The present invention relates to a device for accomplishing 
noise reduction in a photoacoustic 
gas detector using a sound damping element and / or a background or reference 
microphone where a preferably larger external volume that acts as a sound damping element (SDE) is coupled to a smaller volume through which the gas diffuses. The 
coupling is accomplished in such a way that the externally generated sound 
waves incident upon the photoacoustic 
detector are adequately attenuated by the larger volume SDE without adversely affecting 
diffusion of the gaseous species of interest through the smaller volume for measurement by the 
detector. Preferably this is accomplished by 
coupling the larger SDE volume to the smaller gas 
diffusion volume by a long and thin pressure channel. Another photoacoustic 
detector includes a measuring 
system to measure the photoacoustic excitation of 
analyte gas entering the photoacoustic detector, a reference 
system to measure the effect of pressure 
waves in the environment, and a 
system for offsetting an output from the measuring system with an output from the reference system to reduce 
noise resulting from pressure 
waves in the environment in an output 
signal of the photoacoustic detector. The present invention also relates to a device for testing the integrity of a porous member and includes a source of pressure waves and a sensor for measuring a 
signal resulting from the transmittal of pressure waves from the 
transmitter. The 
signal is proportional to pressure losses through the porous member. The pressure losses through the porous member are, in turn, a measure of the degree to which the porous member has become clogged.