An experimental investigation of the parametric array in air was conducted using a circular piston transducer which produced spherically spreading, collinear, primary beams at frequencies of 18.6 and 23.6 kHz. Since source levels were not strong (about 110 dB re 0.0002 μbar at 1 ft), the 5−kHz difference frequency signal generated by the parametric array was relatively weak. Because of space limitations, all measurements were made in the nearfield of the array. Spurious difference frequency signals resulting from intermodulation distortion in the receiving system were suppressed by judicious choice of electronic components and by the addition of an acoustical filter in front of the microphone. The classic properties of the parametric array were observed. The 5−kHz beam was narrow, and no minor lobes were evident. The propagation curve first increased with increasing range, reached a broad maximum, and then gradually decreased. Theoretical predictions were based on a perturbation solution of Burgers’ equation and on the integral solution of the inhomogeneous wave equation. Comparison of measured results with these predictions conclusively demonstrated the existence of the parametric array in air. Beam patterns and propagation data obtained for the second−harmonic and sum−frequency signals also confirmed theoretical predictions. Subject Classification: 25.35.

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Most reading disabilities can be traced to difficulties acquiring oral language during preschool years due to insufficient linguistic stimulation. The present 2-year project aimed to improve the literacy-related oral language skills of 48 low-income, primarily ELL 4-year-old children in local public preschool by providing for individual conversational experiences with trained university students. Their results were compared to 48 peers at two comparable preschools. Children were tested in the fall and spring on multiple measures. Throughout the year, intervention children met with volunteers each week (26 weeks) for 20 minutes to dictate personal narratives. The control group received the regular public school preschool curriculum only. The improvement of intervention children on multiple measures of oral language ability—notably vocabulary and quality of narrative—was significantly greater than that of their peers.