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The accuracy of speech recognition through an air-conducted microphone can be less accurate under a highly noisy environment or when the volume of the user’s voice is relatively low. One solution to this problem is the use of contact microphones. However, neither the microphone locations that provide optimal speech recognition accuracy for each user nor the mechanisms underlying these contact forces have been clarified. In this study, we experimentally investigated the effects of placement, contact force, user gender, and speech recognition platform on the accuracy of speech recognition with contact microphones placed on the surface of the head and neck. The experimental results indicated that the mechanism underlying the influence of each factor on speech recognition accuracy differs for speech acquired at the neck and head locations. In particular, the effect of the user’s gender was significant for the neck-acquired sound, but not the head-acquired sound. The results also revealed that the microphone contact force did not affect the recognition accuracy or user discomfort for the head-acquired sound. Moreover, the results of speech recognition experiments in a simulated noisy environment showed that bone-conducted sounds acquired on the head and neck surfaces were more robust than air-conducted sounds.