2 Ohm, 4 Ohm, 8 Ohm, all refer to the impedance of a speaker, which is the combined resistance and reactance of a speaker. The resistance being the DC component and the reactance being the AC component. If you use a digital voltmeter to measure the resistance of a speaker, it will always read low as it doesn't measure the AC reactance. The impedance value determines the amount of current that will flow through a speaker when it is being driven by a specific voltage signal. If you cut the resistance in half, twice the current will flow and therefore twice the power will be produced.
Car systems generally use 4 Ohm speakers as the peak voltage available from an amplifier running off a 12 volt battery is limited to 12 volts. Let us assume for the moment that the amplifier is designed to swing the voltage on the speaker 12 volts in one direction and 12 volts in the other direction. This produces a peak to peak voltage swing of 24 volts with a peak current of 3 Amperes. (Amperes = Voltage / impedance.) Therefore peak power is limited to 72 watts! (Power = Amperes X Voltage) RMS power ( root means squared ) is roughly 60 percent of this. Therefore with a 4 Ohm speaker you should be limited to about 45 watts RMS per channel. That doesn't sound like much but consider that even high quality speakers are about 5 percent efficient, therefor, almost all of this heat has to be dissipated by the fragile voice coil of the speaker. In order to get more power you would have to decrease the impedance of the speaker. SPL ( sound pressure level) goes up linearly and inversely with the enclosed volume of the listening space. Consider this; 90 watts RMS through a pair of efficient speakers is going to damage your hearing really quickly in the tiny enclosed space of the Insight, if it doesn't fry the voice coils first, but you will probably have fun doing it :wink: .
OK, that is probably more than you wanted to know about Ohms, but thanks for asking.
Car systems generally use 4 Ohm speakers as the peak voltage available from an amplifier running off a 12 volt battery is limited to 12 volts. Let us assume for the moment that the amplifier is designed to swing the voltage on the speaker 12 volts in one direction and 12 volts in the other direction. This produces a peak to peak voltage swing of 24 volts with a peak current of 3 Amperes. (Amperes = Voltage / impedance.) Therefore peak power is limited to 72 watts! (Power = Amperes X Voltage) RMS power ( root means squared ) is roughly 60 percent of this. Therefore with a 4 Ohm speaker you should be limited to about 45 watts RMS per channel. That doesn't sound like much but consider that even high quality speakers are about 5 percent efficient, therefor, almost all of this heat has to be dissipated by the fragile voice coil of the speaker. In order to get more power you would have to decrease the impedance of the speaker. SPL ( sound pressure level) goes up linearly and inversely with the enclosed volume of the listening space. Consider this; 90 watts RMS through a pair of efficient speakers is going to damage your hearing really quickly in the tiny enclosed space of the Insight, if it doesn't fry the voice coils first, but you will probably have fun doing it :wink: .
OK, that is probably more than you wanted to know about Ohms, but thanks for asking.
