Saturday, April 16, 2016

Generator Resonator

As I have noted in the past, one of the very few things that I am not happy with on the Fuse 23a is the generator noise.    It is really louder than I think is reasonable.

The generator is mounted under the coach more or less centered under the walkway near the bathroom.   It is about as noisy next to the beds as it is outside next to the exhaust.   Up front at the couch it is much quieter.  It is interesting how much of a difference 10 feet makes.

I keep wondering what can be done to make this more acceptable.  I have still got a lot of exploring to do underneath the unit, but one idea on the forums was to install a resonator.

Cummins Resonator

The proper resonator for the Onan Cummins microquiet 2500 watt LP generator is a 155-2449.  I bought one for about $46.00 including shipping from Tweetys RV to see if it would help with the noise.

I will say that this was an experiment.  If it helps, I would bring it to a muffler shop and have it installed permanently.  If not, a small dent in the wallet.

Cummins Resonator

I got the resonator and I was surprised by the small size.  It was about 12 inches long and 2 1/2 inches in diameter.  It should be able to be mounted fairly easily even though the space under the Fuse is at a premium.

I downloaded a sound meter app for my iPhone.  Knowing that it is not calibrated, it is mostly to see if the resonator makes a difference,  not to see an absolute value.   I also just tested by placing the resonator over the end of the exhaust pipe. Again,  just looking to see if it makes a difference.  In the 2-3 min. we held it there, it did not seem to get very warm.  The LP exhaust does not seem to be anywhere near as hot a a car tailpipe.

Cummins Resonator

To the ear, the difference was immediate.  Sounded much more acceptable.  The interesting thing is that the measurement only showed about a 1db difference.  This was the same inside and out.  But  more interesting is that all of the high notes were gone.   The low notes were still coming through but all of the irritating high notes were gone.  The metallic clacking disappeared.

We took it off and put it back on several times and the results were the same.  It definitely helped.

This in my opinion was a resounding success and would calm down many noise complaints.   Don't get the impression that it fixed the problem.  It is still louder than I think it should be.    I am still going to have to look for more help with this.   But now I am going to have to find a muffler shop to mount it permanently.

Several other things came to mind while I was experimenting:

  • We were parked on the concrete driveway.  I am betting some of the noise is reflecting back from the hard surface driveway making it louder that it should be.  
  • I want to look to see if the attachments are isolated or not.  There seems to be much vibration in the floor while running probably amplifying the noise. 
  • I also wonder if some Dynamat could be placed to deaden some of the inside noise.


  1. What did you end up doing about the generator noise? Did this do the trick? Have you come up with other ideas that work?

  2. The resonator helps a lot. The noise is still there tone is less harsh. The other thing that helps is to stiffen/tighten up the hanger connections for the generator muffler especially where it passes the outside wall. I have not done this yet (on my list for the dealer to do) but several others have said this helps a lot as well. I believe this since my noise levels are much less if the motorhome is at a small tilt or when I hold the muffler. Either of these would get rid of some of the mechanical noise.

    I wil caution that even with both of these done there will still be noise. Just less of it.