Return to Home Page
Home
People
HW Design
SW Design
Status

Speaker Rotation  

You are here:  home > status > experiments > speaker rotation

Introduction

The results of the HiBall vs. Whisper comparison were better with the conventional speaker than previous results obtained with the flat speaker. However, the differences were still more than we had hoped.

This experiment was conducted to investigate the effects of speaker orientation on the range measurements. The thinking was that the speaker cone might be acting as many tiny "point emitters" and thus one edge of the cone (for example) might appear to the Whisper system as a physically separate emitter from the opposite edge of the cone. This might result in a phenomenon similar to that observed for the flat speaker where, as the speaker orientation changed wrt a particular microphone, parts of the speaker that were acting as separate emitters would get closer while others moved farther away. For the flat speaker, this resulted in four distinct points in space competing to represent a single point. See the flat vs. conventional speaker comparison for more details.

This rotation experiment was performed informally during the flat vs. conventional speaker comparison. The results did not appear to exhibit the "multiple emitter problem." However, the speaker was handheld during these trials, and thus a more rigorous experiment needed to be performed.

Setup

To better control the rotation, an optical rotation stage was mounted to an optical rail, with an xy stage mounted to the rotation stage, and the speaker mounted to the xy stage. A microphone was then placed directly in front of the speaker. Several 45-second trials were then performed to fine tune the speaker location. Each trial began with the speaker directly facing the microphone. Then the speaker was rotated 45 degrees clockwise, then back to center, then 45 degrees counter clockwise, and finally back to center again. The resulting range data was then plotted, and the xy stage was adjusted. The intent was to get the center of the speaker aligned with the axis of rotation.

A picture of the setup will be added soon. However, for now, letís just move on to the results.

Results

Figure 1 shows the resulting range measurement after the setup had been calibrated to place the speaker directly over the center of rotation. Figure 2 shows the same results with highlighted areas representing stationary periods. The vertical axes represent chips (i.e. range). Each chip is about three millimeters. The horizontal axes can roughly be thought of as milliseconds. They are scaled by 104 and so a value of 1 (for example) corresponds to 10000 milliseconds or 10 seconds.

speaker rotation results

Figure 1: Range results.

The experiment began with the speaker directly facing the microphone. The motion of the speaker was as follows:

  • The speaker was directly facing the microphone for approximately five seconds (Region 1 in Figure 2).
  • It was then slowly rotated 45 degrees clockwise.
  • It remained in this position for approximately five seconds (Region 2 in Figure 2).
  • It was then slowly moved back to center.
  • It remained in this position for approximately five seconds (Region 3 in Figure 2).
  • It was then slowly rotated 45 degrees counterclockwise.
  • It remained in this position for approximately five seconds (Region 4 in Figure 2).
  • It was then slowly moved back to center.
  • It remained in this position for approximately two seconds (Region 5 in Figure 2).
speaker rotation results

Figure 2: Range results.

Matlab standard deviation calculations appear below for two portions of the range data. The first range, 1:5000, represents data when the speaker was directly facing the microphone. The second range, 10000:15000, represents data when the speaker was turned away 45 degrees.


>> std(res.KFStateHist(2,50:5000)) ans = 0.023651 >> std(res.KFStateHist(2,10000:15000)) ans = 0.066416

Since, in general, 96 percent of sample values fall with ±3 standard deviations, these results indicate that 96 percent of the values are within ±0.070953 chips or roughly ±0.2 mm when the speaker is directly facing the microphone. Similarly, 96 percent of the values are within ±0.199248 chips or roughly ±0.6 mm when the speaker is turned away from the microphone. Moreover, from the plots above, all range values are within half a chip (that is, they are all contained in the region from 68.5 to 69). Half a chip equates to less than two millimeters.

The point is, we were interested in determining how much the range changed as the speaker rotates, and the simple answer is "not very much." Thus, it does not appear that speaker orientation is a significant factor.


Last updated on:
Monday, June 24, 2002