Rob Danielson wrote:
> Yes, the lowest 3-4 octaves often seem disproportionately
> amplified--especially when the headphone volume is up (as it often
> is). All mics I've tried exhibit this accentuation including some
> praised for very smooth, extended low end response. Frequency response
> for mics is measured at much higher sound levels than those we record
> in quiet settings. I suspect that low frequency response and
> distortion is quite irregular for low sound levels and that some odd
> things are going on.
>
> The sound energy from a distance that is ~30 Hz and lower is perceived
> as a "heaviness" more than traditional tones. Lots of the energy is
> down here and when the gain goes up, this content does too.
>
> Does the undesirable bass occur as sustained tones (drones) between
> ~80-200Hz or does the offensive bass vary in frequency and amplitude?
Not tones or drones, just a general feeling of disproportional low end
like you're describing above.
> Variation would be expected with recordings from natural settings. If
> the offensive bass occurs as a constant, low, chord and it sounds the
> same with recordings from several locations, it may be a fixed tonal
> structure and not a boost in low end amplitude. Sustained tones stand
> out to the ears and efficiently mask adjacent tones with more dynamic.
> If you suspect the boundary is creating exaggerated low Hz chords, you
> can sweep a narrow band of parametric EQ across the bottom end of
> files that were recorded with the boundary and then with the mics in
> the open. If the same bands are accentuated, its not the boundary.
Good thought, Rob. I have made comparisons -- with boundary/without
boundary -- but mostly listening for general impressions. I haven't
studied them as closely as you recommend here. (Side note: I can report
big differences between flush-mounting the mic capsule into the
boundary plane and side-mounding the mic body to a boundary, but that's
another conversation altogether.)
umashankar wrote:
> a flush mounted omni in fact works exactly like a pzm microphone. i
> cannot offhand refer to them but there are several papers and articles
> pointing this out.
>
> think of this: at the boundary, the direct and reflected sound are
> essentially in phase, and the omni microphone is sampling this. in
> what way can the direction in which it points really matter?
Thank you, folks, for the questions and insights. I'll post some photos
and audio samples one of these days. Now back to our playback
debates...
Curt Olson
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