Wireless loudspeakers are propagating at a remarkable rate. The first appeared in the 1990s, and received music signals from the source components via RF. But they sounded pretty awful, and didn’t catch on. The next wireless speakers used Bluetooth, which have gradually become better as Bluetooth’s codecs have improved, from SBC to aptX to the new aptX HD. Lately we’ve seen a proliferation of wireless speakers that work via Wi-Fi; these are easy to implement, as most people’s homes now have a wireless network. Apple, Google, and Amazon are the latest and biggest players in this market, with voice-activated products that also play music.