stereo problems
Extreme HDF Member
Joined: Nov 2007
Posts: 14,670
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From: East of the Sun, West of the Moon
I agree with JohnnyC in respect to testing a speaker. The only way you can truly test impedance is by measuring the actual AC voltage (yes folks AC voltage is what is sent from a headunit or amplifier to a speaker, NOT DC voltage as most would assume). The key thing to remember here is voltage and current being applied to a speaker WILL both fluctuate with volume position.
If you can accurately measure that AC voltage then you can determine the current (in amps), at this point then you can determine the actual impedance of the speaker. To determine the current you must know the voltage being applied to the speaker at a given volume (yes the voltage will change depending on where your volume is).
To get current (amps) you take the voltage you measured, and divide it by the "nominal impedance" (in ohms). Nominal impedance = whatever is printed on the speaker or box. Pay no attention to what a meter says when measuring ohms across the speaker terminals unless you have a direct short in which case you will see 0 on your meter. To get accurate impedance at a given volume, you take your voltage figure from above and divide it by your current determined in previous step.
The bottom line is stick with the ohm rating on the box or speaker. If in doubt, put an ohm meter across the speaker terminals and if it reads anything other than 0, you're good. I've seen 8 ohm speakers "ohm out" to as low as 4.9 ohms and as high as 8.2 ohms.
To clarify the interaction with the throttle: Your actual throttle position has nothing to do (unless you're moving of course) with the AVC (automatic volume control). It's based strictly on speed and gets it's signal to increase and decrease volume from either a speed sensor or the ECM.
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Harley5227
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Oct 14, 2012 08:09 AM
