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Generator noise abatement


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Back in '06 I bought a 7kw Diesel generator, a Multiquip DAC-7000SS. It was bolted to the deck of my old 4700 which was written off in a crash in 2011. The case was crushed on one corner but no damage to the generator itself which continued to run fine. Multiquip was contacted several times for replacement parts but didn't respond.


So when the 730 came along, the generator was removed from its case except for the base and attached to the passengers side of the truck under the sleeper cab. The unit runs fine but it is noisy, not sure how noisy. Back off 50' and it's not too bad but definitely noisier than an Onan. Running at 3600 doesn't help as opposed to 1800rpm.


Maybe it's a lost cause but I'm wondering if there is or are ways of reducing the noise. There are lots of sound deadening products out there. The considerations would be removing and relocating the electric fan and radiator. Building a 4 sided enclosure plus a lid but generator cooling would need to be addressed.


To oversimplify things,

  • 4 sided box built with a lid
  • allowance for air intake
  • vents with baffles
  • inline fans, maybe staring up with engine preheat.
  • Better muffler

As it is now the control panel was relocated to the same truck body compartment the houses the winch for the car. Passengers side forward of the wheels and aft of the 100 gallon fuel tank.


Even a used 7> 8kw Onan is 4-5k US used from an RV wrecker plus shipping, taxes plus installation . Then it would mean the old one removed and sold for peanuts and the new one installed.


There are some pics floating around if needed.....I hate to toss a perfectly good piece of machinery that doesn't get used that much but is nice to have around just in case.



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I'm no sound engineer but...

1) a good muffler, routed either under the truck between the wheels or up into the air 10' will help a lot

2) an enclosure is only as good as the material its made from. Sheet metal is resonant---it must be lined with a sound material for good results. An underhood material or good old fiberglass batting works great.

3) If I had a small genset I KNEW ran well, I'd be really hesitant to trade it off...

4) Use a air duct/baffle approach for the cooling air flow, route down into the ground or in toward the frame....just be careful not to restrict air flow too much.


I've helped design a small power house building where we routed the mufflers out the roof, and used a wire mesh w/R20 fiberglass batting for the ceiling. With (2) 25KW open gensets running full bore, you could stand beside the gensets and talk normally with only slightly raised voices. The batting just absorbed the sound. Between the roof batting, the solid concrete walls, and concrete baffle walls in front of the intake and exhaust, standing outside you could only hear a quiet murmur.

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Years ago, I owned a MiniWinnie. If a big rig passed us, the Minni would change lanes, from the pressure wave of the big rig!


I installed a generator in one of its compartments. The noise was horrendous, inside and outside the MH. I used the blankets, below, on the inside of the compartment. The stuff did a fabulous job of keeping the noise and the heat down. As I recall, I used spray glue to hold it in place.




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A good material to use for the enclosure is James Hardie 1/2" concrete backer board available at most any home store. It is NOT resonate like steel and is fireproof, waterproof, paintable and can be cut with a carbide blade on a circular saw. Sections are bolted together with aluminum angle iron. In the past I experimented with every imaginable material and honestly this stuff and a cardboard box came out on top for sound reduction.


Jeff is right on muffler and cooling fan advice. I have had better success with an exhaust fan rather than a pusher. Lots of nice 10" electric fans in the auto bone yards with blades that give good air movement. Sound does not move around baffles as well as air does.

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Great topic. Cant wait to read the replies. I have watched maybe 100 youtube videos on the very concept as I have a Harbor freight 8750 that is very noisy.


So far, all the vidoes of installing auto mufflers etc., seem to not work very well. It seems the generator itself and the engine design are the cause of the noise, more so than the exhaust note. So the box idea seems to work as long as the generator is mounted to something solid and substantial.


But I'm curious what others come up on this.

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An amazing amount of the noise generated by an engine is mechanical and air movement, the marine/boat industry use curved ducted baffles, some with an airfoil shape to break up the sound waves, they also use a lead lined sheet foam rubber product that absorbs lots of the sound waves.

If you are leaning towards a remote mounted radiator and fan combination, i would recommend looking at something that the automakers have had in production for lots years so that parts availability is good, check with your local independent body shop for advice, Ford Taurus comes to mind.

Finding a quiet muffler is always a challenge, probably the easiest thing is to bite the bullet and buy the factory muffler

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Lots of good ideas have been presented. Many years ago I worked for a generator manufacturer. We were constantly fighting noise issues. The engine is probably creating a lot of internal noise from connecting rod slap, valve noise. etc.


As I recall some of our dealers would use a multi-chamber motorcycle or import car muffler to reduce engine noise output. Another consideration as mentioned above is keeping the unit cool. The idea of using a fan is a good one.


Multiquip builds a good unit. To find a replacement part you might look on the internet for their servicing dealer base. There might be a large dealer with a big "bones pile" of dead units they use for parts. When I was in the trade (30+ years ago) I had dealers that kept old non-servicable units for parts. We (as a competing manufacturer) also had some big dealers that would buy excess/obsolete parts inventory. Our local dealers would contact these big parts houses for obsolete parts. You might check with some Multiquip dealer service shops and inquire if they have a source for obsolete parts and go from there. You might also check with Multiquip's corporate service dept/warranty dept for an idea where to find your replacement part.- a servicing dealer can give you a phone # or email address. A service shop will have a source to contact when he/she has a diagnostic problem.

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Well, if'n it was me, I'd take a big ice chest & remove the lid. Flip it over the gen while running for a couple secs, & see if it helps. If so, you're on the right track, just need to perfect it. Many cars now have electric fans, don't spend for some special "race-car" thing. The other thing that might work is an enclosure for a home-power emergency generator if you can find one cheap.

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Well, if'n it was me, I'd take a big ice chest & remove the lid. Flip it over the gen while running for a couple secs, & see if it helps. If so, you're on the right track, just need to perfect it. Many cars now have electric fans, don't spend for some special "race-car" thing. The other thing that might work is an enclosure for a home-power emergency generator if you can find one cheap.

If your "race car" comment was directed at my post, the Mercedes fans I reference can be had at most wrecking yards for $5!

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