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Plenum Designs??
- Thread starter Nathan
- Start date
I had a design that worked fairly well at my last shop. I built a closet around my CV. The air exiting the filters had to go up to flow past the motor to keep it cool. The exit was a simple 6" by 32" hole at the bottom behind a wall mounted cabinet. That was enough distance to muffle the sound. The tradeoff is that is I lost about 6" of depth in the cabinet drawers.
I have moved and am still trying to decide what to do at my current location. I am thinking about building a box about 32" cubed with baffles to make the air travel up and down a few times before exiting. The important thing is to keep from restricting the cross section through the entire distance.
Steve
I have moved and am still trying to decide what to do at my current location. I am thinking about building a box about 32" cubed with baffles to make the air travel up and down a few times before exiting. The important thing is to keep from restricting the cross section through the entire distance.
Steve
Thanks.
I am thinking more of a plenum between the exhaust of the blower and the filtration. For a six bladed fan running 3400-3600 rpm should keep the main frequency at 340-360 hz. I am sure that someone out there (NDT guys or audio studs) that could give some solid advice with a little math have come up with a valid design to address this frequency zone.
Nate
I am thinking more of a plenum between the exhaust of the blower and the filtration. For a six bladed fan running 3400-3600 rpm should keep the main frequency at 340-360 hz. I am sure that someone out there (NDT guys or audio studs) that could give some solid advice with a little math have come up with a valid design to address this frequency zone.
Nate
Nathan,
If you do a search on jgveill you will find a post in noise control on the 6th page that has spectrums (FFTs). Surprisingly (to me), there are no visible lines or spikes and the levels below 350 HZ are increasingly large. Also, the spectrum is very wide with significant high frequency content. So I doubt anything like simple resonators would be very effective. People have had good results with the closet and lengths of insulated duct.
bababrown
If you do a search on jgveill you will find a post in noise control on the 6th page that has spectrums (FFTs). Surprisingly (to me), there are no visible lines or spikes and the levels below 350 HZ are increasingly large. Also, the spectrum is very wide with significant high frequency content. So I doubt anything like simple resonators would be very effective. People have had good results with the closet and lengths of insulated duct.
bababrown
Thanks Bababrown. I was not thinking resonators as much as I am trying to keep the restriction down. I was thinking more of absorption and bass traps in the corners, etc.. The mufflers that Bill Pentz and others have been using based soley on this but I think they may be missing some effectiveness if they could change the volumes of the muffler but this is only speculation at this point.
I am putting the filters side by side and having the exhaust (from the blower) come into the middle of the "top" chamber of the two tiered plenum. I can effectively split the flow into two halves and keep the channels quite large (75" square each) so the air velocities will be slowed down significantly and therefore sound waves begin to act more predictable (at least with my limited experience/knowledge)
The sound wave analysis given was for a complete system I would think (with the 90 degree transition and stacked filters) which will give different results than what I have in mind. Even so, I can see an excitation from the fan at multiples of roughly 350 hz. This would be much greater if the block was removed from the blower unit. What I do not see is any resonate frequencies that stand out. I have not seen any "bump" testing on any of the components to see any natural harmonics within the system but I doubt they would be very conclusive either.
I do appreciate your help,
NAte
I am putting the filters side by side and having the exhaust (from the blower) come into the middle of the "top" chamber of the two tiered plenum. I can effectively split the flow into two halves and keep the channels quite large (75" square each) so the air velocities will be slowed down significantly and therefore sound waves begin to act more predictable (at least with my limited experience/knowledge)
The sound wave analysis given was for a complete system I would think (with the 90 degree transition and stacked filters) which will give different results than what I have in mind. Even so, I can see an excitation from the fan at multiples of roughly 350 hz. This would be much greater if the block was removed from the blower unit. What I do not see is any resonate frequencies that stand out. I have not seen any "bump" testing on any of the components to see any natural harmonics within the system but I doubt they would be very conclusive either.
I do appreciate your help,
NAte