Calculating for Low Impedance Amplifiers

Last time we introduced how to calculate for a Line Volt amplifier, but there is still one more amplifier calculation method left — namely, how to calculate for a Low Impedance amplifier. What do we need to consider when calculating this type of amplifier? Let's take a look together.

There are two things to consider in the calculation: the speaker's wattage and the speaker's impedance — most speakers have an internal impedance of 8 ohms. Also, to properly match the amplifier and speakers, the amplifier's wattage should be slightly higher than the speakers' wattage so it can drive the speakers at full power. Here is an example calculation:

Suppose the speaker we want to use has an impedance of 8 ohms and a rating of 500 watts. If we connect many of them in parallel, the amplifier's wattage must be higher, and the speakers' total wattage varies with the number of drivers, as in the following example:

Impedance formula: Total impedance = speaker impedance / number of speakers *used when all speakers have equal impedance. Speaker wattage formula: Total speaker wattage = speaker wattage x number of speakers.

If we use 2 speakers, the impedance = 8 / 2 = 4 ohms, and the speaker wattage = 500 x 2 = 1,000 watts. If we use 4 speakers, the impedance = 8 / 4 = 2 ohms, and the speaker wattage = 500 x 4 = 2,000 watts.

Once we know the total impedance and the speakers' wattage, we then select an amplifier suited to the speakers by checking that brand's amplifier specs to see how much wattage it delivers per total impedance. For example, if we want to use 2 speakers per channel, we should find an amplifier rated at 4 ohms with a minimum of 1,000 watts; or if we want to use 4 speakers per channel, we should find an amplifier rated at 2 ohms with a minimum of 2,000 watts.