Infrasonic Microphones - New Mexico Tech

Custom, low-cost infrasonic microphones for deployment at volcanoes (updated Nov. 2005)

This page is part of an effort to encourage the proliferation of infrasonic studies and monitoring at active volcanoes. The following list describes low-frequency microphones purchased or custom built for deployment at volcanoes with links to more detailed information (.pdf files). For additional information contact Jeffrey Johnson at the Department of Earth and Environmental Science, New Mexico Tech.

NAME	WHERE DEPLOYED	DATE FIRST USED	DESCRIPTION
Honeywell PT	Erebus, Volcan de Colima	2005	The Honeywell PT microphone uses a silicon-membrane, differential pressure transducer (DC001NDR5 / DC005NDC4) operated in absolute mode. Barometric changes are filtered out using high-pass capillary tubing attached to one of the pressure ports. These instruments allow high dynamic range and provide very good response at low frequencies. They are currently being tested at Erebus and Volcan de Colima.
J4	Popocatepetl, Volcan de Colima. New Mexico	2003	The J4 microphone is similar to the McChesney4 microphone, but all four microphone elements are co-located within the enclosure. Its modularity allows external or internal power supply (single-ended), easy swapping of microphone elements, and variable gain/filtering controls. Two variants currently exist, the J4 New Mexico, which is deployed in New Mexico and at Colima, and the J4 Popo currently deployed at Popocatepetl, Colima, and in New Mexico.
J1 Basic	Stromboli, Villarrica, Santiaguito, Fuego, Colima, Erte Ale, Reventador	2002	The J1 Basic is a very simple, extremely cheap (less than $10), unamplified, single-element (WM-034BY) microphone with corner frequencies between 0.5 and 0.8 Hz. It has an unbuffered output, but is extremely low-powered (6 months on two alkaline AA's). Different versions have single-pole anti-aliasing filters at 12 Hz and 38 Hz. The low cost and compact size enables deployments in multi-element arrays. Very successful array deployments have been conducted at Stromboli, Villarrica, Santiaguito, Fuego, Colima, and soon Erte Ale.
ISLA4	Erebus	2002	The ISLA4 is a variant of the ISLA14, but with only four microphone elements. It was built for permanent deployment at Erebus
ISLA14	Kilauea	2002	The ISLA14 microphone was adapted from the McChesney microphones, but utilizes 14 individual co-located WM-034BY Panasonic electret condenser elements. These buttons, which are used in the Seattle P and Q microphones (designed by Chris Hayward, Southern Methodist University), appear to have a much lower corner frequency (0.5 to 0.8 Hz). Positive and negative power supplies are required. Design and construction by Jeff Johnson with support from Infrasound Laboratory (ISLA), HIGP, UH. Deployed at Pu'u 'O'o, Kilauea.
McC#	Erebus, Pichincha, Tungurahua, Stromboli	1999	The McChesney1, McChesney4, and McChesney16 element microphones consist of a variable gain amplifier, low-pass RC filters (~20 Hz), and 1 to 16 individual WM-52BM Panasonic omnidirectional condenser elements. Each Panasonic condenser element has a slightly different sensitivity and corner frequency (~1 to ~5 Hz) which limit their application for infrasonic waveform modeling. However, the spatial wind filtering abilities of the McChesney 4 and 16 boxes allow identification of acoustic pulses in windy conditions (see section on noise in this appendix). Of all the McChesney units used in this study, only the microphones deployed at Erebus have undergone careful laboratory calibration tests to determine sensitivity and corner frequency so that instrument responses may be removed. McChesney microphones deployed at Karymksy were calibrated only by temporary co-location with the Larson-Davis microphone. Frequency response of the McChesney microphones resembles a single-pole high-pass filter to first order. Design and construction of the McChesney microphones is by both the author and Pat McChesney (University of Washington). Deployed at Erebus, Pichincha, Tungurahua, and Stromboli.).
Larsen- Davis	Karymsky, Erebus, Reventador, Tungurahua	1999	The Larsen-Davis free-field precision microphone is a commercially available electret condenser microphone suitable for engineering purposes and sensitive to near infrasound. The instrument deployed at Karymsky and Erebus consisted of a one-inch electret condenser element #2570, preamp PRM900C, and a power supply 2200C. Specifications are provided by Larson-Davis and verified in the McChesney laboratory calibration box. Laboratory calibration tests reveal a behavior which closely resembles a single-pole high pass filter with corner frequency at 0.27 Hz. In many experiments, the Larson-Davis microphone was temporarily co-deployed with other electret condenser microphones to assess the relative response of the other instruments. Deployed at Karymsky and Erebus.
Venema	Karymksy, Sangay, Pichincha	1998	The Venema microphones (low and high gain) use Radio Shack omnidirectional electret condenser elements (catalog number 270-092B). The attached variable-gain amplifier and low-pass filters (~20 Hz) were designed and built by Brian Venema and the UW Physics electronics shop. Unfortunately, laboratory calibration tests conducted in 2000 may reflect deterioration of the sensing elements during their long life span. Absolute sensitivity at Pichincha is entirely unknown because signals were conveyed by telemetry atunknown gain. Deployments at Karymsky, Sangay, and Pichincha
Ramey	Karymsky	1997	The Ramey microphone is a replica of the Dibble microphone in that it uses a similar enclosure and a pressure transducer with one of the differential pressure ports blocked. Pressure sensing element is a SenSym LX06002D transducer. Construction of microphone is by Jim Ramey (University of Washington). Deployment at Karymsky in 1997.