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Old 09-13-2021, 08:01 PM   #1
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Onan Cummings 4000 any reduce sound modifications?

We have a 2019 Cummings 4000 gas generator.
My wife was asking if any modifications to reduce noise in coach?

I said the experts here may know

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Old 09-13-2021, 09:26 PM   #2
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I do not answer to expert......but I have a few hair brained ideas..

My plan is to line the inside of the generator enclosure with a product such as KilMat or MAT66. These are self stick sound deadeners. Also, this can go inside any cabinets or closets nearby that may bring sound into the living area.

Also plan to add a Gen-Turi which is long exhaust pipe to vent exhaust up above the roof. This will take some sound with it as well as exhaust.

Also, my understanding is that the sound or the perception of sound can be lessened by making sure the rubber mounts that hold gen to the motorhome are still rubbery and not becoming brittle. The generators attachment point can transmit deep bass tones that are not heard if you can isolate the generator.
To that end I may try to mount the generator on a rubber pad and the pad will be mounted to the motorhome.
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Old 09-13-2021, 09:34 PM   #3
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So the real question is:

Sound inside the MH? or,
Sound outside the MH?
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Old 09-13-2021, 09:57 PM   #4
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Quote:
Originally Posted by happy View Post
I do not answer to expert......but I have a few hair brained ideas..

My plan is to line the inside of the generator enclosure with a product such as KilMat or MAT66. These are self stick sound deadeners. Also, this can go inside any cabinets or closets nearby that may bring sound into the living area.

Also plan to add a Gen-Turi which is long exhaust pipe to vent exhaust up above the roof. This will take some sound with it as well as exhaust.

Also, my understanding is that the sound or the perception of sound can be lessened by making sure the rubber mounts that hold gen to the motorhome are still rubbery and not becoming brittle. The generators attachment point can transmit deep bass tones that are not heard if you can isolate the generator.
To that end I may try to mount the generator on a rubber pad and the pad will be mounted to the motorhome.
X 2!
You could also lay a sound deadening pad on the ground under the generator bay.
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Old 09-13-2021, 11:18 PM   #5
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Originally Posted by Scubawise View Post
We have a 2019 Cummings 4000 gas generator.
My wife was asking if any modifications to reduce noise in coach?
I said the experts here may know
My KY has a muffler and 9 ft long 7/8" exhaust pipe. The cell phone shows 60 db at 10 ft outside. Its noise doesn't bother us when watching TV or listening to the radio and it is directly under the reclining love seat. I can't hear or feel the KY in the bedroom.
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Old 09-13-2021, 11:59 PM   #6
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Thanks will review all suggestions. You all are the best
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Old 09-14-2021, 01:45 AM   #7
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When I first bought my Hurricane the genset exhaust pipe was routed to were it vibrated against the bottom edge of the coach wall. The pipe also touched a support bracket and made a loudish tinging sound. I repositioned the clamp on the pipe and all was better. My genset is under the bedroom and now you can hardly hear it in the summer time when the A/C is running. When the microwave is running you can't hear it at all. Turn on the TV and it is as quiet as a campground pedestal.
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Old 09-14-2021, 01:51 AM   #8
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When I first bought my Hurricane the genset exhaust pipe was routed to were it vibrated against the bottom edge of the coach wall. The pipe also touched a support bracket and made a loudish tinging sound. I repositioned the clamp on the pipe and all was better. My genset is under the bedroom and now you can hardly hear it in the summer time when the A/C is running. When the microwave is running you can't hear it at all. Turn on the TV and it is as quiet as a campground pedestal.
I'm betting if you stick a Slipknot CD on and crank it up really loud... you won't even hear the wife complaining about how loud the generator is...
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Old 09-14-2021, 02:53 PM   #9
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Originally Posted by happy View Post
I do not answer to expert......but I have a few hair brained ideas..

My plan is to line the inside of the generator enclosure with a product such as KilMat or MAT66. These are self stick sound deadeners. Also, this can go inside any cabinets or closets nearby that may bring sound into the living area.

Also plan to add a Gen-Turi which is long exhaust pipe to vent exhaust up above the roof. This will take some sound with it as well as exhaust.

Also, my understanding is that the sound or the perception of sound can be lessened by making sure the rubber mounts that hold gen to the motorhome are still rubbery and not becoming brittle. The generators attachment point can transmit deep bass tones that are not heard if you can isolate the generator.
To that end I may try to mount the generator on a rubber pad and the pad will be mounted to the motorhome.
Be careful. Onan has very specific dimensions and requirements for installation of the generators to permit adequate airflow for cooling. Using any type of sound deadening or insulating material could result in over heating problems. Check the Onan Installation Manual (not the owners manual) for the specs and then start measuring the distances. My bet is Thor installed the generator right at the minimum clearance required.
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Old 09-14-2021, 05:01 PM   #10
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Be careful. Onan has very specific dimensions and requirements for installation of the generators to permit adequate airflow for cooling. Using any type of sound deadening or insulating material could result in over heating problems. Check the Onan Installation Manual (not the owners manual) for the specs and then start measuring the distances. My bet is Thor installed the generator right at the minimum clearance required.
IMO, it's a safer option to install the sound deadening material in the interior of the motorhome. But FIRST - understand how sound deadening materials actually work - you could at minimum, waste money, time and effort with little gain. Or at most you could actually make things worse!

If you are REALLY serious about sound deadening, talk to a qualified acoustics engineer. Do some research... make some phone calls. A car audio shop may be able to point you towards a solution that works for you.
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Old 09-14-2021, 05:23 PM   #11
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We still don't know if the OP is concerned about the noise inside the MH, or outside the MH. Two different issues; two different solutions.
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Old 09-14-2021, 06:31 PM   #12
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I really like the “auto-idle” feature on Honda (and others) generators.

It reduces engine speed when all electrical loads have been turned off and automatically returns to rated speed when loads are turned back on.
Less noise (& fuel).

Would be a nice feature on an RV generator.
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Old 09-14-2021, 07:34 PM   #13
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Originally Posted by 16ACE27 View Post
We still don't know if the OP is concerned about the noise inside the MH, or outside the MH. Two different issues; two different solutions.
OP said “reduce noise in coach”
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Old 09-14-2021, 09:22 PM   #14
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Originally Posted by taylorbob1 View Post
I really like the “auto-idle” feature on Honda (and others) generators.

It reduces engine speed when all electrical loads have been turned off and automatically returns to rated speed when loads are turned back on.
Less noise (& fuel).

Would be a nice feature on an RV generator.
It would never be used on an RV generator as the converter always has a load on the AC circuit so an "auto-idle" would never happen as it changes the output frequency and voltage. Now inverter generators that have an "ECO" mode that reduces the speed of the generator to match engine power to drawn electrical power is where the RV world is finally headed after Honda, Yamaha and others have had this feature for at least 2 decades. I even carry a first generation Honda 2000 on trips that I'll be boondocking for several days as it can carry any load in the MH but the big A/C and continuously charge the batteries in ECO mode with a lot less noise than the Onan 4K.
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Old 09-14-2021, 09:25 PM   #15
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OP said “reduce noise in coach”
But is that meant as "inside the coach"? Many others have answered in ways to reduce noise outside the coach. Of course reducing outside noise may also reduce inside noise.
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Old 09-14-2021, 09:49 PM   #16
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Originally Posted by taylorbob1 View Post
I really like the “auto-idle” feature on Honda (and others) generators.

It reduces engine speed when all electrical loads have been turned off and automatically returns to rated speed when loads are turned back on.
Less noise (& fuel).

Would be a nice feature on an RV generator.
I like that too, but it would take an inverter generator. Non-inverter generators have to spin the alternator at a constant speed in order to produce 60Hz power. One of the primary reasons that inverter generators are quieter is that they can vary the speed of the engine according to load, and even under high load are usually designed to spin at a lower speed than non-inverter generators.

I'd love to see the Onan inverter-generator offered as an option for all Thor models that have a generator of the appropriate size.
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Old 09-15-2021, 12:56 AM   #17
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I like that too, but it would take an inverter generator. Non-inverter generators have to spin the alternator at a constant speed in order to produce 60Hz power. One of the primary reasons that inverter generators are quieter is that they can vary the speed of the engine according to load, and even under high load are usually designed to spin at a lower speed than non-inverter generators.

I'd love to see the Onan inverter-generator offered as an option for all Thor models that have a generator of the appropriate size.
Onan is changing their RV offerings. New is the QG2800i A variable speed, inverter model. The plan is to offer inverter options on all gas models up to 7,000 watts. The MSRP is $3,800 for the QG2800i model. The 5,500 watt and up models will continue to be available in evap or fuel injection models with EFI coating about $150 more. I have head that a KY will have EFI option also.
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Old 09-15-2021, 01:05 AM   #18
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Originally Posted by 16ACE27 View Post
It would never be used on an RV generator as the converter always has a load on the AC circuit so an "auto-idle" would never happen as it changes the output frequency and voltage. Now inverter generators that have an "ECO" mode that reduces the speed of the generator to match engine power to drawn electrical power is where the RV world is finally headed after Honda, Yamaha and others have had this feature for at least 2 decades. I even carry a first generation Honda 2000 on trips that I'll be boondocking for several days as it can carry any load in the MH but the big A/C and continuously charge the batteries in ECO mode with a lot less noise than the Onan 4K.
Auto-idle and eco-mode are the same thing
Different manufacturers use different lingo

Bottomline…the generator runs at a lower RPM when loads are lowered.

Example: There are times in my coach where 4amps, a low draw is being pulled.
In that case, the generator would run at or just above idle speed.

Then when the AC or Microwave is on, generator runs at a higher speed.
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Old 09-15-2021, 01:07 AM   #19
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Old 09-15-2021, 01:32 AM   #20
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Quote:
Originally Posted by Scubawise View Post
We have a 2019 Cummings 4000 gas generator.
My wife was asking if any modifications to reduce noise in coach?

I said the experts here may know
So is this an item that should be on the Top Things I Hate ( I mean improve ) list ?

You may wish to define your current noise level. I bought an inexpensive sound level meter and found my 5500 to be a quieter than portable inverter generators. I measured at 10 ft away.

Week before last while driving from Memphis, TN I thought I was getting hot, and I could not see the light on the genset wall to tell if was so my wife goes back and look at the controls but was confused because both ACs were off; she knew they were suppose to be on because the genset was saying Auto Mode. Since I am driving, I was kind of helpless so I asked her could she hear the generator and she said no So I pull over and sure enough the genset was running and she could not hear while driving with both ACs off. Now the only time I know we can hear our generator use to be BEFORE we got the new AGM batteries. Our Genset would start up at 7:00 AM every morning with no shore power, we could feel the vibration more so than the noise, but you could hear it.

When we tailgate ( which I do a lot), unless you go on service side of RV you will never know the genset is running.
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