sub frame bracing

so these attenuators are essentially 'elephant ears' for the exhaust, the longer the tube, the lower the Hz range it affects...nominally 33.75'' might be somehwere around 30-80Hz I'd bet, barely above the lower limit of human hearing
 
Right.

[(target rpm for noise cancellation) x 4] / 60 = frequency

(speed of sound in the exhausted air) / frequency = wavelength

wavelength / 4 = length of quarter-wave


So for a 1500 rpm drone:

(1500 x 4) / 60 = 100 Hz

1125 fps / 100 Hz = 11.25 feet

11.25 feet / 4 = 2.8125 feet or 33.75 inches
 
simple! I just need space next to existing pipes for a 34" x 2.5'' tube with an elbow on it ! :)
-and..what's the rationale behind targeting the 1/4 wavelength?
 
The sound travels down the tube, hits the capped end, and travels back to the exhaust system, which effectively puts it 1/2 of a wavelength out of sync. Hence the drone/noise cancellation at the frequency it's tuned for.
 
The sound travels down the tube, hits the capped end, and travels back to the exhaust system, which effectively puts it 1/2 of a wavelength out of sync. Hence the drone/noise cancellation at the frequency it's tuned for.

ah yes, destructive interference to the drone rescue!!! and whatever rpm's (3000 or 750?) create a wavelength 2x or 1/2 that of 1500 rpm's will undergo CONSTRUCTIVE interference? that 33.75'' attenuator doubles as an amplifier?
 
Started making mine today. :)

20121130_165629.jpg
 
The fabrication skills of many of my fellow Mark owners continue to blow me away. Imagination is not a lost talent among the users of this site. My hat is off to all of you for thinking outside of the box. Let me re-state - not just out of the box. You're thinking outside the house. You guys have the pride to not only accomplish the task, you make it look good, too. I gave the Piston Slap guy sh*t for spending too much time here - now, I get it. Every time I log on, you give me a different solution or design idea. My wife says she thinks this will end up a never-ending project. She's probably right. Just as soon as I decide - yes, that's the way I want my car to look and drive - I see someone else's ideas that change my mind. You keep an old man thinking - and judging from some of my PM's, I am not the only guy of advancing years who appreciates seeing this avocation being driven by new blood. Thank you
 

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