> As has become clear from these discussions so far, there are many factors to
> consider when determining the best height for a recording:
> - sound horizons
> - primary ground reflections
> - phase issues
> - shadows from ground contours and obstacles
> - vertical angle of mic axis
> - shelter from wind
> What else?
>
Temperature and wind ?
- ground material and coverage e.g snow is an excellent absorber.
- resonance / recording in a cave?
- reflection, or flutter echo if in an enclosed cavern as the sound bounces
from one wall to the next. - Mind you that would be natural, where the mic is
placed
to capture the effect may be challenging.
- diffraction effects, sound over walls, bushes/trees/houses, road noise
barriers (specifically for low frequencies) - apertures / gaps between trees
etc. someone's head in the way, standing too close to the rig.
- refraction - time of day, temperature and wind effects
a sound source in uniform conditions will reach the mic directly (or rather
the wavefronts will) a source propagating where the temperature change is from
cool to warm, causes the source to propagate down. - opposite is where the
change is from cool to warm, the source bends up. Depending on the temperature
gradient. - This may be in effect near lakes / sea - or in general temperature
boundaries.
- wind gradients, a source will be heard downwind, yet will be in an acoustic
shadow if upwind.
some of the above is paraphrased form the Master Handbook of Acoustics 5th
Edition.
Quite an eye opener.
BR,
Mike.
>
>
> height affects the recording in many ways main obstacle in experimenting
> with that is my rigs as the are do not conveniMaybe to find a down low sweet
> spot like Curt and Greg have described
>
>
> --- In "picnet2" <yg@> wrote:
> >
> > Hi,
> >
> > I found out this the hard way during a recent beach recording in Portugal.
> > A dummy head was used at around 6ft, and then lower to get it out of the
> > wind, except the waves caused some pressure difference and "swooshing" as
> > they rolled in. Higher up the effect wasn't as pronounced. - sand and with
> > the mic low down, plus a slight bank behind the mic were now causing what I
> > understand to be some reverberation from the direct (sea in front of the
> > mic) vs reflections from the ground and back behind the mic. and my body
> > standing about 4 ft away may of also caused some effect.
> >
> > Side foliage, walls/building, structures under the mic rocks, sand, smooth
> > concrete etc. All of these have an effect on reverberation times, and
> > moving the mic down may cause changes in the direct to reverberant ratio -
> > in effect you are EQ'ing the mic to sound more pleasing to you. All depends
> > on the mic stereo recording angle involved and elevation. - Michael
> > Williams has written papers on this subject in the past.
> >
> > BR,
> > Mike.
> >
> > PS Rob, that's the author.
> >
> > --- In Curt Olson <cro@> wrote:
> > >
> > > Thanks Greg,
> > >
> > > I've experimented with ground effect quite a bit over the last year.
> > > To my ear, the "fuller sound" you mention seems to become quite
> > > noticeable at about 15" or so and increases rapidly to the point of
> > > serious ugliness at ground level. But in the 18" to 24" range, there
> > > seems to be a certain sweet clarity that seems to drop off ever so
> > > slightly as the mic moves upward to about head height -- at least
> > > that's what I've ovserved.
> > >
> > > I've never done any serious experiments with higher elevations like
> > > Walt and Dave have done. Hmmm... yup, that's definitely another
> > > element to look into.
> > >
> > > Curt Olson
> > >
> > > Greg Weddig wrote:
> > >
> > > > Curt,
> > > > I would generally agree with you, though I don't have any evidence
> > > > of such. Most of my ORTF recordings are done in that same range. I
> > > > think the ground effect most likely provides a bit of a fuller
> > > > sound, much like a PZM microphone would.
> > > >
> > > > Mostly I am trying to keep the mics out of the wind, and keeping
> > > > them low I find, depending on the geography, helps shield them from
> > > > nearby highway and city noise.
> > > >
> > > > --greg weddig
> > > > http://gregweddig.net
> > > > Paradise, CA
> > > >
> > > >
> > > > --- In Curt Olson <cro@> wrote:
> > > >
> > > >> Ever the respectful contrarian, I've recently discovered -- much to
> > > >> my surprise -- that the head-spaced barrier type mic rigs I'm
> > > >> currently using seem to render a slightly cleaner image when I have
> > > >> them in a "sweet spot" approximately 18" to 24" above the ground.
> > > >> This improvement is very subtle, and might be peculiar to my
> > > >> current rigs. I'm curious if anyone else has experienced the same
> > > >> thing.
> > > >>
> > > >> Curt Olson
> > >
> >
>
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