Adding a 2nd muffler on a JD 790

[Diamondpilot]

I would be worried about back pressure problems with a second muffler.

Chris

 

[patrick_g]

There are noise canceling headphones like Bose etc (consumer grade) and there are NOISE CANCELING HEADPHONES, pro grade such as are sold via Sporty's pilot shop and the like.

Sporty's Home Page

Not cheap but effective.

Pat

 

[crashz]

The newer 790s and the 3005 have the exhaust routed to the front, under the engine compartment. I'm not sure if this is any better at reducing noise, but will allow easier attachement of a second muffler and will get the noise further from you.

You may also be unterested in using a sound deadening material on the side panels and hood to isolate engine noise.

 

[patrick_g]

Lead loaded foam is very effective for noise reduction. I used it to surround an Onan 12.5 KW air cooled diesel genset I mounted in a Helicopt Hut (environmental enclosure that fits on a deuce and a half) next to the two equipment operators (computer controlled microwave test gear.)

You can buy it in various thicknesses, with or without a thin layer of lead sandwiched in. They put fine lead powder in the foam acoustic insulation and it has a very high coeficient of extinction at frequencies of interest.

Pat

 

[kebo]

Lead loaded foam is very effective for noise reduction. I used it to surround an Onan 12.5 KW air cooled diesel genset I mounted in a Helicopt Hut (environmental enclosure that fits on a deuce and a half) next to the two equipment operators (computer controlled microwave test gear.)

You can buy it in various thicknesses, with or without a thin layer of lead sandwiched in. They put fine lead powder in the foam acoustic insulation and it has a very high coeficient of extinction at frequencies of interest.

Pat

Pat, is it pricey? Where can you buy it at?? Is it fairly heat resistant? Any danger of the lead leaching from the material? I guess you would want to wear gloves while handling it??

I had thought of lining the hood and the two side panels with some of that insulation that you used to see underneath car hoods. I'm sure it would help reduce noise being radiated from those three pieces of metal.
Thanks,
Keith

 

[patrick_g]

Keith, It was decades ago that I used the lead loaded foam. I thought it was moderately pricey but it has terrific performance so the price/performance ratio is really good.

The lead is captured in the foam plastic. I suppose if you cut it with a circular saw the dust could be bad but it cuts with a sharp knife too. I'd consider using some of the aluminum coated cloth or similar to protect the foam from the underhood environment. We didn't but after the project shipped I lost track of it and don't know how it held up over the years.

A friend of mine who lived on his twin diesel yacht a few boats down the dock from me when I lived on my sailboat had the wall between the engine room and his stateroom covered with it. It came that way when he bought the boat used so I have no A-B comparison data but from the engineering specs and my general acoustics background I'd say it would have made a very noticeable difference.

Remember, If you can see the muffler, you are going to hear it quite well. Mufflers do directly transmit a fair amount of sound right out through their sides and ends.

A HD steel box built around your current muffler and filled with sand between the box and muffler will deaden the mufflers sound transmission by quite a fair margin. Directing your original mufflers output pipe away from you and away from any reflecting surfaces will help a lot too. These two things may do as much as adding sound proofing under the hood and or a second muffler, not to be necessarily done instead but at least in addition to if not instead.

Finding lead loaded foam??? I'd Google.

I Googled on lead loaded foam and got -->

Soundproofing & Noise Control Materiels Prices

BARRIER: "Super Soundproofing Silencer (MLV) Mass Loaded Vinyl", "Limpid Mass Barrier", a heavy-duty wear resistant "mass loaded" vinyl mat with a foam ...
Soundproofing & Noise Control Materiels Prices - 74k - Cached - Similar pages -

Never underestimate the power of Google!!!

Pat

 

[RWolf]

Question I'd have is what thickness to use. I'm fixing to mount a 4kw onan genset (1800rpm) on my horse trailer and want to deaden the sound.

 

[Egon]

A friend of mine who lived on his twin diesel yacht a few boats down the dock from me when I lived on my sailboat had the wall between the engine room and his stateroom covered with it

Was this not a very common practice for engine compartments on small boats?

 

[Travelover]

...............
Remember, If you can see the muffler, you are going to hear it quite well. Mufflers do directly transmit a fair amount of sound right out through their sides and ends.

A HD steel box built around your current muffler and filled with sand between the box and muffler will deaden the mufflers sound transmission by quite a fair margin. Directing your original mufflers output pipe away from you and away from any reflecting surfaces will help a lot too. These two things may do as much as adding sound proofing under the hood and or a second muffler, not to be necessarily done instead but at least in addition to if not instead.

................
Pat

Sheet lead wrapped over a muffler really quiets it down, too, if you can find some. The exhaust manifold would probably be hot enough to melt it, but not the muffler.

 

[patrick_g]

Question I'd have is what thickness to use. I'm fixing to mount a 4kw onan genset (1800rpm) on my horse trailer and want to deaden the sound.

Richard, There are more issues to consider than thickness of sound dampening material. There are multiple sound paths. The method and materials used to mount the genset to the deck or whatever is also important. Vibration conducted into the deck via the mounts can be re-radiated as sound. To get a really quiet installation yo need more in the way of anti-bration mounts/pads than the ones that come on the equipment. A good Onan dealer should be able to get them or give you a source. If they don't know what I am talking about, don't be too surprised as lots of good ole boys don't.

The anti-vibration mounts go between the packaged unit and the mounting surface. They are are not too expensive for what they do. You need to supply certain information to the vendor of the pads to get the RIGHT STUFF for your needs. You need to tell them how much weight each pad will support (I guess I would assume half a tank of fuel if the tank is built into the unit) and the running RPM of the unit (this tells them the frequency band at which you want the mounts to operate.) These will isolate the vibration of the gen set from the mounting surface and make the installation much quieter.

Next, you can put acoustic dampening material (sound proofing) around the unit. Do be careful regarding the cooling air flow. I am not familiar with the 4KW Onan as I only worked with 12.5KW units. The 12.5's had kits available for shrouding the motor so you could duct the effluent cooling air to wherever.

The lead loaded foam plastic (lead dust in the foam) is a high performance material with greater sound deadening per inch of thickness than fiberglass and similar materials. It works sort of like R value with insulation, thicker is better. Higher performance is attained with thin sheets of lead sandwiched into the material (comes that way from supplier.)

If you have the space and inclination for a DIY project you can get good results for way less $. Build a double wall enclosure for the gen set and fill the space between the walls with sand. We used to do this years ago when we were building big high power speaker enclosures. You don't want the weight of the enclosure and sand supported by the anti-vibration mounts. You want the gen set enclosed by the double wall box but open on the side as needed for cooling air.

You will want the open side aimed away from the area you are trying to keep quiet. I put a louvered panel in the side of the "BOX" I installed the 12.5 into to dump the hot air and let cool air in. Since the intake air is a diffuse current and the effluent air is a strong current, separating the two so you don't recirculate the hot air was easy.

Hope the above helps. Feel free to ask any questions. Google should turn up sources of supply for the lead loaded foam or other acoustic dampening materials. The lead type is high performance but if you have the space a thicker layer of cheaper material may give more bang for your buck.

Pat