For a long time I have wondered why manufacturers would design their speakers with different impedances, and if there was any advantage to making a 4ohm speaker over an 8phm speaker, or visa versa. Is there any reason a speaker manufacturer would try and design their speaker for a specific nominal impedance?
I haven't been able to find any information about this online, so I figured someone at Audioholics has to have some insight.
If a speaker manufacturer has their head on straight, they'll design their speakers to be used by as many people as possible. That just makes sense if they want to sell to anyone other than the ones who have amplifiers that can tolerate a dead short across the output terminals. Receivers are made to do several things, but handling extremely low impedance loads isn't one of them, mainly because it takes a more hefty power supply and different (read "more expensive") output devices. This puts that receiver out of the intended price range and the targeted market segment. With 120/240VAC line voltage, power supply voltage isn't a problem, so 8 Ohm speakers are fine- if higher voltage is needed, the power transformer can step up the line voltage and it's done. In a car/truck with a 12VDC electrical system, it's not that simple. You can't use a transformer to step up the supply voltage in the same way. An AC voltage source is needed and that section of an amplifier isn't cheap when it's designed for high current and that brings us to another issue- when impedance drops, current increases with stable voltage. If the power supply and amplifier can't perform, the voltage drops, reducing output power and increasing heat in the circuits. Heat kills electronics and this means the amplifier needs larger and more efficient heat sinks, which cost more.
So, low impedance speakers aren't really an advantage- they cause more problems, if anything. Stable impedance loads make amplifiers happy and we all want our amplifiers to be happy.
