The authors posit that in an initial exposure to a broadcast video, hearing different voices narrate (in succession) a persuasive message encourages consumers’ attention and processing of the message, thereby facilitating persuasion; this is referred to as the voice numerosity effect. Across four studies (plus validation and replication studies)—including two large-scale, real-world data sets (with more than 11,000 crowdfunding videos and over 3.6 million customer transactions, and more than 1,600 video ads) and two controlled experiments (with over 1,800 participants)—the results provide support for the hypothesized effect. The effect (1) has consequential, economic implications in a real-world marketplace, (2) is more pronounced when the message is easier to comprehend, (3) is more pronounced when consumers have the capacity to process the ad message, and (4) is mediated by the favorability of consumers’ cognitive responses. The authors demonstrate the use of machine learning, text mining, and natural language processing to process and analyze unstructured (multimedia) data. Theoretical and marketing implications are discussed.