Okay, as I sit at home being bored recovering from surgery, I am using my Frankford Arsenal Rotary Tumblr to clean some brass for my friend. It is in the garage sitting on a styrofoam board, which is sitting on top of a rubber mat. I can still hear the whirr of the gears from inside the house.

What would be a cheap but effective way to kill the noise, without cutting off cooling air that the motor draws from the bottom of the unit, and overheating the motor? I’m more curious to see how quiet I can make this without spending a bunch of money on it.

By all means, I’m interested in hearing excellent methods as well, but it’s still curiosity more than necessity.

Cheapest way I can think to do this would be to build a shielding half box. 2 side walls anb a roof. The “box” would then be insulated on the inside walls with sound absorbing material. Could use foam, or better yet Rockwool sound matting.

The tumbler would be covered between your common wall and the tumbler. Still get airflow from the 2 open sides. Would not be silent because sound waves would still be projecting out and bouncing off open side walls. But would cut down in your general direction.

I think this would work, be cheap, and still allow great airflow. But not an engineer or sound expert. Just sounds sensible and reasonable to me.

Move it closer to the garage door.
Then move it to the other side of the garage door.


Personally I've found it's better if you hear it. Otherwise three days from now you'll find it still running.

Maybe a box with a labyrinth for an opening?

is it possible to lube the gears?

^^^
The tumbler says the gears don’t need to be lubed. I highly doubt that. But I’ve never taken it apart to look at it. It doesn’t seem to be louder now than when new but that can change so slowly I might not realize it.

Wooden board, bedded in sand, under the rubber mat?

cheap styrofoam cooler? Cut out a hole in one side so the motor can take in fresh air?

The styrofoam cooler might work well. Maybe throw a moving blanket on top.

Sealing it in a box might cause it to overheat?

Having designed AC compressors that were among the quietest on the market, at the largest US compressor manufacturer, we luxuriated in our sound lab. There is nothing like walking into a semi-anechoic chamber and hearing only yourself. Learning as I went, I soon realized that sonic energy takes several paths. Let's think of them as we do heat transfer...

1. Conduction -- with what material are you mounting the offending device?
2. Convection -- what features of the offending device can move a lot of air molecules?
3. Radiation -- what is the actual acoustic energy source and how much does it have?

Brass tumbling in a bowl of rocks? Lots of air being disturbed by the bowl, and lots of source energy.
Electric motor with gearing? Plenty of metal to metal contact conducting sound.

Attack the problem by reducing any or all of the sources.

Reduce the number of rocks and brass? (radiation) Add mass to the bowl exterior to reduce the magnitude of the impacts.

Wrap the bowl in soft porous material (a towel, an absorbent pig mat, etc.) to prevent easy access by air molecules? (convection)

Grease the gears to dampen any transmitted gear error? (conduction)

Place the tumbler on very soft rubber mounts? (conduction, as well as convection)

Duct the electric motor fan to a box, which is open to the air with another duct. The box serves as a muffler. (convection)

There is also the potential for resonance, but that is another matter entirely. Here you would seek to change the natural frequency of the bowl, motor, gears, etc. Very hard to do well.

OR, put your shooting ear plugs and muffs on?

Is suspending it from overhead with a chain or bungee out of the question?

With a liquid load, I’d say no.

Thinking outside the box, since it's already in the garage, could you put the tumbler in a car and run it there? (being careful not to pinch the power cord as you gently closed the door as much as possible, of course)

I like 4MUL*R's way to break down the noise aspects - in that paradigm, this would be a way to cut down on the sound radiation.

Put it in your beer fridge