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  • active noise canceling

    Is anybody working on active noise canceling? I'd like to make some units for my woodworking shop. Some of the equipment is very loud, as much as 115db, and others are just super annoying. My thoughts are to put a small unit on each piece where I need to cancel the noise. Some of the pieces are:
    1. Planer/joiner
    2. Tablesaw
    3. Dust Collector
    4. Router table
    5. Miter saw
    6. Air compressor
    7. Misc shop vacs
    Smaller pieces of equipment can also be noisy and would possibly require a smaller unit.
    1. Palm sanders
    2. power hand tools
    I've searched the internet but was not able to find anything.

  • #2
    I believe most/all of active noise cancelling is VERY location and distance dependent, so you'll need the speaker AND microphone AND yourself all in the right places for it to work well. This is why it's getting pretty common in headphones (and somewhat in vehicles) but not many other things that I'm aware of. The locations of the speakers and mics and yourself are relatively known quantities in those things.
    ALSO, active noise cancelling is MUCH more effective for lower frequencies where the long wavelengths are more forgiving compared to higher-frequencies where very small distance changes can turn an actively canceled noise into a louder noise instead. A lot of car and headphone interferance in low-frequencies because those sounds have an easier time getting through the physical blocks of the car panels and headphones/plugs so ANC is able to be one of the more effective ways to block the most annoying frequencies.

    In a woodshop, however, many of the frequencies you'll be trying to block or tame are high in pitch/frequency, so the already nit-picky location of everything for the noise cancelling to work becomes extra extra precise.

    Not saying it can't be done. But those are some really big hurdles unless I'm misunderstanding something.


    You might have slightly better luck combining earplugs AND active noise canceling....because common foam earplugs are great at reducing mid/high frequency sounds but not as good against low-frequencies, and active noise canceling will typically have an easier time fighting low-frequency sounds.
    I'm guessing from your "some sounds are super annoying" comment that you're mosting hoping to fight mid/high frequencies though...so more effective earplugs will probably go a lot farther than active noise canceling in that regard. :(
    My first 2way build

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    • #3
      I've designed noise cancellation systems. LOUT is mostly right, but doesn't go quite far enough. So let me be clear: What you want to do can't be done. It violates the laws of physics unless the anti-noise transducers (speakers in this case) are right up next to your head. Like inches from your ears. Even then, I doubt that you could get more than 10 or 15db of cancellation above a few kHz (which is where most of the noise from power tools live) even with headphone style units.

      In every noise cancellation system the noise source MUST be further from you than the anti-noise (speaker) source. The error microphone must be somewhere in between. The time difference between the arrival of noise and anti-noise is the total time the system has to figure out what to do to cancel the noise. If the anti-noise source is 1" from your ear and the error microphone is at the noise source (the absolute best case scenario) you can reliably get 10db of cancelation at about 1.4kHz going down to zero cancelation at 14kHz. This assumes that the computation engine is infinitely fast and that the noise source is periodic (no impulses) AND the distance from the anti-noise transducer to your ear NEVER changes. In-ear monitors might do a little better as the distance to your ear drum is shorter and they don't really move much. But this isn't really what your asking for anyways. Now if you want to cancel low frequencies (under 200Hz, say) wavelengths are longer so things get a lot easier and you can build a practical system to make your car quieter. But power tools, forget about it.

      Here's what you do - get some decent foam ear plugs and put em in. Then get a good pair of gun muffs and put em on. Don't forget your safety glasses. You are now ready to work with power tools ;-)

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      • #4
        The best you can get are active headphones. Bose, David & Clark, and I assume others. They are effective to some extent. A little more than standard muffs. I think I read somewhere than no protection can go past 35 dB as it wil travel through your skull. Ironic though. People put on noise canceling headphones and then crank up the music and go deaf that way, right along with al the ear-bud users. But look on the bright side, when you get older, you will be used to a hearing aid.

        The best muffs I have found are branded as Huscavarna and sold in HD by the chain saws. You can use both foam plugs and muffs. That is about as good as it gets.
        You can also work to reduce the noise of the tools. I put my DC and big compressor in another room. Unfortunately using sound management materials in a wood shop is a no-go because of the dust.

        If yu want, you can go to the OSHA site and see what they deem as safe exposure is. Than take a good 6dB off that for what is actually safe. Level and time.

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        • #5
          Can't you just turn the music up so loud you can't hear the noise? Works for loud cars

          * Note: Don't try this at home. Or anywhere else for that matter.
          Francis

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          • #6
            Not to hijack the thread but I was thinking about some DIY noise cancelling this summer as I fell asleep to the drone of the generator. So to LIDAR I've got a few questions....

            1. For a repetitive noise source, such as a generator, does the speed of the DSP processor matter or could you still achieve noise cancelling even if the anti-noise was delayed by a few cycles?
            2. Where should the noise measurement be made? Next to the generator, outside window pane, inside window pane?
            3. What do you think about using a transducer on the inside pane of picture window as the "speaker"? I'm assuming most of the noise is coming through the window because the rest of the house is brick with an airspace between the brick and standard sheathing, studs, insulation and drywall. I'm thinking that if it's what's vibrating then attenuating the vibrations is the most effective way to reduce the noise.
            4. Is there any kind of correction curve applied to the noise cancelling? i.e. is less correction applied at higher frequencies that are naturally attenuated by the physical barriers?

            My solution last summer was a big roll of 8/4 pond cable and the genny as far away from the house as possible but I'd like something a little more convenient especially if it's raining/snowing out.

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            • #7
              An enclosure around the generator is by far the best bet. Surprisingly, most of the noise is not from the exhaust, but from the air cooled engines with no water jacket to quiet them down.
              A plywood 4 side box ( far side open) would give quite a good reduction.

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              • #8
                Bummer!!!!
                I currently use “Fnova 34dB Highest NRR Safety Ear Muffs - Professional Ear Defenders for Shooting, Adjustable Headband Ear Protection/Shooting Hearing Protector Earmuffs Fits Adults to Kids”, see https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

                These work great.

                Recently I got a pair of “Sony WH-1000XM4 Wireless Industry Leading Noise Canceling Overhead Headphones with Mic for Phone-Call and Alexa Voice Control, Black”, see https://www.amazon.com/Sony-WH-1000X...Q2xpY2s9dHJ1ZQ==
                These work better than the Fnova ear muffs. I REALLY, REALLY like them!!!!

                I failed to mention the main issue with the noise is what my wife hears. We have a two-story house where my workshop is on the ground level and the living area is above it. We purchased the house and it was about 1 year old thus we did not have any input to the actual build. The area on the ground level has sheetrock on the walls and the 12' ceiling thus it would be a huge issue and expense to take it all out and install sound insulation. Possibly I need to get her a set of the Sony WH-1000XM4s. After reading the replies (MUCH THANKS) I'm leaning toward the headset for her.


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                • #9
                  What tvrgeek said. A place I worked at long ago had a big, loud, compressor. We tried a bunch of things to quite it down. Turned out the most effective thing was routing the air intake outside the building (and then building an enclosure around the compressor). It helped a lot.

                  As to your specific questions:
                  1) If the noise is REALLY periodic, then you can be several cycles out and it won't matter. As a practical matter your generator probably has most of it's noise energy <200Hz and any reasonable DSP should be up to the task. (BTW - the DSP won't be the problem. See below)
                  2) The noise measurement should be made as close to the noise source as possible. Several automotive ANC systems use an accelerometer on the engine and suspension points rather than a microphone (but they do also use error microphones in the cabin). The reason you want the error transducer close to the noise source is that it gives you (and your anti-noise speaker) more time to act.
                  3) I think that most of the noise is coming around your windows. Windows tend to be poorly acoustically blocked around their edges. Now it could be that your windows are vibrating, but you can easily test that by sticking some high mass vinyl or the like on the window and see what happens. If the noise is coming from around the edges, remove the molding, stuff some poly backer rod in there, and fill the remaining gaps with silicone caulking. That will help a lot.
                  4) There is no need to have such a curve. ANC run out of steam at high frequencies anyways (see below). We just low pass filter the whole system in order to ensure stability.

                  So here's the bad news. What you want to do probably won't work. What you need to understand is that there is no such thing as noise cancellation in a general sense. You can cancel noise in one location, but it will just be louder somewhere else. So we can make a car seem quiet to the passengers (whose ears are all more or less in known locations), but if you bent over to tie your shoe, for example, you'd find it really loud down there. This is because if I am applying anti-noise at, for example, 200Hz (wavelength of about 6 feet), if I move 3 feet away the anti-noise in now 180 degrees out of phase of what I want. It is now reinforcing the 200Hz noise! Move up to 1kHz (with ~1 foot wavelength) and you can see why you need to put your head in a vise to have it work. If your generator noise is mostly <50Hz you MAY be able to help things with ANC, but I'd just build a good acoustic isolation box.

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                  • #10
                    Thanks for the answers. I don't think the windows are leaking, they were foamed all the way around and caulked inside and outside. Before I pull the trim I'll take a look at them with a thermal imager, the neighbor just happens to have one from work at home this weekend. Should be easy to spot air leaks, it was able to show the dog's paw prints on the driveway.

                    More questions.....

                    1. my initial thought is a V shaped enclosure with hinges so it folds for easier storage. Yes, no, maybe so?
                    2. Would sound absorber, something like Owens corning 703, on the inside of the V help? If so, how much do think for an initial starting point?

                    Again thanks for the feedback

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                    • #11
                      So far the Sony WH-1000XM4 Wireless Noise Canceling Headphones have been working super great for me. Because the woodshop is on the ground level of our 2-story house I need to get a pair for my wife. She spends most of her time on the 2nd level, e.g. the living level, and hears the various tools. The only issue of getting my wife to use the headset! She is in the early stages of Alzheimer’s Disease and getting her to adapt to new technology is a steep uphill battle. Anything new greatly confuses her.

                      LIDAR, in our previous house my workshop was in an attached garage. When I built the house I added a sound damping wall between the garage and the house. On the other side of the wall was two rooms, my office and a laundry room. They and the sound damping wall greatly reduced the noise. I enclosed my large large air compressor and ensured it had air flow by installing a powered vent to the attic area. The fan was tied into the air compressor thus it ran anytime the compressor ran. When I closed the door to the air compressor the noise it produced was greatly reduced in the shop as well. I will try the same here taking care to add sound damping in the ceiling of the enclosure. However various other tools present a lot of challenges, router (this tool screams), tablesaw (not too bad), planer/joiner (I need to install a spiral head), sanders (different sounds from each), We had thought this would be our last house because we are getting old. However, I may be building again. If we do it will be a one-story with the workshop attached to the end or a separate building. Time will tell.......

                      Comment


                      • #12
                        Look at the specs on 703 through 709. Density and thickness define the amount of absorption.
                        To prevent transmission, there is a special sheet rock with a polymer inner sheet that is said to do an excellent job. Calking under the plate, sheetrock to plate, etc to reduce the slightest air leakage is critical.

                        With any material, you are dealing with a dusty environment as well as fire hazard. Exposed FG must be covered and for a shop, really must be retardant.

                        There is no need for a detached shop for noise suppression. A double studded wall with rock wool and double doors will do just fine and be cheaper than a separate building. Plus, you don't get rained on in between. There is a ton of information on the web under the "sound control" topic. See what the pros have to say, not rum-int in diy speaker forums. It is engineering with actual science behind it.

                        Windows with "hurricane glass" pass less sound than plane glass. Argon filed pass less sound. Double thick or triple pane pass less sound. Sound does not like to transition between materials.

                        Remember, sound control is not just absorption.

                        If I were building from scratch, the house would adjoin the garage. Behind the garage would be the shop so bay doors would be into the garage. Continuing to the side of the main garage would be my bays for my LBC's having enough height for a lift. Behind and forming a square with the wood shop would be a paint booth, accessible to both cars and furniture. Somewhere in the middle would be a half-bath. One story. All doors 36 inches. Roll-in shower. Cheap to do when new and can keep you in a house much longer. Retrofitting is expensive. Besides, with 36 inch doors, yo can carry a laundry basket busting your knuckles. We really need to update how we build houses.

                        OK, where is the Publishers Clearing House contest van?

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                        • #13
                          I built a (mostly) sound insulated room in the basement of the last house. It had inner and outer walls that were not connected to each other (I think this is what tvrgeek means by "double studded wall") and the ceiling was hung from the walls (i.e. not connected to the floor above). I also used a very heavy solid door that was gasketed all around. It was very effective. Band practice downstairs was rendered almost silent upstairs. Those construction techniques really work.

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                          • #14
                            Originally posted by LIDAR View Post
                            I built a (mostly) sound insulated room in the basement of the last house. It had inner and outer walls that were not connected to each other (I think this is what tvrgeek means by "double studded wall") and the ceiling was hung from the walls (i.e. not connected to the floor above). I also used a very heavy solid door that was gasketed all around. It was very effective. Band practice downstairs was rendered almost silent upstairs. Those construction techniques really work.
                            Can you share some shots or maybe write more information about materials you have used and more steps on how you have achieved such a result. I need to get less noise as it makes me crazy.

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                            • #15
                              I've used Bose noise cancelling headphones for years, on commuter rail and airlines. Let's you easily listen to music/movies while travelling. Great for that, the worst noise is lower in frequency and can be mostly cancelled. I almost bought the Bose in-ear noise cancelling ones, the reviews said that they cancelled everything, but I didn't want in-ear. I would suggest checking them out. They are evidently so effective due to being in-ear and effective to much higher frequencies. Not cheap, but it you want the absolutely most effective, in-ear is the way to go. How high in frequency they are effective I don't know, but certainly must be better than over-the-ear cans.

                              When running my snow blower I use foam inserts AND the standard over-the-ear damping ear muffs. I compared the Bose headphones to the ear muffs (with the foam plugs for both) and actually found little difference with the snow blower. I thought they would do better.

                              dlr
                              WinPCD - Windows .NET Passive Crossover Designer

                              Dave's Speaker Pages

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