It is well known that the support conditions of a specimen can significantly affect the results of the impedance tube measurement. In theory, the specimen should be mounted under the ideal slip condition without any circumferential air gaps. However, this cannot be fully realized due to the inaccuracy of material cutting, thus causing a constraint or gapped condition. Furthermore, the specimen is normally mounted lightly in contact with the bottom of the tube, or with a back air layer. In this paper, the effect of realistic support conditions for poroelastic materials is investigated by numerical simulation with the finite element method. Under each condition, the behaviors of calculated values of normal-incidence absorption coefficient and transmission loss are discussed by comparison with theoretical values for the infinite-area material. It is shown that several mechanical and acoustical parameters of poroelastic materials can be estimated from impedance tube measurement under the circumferential constraint and gapped conditions.