Noise Reduction Techniques for Your Shop-Vac

shop vac noise-reduction setup

Shop-Vacs are great tools, but they do have the notable disadvantage of being loud.  Fortunately, much of the noise emanates from the exhaust, and with a muffler or “silencer”, this can be controlled. The results of my noise-recustion experiments were noticeable, reducing the noise by roughly 5.6 decibels. This may not sound like a huge improvement, but since the scale is logarithmic the sound intensity is actually cut by roughly two-thirds, according to this calculator.

As for how to actually make the muffler, I’ve outlined everything in this post.  As of now, the Shop-Vac muffler is used in a static configuration, but with some changes it could be used on a mobile vacuum.  The disadvantage of this reduction in noise is a slight reduction in suction, but it seems to be an acceptable trade-off in this situation – used for a little CNC router with this adapter.

For a video of the Shop-Vac in action with the CNC router in question, check out the video after the break.  Note that this is pre-silencer, so you can definitely hear the vacuum noise!

If you’d like more dust-collection fun, why not check out these mini-kegs turned into a cyclonic dust collector!

Comments

  1. phisrow says:
  2. th3BadWolf says:

    I’d like to add my 2cents of engineering by saying that overdoing the muffler will induce a counter pressure on the propeller thus creating stress. Usually,shop-vac come with a warranty and I wouldn’t be surprised if the shop told me it was voided because of this induced stress.

    Idea is great,but the inner workings of this muffler aren’t the best for this application.

    May suggest baffles instead of cloth?

    • Deg says:

      If there are restrictions/back pressure causing less airflow through the blower, the motor will spin faster, use less current and the impeller will experience less stress.
      My intuition would say modifications will risk burning out the motor (burned windings or worn bearings) rather than a mechanical failure in the blower, but I wouldn’t worry in this case.

      • th3BadWolf says:

        I’m not sure about your point…
        I rather see that the restriction will require more W from the motor (like when you hold a motor shaft) and therefore pump in more current. The impeller will therefore try to push the same amount of air toward a confined area thus creating pressure ( easy to see when you obstruct the exit with your hand).

        I’m pretty darn certain the motor is actually working a tad harder.

    • Motor cooling is usually also done via the exhaust, so reducing air flow has the effect of also reducing motor cooling (and vacuum motor fans are stressed to the max by design) and shortening its life span.

      • jbiehler says:

        There has been many a shop vac fried from trying to use them as vacuum pumps. Restricted flow is a no-no.

        If you want a quite compressor look at the scroll silencer ones made by Rigid at Home Depot. They are pretty quiet. There are also a few different dust collector vacs at woodworking stores like rockler.

        I had one of those one gallon vacs. For anything more than cleaning out your car they are pretty useless. Plug up in femtoseconds and the filters cost near the price of a new one.

    • M4CGYV3R says:

      Fill it with cotton balls instead. I have used them as baffle material for subwoofers with great success.

  3. William says:

    The guy needs to tread lightly… if the ATF thinks this could be put on any sort of firearm he can be prosecuted…. just FYI not trying to start anything….

    • dale says:

      While the ATF is serious about anyone making suppressors that might be used on firearms, they aren’t without common sense. This is designed like any muffler on a car or other combustion engine, and not a firearm suppressor. Additionally the size of it and the attachment point is not anyway appropriate for use with a firearm. If someone did try to modify this in some way for use on a firearm (in the USA) that would be bad and they should know better. Otherwise there should not be any concern.

    • barry99705 says:

      Better not keep any car mufflers in your house then.

  4. DerAxeman says:

    To reduce the sound level so it sounds half as loud you need to drop it by 10dB or one Bel. You might have dropped the perceived noise level by about 1/4 but not 2/3.

    http://trace.wisc.edu/docs/2004-About-dB/

    “Interestingly, our perception of loudness is not the same as sound pressure level. Although the actual formulae is somewhat complex, as a rough rule of thumb, an increase of 10db SPL is perceived to be approximately twice as loud.”

  5. Jerry says:

    I once tried a very simple-minded variant on silencing the vacuum cleaner with informative but spectacularly bad results. My brilliant idea was to attach a pool vacuum hose (20+ feet) to the shop vac and park the vac outside, running the hose in through the window.

    Although this did remove the rushing noise of the vac from the house, the longer hose created oscillation that caused a deafening siren-like howl at the business end. After I ran over to turn it off, dogs could be heard howling all over the neighborhood. You have been warned.

  6. AussieTech says:

    The high frequency nature of vac noise means that it should be fairly easy to reduce by baffling (unlike low frequency rumble). It’s not so much a small increase in motor loading that is the concern here, so much as any reduction in air flow, since these appliances (and electric mowers) are pretty marginal and depend heavily on a good flow of cooling air just to survive. Perhaps adding some sort of protective thermal cutout to the motor would turn this neat hack into a neat hack-plus.

  7. Vakyouum says:

    Restricting air flow into a shop-vac (or any other vacuum cleaner) will REDUCE the load on the device’s motor, causing it to spin faster – that’s why you hear the motor whine get higher in pitch when you block the hose – it’s not because the motor is “working harder.” The impeller is actually turning in a lower air pressure environment in this situation, thus there is less air resistance to the fan’s rotation and less current is drawn. That said, there is a risk to burning out a shop-vac motor if you block the airflow because the air that is being moved is also used for motor cooling. The blockage caused by the muffler likely causes just a minor temperature delta by itself from running the shop-vac without it, I’d be more concerned about how LONG you run the vac when CNC routing something that takes a long time to complete. In the hackaday tradition, maybe you could add an arduino control to monitor vac motor temperature :-)

  8. Gary Moriarty says:

    …it’s a shop vac mod for use as a shop vac. Also, it’s a small one. Personal experience, shop vac continious duty is brief. If user observes a reasonable duty cycle most of the good acvice, above, is effectively implemented. Remember dot-matrix and impact printer noise??? What if entire shop-vac is placed inside a spacious sound isolation chamber/box. I imagine a dsign like that would afford greater lattitude in mitigating the back-pressure or reduced air-flow issues. The addition if another quiet/efficient exhaust fan and/or tuned duct work could compliment the design. This project is certaintly on my to-do list.

  9. Hirudinea says:

    It’s very nicely done but haven’t you ever heard of ear plugs? They’re also good because no man can muffle a wife.

  10. Jake says:

    FYI, Shop vac sells a silencer which reduces the noise nicely and doesn’t void the warranty (nor would I presume that it reduces the life of the motor). The motor sounds like it runs at virtually the same speed, but that ear piercing whine is gone. I can use it in my cinderblock/concrete basement without feeling like I am doing any hearing damage.

    I would prefer the shop vac one since it is really small, about the size of a grapefruit, versus this big thing…

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