Hi John, Dan and Umashankar--
With less than 1dB difference in gain, I assume there's little
potential for the self-noise advantage Umashankar correctly
proposes-- at least with the boundaries many folks have been using
with Curt's and similar rigs. From other tests I've done with
boundary size and setback dsitance like that used in MBP 648 PZ that
it would have similar, minimal gain used alone. MBHO may assume that
the marble boundary would be set on the floor. In my experience, the
bass response changes with large boundaries, but less so the gain.
Its been almost 4 years since I tested the PZM boundary set-up that
Dan alludes to with an omni capsule facing a hard plate with gap
distances from 1/10" to 1/50"
https://pantherfile.uwm.edu/type/www/audio-reports/BoundaryMicExperiments/B=
oundaryMicsStudy/BoundaryMicsStudy.htm,.
As I recall, the gain was not on the scale of 6dB. It would be good
to try that test again and get some particulars to listen to and
discuss. Several accounts suggest that a hard finish like polished
metal is important right under the capsule and that the boundary
needs to be 4' X 4' or larger for "flat" bass response.
Yes, John, the tonal quality differences are quite profound. I would
observe that the overall impact of the small boundary is "radical"
compared to differences typically heard between other arrays/mic
arrangements. Because of this, I was able to correctly ID the
boundary mic as the B sample through the reduction in bass and lower
midrange response (<500Hz). The B sample seems to have more more high
frequency presence because of this shift in overall tonal balance.
Small boundary mounting typically creates "lift" in the lower to
upper-range response which adds to the enhanced presence as well.
Starting with the comparison Paul and Andrew did with PBA and SASS
arrays, quite a bit of discussion and testing follows here:
http://diystereoboundarymics.blogspot.com/2010/03/frequency-response-differ=
ences-between.html
There are several basic types and many variations of boundary arrays.
Every stereo array I know of has problems and strengths. Exploring
what arrays tend to do in the field through listening comparisons and
building upon what seems to work towards my preferences has taken me
in a different direction than the Crown and other Studies seemed to
predict.
Boundary mics and PZM's have received very harsh criticism from the
time they first came to people's attention. To this I counter that
quite a few recordists, most of whom work with natural ambience, have
adopted types of boundary arrays over other stereo arrays they
previously loved. Maybe these recordists suffer similar,
perceptual/mental quirks? I feel there is some truth to this.
Listening, especially within the realm of speakers, is a very active
process. Observing myself and others involved in this process, I'm
getting the odd feeling that the mics and arrays we use affect the
mental processes we develop to discern subtle tonality/spatial cues.
Every listener's impressions are correct, so not only do we sit in
different rooms when we play the same sound file, each of us has has
learned to hear stereo and surround "sound reproduction" differently.
It might be that we need to consciously attempt to start
understanding these differences as we develop our tools and
techniques. Rob D.
At 6:01 AM +0000 7/16/10, hartogj wrote:
>
>
>That is a tough one, Rob. There is definitely a shift in qualities
>between the two, but one does not seem to have 6dB less noise than
>the other. That may be because the subject clock and crow are on
>axis to the mic capsule in both, where I would expect the biggest
>difference would be for sounds the boundary itself is facing. I'm
>going to guess that A is on the boundary, because it sounds like the
>barrier shadows some of the higher frequency content heard in B.
>Even with 50% chance to get it right, I bet I am wrong.
>
>John Hartog
>
>>
>> <http://tinyurl.com/28aqxkw>http://tinyurl.com/28aqxkw
> >
>> Which is the boundary mic arrangement and which is open air? Is
>> there a significant difference in self-noise performance? Is there
> > "awful comb filtering" in one sample that is not in the other?
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