The purpose of this paper is to study the effect of the front cavity resonance and the vocal tract area function on the quality of synthesized unvoiced speech. From prior experiments, it has been determined that unvoiced speech is highly related to the vocal tract front cavity resonance. The noise source is located near the vocal tract constriction and the front cavity serves as a spectral shaping filter. An algorithm is proposed to estimate front cavity resonances, from which effective length of the vocal tract front cavity can be calculated. The parameters are used to construct a simple vocal tract area function. Unvoiced speech is generated using an articulatory synthesizer. And effects of the front cavity length, back cavity shape on the perception of unvoiced fricatives are investigated.