Ok, I have looked and looked, but cannot find an answer, so I will have to be shamed into asking this BASIC Noob question! Is impedence (resistance) measured at the back of the speaker cabinet through the crossover, or do I need to take out the speaker to measure?
Second....I have read some posts that explain how Ohms vary depending on frequency, so does measuring in either place do really anything at all...like maybe give you a ballpark idea of what the speakers are rated at?
Thanks and please don't flame ;-0 Everyone has to start somewhere.
Resistance is not impedance. Measuring resistance of a total speaker is meaningless, as you are measuring ONLY the DC resistance of the woofer, plus the DC resistance of all inductors in series with the woofer. That's all. If the speaker has access to low and high pass filters, and is a two, or two and a half way, then th DC resistance of the total speaker, and the resistance when accessing the low pass filter will be the same. The DC resistance at the high pass filter will be infinite. A cap will no pass DC. There are one or more caps in series with the tweeter.
Now the DC resistance of the drivers is of concern only to the speaker designer, as is the impedance curve of each driver. Now since all speaker voice coils are inductors, impedance rises with frequency although bass tuning and type cause impedance peaks at tuning, one for sealed, two for ported and TL.
Now the impedance curve of the total speaker is the sum of the resistances, and inductive and capacitative loads in the total system.
Now the impedance curve of the drivers in the total system in it and out of it are different.
Now if you want a headache, there is not only the impedance curve to worry about but the phase response curve. The reason being that not even the impedance at a given frequency tells you what the current draw form the amp will be.
Look at this thread from last week. This goes over ground we went over last week, that has a large bearing on what you are asking about.
http://forums.audioholics.com/forums/showthread.php?t=42432
Now if you want to measure the impedance curve of a driver or total speaker, then you need an audio oscillator (Known as an audio signal generator) , an amp, a suitable resistor and an amplified meter. You put a suitable resistor in series with the driver, if that is what you are measuring, or the speaker terminals if it is the total speaker you are measuring. You then keep the driving voltage constant at the input to the series resistor, as you increase frequency. You select suitable frequency intervals to do measurements. You measure the voltage across the series resistor and the speaker. You can then work out the current at that frequency from ohms law. You know the voltage across the speaker, so you can work out the impedance at that frequency.
Now I think you need to purchase a few books on these subjects you are interested in. If you want to become a serious enthusiast, and I think and hope you do, you need to do some serious reading on the physical and electrical principles that have a bearing on this.
If you are a university student, may be you should consider some courses, in mathematics, physics and electrical engineering? You would not be the first youngster to be lead to en education and career through a hobby.
I have a feeling we can not provide what you want, and need, on a forum like this. If you think I'm advising further self education before posing these kind of questions, then you have drawn the correct conclusion.
