An acoustic apparatus adapted to operate in a gas filled space from a first side of an object to be measured for making a non-contact thickness measurement thereof includes an electro acoustic transducer, a transceiver coupled with the electro acoustic transducer and adapted to excite electro acoustic transducer to output an acoustic signal towards the object to be measured and receive an acoustic response signal therefrom, and a signal processor adapted to process the response signal and determine a thickness of the object. The electroacoustic transducer has a transducer-to-gas acoustic interface, and the transceiver is adapted to operate the electroacoustic transducer so as to emit into a gas filled gap an acoustic broad band pulse towards the object and to receive an acoustic resonance response signal in the acoustic response signal at a level that allows acquisition of the resonance response signal above a predetermined signal to noise level.