There's a Light
Wireless speakers have no direct connection to a stereo system or other source. Instead, the system must send a signal that the speakers can receive and convert into electricity in order to drive the voice coil inside the speaker itself. There are a few ways to do this.
One way is to use infrared signals. This is similar to how many remote controls work. The stereo system has a transmitter that sends out a beam of infrared light. Because infrared is outside the spectrum of visible light, we can't see it.
The transmitter's job is to take the fluctuations of electricity -- the same ones that would control the speaker if it were wired to the stereo -- and convert it into an infrared beam. The beam carries information through pulses. An IR system can send out millions of pulses per second. The wireless speakers have sensors that can detect these transmissions.
Once detected, the sensor sends electronic signals to an amplifier. Its job is to increase the strength of the sensor's output. Without the amplifier, the signals would be too weak to drive the voice coil within the speaker. This is why many wireless speakers still require wired power to work.
The amplifier sends electricity to the voice coil, alternating the flow of electricity as directed by the signals the sensor sends along. The alternating current will cause the voice coil's electromagnet to change polarity rapidly. The magnetic fields of the electromagnet and the speaker's permanent magnet do the rest of the work, pulling and pushing the voice coil and causing the speaker's diaphragm to vibrate.
There are several drawbacks to this type of wireless speaker. One of the big ones is that an infrared beam requires line of sight. That means there needs to be an unobstructed path for the infrared beam to follow from the stereo system to the speaker. Anything blocking that pathway will prevent the signal from reaching the speaker's sensor and the speaker will remain silent.
Another problem is that infrared signals are pretty common. Devices like most remote controls use IR technology. But even lights and human beings give off some infrared radiation. This can cause interference, making it difficult for the speaker to detect a clear signal from a stereo system. Even the most casual music fan might find it a chore to listen to a system that delivers a choppy or inconsistent experience.
There are other ways to send signals wirelessly. Next, we turn to the world of radio.