Mulitplication in Frequency Domain as a Similarity Measure of Audio Clips
The fft product alone is not the convolution, but the frequency domain of the convolution. To complete the operation the OP must also take the inverse FFT to get a circular convolution result.
$$CONV = \text{ifft}(\text{fft}(a) \text{fft}(b))$$
However, similarity would be determined using correlation not convolution. To do this, simply complex conjugate one of the FFT results as follows:
$$XCORR = \text{ifft}(\text{fft}(a) \text{fft}^*(b))$$
The above is the cross-correlation function (using circular convolution). The result is the correlation of $a$ and $b$ at repeated circular shifts in time.