Due to its physical and chemical effects, ultrasound is widely used for industrial purposes, especially in heterogeneousmedium. Nevertheless, this heterogeneity can influence the ultrasonic activity. In this study, theeffect of the addition of inert glass beads on the sonochemical activity inside an ultrasonic reactor is investigatedby monitoring the formation rate of triiodide, and the ultrasonic power is measured by calorimetry and byacoustic radiation. It was found that the sonochemical activity strongly depends on the surface area of the glassbeads in the medium: it decreases above a critical area value (around 10-² m²), partly due to wave scattering andattenuation. This result is confirmed for a large range of frequencies (from 20 to 1135 kHz) and glass beadsdiameters (from 8-12 μm to 6 mm). It was also demonstrated that above a given threshold of the surface area,only part of the supplied ultrasonic power is devoted to chemical effects of ultrasound. Finally, the acousticradiation power appears to describe the influence of solids on sonochemical activity, contrary to the calorimetricpower.