For almost every speaker or set of headphones you can buy, you’ll find a specification for impedance, measured in ohms (referred to as Ω). It’s rare that packaging and accompanying product manuals explain what impedance means or why it’s important to you.
Impedance is like great rock and roll. Understanding everything about it is hard, but you don’t need to understand everything to «get» it.
About Impedance Dynamics
Talking about things like watt , voltage and power, many audio writers use the analogy of water flowing through a pipe because it’s an analogy that people can visualize and relate to.
Think of a speaker as a pipe. Sound signal — your music — performs in water quality, flowing through the pipe. The larger the pipe, the easier the water flows. Larger pipes also handle a larger volume of running water. A lower impedance speaker is similar to a larger tube in that it allows more of the electrical signal to pass through and allows it to flow more easily.
As a result, you see amplifiers that are rated at 100 watts into 8 ohms or 150 or 200 watts into 4 ohms. The lower the impedance, the more easily electricity (signal or music) flows through the speaker.
Many amplifiers are not designed to drive 4 ohm speakers. Using the pipe analogy, you can put in a larger pipe, but it will carry more water (audio) if you have a pump (amplifier) powerful enough to provide the extra water flow.
Does low resistance guarantee high quality?
Using low-impedance speakers without equipment that can support them can cause the amplifier to be fully turned on, which could damage the equipment.
Using the wrong speakers and amplifiers can cause problems when the receiver or amplifier is not up to the task.
Take just about any modern speaker and plug it into any modern amplifier and you’ll have more than enough volume for your living room. So, what is the advantage of a 4 ohm speaker over a 6 ohm or 8 ohm speaker? Not much, just that the low impedance sometimes indicates fine tuning the engineers made when they designed the speaker.
The impedance of a speaker changes as the sound increases or decreases in pitch (or frequency). For example, at 41 hertz (the lowest note on a standard bass guitar), the speaker impedance might be 10 ohms. At 2000 hertz (the upper range of the violin), the resistance can be as low as 3 ohms. The impedance specification seen on the speaker is only an approximate average.
Some of the more demanding acoustic engineers prefer to equalize the speaker impedance for consistent sound throughout the audio range. Just as someone might sand down a piece of wood to remove high ridges of grain, a reporting engineer might use an electrical circuit to smooth out high impedance areas. This is a side note as to why 4 ohm speakers are common in high end audio but rarely seen in the mainstream market.
Can your system handle it?
Before you buy a 4 ohm speaker, make sure your amplifier or receiver can handle it. This may not be clear, but if the manufacturer of the amplifier or receiver publishes power ratings of 8 and 4 ohms, you are safe. Most stand-alone amplifiers without a built-in preamp or tuner can drive 4 ohm speakers, as can most high performance A/V receivers .
Relatively inexpensive receiver may not be suitable for 4 ohm speakers. It might work fine at low volume, but crank it up and the amp might not have power to power the speaker. The receiver may temporarily shut down, or you may burn the receiver.