"I'd like a number three with no pickles and a large Coke." The drive-through speaker crackled back: "Number free, extra pickles, large smoke?" Close enough, apparently, because what arrived at the window was a number five with extra onions and a medium Sprite. The customer had learned to simply accept whatever the restaurant decided to give them.

The drive-through intercom was a 3-inch speaker mounted in a metal enclosure at car-window height. Its frequency response dropped off a cliff above 2.5 kHz — removing exactly the consonant frequencies that distinguish "three" from "free," "Coke" from "smoke," and "no pickles" from "extra pickles." The STI of the system was approximately 0.25 under ideal conditions and dropped to 0.15 when a car engine was running.

Adding to the problem, the menu board's metal canopy created a small reverberant enclosure that colored the customer's voice before the microphone captured it. The intercom amplifier was set to AGC mode, which pumped the gain up during quiet moments (capturing engine noise) and compressed it during speech (reducing dynamic range). Every element of the signal chain actively degraded intelligibility.

Drive-through ordering systems operate at the intersection of terrible acoustics, minimal speaker quality, and high ambient noise. Industry estimates suggest 10-15% of orders are incorrect, costing billions annually.

The Moral: Intelligibility has a dollar value. Even simple PA systems benefit from STI measurement with SonaVyx STI — knowing your baseline is the first step to reducing errors.