Posted by Rick Denney on July 25, 2001 at 10:33:04:
In Reply to: Re: Re: Re: Re: more tuba spectra posted by Kenneth Sloan on July 24, 2001 at 23:10:55:
Only further testing will answer the question. The only surface of any sort within half a wavelength of the microphone was the ceiling, and, marginally, the floor. The ceiling, however, is not a smooth reflective surface, being a typical unfinished basement ceiling with exposed joists and ductwork, etc.
And I suspect, as Gerald suggested, that it would affect one particular overtone--perhaps quite significantly. It probably would not change the overall shape of the spectrum.
Until further testing sorts that out, it should probably be left that while we can compare different horns with the same placement with some credibility, we probably cannot compare spectra recording in different places.
And I wouldn't be too sure that the microphone Ken used is generally applicable for this sort of stuff. That microphone is intended for spoken voice, and will thus have a frequency response tailored to that application. In any case, Audio Technica didn't include their usual frequency response chart in the description of this microphone, and though they quoted the response as 50 Hz - 15 KHz, they didn't say over what output tolerance that response was measured. Since they didn't say, I'd suspect +/- 3dB, which is not particularly linear. And the bass roll-off is probably substantial to keep the microphone from feeding back through a conference room table. Bass roll-off is a Bad Thing for recording tuba. Finally, the maximum dynamic range is probably limited to 80 or 90 dB sound pressure level, which could easily be blown away by a tuba in the same room. As long as the limitations are known, then you can probably work within them, but keep them in mind.
Rick "who bought a good microphone but labors with an old monitor" Denney