Noise cancelling vacuum pumps for boffins.

[simon]

Hi
I have a couple of large identical roots blowers /suckers and 30hp motors. Currently I have one installed with an electronic speed controller and it works brilliant, even at a very low speed, holding work onto the deck.
BUT
The noise is like a formula 1 car running in my enclosed workshop.
Wot I was thinking was...if I connect Both up in such a way as they both blow in opposite directions at the same time, or something like that, will they cancel each other s noise?
Any comments gratefully recieved.

Simon

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[thewoodcrafter]

I have a 15HP Roots and keep threatening to mount it on the roof and be rid of the noise. Short of that I don't think your going to do much about the noise.

[davidp]

Put a truck muffler on the exhaust port. You will be surprised at the noise reduction. Just be careful of all the junk that gets blown out of the exhaust if you use a muffler from a wrecker.

[simon]

Noise cancelling headphones are supposed to put out an identical noise but somehow opposite to the real noise, and they really work. I think that principal is aching to be employed here?

[paul_z]

Noise cancelling headphones do help but they do not produce "silence". I have tried two different brands, one cheap and one very expensive, and they both worked "OK". There was one interesting benefit - they canceled the router noise more than the noise from the bit. I was able to hear the bit noise well enough to be sure it was cutting well.

Paul Z

[waynelocke]

I posted this on a different thread and it was promptly discounted but here goes again. I used insulated ductwork from Home Depot, $35 for 12' Diameter X 25', on the exhaust side of my 7.5Hp cyclone dust collector and brought the exhaust back into the shop to some filters. The sound level went from a jet taking off to a low, barely discernible rumble. The noise reduction apparently depends on the length of duct used, so use all of the 25' if you can.

I would buy some as close to the exhaust size as possible and try it. For $25 to $35 there's not much to lose.

I was looking at building a structure around the cyclone and putting a $500 or more muffler when I tried it. It was pretty unbelievable to me.

[khaos]

Wayne i will be trying this on my next setup. Good tip.

[dana_swift]

Active devices sound so attractive, but don't live up to their promise. I use foam earplugs under the fluid ear muff type and get much better results than I have ever found from active noise canceling devices. I can run the bot, an air compressor, multiple vacuum pumps, dust collection, and a saw all at once and not have my ears ringing when the day is over.

Insulating the shop is still such a great idea, I may do that yet. And then wear the double layer I just listed. Quieter still.

Wayne- That is an excellent suggestion.. someday I will get a roots blower system and that sounds like a tremendously good idea, you can count on my using it. Too bad anybody discounted your idea, if it works and saves money that is the best measure of an idea there is. My personal thank you!

D

[erik_f]

You could try facing the exhaust ports towards each other and play with the distance of the gap into free air. At some point you might get the right distance so that most of the sound waves are out of phase...this could work. You might also increase your sound level is the waves are in phase. The problem with trying to get things to cancel is that you have many frequencies coming out of the pump. Isolation I think would be a better choice as well as some sort of muffler. If your pump is hard mounted to its stand and plumbing...you are creating a chain of vibrations. Isolation and dampening the mechanical vibrations as well muffling your air port noise is your best bet.

[jseiler]

Remember too, that if active noise cancelling is going to work, the output power of the noise generated by the tool has to be less than the power of the phase cancellation amp/speakers (probably a lot less to account for inefficiencies). For a 700W dust collector or vacuum pump, the noise power would be what's left after you account for generated heat and true output power of the vacuum. This might be 5-20% in sound depending on how well things are done up front.

Certainly the best bet would be to damp and dissipate as much as possible with resilient mountings and noise absorbing baffles. Sheer assembly weight does a lot to help damp things too, lowering the fundamental vibration frequecies and resonances.

John