--- In Rob Danielson <> wrote:
>Hi Tom-- I may be confused. In this test, are you are comparing:
>(A) The focal point capsules + the side-facing front capsules ->
>(B) just the the focal point capsules?
>If so, didn't we already tested this in your clock sweep test and
>found the difference to be significant?
Hello Rob and the Group
Thanks for your comments. I jotted my last post down in a hurry when
I returned home having done the test seven days previously. I was
anxiuos to get on with the next version of the "parabar" so probably >
>I agree, in this test, there's not much localization difference in
>content > 1000Hz like the fountain and your whispers.
>The (A) focal point capsules + the side-facing front capsules seem
>to have more bottom end than (B) just the the focal point capsules.
>There is also less high-end and more Hi-HZ noise in (A.).
>I think I am hearing some low Hz modulation in (A) that I did not
>notice before. This could be stem from the increased Lo Hz content in
>this range outside compared to indoors,.. Could it be that your mixer
>circuit has changed-eliminated the improved stereo field we tested
>before somehow?
I don't know the answer to that one but further experimentation might
give some clues.
>There is considerable tonal change already so it might not be only a
>question of the amount of attenuation in the (forward-mounted)
>side-directed mics.
>I suspect the additional low hz response is important in the
>creation/impression of a wider stereo image.
These points are all taken on board - thanks for poking the stick in
my grey matter and giving it a stir :-)
My gut feel is that the Jecklin sized disc (that was the mount for the
capsules also had something to do with the results I got. I think the
MKII "parabar" will throw some light on the matter when it is operational.
Its construction is progressing. The holder for the six focal point
capsules, and the lightweight barrier have been made, but are not
capsuled up as yet. This is what they look like
http://ad2004.hku.nl/naturesound/TomR/Parabar/parabar%20capsule%20holders.JPG
and this is how they fit in the parabolic reflector.
http://ad2004.hku.nl/naturesound/TomR/Parabar/capsule%20holders%20in%20reflector.JPG
The two holders are not connected in any way (other than by the thin
wire connecting the four groups of capsules). The distance between
the planes of the front and focal point capsules can be reduced to a
minimum of about 2 inches (50mm), although at the minimum distance the
front capsules will be inside the dish.
I was a little worried how the lightweight barrier would perform - it
is very light at 4 ounces (113 grams) without the capsules. I
therefore gave it a test a sunset today. For this I used a set of
triplet capsules fastened to the sides of the barrier with crocodile clips
http://ad2004.hku.nl/naturesound/TomR/Parabar/barrier%20test.JPG
It seems to give reasonable stereo imaging. Sorry about the same old
sound scene from my back garden ( however, I have not inflicted
another geese arrival even though it happened towards the end of the
recording).
http://ad2004.hku.nl/naturesound/TomR/Parabar/Lightweight%20Barrier%20Test.mp3
When making the lightweight barrier I had enough material to make two
- so I did. If the master plan works one will remain in the reflector
and the other will be used as an ultra portable "normal" barrier.
This second barrier will also allow simultaneous test recording
thereby giving a direct comparison of the parabar with a normal
barrier arrangement.
In order to incorporate the potentiometer (this time acting as a
potential divider between the focal point and front sets of capsules)
in the circuit it has been necessary to take the powering arrangements
off the capsule mounting plates. These have been placed in another
small box velcroed onto the handle of the reflector. All that remains
to be done is to mount the capsules on their carrier PCBs and wire in
the potential divider. There will be quite a bit more unshielded wire
in this arrangement. If it gives problems shielded wire will be
substituted.
Cheers - Tom Robinson
|
