weird; noise annoys

[marc rosen]

(if there are any Buzzcocks fans out there, my Festool Hat's off to you) I always thought my planer was much louder when the dust collector was running so I borrowed a sound level meter from work to verify it quantitatively . Standing at a location where you would be feeding stock into the planer (15 inch Delta, Chinese made) I first measured the sound with just the planer motor on and no DC running and got

85db. With the planer off I then opened the 5 inch blast gate and turned on the DC (3hp Oneida) which resides in a separate room and runs from 7 to 6 to a final 5 inch diameter pipe at the planer. The sound level was 82db. With the DC on I turned on the planer and measured 106db. Planing 4 inch wide oak - light cuts - only increased the sound level to 108db. With the planer still under power I truned off the DC and watched as the level decreased slowly to 85 again. I cycled the DC once more just to repeat the readings and it was as before. I never gave it much thought but it seems like you can suck the sound out of a machine. I know very little about sound technology but I am aware that the db range is logarithmic however I don't know how to calculate what occurred. I'm sure the sound produced by the combination of planer and DC is greater than the additive effect of each device. Any sound experts reading this? Thanks for any feedback. Marc

[Swingman]

Adding two identical sound sources can indeed increase the sound power level significantly.

There a few other possibilities, one being the result of standing waves due to acoustic "nodes" in the shop room itself. Try moving the instrument to another location in the room and see if you get the same results.

Check out the SPL calculator here:

[-MIKE-]

[Swingman]

They also have some handy Sketchup engineering models.

[marc rosen]

Hi Swing, Thanks for the link and the comment. I did not measure the sound at different locations but I have listened to it throughout my shop and the living room area above. In all cases the sounds produced by either the DC or the planer are insignificant. But turn them both on and it is an unpleasant level. =20 Marc

[Leon]

the DC.

[Leon]

I have the same set up and agree that the sound significantly increases in volume. I wonder if a jointer would show the same increase.

[Swingman]

IME, there at least a couple of things at play.

Each motor is producing varying frequencies which, when they coincide with the other motor, the perceived intensity of those frequencies is increased, either by adding together, or by exciting a resonance in the room at those frequencies (think of a drum), or both.

In addition, and since loudness is actually perceived by the firing of nerves, and the number of nerves, in different areas of the ears, with both motors running and producing sound waves at their varying frequencies, many more nerves are firing in your ears, which will also result in an increase in perceived loudness.

And example would be in a symphony ... a section of ten violins playing the same note will generally sound twice as loud as one violin. But ten different instruments playing in harmony (different frequencies) at the same time will sound more than twice as loud as any individual instrument.

From your description, most likely a combination of the above is what is causing the phenomenon you are describing.

[John Grossbohlin]

John

[Russ Stanton]

The most likely cause of the increase is the airflow within the planer. If your Delta is like mine the dust collector hood has a 4 inch round opening for the hose and a narrow wide slit that attaches to the planer to suck up the chips. Pulling your dust collector airflow thru the slit will produc noise on its own. Sort of like blowing over the top of a soda bottle.

[Swingman]

In theory, yes. Practically ... easier, and cheaper to stick with ear muffs. ;)

[Steve Turner]

Well sorta. I have a 15" Grizzly planer and a Grizzly cyclone, and the planer makes a LOT more noise when the dust collector comes on. The collector pulls a

*considerable* amount of air past the planer knives, and those rapidly spinning knives will make a huge whirring noise as they "cut" through that high-speed flow of air. Any fan or propeller is going to make a quite a bit of wind noise at high speed, but planer blades are far less aerodynamic so the noise is much greater.

I'm curious to hear what the noise factor might be on a planer that has the network of spiral cutters rather than full length knives. I'll bet they are much quieter.

[Swingman]

That doesn't explain the additive nature of the increase with two machines running, neither one being louder than the other, which I think is what his question was ... could have misunderstood the original question

[John Grossbohlin]

Maybe for you or me... but there are folks out there that would buy it. ;~)

John

[Leon]

Could the hose be acting as a megaphone?

[-MIKE-]

Might want to check everything for Oak Rust©.

[Markem]

Quite possible all it takes is money.

Mark

[Morgans]

Thanks for the link and the comment. I did not measure the sound at different locations but I have listened to it throughout my shop and the living room area above. In all cases the sounds produced by either the DC or the planer are insignificant. But turn them both on and it is an unpleasant level.

*************************************************** What is probably happening, is the air moving past the head is causing it to act somewhat like a siren. All a siren is, is an air pump with the air blown over revolving fins, or vise-versa.

If you can, try to cut down the air flow to just enough to clear the shavings. Also, look for a possible way to control the places the air is drawn in, so it blows though where the chips spit out, but not directly past the cutter head.

-- Jim in NC

[Morgans]

"John Grossbohlin" wrote

So.... is it possible to develop noise cancelling sound for the shop? This along the lines of the noise cancelling systems in car audio systems?

***************************************** The short answer is yes. They have done it in small business type aircraft.

The thing is, the noise at each seat is different. You end up putting a microphone at each seat with its own canceling computer and speakers.

So, if you put 20 or 30 systems around the shop, you could help, a lot. You would also be much poorer.

If you want to help cut noise in the shop, you can also go for the sound absorbing approach. Brown builders board with burlap type material all over as much of the walls and ceiling you can manage. There are also many expensive materials commercially available.

-- Jim in NC

[Morgans]

"Swingman" wrote

That doesn't explain the additive nature of the increase with two machines running, neither one being louder than the other, which I think is what his question was ... could have misunderstood the original question

********************************** Part of it does. The blades cutting though the rapidly moving air does not happen until you get both of them going at the same time.

-- Jim in NC