RESUMEN
The thermophone, conceived in 1917 by Arnold and Crandall, was a unique thermoacoustic loudspeaker. The high heat capacity per unit area (HCPUA) of thin-film materials at that time limited the usefulness of thermophones. Recently, researchers of carbon nanotubes (CNTs) have developed techniques to create a super-aligned thin-film of multi-walled CNTs, possessing extremely low HCPUA. This paper will discuss CNT thin-film loudspeaker theory as well as some initial investigations into the feasibility of a high-powered audio CNT speaker. The advantages of such a loudspeaker include: Ultra-lightweight, compact, no moving parts, low cost, and independence from expensive rare-earth materials.
Asunto(s)
Acústica/instrumentación , Amplificadores Electrónicos , Nanotubos de Carbono , Sonido , Transductores , Diseño de Equipo , Estudios de Factibilidad , Modelos Teóricos , Movimiento (Física) , Presión , Temperatura , Conductividad TérmicaRESUMEN
Voice command sound pressure levels (SPLs) were recorded at distances up to 1500 m. Received SPLs were related to the meteorological condition during sound propagation and compared with the outdoor sound propagation standard ISO 9613-2. Intelligibility of received signals was calculated using ANSI S3.5. Intelligibility results for the present voice command indicate that meteorological condition imposes little to no effect on intelligibility when the signal-to-noise ratio (SNR) is low (<-9 dB) or high (>0 dB). In these two cases the signal is firmly unintelligible or intelligible, respectively. However, at moderate SNRs, variations in received SPL can cause a fully intelligible voice command to become unintelligible, depending on the meteorological condition along the sound propagation path. These changes in voice command intelligibility often occur on time scales as short as minutes during upward refracting conditions, typically found above ground during the day or upwind of a sound source. Reliably predicting the intelligibility of a voice command in a moderate SNR environment can be challenging due to the inherent variability imposed by sound propagation through the atmosphere.