Once I had my ZTW foam cutter working (here’s my original post), inspiration immediately struck! Why not make a muffler with foam baffles to bounce the air and sound around before leaving into the atmosphere? With the foam cutter and some Styrofoam that an item I recently purchased was packaged in, this was really easy to do.
As seen in the pictures after the “more”, I traced the inside of some 4 inch PVC pipe that was used in my original cloth-based muffler to the Styrofoam. Using this pattern, I then cut out four foam baffles to make the air snake around in the muffler before hitting my ears. The holes cut out were then used as spacers between the baffles, and everything was attached with a cord to keep things in their respective positions.
Once everything was strung together with the air holes each alternating sides so the sound wouldn’t have a straight path out, the assembly was then slid into the four inch diameter PVC pipe. A 4 inch to 2 inch bell fitting was then put onto the side that would interface with the Shop-Vac using a 2 inch to 1 1/4 inch reducer. This was accomplished with some duct tape and zip-ties. The side exposed to the environment was also duct taped to keep everything together.
When tested, the muffler seemed to reduce the noise a few decibels, especially dampening the higher frequencies. Overall though, I’m not sure it was quite as effective as the original cloth-based muffler. On the other hand, I believe the air flow was less restricted, and the muffler was much lighter. Because of this weight reduction, it didn’t necessarily require a supporting string, and would probably work better in a mobile application. I’ve kept it on my CNC router’s Shop-Vac for now.
When testing this muffler, the readings on my sound level meter, a Pyle PSPL01, seemed to bounce around a bit, so it was tough to figure out what the noise reduction level was. In the meter’s defense, I had dropped it on the floor before this, so who knows. I do like it for figuring out if my noise-reduction efforts have been effective, but I really have no way to tell if it’s calibrated correctly.
In conclusion, I think this is a good way to do a little noise-reduction on your Shop-Vac. It’s got fewer parts than the first version, so it’s a bit cheaper and easier to make. It’s nice to have a hot foam cutter, but obviously there are other ways of cutting foam if you want to try this! Also, this is a great example about how wonderful duct tape and zip ties are.