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Flat Speaker vs. Conventional Speaker  

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Comparison of Frequency Response

This page presents a comparison of the frequency spectra of two conventional speakers and the flat speaker. The conventional speakers used were the Calrad 20-224A and 20-175A. In the plots below, the 20-224A is referred to as the "28mm Round Conventional Speaker" and the larger 20-175A is referred to as the "40mm Round Conventional Speaker."

Figure 8 shows the results of separate experiments where each speaker was placed in roughly the same position and a random code from the Whisper system was played for several seconds. The volume was adjusted for each speaker to be comparable across the experiments. The 20-224A results appear in the top plot, the 20-175A is in the middle, and the flat speaker is on the bottom. The horizontal axis is scaled by 104, so a value of 2 (for example) represents 20000 Hz or 20 kHz.

power spectral density (PSD) comparison

Figure 8: Power Spectral Density (PSD) comparison.

Note the familiar "terrible null" at about 5 kHz for the flat speaker. Note also the spike that appears in all three plots at about 38 kHz. This resulted from the Whisper system picking up equipment in the lab (particularly monitors). When all extraneous equipment was turned off, the spike disappeared (see Figure 9 below). As to why the system was picking this up, there was a test wire coming from the breakout box that may have been acting as an antenna, though this was never verified.

power spectral density (PSD) comparison

Figure 9: Power Spectral Density (PSD) comparison (without spike).

Informally comparing the spectra, the smaller conventional speaker (top plot) appears to be the winner. Its response is (fairly) flat from about 3 kHz to 18 kHz. The larger conventional speaker (middle plot) has a wider response, as expected. However, its spectrum seems to be less flat (e.g. the drop off at about 12 kHz).

At this point, the smaller conventional speaker was chosen, and the experiments comparing the HiBall tracker with Whisper were repeated. More details on these experiments can be found here.

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Last updated on:
Monday, June 24, 2002