This a step by step (somewhat ) on making a quiet vacuum box.

[knight_toolworks]

his was my quest to get a quiet vac setup to replace my two melted fein vac setup. By themselves the fein motor is almost 100 decibels it is a real screamer for sure. but You stick it in a simple baffled housing and and it is 76dbs and you have a 450.00 fein vacuum. depending on what motors you use you can make this setup for less then one fein.
for this setup I used two of these http://www.grainger.com/Grainger/AME...um-Motor-2M433 but I am going to hunt for the exact fein motor and check the prices. these do drop into a fein vacuum though and are about as big as they make them.
This design only works for this type of motor. it will work for others but it will not muffle them to my disappointment. I am not sure why as most of the noise is the screaming fan on top.
measurements are not critical for this setup. The box the motors are in is sealed on the bottom for the vacuum ( I have a separate filter box because I have two vac boxes) so you want to make the box large enough to fit a shopvac cartridge filter in.
I use 3/4" plywood for the box as it is airtight and strong but mdf will work as long as you seal the insides of the box (I use yellow glue) I use a hole in the side for a pvc coupler fitting. the platform the motors sit on have two holes for the motor. the size is not critical as the hole in the bottom of the motor is only about 1.25" Then a hole in the box the same size as the bottom one for the blower air output. I will be putting a muffler on mine to see how much it reduces noise. the one critical measurement is to have the top of the box either be about 1/8" to 1/4" below the top of the motors or if you want to use thick neoprene as a seal on the bottom of the lid slightly above the motors. even if the top is a bit high you can make rings to bring it down to the right level.

[knight_toolworks]

the pics are several setups as they evolved. these pics are my first box that actually muffled the sound. It does not need all the baffling or foam as the box at most knocks down the sound by 2dbs if your lucky. the last pic is a wide open air outlet but it was a box for different motors. you really just want a pvc fitting there so you can control the airflow.
The motors sit on a neoprene sheet to keep vibration down. I just bought a neoprene floor mat off ebay for this. I used a simple ring clamp and neoprene to clamp the motors in place. You just need enough force to keep the motors from twisting when they start.
You can make a pocket for them to sit lined with neoprene too as long as they fit snug. but I was afraid the neoprene would compact and they would loosen.
Ok I made the pvc fittings from a couple and a ring from (sintra )pvc foam I just make assure they are snug (fittings vary so be sure to check the fit) I glued them with standard pvc cement. Then I used silicone around it and screwed it to the box.

you can also use 2" gray conduit male and female and screw them together between the plywood. but this is easy strong and works well.
I made a separate filter box because I have two vac boxes so I only wanted one filter. I just screwed the filter with screws through the box face into the filter to hold it in place. the filter box has two check valves so I can use one vac box and it shuts the other off. I also used screw connectors so I can remove each peice without having to cut it apart.


You can put these both inside the box as I did that for my last setup.
this is a dirt easy project to make you just need to make sure the bottom is airtight the box is glued and screwed together as there is a lot of force involved.
for sound the baffle is critical. I have made 4 different ones. the first two were simple boxes with flat baffles with air holes alternating and texture to bounce the sound around and quiet the motors. they all worked well but they were tall and in the way. I did not noticed much of a difference between plywood or mdf. but I also did not find a difference been textured and not as my last one is smooth. I just made this last one and it is far simpler in design single pieces. these are for air intake and sound output. so the sound heads out and the air is drawn in. in the last one the air is drawn in the outside ring down to the bottom up the middle and down the tubes.

[knight_toolworks]

I use a lip to keep sawdust from falling in and I just screw it onto the lid. it's best to maker it smaller so it is easy to screw the lid on.
The wiring is simple. I used two switches as I kept popping the breaker if both motors turned on at the same time. I just used heavy duty switches and a heavy extension cord. I don't know jack about wiring but this is simple and it does not matter what wires on the motors are on the white or black wires on the cord.
I bought the biggest motors of this type I could get but you can get smaller ones for 100.00 or less. the prices change with granger as mine were 150.00 or so each. so for about 350.00 or so you have the suction of two fein vacuums for less then 1/2 the cost. they are almost as quiet (hoping the muffler will make them as quiet) with a lot less room taken up and no chance of melting the feins if you set them on a box like I did.
this setup does most of what I need and it is quiet and cheap.

[sailfl]

I wish you post a video with sound so we can hear how quiet you box is.

Thanks

[knight_toolworks]

here you go
http://youtu.be/zCk-0AJ-ha8
my fein is a bit louder as I replaced the motor and lost a piece of foam. the first pic is the fein the second my vac box.

[sailfl]

What did the meter cost you and where did you get it?

Thanks for the input. I am building a box and I want to see what the noise level was like with yours and I will post when I am done with mine.

[bob_s]

there is a decent Iphone app from studio six digital that I found to be pretty accurate for $.99 the price is right

I bought it to check the sound on a Penn State 2 1/2 hp cyclone. The issue that came up is that they claim its 75 db I find it's 92db. That is a huge difference. Some of the difference is that they are testing them in an open factory, and mine is in the corner of a room. Sound reflects off of sheet rock very effectively and dissipates completely into an open factory space.

This issue has to be considered when doing any sound management.
I am going to pad the corner where I installed the cyclone withUltraTouch Cotton Insulation and install some baffles. It isn't simple, as Steve has definitely demonstrated, and some of the solution seems to be outside of the machinery and in the room around it.

[knight_toolworks]

I have three iphone apps two read close to the same so those I wil lgo by. but whats another app?

[knight_toolworks]

I wish this method worked with all the motors but it does not. I am hoping the muffler will work well for my others.

[knight_toolworks]

got the mufflers today all they are are thin pipe with acoustic foam around the inside. But they do work. with the baffle on top and the mufflers I get the sound around 85 dbs down from 100. but I find I have to have both one or the other don't do a lot. I was only going to use one on this box and one on the quiet box but they don't do a lot for the quiet box.