Model 25/21

Cost-effective and durable sensors for the mid-infrasound to low-audio bandwidth. 

The Model 21 and 25 are an excellent choice for any application requiring a high resolution infrasound sensor in a small form factor at a moderate cost. It excels ataccurately recording signals which span the low audio/infrasound boundary, such asexplosions and avalanches, and makes an excellent sensor for campaign styleexperiments because of its rugged construction. If your application requires a highquality infrasound sensor, the Chaparral Physics Model 21/25 provides you with acompact, robust solution with excellent value.


Nominal Sensitivity
High: 2.0 volts/Pa @ 1 Hz, 18 Pa full scale range
Low: 0.4 volts/Pa @ 1 Hz, 90 Pa full scale range
Individual sensor’s calibrated value is +/-5% from nominal. Calibration value istraceable to the Los Alamos National Laboratory (LANL) calibration chamber.
Output Type: Differential
Maximum 36 volts peak-to-peak (signal+ to signal-)
Frequency Response Flat to within +0, -3 dB from 0.1 Hz to 200 Hz 
Flat to within +0, -0.5 dB from 0.3 Hz to 50 Hz
Self Noise Less then 0.63µPa2/Hz @ 1 Hz (-62dB Pa2/Hz, rel to 1 Pa)
Less than 3 mPa RMS 0.1 to 40 Hz
Less than 0.8mPa RMS 0.5 to 2 Hz
Dynamic Range 99dB high gain, 113dB in low gain @ 0.5 Hz to 2 Hz
Output Impedance 150Ω non-reactive, (recommend load >10kΩ)(Recommended less than 10,000pf loading)
Short circuit protected signal+ to signal–, and signal to ground
Power Requirements
DC Source 12 volts (9-18 volts) DC, reverse voltage protected.
Current Drain Less than 40 ma @ 12 v
Sensor will function in any position or attitude. Sealed to IP-64 with acoustic inlet sealed and mating electrical connector installed.
Operating Temperature -40℃ to + 65℃
Humidity 95% (non-condensing)
Dimensions 16.5” (42 cm) maximum height, 9.9” (25 cm) maximum diameter
Weight 17.6 lbs (8 Kg), for 4-port version
Std. Acoustic Inlets 4 inlet ports (maximum 12), male, Garden-Hose-Thread,and a calibration port. Total fore-volume of a 4 port Model50A with capped GHT inlets is ~55 cubic cm.

Model 21/25 Specifications (PDF)

Model 21 Manual (PDF)

Model 25 Manual (PDF)