 14 64.08 1.628 4107 0.003226 2.08 118.4 388.35 9 400W 25 Ft 12 80.81 2.053 6530 0.005129 3.31 188.3 617.7 12 800W 40 Ft 0 101.9 2.588 10380 0.008155 5.26 299.5 982.32 17 2,000W 65 Ft Quote Link to comment Share on other sites More sharing options...
wstrickland1 Posted September 23, 2005 Share Posted September 23, 2005 Viagra ? Cialis ? Consult your physician . [W]lmao george hamilton Quote Link to comment Share on other sites More sharing options...
WMcD Posted September 23, 2005 Share Posted September 23, 2005 I think this is always explained a bit wrong. Yeah, I should write my own white paper. Impedance of a device, or black box with two terminals, is always, ALWAYS, the relation between the voltage acoss the terminals and the current into the terminals. You really have to start with that, and get back to it. So consider a pure resistance, which is always described by Ohms law. Impedance = Voltage / Current. Look at any complicated squigley voltage (in time) wave form applied to an 8 ohm resistor. The current is always the exact same waveform but 1/8 th as big. If voltage goes negative, current goes negative. It would look very logical on a graph in time. The problem comes up with capacitors (and inductors). The current through a capacitor is the rate of change of voltage times the value of the cap in farads. Ic = C dv/dt in calculus, or differentiation. When we put in the squigley voltage, the current is not just a scaled version, as it is with a reistor). It is the slope of the squigley voltage times the value of the cap. If we drew those on on the same graph paper, the current would look like a mess. The concept of impedance would be very difficult to fathom. But maybe there is a more simple way to look at things. Lets just stick to a sine wave voltage at some frequency. All we have to do is take the slope of a sine wave at every point as it goes up and down. What do we get? Technically, we get a cosine wave. But that is just a sine wave shifted 90 degrees. It is pretty much one of the wonders of calculus and math. If we stick to a single frequency, we have current in the same waveform, but shifted in phase. No calculus needed. It must be scaled by the value of the cap, but that is all. - - - There is a lot more to this. One thing is that the voltage across the cap is the integral of the current which has been applied, over time. Integration (adding up) and taking the slope (differentiation) , are inverse functions. This another wonder. If you have a sine wave you could add up all the little values under the curve. What does all this adding up give you? It is another sine wave shifed the other way. I have a little spread sheet showing this wonderful effect. Maybe I can zip it and post. It is difficult to believe. Taking a slope of a sine, or adding up the values just gives you the same waveform, shifted plus and minus 90 degrees. = = = = Keeping track of all this shifting is difficult. We could just draw an arrow on a circular graph so we can rotate as needed for an angle and give it a length for magnitude. But what to use as axes? Enter a wild concept of the square root of -1. Now you say that is crazy. Any number (even a negative one) squared (multiplied by itself) is positive. So there can't be any number squared which gives a -1. We could say this is all imaginary. So we could call the square root of -1 . . "i". Drat. we're using i for current intensity. So let's use the letter "j". Lets see if the math works out. If we take a real number A and multiply it by j we get Aj. If we multiply it by j again we get? If we multipy the square root of negative one by negative one we get . . . -1 (or -A here). And if we multiply that by j again we get -j A. And if we multiply that again by j we get A. This last step is hard to follow. We have square root of -1 multipled by a negative value of itself, itself which give a negative 1, but one term is negative, so the result is positive. Lets put that on the graph were j is the vertical axis. We see that every time we take a real value and multiply it by j, we are rotating it up to the positive j. But that vertical axis gives us a phase shift of 90 degrees. One axis is an imaginary number. The other is real. The combination is called "complex". Please remember high school graphs. There is some point which is 3x and 4y. If y is said to be j, and x is R (resistance) we have 3r +4j. You see this nomenclature in technical matters. Another way of of expressing the same is to say the hypotenuse is 5 and there is some angle (which is the arc tangent). The hypotenuse is the impedance magnitude and the angle is the "phase shift." There, you see, they did teach you impedance in high school and did not know it. I know this is difficult without diagrams. There are a few key concepts. Inductors and caps are little calculus machines. The current and voltage relations are set by differentiation (slope) and intergration (adding up). Those two concepts are inverse functions, per Sir Issac. Start with a graph in time. You can graph the slope. If you add up the little areas under the slope graph, you get back the original graph. This is super genius, and only a fraction of his work. This would be very difficult to deal with in real time and complicated wave forms. But lets stick to sine waves. Integration and differentiation of a sine wave results in phase shifts and scaling. Phase shifts and scaling is best done on a graph of real and imaginary numbers. Mr. Steinmetz created this. We've simplified things a bit, but we now have to deal with multiplication of j. We use the complex number graph to show . . . gasp .. . the relation between voltage and current. That is called impedance, at one freqency. I know this creates confusion for the newcomer. However, it might give some people who are halfway to understanding another step up. It took me a long time. I'm always learning. Best, Gil Quote Link to comment Share on other sites More sharing options...
Deang Posted September 23, 2005 Author Share Posted September 23, 2005 We could say this is all imaginary. Actually, it is. I about gave up on the math when I started reading about "imaginary numbers". I've spent the last three or four days reading about acoustic impedance. It's very unpleansant stuff. Quote Link to comment Share on other sites More sharing options...
sunburnwilly Posted September 24, 2005 Share Posted September 24, 2005 Viagra ? Cialis ? Consult your physician . [W]lmao george hamilton Who's this George Hamilton You Speak Of ? Hi Billy , Haven't seen ya' around for awhile , How Ya' Been ! WP Quote Link to comment Share on other sites More sharing options...
Spkrdctr Posted September 25, 2005 Share Posted September 25, 2005 GIL, Please take two asprin and hopefully you will be better in the morning. After reading that post, I decided you were trying to make me work for my morning ocffee. At least wait until I have had my coffee!!!![] Quote Link to comment Share on other sites More sharing options...
wstrickland1 Posted September 25, 2005 Share Posted September 25, 2005 Viagra ? Cialis ? Consult your physician . [W]lmao george hamilton Who's this George Hamilton You Speak Of ? Hi Billy , Haven't seen ya' around for awhile , How Ya' Been ! WP GH, yer avatar. dewin good, jst been listinin to my raggy ole legends. was in town last week, the Tides is comin out the ground. Killer view of the new bridge. better be for a $1 mil. condo peace Quote Link to comment Share on other sites More sharing options...
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