Impedance Introduction
Impedance and resistance share the same unit, Ω. Just as resistance impedes current flow, so does impedance.
Impedance can be the resistance to current created by any combination of resistance, capacitance, and inductance. Since capacitors have infinite impedance for DC current, while inductors have zero impedance for DC current, the term is more commonly used to describe the resistance to current flow in AC circuits.
High impedance refers to a high impedance value, while low impedance refers to a low impedance value.

What is a Speaker?
Speakers come in several different types. One type is a wind instrument, thin at the top and thick at the bottom, often made of copper. Another type is a modern electroacoustic component that converts electrical signals into sound, also called a loudspeaker. It can also be used to describe someone who advocates for others or promotes something.

A speaker is essentially a device that converts electrical energy into sound. When varying electron energies are transmitted to the coil, the coil generates energy that interacts with the magnetic field of a magnet. This interaction causes the paper plate to vibrate. As the electron energy fluctuates, the speaker coil moves forward or backward, and the paper plate moves accordingly. This movement causes the air density to change, producing sound.

Speaker Impedance
Commonly mentioned in audio equipment contexts include speaker impedance, the input impedance of pre- and post-amplifiers, the output impedance of pre-amplifiers (pre-amplifiers are usually referred to as output internal resistance, not output impedance), and the transmission impedance (or characteristic impedance) of signal lines. Since impedance is still measured in ohms, Ohm's law applies. Simply put, for the same voltage, higher impedance means less current will flow, while lower impedance means more current will flow. The most common speaker impedance rating is 8 ohms. This indicates that, during factory testing, the speaker exhibits an impedance of 8 ohms when fed a 1 kHz sine wave signal. Alternatively, it represents an average impedance within the speaker's operating frequency response range.

This value isn't a fixed value, but rather varies with frequency. When a power amplifier outputs a fixed voltage to a speaker, according to Ohm's law, a 4-ohm speaker will draw twice as much current as an 8-ohm speaker. Theoretically, a solid-state power amplifier with an 8-ohm output of 100 watts will automatically output 200 watts when connected to a 4-ohm speaker. As the speaker's impedance decreases, the current flowing through the power amplifier at a fixed voltage increases, eventually acting like a short circuit in the speaker cable. Therefore, the impedance can sometimes drop as low as the 1-ohm limit. Exceeding this range will cause the unit to burn out. This explains the common saying: a power amplifier doesn't need to be high-power, but it does need to output high current.

The difference between 4-ohm and 8-ohm speakers is:
1. The internal resistance of a 4-ohm speaker is 4Ω; the internal resistance of an 8-ohm speaker is 8Ω.
2. Because 4-ohm speakers have lower internal resistance, voltage changes are more noticeable than 8-ohm speakers, resulting in higher sound sensitivity.
3. 8-ohm speakers have lower power consumption, making them suitable for bass, resulting in a deeper sound and making them ideal for high-quality audio.