The negative effects of environmental noise on sound recordings are recognized in the professional literature. Sound booths and anechoic chambers are examples of controlled acoustical environments widely used in research. However, both enclosures are expensive, require substantial space, and are not portable. Our research has been directed to measuring vocal endurance and voice characteristics of singers before and after sustained voice use. Our desire to acquire high-quality onsite recordings necessitated the development of a portable recording environment. In this article, we report the design, construction, and acoustic characterization of a prototype portable sound box (PSB) to acquire high-quality voice recordings in a controlled, portable acoustical measurement. Simulations were conducted to model the intended use of the PSB by voice users, using two acoustic characterization procedures. The first method showed higher intensity variations by region and depth as frequency changed. For the modified method, intensity response was more uniform and displayed less variation with frequency change. Both methods enabled us to (1) refine the onsite recording procedure, (2) provide insight into potential sources of analysis errors, and (3) develop detailed analysis of frequency intensity response affected by equipment variability. We found that it is possible to construct a PSB for onsite high-quality voice recording.