Quote:
Originally Posted by Jamaica2G
Troys:
They actually messed up.
They are dual voice coil subs that were supposed to be made to give me a 2 ohm or (1.4ohm) reading for each sub... so when wired up, they would show up at 4 ohm or (2.8 ohm) load...
They sent me the subs with them wired up at 1 ohm (0.7 ohm) load.... They are internally wired to avoid seeing wires in the trunk, so I def have to send them back.
PFarmer, when I play music and watch the meter, the impedance just goes up from the 1.4 ohm load. I havent seen it drop below the original number. I might be talking about something completely different from what you meant though
What's the equation to make the proper calculation?
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If you are using a standard DMM meter and are measuring resistance you will most likely not get a good reading with the system in service. With it out of service you will be measuring resistance ( and disconnected) but the value will not give you an accurate impedance reading.
A test tone in the frequency range can be used to calculate it.
Basically resistance = voltage/current (dc circuit). The same equation can be used. Technically impedance is the 'resistance' to current flow. The difference is that in the case of something like a speaker it constantly changes.
I don't know what meter you may be using but there are some that can directly measure this in service, but it is easy enough to calculate it.
One factor that makes a speaker a little more complicated than simply a coil attached to the same place is when the speaker moves back to rest. Remember a speaker can be used as a mike (depends on the speaker), if the speaker is fully extended for example and then the current is removed it will move back to rest and generate its own current flow. When playing music it does the same thing. Because the moving coil has inductance, resistance, and capacitance it will act differently at different loads and frequencies. That is why the ohm rating is 'nominal'. Consider what occurs if the same load was presented and the voltage was increased - Power = Voltage (squared) / resistance (dc circuit). In an ac system power companies will increase or decrease voltage to make the load look different to the generating facilities. This works because the system has capacitance, resistance, and inductance. If it had only resistance than what would occur is an increase in power and therefore load although heat would increase the resistance.
A speaker will do the same thing, increase the temperature due to load (power output of the amp) and what will occur? What will occur if not limited in some fashion?