April 5, 2014

AV8 directivity sonogram

Here we can't provide the normal 6 dB down line due to sharp diffraction dip that occurs on axis around 2.7k. This quickly disappears off axis and so in this normalised sonogram it does skew the perspective a little. In practical terms, although the audibility is not likely a real issue, listening a few degrees off axis removes the dip.

If more smoothing is used, or a shorter time window with the measured (caused by gating where the speaker is not elevated high outdoors), then this issue becomes spread out over a broader range.

Overall we see good directivity performance with a gradual narrowing trend towards 3k above which the directivity is fairly constant before narrowing at the top end.


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2 comments:

  1. ChrisApril 24, 2014 at 4:27 AM

    Paul, do you have any feeling for what level of smoothing matches well with what we hear perceptually. Minimum smoothing shows some issues that are not of relevance for humans with ears sitting in normal rooms. Another issue that comes to mind would be damping of room surfaces would change that issue at 2.7kHz. I'd better do some more reading myself now that I think on this a little.

    Cheers,
    Chris

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  2. Paul SpencerApril 24, 2014 at 5:02 AM

    Smoothing not only hides things we don't perceive well, it also can serve to make an issue like that one appear bigger than it is. The issue at 2.7k becomes magnified in a sonogram that is smoothed 1/3 or 1/6 octave. Those are closer to what our ears perceive but the goal is to see a clear picture on the performance rather than represent what we perceive.

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