An electronic device may have an upper housing and a lower housing separated by a slot. An antenna module may be mounted in the lower housing and may include a cavity. An antenna element may be disposed within the cavity. Grounded traces may be patterned onto walls of the module and may be coupled to conductive walls of the lower housing by conductive gaskets. The antenna element may have a high band arm displaced farther into the cavity than a low band arm by a shim. The antenna module may have an acoustic port aligned with a speaker port. The acoustic port may allow sound waves from a speaker to pass into the cavity from the speaker port. The cavity may be configured to optimize an audio response of the speaker while concurrently optimizing radio-frequency performance of the antenna element.