Noise Control

Wood shaper emissions are usually controlled by an exhaust hood located at the back edge of the work table which allows the operator to freely move the work piece over the table. Placing the exhaust hood nearer the cutting head would maximize dust collection; however, this would restrict the operator’s freedom to move the work piece.

To overcome this problem, a hood extension with a flexible face opening is added. The flexible face opening consists of cloth-covered chains that allow the wood to pass through, but stops the wood dust particles. The extension also increases the hood face velocity by minimizing the open face area.

A. Static Electricity

There is always someone who will bring up the concerns about duct static potentially causing an explosion when you use PVC pipe. PVC pipe is an excellent insulator that will build up a static charge, particularly in a dry cold climate. Although that charge can shock you, the experts say it is not ample to cause an explosion in hobbyist based systems. Dr. Rod Cole wrote an excellent article in Fine Woodworking that debunked the static myth with PVC pipe. He also posted that article on a woodworking forum and gave me permission to include a link to his article. If you are still concerned, go read his information. Dr. Rod Cole has some excellent additional information on grounding PVC on his site:
Explosion or not, getting a good zap while next to a sharp blade or cutter can be plenty dangerous, so if you live in a dry climate and chose to use PVC, you might want to seriously consider grounding your ducting. Running a single grounded wire around the outside of your PVC that also attaches to the metal coil spring inside your flex hose helps if you ground that wire both at your machine and your blower. However in dry climates, static can be a real pain around tools and doing a better job of grounding your dust collection piping is worth doing. As I said before most grounding approaches do not work well at all and often lead to plugged pipes. Here is a workable solution shared by one of the many contributors to this site. Thanks for sharing Brent!

Brent Dugan was the Maintenance Supervisor/Plant Engineer for a large ‘Meltblown’ polypropylene manufacturer (oil sorbents) for 9 years. He shared his way to eliminate those nasty static shocks, “Our product was plastic and our conveying systems both air and mechanical were plastic. Polypropylene fibers traveling through 3″ or 4″ PVC piping creates massive amounts of static electricity. Our problem was so severe that we had sparks jumping 1 1/4” from our piping that would leave burn marks on your skin. Our employees dreaded working with the equipment. We tried all of the available methods you proposed and more; e.g., wire inside, wire outside, wrapped wire outside, etc. We spent quite a bit of my company’s money to try and solve the problem with consultants and experts all to no avail.

I finally came up with a solution. It was so simple and inexpensive that you will not believe it. As you stated, static means electrons building on the surface of an object. Well, I solved the problem by sticking 2″ wide aluminum foil tape to the outside and inside of the PVC piping and then grounding that tape. It is easy to just stick the tape on the outside of the pipe. Unfortunately that was not enough and I also had to put a strip of tape on the inside of the duct.

Putting the tape on the inside was an interesting challenge. I wanted my tape inside and tape outside to end up right next to each other with just the PVC in between so I could use a screw and nut to ground the two layers together. I was only able to make the aluminum tape with a backing like double-sided tape work on the inside. To do so I started by sticking the aluminum tape to the bottom edge of the PVC pipe. Slightly peel the backing and adhere the aluminum tape to the end of a piece of 1/2″ EMT, conduit pipe, or other long rod. Feed the aluminum tape through the pipe as you unroll it from the roll. When you have the tape through the PVC, stick the aluminum tape to the end of the PVC pipe. Now ‘tape’ the backing to the rod then stretch the aluminum tape tightly angling it towards the top of the PVC piping (12 o’clock position). This keeps it from sticking prematurely. Now gently pull the rod out of the PVC that also removes the ‘backing strip’ off as you go. Keeping the aluminum tape stretched tightly lower it to the bottom side of the PVC pipe. To smooth it onto the inside I slipped in a longer piece of PVC and simply rolled that pipe inside to “iron” the aluminum tape down.

Having the tape back to back made grounding easy. I drilled a hole near each pipe end through both layers of foil, inserted a 1/4-20 screw from the inside of the pipe, put on a nut to make a good circuit, then connected each section using 14 gauge wire. I connected each end with alligator clips to another strip of the aluminum tape adhered to the concrete floor. That totally eliminated the massive static electrical discharges and earned me a bonus!”

B. Noise Control

One of the most difficult parts of dust collection is having enough airflow without so much noise that it drives you out of your shop. The difference between an air raid siren and a blower is impeller speed and clearance between the blades and impeller housing. Much of this noise is lower in frequency, so not too bothersome, but it is important to address noise throughout your dust collection and ducting efforts. I measured almost every major brand of small shop cyclone through 2003 and all put out between 85 to 95 dB measured at blower height at 5 feet distance by a calibrated digital dB sound meter. Sadly, the vendor ads strongly disagree with my measurements because most choose to measure at different heights and much further distances. My own galvanized steel cyclone measured 92 dB. I found that by making a few minor changes I could cut the overall noise created by my cyclone from 92 dB to 73 dB, meaning a quarter as noisy. Remember that the dB scale is a log scale so every 10 dB saved halves the overall noise.

Quieting my cyclone involved a lot of work. On the test bench my cyclone was over 100 db. I hung the whole setup using shock mounts and dropped it to about 92 dB. I used a big home-made muffler that pulled it down a few more dB. I put a piece of neoprene foam between the blower and cyclone to isolate the blower and keep the cyclone from being a sounding board, plus sprayed the inside of the cyclone with rubberized (not asphalt) automotive undercoating saving another few dB. I also tried spray coating the cyclone outside, but that did not seem to help any more than just spraying the inside. Spraying the outside metal sides of the blower helped some, but wrapping the outside of the entire blower except for the motor in heavy foam rubber foam helped more. Using a PVC pipe from the blower to the muffler wrapped with pipe wrap helped a little. Using MDF instead of my original plywood top on my cyclone and blower helped some. I also tried putting the cyclone outside, but it was way too close to my wife’s study/craft room and it quickly found itself back inside. Probably the biggest help was building a new cyclone that was far more carefully finished so the airflow was very clean. Here is more detail on some of the things I did.

1. Locate your dust collector or cyclone so it does not impact on other parts of your home.
2. If you bolt directly to your framing, most of the noise is fairly low frequency so like a subwoofer will go all over your shop and house if they are attached. I know as 12″ of well-insulated plenum between my and my teen’s room still let me hear the bass. You need to change over the mounting to use a floor mount or use shock mounts so the low frequency stuff does not make your shop and or home walls into sounding boards. carries them (search under vibration hanger), but pick a set that is sized near the overall weight as heavier mounts provide little vibration protection. Using springs, heavy rubber cords, or nylon straps instead of metal bolts for mounting will help keep the noise from transferring into your shop or home framing.
3. Ducting can make considerable noise and often serves as a transmitter or even speaker cone to spread noise all over your shop and into your adjacent home. Using PVC pipe instead of dust collector spiral pipe or thick HVAC pipe helps considerably as you don’t hear nearly as much sawdust rattling in the pipes. If you use a small section of flex hose between your ducting and your blower and cyclone that will also make a huge difference. The flex hose absorbs the vibrations. Using a piece of insulated HVAC flexible duct on the exhaust part of your blower will also help.
4. Muffling the exhaust side of your blower is a huge help because that is the source of most of the noise. You can do this with a muffler or a long length of heavily insulated HVAC flex hose. Larry Adcock, creator of the WoodSucker, told me that using a length of fiberglass insulated HVAC flex duct instead of building a muffler is easier and costs far less. He is right, but it takes a fairly long length to be as efficient. PSI sells an inexpensive muffler that saves about 10 dB, but it only fits a 5″ outlet that is too small. We really should use 8” exhaust ports on our cyclones and that requires a muffler with an 8” center tube. Quite a few have made their own mufflers out of perforated pipe wrapped with screen then with fiberglass followed by being slipped into a larger tube. I tried making one using PVC pipe because PVC helps dampen the noise, but found sliding the outer pipe onto the insulated inner was difficult. Take a look at my for more details on how to build your own muffler.

   I did a little testing on the various forums of mufflers. On my cyclone with its biggest blower, a 15.5” diameter impeller powered by a 5 hp motor, my galvanized metal cyclone measured 96 db with the blower just going directly into the filter through metal duct. Trading the metal duct from the blower to the filters for PVC dropped it to 92 dB. Adding my homemade muffler in place of that duct dropped it to 88 dB. Using 8’ of insulated HVAC duct in place of the muffler dropped it to 87 dB. Using insulated HVAC duct and my own homemade muffler it went down to 82 dB. These test results will vary considerably depending upon how you made your blower, your choice of impeller, motor choice, any coatings or insulation you use, and depending if you use anti-vibration mounts.

5. Use one of the rubberized automotive under coatings (not oil or tar based) sprayed inside of your cyclone. This protects wear areas and makes a huge difference in noise. You can get better results by taking your cyclone to a truck bed liner retailer and have them spray the inside with the heavy bed liner spray which works even better. You can also use compounds such as Dip-It or a plastic based coating. Be careful as the odors from some of these coatings can be terrible.
6. Adding the baffling and sound deadening materials around the blower and blower outlet helps considerably. Don’t cover the motor as that needs to be open for cooling. Also, I suggest using something that is covered so it does not becoming a place for dust to gather.
7. Yitah R. Wu says: “With regards to cyclone noise, I work in automotive and one product which probably be good for reducing cyclone noise is what we call peel and stick mastic. It’s usually in 8×10 sheets and is basically a 1/16″ sheet of asphalt and recycled rubber with adhesive on it. This thick material adds both mass and damping for sound deadening of the cyclone itself. Auto parts and auto stereo stores typically carry it, some brands are Evercoat Q-Pads and Dynamat.”
8. I have not tried an enclosure myself, but I know a few of the folks who have. They consistently said it did little to no good in terms of reducing the noise. Since those early comments, others have responded with solutions that apparently do work. They have built enclosures with enough room to access the cyclone using either two layers of sheetrock inside and a third outside or sheetrock outside and a 3M construction sound deadening board inside. They also recommended mounting the cyclone on a wall with isolation dampers to keep the wall from being used as a sounding board.

C. PVC Confusion

Let’s see if I can help with the confusion on PVC caused by many mixed up terms and names that often refer to the same kind of pipe. There are many, many different classes of piping/tubing used for many different applications and have different characteristics. Many of these pipes are used for irrigation and would be suitable, but most limit their looking to one of the three most commonly found classes of PVC pipes. When it is all said and done, most end up going to an irrigation supplier and buying S&D PVC pipe for their dust collectors. It works well, is plenty strong, is easy to shape, and it costs 1/3 or less the cost of the other forms of pipe.

1. In readily available 4″ and 6″ PVC pipe there are two regularly used classes of “drain piping”, this includes DWV (drain waste, vent) and PVC schedule 40. These are “thick wall” relatively expensive products that are normally used inside the house and buildings for carrying clean water. The cost to use this material often exceeds the cost to use inexpensive metal ducts.
2. In areas where we need to install drainage or that do lots of irrigation for agriculture, we often have some other less expensive thinner walled pipe options. The least expensive is rarely found today which is styrene plastic used to work with standard yard drain perforated pipe. Although that 6” pipe is rare and useless for ducting because of its very rough interior, the inexpensive styrene fittings that work with it are about half the price of better quality PVC fittings. Most end up instead having to use a little better and much more expensive sewer and drain pipes known as SDR-35. SDR-35 is the “common name” for the 4″ and 6″ range of this product that has thinner walls than normal schedule 40. The standards, fittings, and details are specified in the ASTM D-3034 standard. Sadly, almost all of these standards which were initially free on the Internet are now publications we must purchase from merican National Standards Organization (ANSI). Many choose to use this class of pipe because it is readily available in or can be ordered by some of the larger hardware stores.
3. There is a less costly PVC option that is priced between styrene and SDR-35 pipe. It comes in light weight 6″ and 8″ pipe commonly known as just “Sewer and Drain Pipe” or S&D. The standards, fittings, and details are specified in the ASTM D-2729 Standard. Personally, if you cannot afford nice spiral smooth interior walled ducting and smooth snap on fittings, this is my next favorite choice. I like it not only for cost reasons, but because you can work with some effort standard 6″ HVAC fittings into the pipe. That gives you tight instant connections, the ability to quickly change out ports on your machines, and a variety of fittings that can let you make a floor sweep, hoods, and just about anything else you would want including transitions to my cyclone from off-the-shelf parts.
4. Both SDR-35 and S&D come in solvent weld systems and fittings with built in gaskets. Both SDR-35 and S&D are available at the home hardware stores in 4″. The amount of 6″ is limited there, but generally found in most irrigation and farm supply stores that carry pipes. These two pipe standards are by far the least expensive and have the least expensive fittings. Many say they are best way to go when building ducting for your shop. Because it is thinner walled it is relatively easy to work, you also can minimize the use of connectors (See working with PVC).

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