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Making Sounds with Analogue Electronics
Published in Russ Martin, Sound Synthesis and Sampling, 2012
Amplifiers take an audio signal and amplify it. Microphone amplifiers are used for low-output microphones or for extra gain with quiet sound sources. Power amplifiers are used to drive loudspeakers in public address (PA) applications. Guitar amplifiers turn the quiet sounds produced by the strings and amplify the outputs from the electromagnetic pickups on the guitar to produce audible sound. By connecting a microphone into an amplifier that is driving a loudspeaker, it is possible to create feedback by adjusting the gain of the amplifier and the positioning of the microphone and loudspeaker. This can be used to create some interesting sounds, especially if the gain is reduced slightly so that it is just about to break into oscillation. Electric guitars can be used instead of a microphone, and the same effects can be produced because the strings and body of the guitar can pick up enough of the amplified audio to create a feedback loop.
An inexpensive sensor for noise
Published in Journal of Occupational and Environmental Hygiene, 2018
Laura Hallett, Marcus Tatum, Geb Thomas, Sinan Sousan, Kirsten Koehler, Thomas Peters
The sound pressure levels measured with 50 noise sensors embedded within the larger monitors were compared to those measured with an SLM (XL2 Audio and Acoustic Analyzer, NTi Audio, Tigard, OR, USA) (Figure 2). Each noise sensor was tested individually inside a quiet office. The microphones of the SLM and noise sensor were placed within 2.5 cm of each other and 30 cm from the center of a guitar amplifier (Fender Musical Instruments Corporation, Frontman 10G, Scottsdale, AZ, USA). The amplifier was connected to a laptop computer with an auxiliary cord. Five target sound levels, ambient, 65 dBA, 75 dBA, 85 dBA, and 94 dBA, were generated to test each noise sensor. These sound levels were adapted from the range used by Kardous and Shaw in their evaluation of smartphone applications and to meet our needs to measure noise in a heavy-vehicle manufacturing facility. For levels from 65–85 dBA, pink noise was produced by playing a computer sound file (NTi Audio Test Signals for Audio and Acoustic Analyzers V1.0) through the guitar amplifier. The sound level was adjusted using the volume settings on the laptop and then verified on the reference SLM before each testing period began. The 94-dBA tone was generated using a sound level calibrator (General Tools & Instruments, SCAL1356, Secaucus, NJ, USA). Each test tone was generated for 30 sec before moving on to the next. Both the noise sensor and SLM reported 1 sound pressure level measurement every 2 sec over each 30-sec testing period, n = 50 sensors × 5 test levels × 1 measurement every 2 sec × 30 sec = 3,750 paired measurements.