New Arrivals in the Acoustics Lab

Intensity Probe - Larson Davis Model 2250

The intensity probe is a standard piece of equipment in many industrial and academic acoustical facilities.  Microphones alone measure sound pressure fluctuations.  But with two precision microphones whose phase responses are well-matched, spaced a precisely known distance apart, the particle velocity at the probe location can be calculated from the difference (gradient) in pressure.  Then, with both pressure and velocity, sound intensity can be calculated from their product.
Larson Davis Intensity Probe
Intensity, the rate of energy flow through a unit area, can tell us about radiation properties of, say, a sheet metal panel that's vibrating, a guitar's top plate, or the tweeter, woofer, and port of a loudspeaker.  Intensity can also be summed or integrated over area to tell us the total sound energy emitted from an object per unit time.  This quantity, Sound Power, is the basis of many regulations (especially in Europe and Japan) governing machinery and noisy equipment such as lawn mowers, earth movers and tractor, and even home vacuums.

Microflown Demo Kit from

SEM image of Microflown elementThis kit contains three Microflown sensors, a new way to measure particle velocity.  The Microflown consists of two very small wires (on the level of MEMS devices).  By sending current through the wires, their resistance can be measured.  Of course, resistance depends on temperature, and air flow across the wires cools them.  In effect, the Microflown is similar to a hot-wire anemometer.  However, it is novel due to its small size, and the use of two wires for differential measurement of the temperature effects (more at

Once the particle velocity is known, it can be combined with pressure measurements for a variety of applications which require sound intensity and/or acoustic impedance.  TheDemo Kit from Microflown sensors included in the kit all have small precision microphones co-located with the Microflown sensor.  The signals are routed through a conditioning unit, and can then be fed to a dynamic signal analyzer or into LabVIEW for recording and processing.

The apparatus is here through a partnership between Microflown and Kettering University.  Daniel Ludwigsen's winning proposal to their University Contest will use the Microflown sensor to measure the input impedance of brass instruments.  The input impedance is an important measure of the characteristics of an instrument, making a significant contribution to proper intonation and playability.