Silencing my cyclone - These things really WORK!

[Glen Blanchard]

As some of you know, I recently walled off my DC/AC closet, removed the DC filter on my Oneida cyclone, and re-routed the exhaust outside. That indeed lowered the noise level in the shop significantly, but I didn't realize how loud it would be outside at the exhaust port. As I am on 2 acres, it probably was not loud enough to trouble the neighbors, but I wanted to decrease that noise level as much as I could. In a different thread asking for advice, Rod Sheridan (Thanks Rod!!!) mentioned Oneida's silencers, specifically designed to do exactly what I was trying to do. I had no idea they made anything like this. I called Oneida and talked with one of their sales/CS guys who helped me locate the (7") silencer on their website. According to the website, this silencer will decrease the noise by 4 - 6 db. I asked the Oneida rep if a second silencer would further decrease the db level, and he replied by telling me that it would. So hoping for a 10 db attenuation, I bought 2.

I installed them both yesterday. As I cranked up the cyclone, I braced myself for disappointment. To my pleasant surprise, there is a HUGE difference. I don't have a way to quantify the result as I don't own a decibel meter, so my findings are strictly empirical. The volume dropped big time and what is left very easily sinks into the background as white noise at any significant distance from the port. A third might help even more, but it is not needed and I would think that at some point one would run into the law of diminishing returns.

I am extremely pleased with the result and would highly recommend this to those who are looking to decrease the noise level of their DC. The 7" Oneida silencer sells for approx. $125 if memory serves.


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[ray hampton]

do it makes any different if the muffler are install backward ? if you got a long pipe or tube already [40 feet] stick the pipe end over the tail pipe and see how this will change the sound

[Glen Blanchard]

There is no directionality to these things.

[Rod Sheridan]

Glad you liked it Glen, I have one silencer..................Regards, Rod.

[David Kumm]

Glen did Oneida talk about how often the silencers would need to be cleaned and how difficult that was? My understanding has been that even after the cyclone the air is dirty enough to reduce the muffler efficiency and require frequent cleanings. I'm interested in opinions. Thanks, Dave

[Glen Blanchard]

David - There was no mention of silencer cleaning. Rod????

[David Kumm]

Glen or others. I looked at silencers and talked to Airhand- Airhandling systems inc I believe. I was ready to buy one which would be located in my attic where the blower sits. The salesman talked me out of it due to the difficulty in cleaning it. He felt it would need to be removed and cleaned every few months or so. I may call him back to verify but one of those rare occasions where the salesman talked me out of a sale. It Oneida say how much additional pressure drop was created? Dave

[ian maybury]

Just for info. Noise attenuators are a pretty standard accessory sold by HVAC sales outfits - probably a lot more cheaply than from a branded supplier. Around $40 for an 8in dia x 36in approx model a few months ago from a local supplier here.

Here's an example of a maker of a very similar looking unit to that I have - they call it a straight silencer: http://tiny.cc/c1umfw There's design/performance information there too. The Oneida unit looks externally similar.

They also come in the form of a 90 deg bend which might suit in come cases.

Maybe there's something different about the type your guy had in mind David (some have baffles, but might cause more pressure drop), but the principle is very simple in the ones I've seen - a perforated inner duct surrounded by a layer of rockwool or similar packing, and enclosed in an outer sheet metal sheath. Exactly the same as an after market motorcycle silencer.

The idea is that sound waves are absorbed/the energy taken out of them. If the motorcycle example is anything to go by the condition and density of the packing makes all the difference - they can go from highly effective to having almost no effect at all. Working well they tend to do best on higher frequency stuff.

Mine is on the fan exhaust from my Pentz/Clear Vue style system - immediately after the cyclone and fan, and before the filters. I'd not thought of there being any likelihood of it blocking up or needing cleaning, in that it's not much different to a piece of duct. Don't know how good a job it does as it's been installed since the first run of the system, but I was pleasantly surprised that it wasn't too noisy....

ian

[Glen Blanchard]

Ian - Your physical description of a typical silencer pretty much sums up the Oneida. In my case it's not much more than 12" of duct with some sound absorbing material AROUND it. There is no physical barrier to the air passing through so it should have absolutely no effect on the performance of the DC. I also don't see anything that would require cleaning.

Rod - How long have you had yours in place? Ever clean it?

[David Kumm]

Ian, Glen, and others, will the packing still perform it's function when covered with dust? My understanding was the dust would coat the Rock wool until it failed to absorb noise and needed to be blown out. I'm not questioning, just trying to figure out why the sales guy killed a sale. Dave

[Rod Sheridan]

I vacuum mine once per year, no idea if it helps or not.............Rod.

Oh, and also when I overfill the bin, however at that point the filter is plugged as well........DOH

P.S. When I converted my machine to an external filter the Oneida filter had a built in silencer, about a 30cm long sponge wrapped around the outlet column which is perforated metal.

[Ron Natalie]

do it makes any different if the muffler are install backward ? if you got a long pipe or tube already [40 feet] stick the pipe end over the tail pipe and see how this will change the sound

Is this something you want to do? I've heard of people putting loud pipes on a motorcycle but not a dust collector.

[ian maybury]

Ta Glen.

All this is hearsay, but it seems that the most effective location for an attenuator is in the exhaust duct (i.e. in the ducting immediately after the fan exhaust) - this gives it the maximum chance to damp out noise producing pressure pulses coming from the tips of the fan blades. It shouldn't matter which way around the unit is installed if it's the perforated tube/packed type.

So far as I understand it it's vibration in the wall of the ducting and other bits of equipment that transmits the noise we hear. Which is in turn caused by pressure pulses inside the system. ( the pressure pulses in a motorcycle exhaust are caused by the engine firing) The perforated inner tube and packing are in effect intended to absorb the energy of the pulses before they reach an external wall that can re-transmit them as the air borne sound waves we hear.

I don't know if dust is likely to reduce performance David, but my suspicion is that given it's low density it's unlikely to have any very immediate effect. It'd probably need to form a semi rigid cake/coating. That said maybe there's a reason - although from what Rod said Oneida are happy to sell/use them.

In the motorcycle situation the packing used is more typically chopped strand glass fibre. The effectiveness falls away in time if the muffler was either too loosely packed so that the fibre over time loses proper contact with the inner and outer sleeves, or the glass fibre becomes saturated with water and hence heavy. (the water is product of combustion, and builds up in the packing - the damp packing I think becomes heavy and rigid enough that it prevents the local movement that enables it to absorb sound pulses) Race teams operating in noise controlled situations (most races are sound checked) take the muffler off and weight it to determine the water build up and hence if it needs re-packing or not. The packing shreds over time time and leaks out through the perforations too because the pulses are pretty powerful - but that doesn't seem likely in a dust system...

[ray hampton]

Is this something you want to do? I've heard of people putting loud pipes on a motorcycle but not a dust collector.

I am thinking that a long enough pipe will damper the sound similar to a drop in water pressure when you are miles away from the tank

[Glen Blanchard]

Spoke with my Oneida rep this morning via email concerning the cleaning issue. Here is what he had to say:

Typically no maintenance is needed. If you find that you are getting dust caking inside your ductwork, a duct cleaning brush like the kind used to clean clothes dryer ducting is fine to use.

[Larry Edgerton]

I went to a truck salvage yard for the summer exhaust at my old shop and picked up a huge 8" straight through muffler and pipe for $55. Worked like a charm and was chrome!

I'm thinking my new shop should have dual exhaust......

Larry

[David Kumm]

Does anyone know if Dc silencers are designed differently than regular HVAC silencers? Does the air velocity require different materials? Wondering the difference between the $75 silencers and the $300 ones. Dave