Design and characterization of an enclosed coaxial carbon nanotube speaker

Automotive mufflers are heavy, large, and loud at low frequencies. Carbon nanotube (CNT) speakers are solid-state, lightweight, flexible, and capable of handling high temperatures. This makes them suitable as loudspeakers in active exhaust noise cancellation applications. A coaxial CNT speaker designed for active noise control in an exhaust system is developed. Test results for resistance, in-pipe axial sound pressure level, and efficiency are presented. The maximum in-pipe sound pressure level was above 120 dB (re 20 μPa) using 105 W of electrical power. The maximum power efficiency was 0.008%. The weight, dimensions, and sound pressure level of the speaker show promise for active exhaust noise cancellation applications.