Picket fence effect

[rdmi...@gmail.com]

Does anyone have a source for information on the picket fence effect
in acoustics, particularly as it relates to finned walls in an
auditorium? Each fin is 2" thick by 7" deep spaced at 9" on center.
These fins are at both sidewalls and continue over the ceiling.

Thanks,
Rob Miller

[Don Pearce]

It is just a matter of geometry. Work out how far each is from where
you are listening, then from that work out how much further each is
than the one before. The wavelength that corresponds to that distance
will be enhanced. As the echo moves down the fence away from you the
note will drop as each picket becomes correspondingly further than the
one before.

The spacing between centres is the only dimension you need.

d

--
Pearce Consulting
http://www.pearce.uk.com

[Don Pearce]

On Tue, 06 May 2008 05:53:17 GMT, nos...@nospam.com (Don Pearce)
wrote:

>On Mon, 5 May 2008 16:25:21 -0700 (PDT), "rdmi...@gmail.com"
><rdmi...@gmail.com> wrote:
>
>>Does anyone have a source for information on the picket fence effect
>>in acoustics, particularly as it relates to finned walls in an
>>auditorium? Each fin is 2" thick by 7" deep spaced at 9" on center.
>>These fins are at both sidewalls and continue over the ceiling.
>>
>>Thanks,
>>Rob Miller
>
>It is just a matter of geometry. Work out how far each is from where
>you are listening, then from that work out how much further each is
>than the one before. The wavelength that corresponds to that distance
>will be enhanced.

Oops! I meant half wavelength, sorry.

[N_Cook]

<rdmi...@gmail.com> wrote in message
news:af0280c9-1a74-4be3...@s33g2000pri.googlegroups.com...

I used to notice this effect walking along a street that had vertically
mounted corrugated iron roofing sheets mounted as fences on both sides.

I was wondering about this effect associated with my "room resonance"
request below. Two venues I come across it have walls where the plaster has
been removed so there is a repeat pattern of about 9 inches per brick in
staggered layers though. Could this repeat , running around all 4 walls, be
the cause of the 2KHz or so resonant ringing

[N_Cook]

N_Cook <div...@tcp.co.uk> wrote in message
news:fvp1lp$io3$1...@registered.motzarella.org...

Using your half wavelength , assuming a square room for convenience , a
repeat pattern of 9.5 inches (with mortar gaps) and optimum reinforcement
angle relative to each wall of 45 degrees and so from sin (45)* 2* 9.5 I
make that about 893 Hz, getting nearer the mark

[N_Cook]

Could the brick-bond staggering mean a doubling of that frequency to 1786 Hz
?

[N_Cook]

<rdmi...@gmail.com> wrote in message
news:af0280c9-1a74-4be3...@s33g2000pri.googlegroups.com...

The Mayans probably had a word for the effect
http://www.ocasa.org/MayanPyramid.htm