Abstract: A quasi-static cone penetrometer for subsoil investigation by simultaneously generating three sets of data, namely cone tip penetration resistance, sleeve friction resistance, and acoustical information, all as a function of depth. The penetrometer has a substantially smooth cylindrical outer surface terminating in a cone tip. The lower portion of the smooth cylindrical outer surface is provided by a friction sleeve immediately above the cone tip insulated from it by acoustic attenuation means. A microphone in the tip (or elsewhere in the penetrometer) is responsive to acoustical input generated, for example, by the tip moving through the soil, and sound barrier means holds said microphone firmly in place. The sound barrier means, the acoustic attenuation means, and the acoustical dampening means substantially isolate the microphone from the core ring and from the friction sleeve. A tip load cell is joined to the cone tip and insulated from it acoustically by acoustical-dampening means.