The Altec Lansing 1684A is a professional 5-channel automatic microphone mixer designed to manage multiple open microphones in conferencing, courtroom, council chamber, and performance applications. Its primary function is to intelligently activate only the microphone channels where someone is speaking, while suppressing or lowering the gain on inactive channels. This automatic gating action prevents the accumulation of background noise, reduces acoustic feedback (howlround), and improves overall system gain before feedback, which is critical when many microphones are used in the same acoustical space. Each of the five independent channels features its own input gain control, mute switch, and status LED to indicate when the channel is "open" or active. The mixer operates on standard AC power and is built into a rugged steel chassis for reliable performance in fixed installations.

The intelligence of the 1684A lies in its comparator circuitry, which continuously monitors the audio level on each channel. When the signal on a channel exceeds a preset threshold, that channel opens, allowing the audio to pass to the main output. Some models incorporate a "last mic on" feature or adjustable hold time to prevent channels from cutting off during short pauses in speech. The output section provides a mixed, balanced line-level signal suitable for connection to a sound reinforcement system, recording device, or broadcast console. By automating the mixing process, it eliminates the need for a dedicated operator to manually mute and unmute microphones, ensuring that the audio system responds naturally and immediately to whoever is speaking.

This mixer is a classic solution for installed sound environments where multiple microphones are permanently deployed. It is commonly found in government council chambers, courtrooms, lecture halls, houses of worship, and corporate boardrooms. In such settings, it ensures clear, intelligible audio pickup from any participant while maintaining a quiet background. For system integrators and audio technicians of its era, the Altec Lansing 1684A represented a reliable, set-and-forget component that solved a fundamental challenge of multi-mic systems. While modern digital automixers offer more channels and advanced features like gain sharing, the 1684A remains a respected example of robust, analog automatic mixing technology.