The DSL 331 Series is manufactured by Tecpel, and is a programmable sound level data logger equipped with back screw hole tripod connection. It has frequency range from 31.5 Hz up to 8 KHz, voltage supply of 9 V DC measuring level range from 30 to 130dB and operating temperature of 40 ºC. This is used in applications such as monitoring of safe working conditions, activity detection and recording, long-term measurement and recording of acoustic levels for environmental impact studies.