D-MAN Posted March 17, 2005 Share Posted March 17, 2005 Impedance refers to the reactive elements in a circuit that "impede" the flow of current. Resistance is used for non-reactive components, like resistors, which exhibit an relatively constant resistance to the flow of current. Impedance is used when specifying a collective resistance in a circuit rather than a single device (resistor, cap, coil, etc.) due to reactance rather than straight resistance, if that makes any sense... For example, a resistor is rated for a fixed resistance to current flow and what does not pass through it is converted to heat, and a coil/capacitor circuit would also display a resistance (in this case impedance) to current flow but because of the ability of the circuit to actually store current/voltage, it varies the amount of resistance (impedance) "seen" by the voltage source because it either stores it or gives it back, and it is phase and frequency dependent. So it is rather like a spring which seeks equalibrium, sort of, not a fixed resistive element whose resistance to current does not vary. Like a coil storing energy in its magnetic field, it will "give back" the stored energy when the current flow drops or stops and the field collapses. This is a "reactance" which is not a property that the device contains in itself, but that it "reacts" to changes in current flow. Same for a capacitor which can store voltage between its plates as long as they are appropriately charged. When the voltage drops (or exceeds the limits), it releases the stored potential as current. Again a reactance. This varying of impedance is called reactance, or a "balancing" effect which at its extremes offers little or alot of impedance to current flow. A resistor, on the other hand, IS a resistive element in that it will resist current flow based on its structure, and is therefore not considered a reactive component, as the resistance it exhibits is relatively fixed and constant (within reason). So although the use of the word impedance CAN be used for a resistor, the use of "resistance" is more appropriate for a non-reactive component. DM Quote Link to comment Share on other sites More sharing options...
m00n Posted March 17, 2005 Author Share Posted March 17, 2005 Here are some definitions that I've copied down for quick reference.. here is the source http://www.bcae1.com/ Voltage: If work is to be done, something has to move. For something to move, a force has to be applied to the object. In electronics, that force is voltage. Voltage is the measure of difference of potential (electrical force) between two points. The volt is the unit of measure. Voltage can be described as electrical pressure. VOLT The volt is the unit measure of electrical pressure. One volt will, when applied across a resistance of one ohm, force one amp of current to flow through the circuit. If you double the resistance in the circuit and still apply one volt across the circuit, the current flow will be 1/2 amp. If you apply two volts across one ohm the current flow through the resistor will be two amps. Current: Current is the measure of the flow of electrons passing through a given point in a circuit in a given amount of time. The unit is the amp(ere). Since it would be impractical to state the actual number of electrons flowing through the conductor, one amp is defined by 1 coulomb per second. One coulomb equals 6,240,000,000,000,000,000 electrons. For now, just remember that it indicates the amount of current flow through a circuit. Amp(ere): The amp is the unit of measure for current flow. One amp of current will flow through a resistance of one ohm if one volt of electrical force is applied to the circuit. The current flow will double if either the voltage is doubled or the circuit's resistance is cut in half. The current flow through the circuit will be cut in half if the voltage is cut in half or the resistance is doubled. Resistance: Resistance is the measure of a device's opposition to the flow of electrical current. Its unit of measure is the ohm. If a device with one ohm of resistance is connected across a one volt power supply, the flow of current through the device will be limited to one amp. If the resistance is doubled, and the power supply voltage remains at one volt, the current flow will be one half amp. As you can see, more "resistance" will reduce the current flow in the circuit (if voltage remains constant). Ohm: As said earlier, the ohm is the unit of measure of a device's opposition to the flow of current. One ohm of resistance will allow only one amp of current to flow through a circuit when one volt of electrical force is applied to the circuit. -------------------------------------------------------------- Ok... the paragraph bellow is what is starting to bake my mellon... I don't see how the following works. If you have a 12 volt power supply that can push 1 amp of current, you put a 12 ohm resistance in the circuit... That seems to me that it would completely block all current... What am I missing? All power sources are designed to operate into some sort of a load. Power supplies are generally designed to maintain a given voltage into some given load. Let's say we have a 12 volt power supply that's designed to deliver 1 amp of current. If we connect a load that has a resistance of 24 ohms, this will allow 1/2 of the power supply's max current to flow through the load. If we connect a second 24 ohm load across the power supply's output terminals, the power supply will be delivering the maximum safe current output possible without damaging the supply. If we connect a third load across the supply, the output current will be 1.5 times as much as the supply can safely deliver (assuming that the supply can maintain it's rated voltage under the heavy load) and the supply will soon blow a fuse or fail. Quote Link to comment Share on other sites More sharing options...
Rockets Posted March 17, 2005 Share Posted March 17, 2005 Moon, you're missing OHM's LAW Voltage(V) = Resistance® X Current(I) conversly V/R=I and V/I=R. Read up on it and the relationship of Volts, Resistance and Current will become very clear. It'd take me too long to type out what I'm sure can be more easily (better) explained and found on the net. Remember zero ohms (dead short) will draw MAXImum current whereas an open draws no current. Quote Link to comment Share on other sites More sharing options...
m00n Posted March 18, 2005 Author Share Posted March 18, 2005 Rockets... thanks for those links! I've been trying to read up on it all on the first link you gave me. http://www.bcae1.com. Lots of good info and he does a great job of explaining it. Quote Link to comment Share on other sites More sharing options...
colterphoto1 Posted March 18, 2005 Share Posted March 18, 2005 boring... Moon, you into cars? Think of impedence as back pressure, like exhaust pipe diameter. smaller diameter pipe/muffler causes more back pressure ( resistence) against engine (amp), so a 16 ohm speaker (lots of resistence) won't get as much wattage as say a 4 ohm speaker (not much back pressure). Now if you take the whole dern exhaust system OFF, you're operating at 2 ohms, then the engine can put out a TON of power, for a while, cause it wasn't designed for this lack of resistence, so it burns up. Like your amp if you run 4 sets of speakers off of it. Get it now? Michael- yer speaker plainspeak guru Quote Link to comment Share on other sites More sharing options...
chuckears Posted March 18, 2005 Share Posted March 18, 2005 Heck, even I get it now, and I got lost on D-Man's second paragraph! (I could never retain this stuff, even if it makes sense while I'm reading it. I almost have to do something to "get" it... I would have to design and build my own crossover network, trial and error, to understand how all of the components are supposed to work. And I call myself a "scientist" ) Quote Link to comment Share on other sites More sharing options...
chuckears Posted March 18, 2005 Share Posted March 18, 2005 ... I still can't make heads or tales of the little circuit diagram... a bunch of lines with a few squiggles mixed in here and there. Good thing I'm so damn handsome... I could never be the Professor, making a battery out of some coconuts. I'd just clown around, and wear them like Baloo singing "The Bare Necessities" Quote Link to comment Share on other sites More sharing options...
colterphoto1 Posted March 18, 2005 Share Posted March 18, 2005 Larry, please check the diagram, I don't believe it is a single signal path that flows 'through' each section before going on to the next 'the signal, minus the woofers lows, travels to the midrange section'. If you look at the diagram, the + pole branches out to each section of the xover, so each section works independently of the others. I don't know exactly how they are wired, but looks to me (and I could be wrong) like each section has to do it's own filtering, with no other section of the xover affecting it's signal. Is this correct D-Man? my brain hurts, can I go home now? M Quote Link to comment Share on other sites More sharing options...
WMcD Posted March 18, 2005 Share Posted March 18, 2005 Gee, makes my head swim too. The description of the d.c. power supply is misleading and lacks accuracy. The author was trying to say that it will put out 12 volts at UP TO a current draw of 1.5 amps. If more current is demanded, the voltage will sag down. The resistance is not a thing. It is always a ratio of V/I. If you have a resistance of 24 ohms, the V/I ratio is just that. The current through it is 1/24th of the voltage across it. Or the voltage is 24 times the current. The lesson was just that resistances in parallel can try to draw more current than the power supply can keep up with. When that happens, voltage sags. Gil Quote Link to comment Share on other sites More sharing options...
LarryC Posted March 18, 2005 Share Posted March 18, 2005 ---------------- On 3/18/2005 9:56:32 PM colterphoto1 wrote: Larry, please check the diagram, I don't believe it is a single signal path that flows 'through' each section before going on to the next 'the signal, minus the woofers lows, travels to the midrange section'. If you look at the diagram, the + pole branches out to each section of the xover, so each section works independently of the others. I don't know exactly how they are wired, but looks to me (and I could be wrong) like each section has to do it's own filtering, with no other section of the xover affecting it's signal. M ---------------- My understanding is similar to yours. I tried to present it in a logical sequence to make it more understandable. I didn't mean to imply that the signal flowed through one driver and then the other, and should have made the point that the signal is simultaneously parsed out into woofer-bound lows, squawker-bound middles, and tweeter-bound highs. I'm not sure how independent each section is from the other, though. Larry Quote Link to comment Share on other sites More sharing options...
st. patrick Posted March 19, 2005 Share Posted March 19, 2005 moon, you are not alone out there. I also have a hard time "relating" to electrical theory, etc. And trying to understand computers and/or software leaves me with a dopey (ok, a dopier than the usual) look on my face. Michael, although i visualize or relate to mechanical things like cars, or construction analogies, i don't quite get what you were trying to convey ................... any chance you could use SEX as the basis for your next analogy.........i know it would keep my attention and, i dare say, alot of others out here. Quote Link to comment Share on other sites More sharing options...
colterphoto1 Posted March 19, 2005 Share Posted March 19, 2005 Okay StPat, I'll bite, but Amy's really not going to like this one. You really did understand the car analogy, just testing me aren't ya? Oh, Larry- yes I understand what you were saying. Okay, here goes..... (and remember, you asked for it) You're the amp and the lady is the resistance, makes sense so far! If you're with the right one (you're both 8 ohms) all is peachy keen and everyone has a good time. She's the right, ahem, load, for you, so your power is used and appreciated in a thoughtful manner. However, if the resistance is too high, and she's fighting you, you don't get to use your power properly, in speaker-speak, a 16 ohm resistance would get maybe 2/3 the wattage that our 'idea' coupling would create. Nobody gets hurt, but it just don't feel right. It's a bit frustrating for you. Likewise, there is also trouble if there is too little resistance, say your gal brought 3 of her pals over to be 'hooked up', you could put out and put out until your heart failed, this is similar to the four pairs of speakers lowering the resisitance until the amp overheats. Not a pretty situation. Not bad, huh? This might even sneak past the censors. I was gonna use the garden hose resistance analogy but it got pretty nasty sounding. LOL Although I secretly want Amy to admire my wordsmithing. Michael Quote Link to comment Share on other sites More sharing options...
WMcD Posted March 19, 2005 Share Posted March 19, 2005 Und zo, vhen did you first haff the impulz to exzplain el-lecrical izzues in terms of zex? Ve are getting clozzer to the problem. Gil Quote Link to comment Share on other sites More sharing options...
ZAKO Posted March 19, 2005 Share Posted March 19, 2005 Dah!!! Das veddy gudt. Quote Link to comment Share on other sites More sharing options...
Fish Posted March 19, 2005 Share Posted March 19, 2005 I never knew electrical theory could be zo intaesting. Quote Link to comment Share on other sites More sharing options...
fini Posted March 19, 2005 Share Posted March 19, 2005 I have never been able to talk my wife into analogy sex. Quote Link to comment Share on other sites More sharing options...
colterphoto1 Posted March 19, 2005 Share Posted March 19, 2005 just wait til Clu gets a read on that one! Michael - never married, prob never will at this rate. too old and to preverted to begin the training! Quote Link to comment Share on other sites More sharing options...
st. patrick Posted March 19, 2005 Share Posted March 19, 2005 suddenly it all seems to make sense to me . . . . . . .but i still have problems understanding my wife . . .LOL . .. great job Michael Quote Link to comment Share on other sites More sharing options...
fini Posted March 19, 2005 Share Posted March 19, 2005 Gee, this thread was going so well... Quote Link to comment Share on other sites More sharing options...
m00n Posted March 19, 2005 Author Share Posted March 19, 2005 nevermind. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.