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Natural Science Forum / Physics / Acoustics / May 2008Picket fence effect
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 >Does anyone have a source for information on the picket fence effect >in acoustics, particularly as it relates to finned walls in an [quoted text clipped - 3 lines] >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. 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  SignaturePearce Consulting http://www.pearce.uk.com >>Does anyone have a source for information on the picket fence effect >>in acoustics, particularly as it relates to finned walls in an [quoted text clipped - 8 lines] >than the one before. The wavelength that corresponds to that distance >will be enhanced. Oops! I meant half wavelength, sorry. >As the echo moves down the fence away from you the >note will drop as each picket becomes correspondingly further than the [quoted text clipped - 3 lines] > >d SignaturePearce Consulting http://www.pearce.uk.com > Does anyone have a source for information on the picket fence effect > in acoustics, particularly as it relates to finned walls in an [quoted text clipped - 3 lines] > Thanks, > Rob Miller 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 > > Does anyone have a source for information on the picket fence effect > > in acoustics, particularly as it relates to finned walls in an [quoted text clipped - 12 lines] > staggered layers though. Could this repeat , running around all 4 walls, be > the cause of the 2KHz or so resonant ringing 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 Could the brick-bond staggering mean a doubling of that frequency to 1786 Hz ? > Does anyone have a source for information on the picket fence effect > in acoustics, particularly as it relates to finned walls in an [quoted text clipped - 3 lines] > Thanks, > Rob Miller The Mayans probably had a word for the effect http://www.ocasa.org/MayanPyramid.htm |
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