With parallels to human speech, rampant diversity within and among species, and a potential role in speciation, acoustic phenotypes in birds have received considerable attention since the 1950s when the spectrograph unlocked our ability to quantify acoustic variation. Studying the relative roles of innovations in and potential constraints on sound production is critical for understanding evolutionary trends in acoustic phenotypes. Most bird vocalizations are produced by vibration of vocal folds within the syrinx, a novel organ to birds located near the juncture between the trachea and bronchi. Morphological structures like the syrinx are expected to scale together as an organism grows, therefore selection on body size might influence the evolution of other size-linked traits. Several studies have demonstrated allometric scaling of fundamental frequency (F0) in avian sub-clades–including songbirds and tinamous. However, there have been no studies looking at the evolution of acoustic allometry across birds. Studying how acoustic allometry evolves is critical for understanding whether sub-clade acoustic allometries reflect overall clade trends and reconstructing sounds made by extinct non-avian dinosaurs. Here, we build a synthetic dataset of body size and F0 in birds and utilize a suite of comparative methods to test the hypothesis that acoustic allometries are shared across birds. We also generate new data for three clades spanning the extremes of body sizes in birds to understand how well we can predict acoustic traits from body size. Our results have implications for reconstructing the sounds of extinct animals and elucidate how innovations and constraints shape acoustic diversity across birds.