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Step 6The Inner Enclosure's Tortuous Path
After making a nice sealed box the problem is that we need to allow air to flow in and out (so that the vacuum can suck stuff up and vent its exhaust air!). If we have holes for the air to go in and out, it is a safe bet that noise from the vacuum's air chopping impeller is going to maliciously exploit them and fire sound out at you. That is, unless we create an elaborate maze in which the noise will get lost (bwahahaha), but which our friendly air will have no problem traversing. People (that is, an author of one of the more obscure books I read) sometimes refer to such a system as a 'tortuous path'.
When we incorporate obstacles into the air stream, we add resistance to its flow. To maintain necessary airflow, most silencers have to increase the cross sectional area, so enough air can run through - making them quite bulky. This tortuous path or baffle system has the same problem.
There are many different designs to reduce sound that is transmitted through airflow passages: reflective, reactive, diffusive, depressive and active. Quick and concise description of different types of silencers can be found here.
For the dust sniper, the back of the inner box is where I made the baffle arrangement. I wanted to keep the two exhaust streams separate so it consisted of two paths, created by fire door off-cuts (produced while making the outer box). It ended up being damped by a sealed off panel of sand (see the pics and descriptions for build info).
Another consideration is that sudden changes in air pressure can be noisy - the sound of a vacuum usually increases when we put a crevice nozzle on the end for example. We can extend the changing pressure gradient though, by breaking the exhaust stream into a series of outlets - the same style of thing that you see on a big motorbike exhaust with lots of holes in.
When we incorporate obstacles into the air stream, we add resistance to its flow. To maintain necessary airflow, most silencers have to increase the cross sectional area, so enough air can run through - making them quite bulky. This tortuous path or baffle system has the same problem.
There are many different designs to reduce sound that is transmitted through airflow passages: reflective, reactive, diffusive, depressive and active. Quick and concise description of different types of silencers can be found here.
For the dust sniper, the back of the inner box is where I made the baffle arrangement. I wanted to keep the two exhaust streams separate so it consisted of two paths, created by fire door off-cuts (produced while making the outer box). It ended up being damped by a sealed off panel of sand (see the pics and descriptions for build info).
Another consideration is that sudden changes in air pressure can be noisy - the sound of a vacuum usually increases when we put a crevice nozzle on the end for example. We can extend the changing pressure gradient though, by breaking the exhaust stream into a series of outlets - the same style of thing that you see on a big motorbike exhaust with lots of holes in.
"Such a device has been shown to accomplish by itself, without any additional muffling, a 10 dB insertion loss in broadband noise in a steam-generating plant blow-out operation." (p434).
So that seems like a good idea, assuming the air coming out is making much noise...| « Previous Step | Download PDFView All Steps | Next Step » |
" Quick and concise description of different types of silencers can be found here."
The HERE seems to be intended to be a link.
But, it does not work