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Old 08-21-2014, 11:04 AM   #1
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Intake Air Silencer - Noise Reduction

I just completed a major upgrade of my engine compartment which included new soft engine mounts, Soundown insulation on every interior surface, new hatch gasket and completely isolating the water lift muffler and exhaust piping with rubber mountings. It helped a lot, but during the process, I noticed that the intake tract was a major source of engine noise.

Now, I'm looking for ideas on how to silence that intake noise on my 56hp Yanmar 4JH3E diesel. It is equipped with a very basic pot-shaped air cleaner with a perforated screen (no foam) and a short snorkel. I have measured the intake noise with a meter and it is loud.

Installing/fabricating some sort of Intake Air Silencer has been mentioned in a number of posts, but no specifics have been offered.

Walker manufactures an AirSep for marine generators of up to 35KW which is supposed to reduce intake noise. It has sufficient air flow capacity for my Yanmar, but at $450, it is a bit pricy.

Cummins Fleetguard offer a number of plastic air filter/silencer assemblies that could be adapted fairly easily, but there are no specs as to what kind of sound reduction they might provide, only that the do quiet the intake tract.

I noticed some rather elaborate air filter/silencers on some recent Next-Gen marine generators. They use Kubota power and what looks like the Fleetguard filter or something similar.

I have found some references to silencing the intake noise on stationery diesel generators, but this was mostly limited to baffling the openings in the enclosures.

I ran across this post somewhere on the Internet that seemed right on point:
"On my Onan/4-cyl Kubota setup, I installed a Kubota tractor round type canister air cleaner. I then took the weather cap off the air intake and put a 1 inch silicone hose and 90 degree elbow that turns the air intake down towards the base of the generator. That pretty much eliminated the intake noise. The trick is to make 90 degree turns to trap the noise inside the intake pipe. Using a rubber hose such as silicone helps take the resonance out of the intake."

Some of the diesel pickup truck performance forums talk about removing the baffles in the intake tract to allow more noise, so I assume that some sort of baffling could be effective if properly done.

If anyone has any actual experience with sound attenuation of the intake noise produced by marine diesels, I would appreciate your comments or ideas. I'm sure all of us could benefit if there is a simple, effective solution to this particular issue.

OTOH, I don't want to experiment my life away on this, ear plugs are cheap . .

Larry
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Old 08-21-2014, 11:19 AM   #2
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You might look in Grainger or McMaster Carr at compressor intake silencers, they come in all sizes and are specifically for silencing but have a pleated paper filter as well.
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Old 08-21-2014, 11:33 AM   #3
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You might look at K&N filters first and see if you could remove that horn like filter housing you have now and replacing it with a large K&N. A lot of the noise may be due to the shape/nature of that housing.

What does it sound like if you run the engine without that house on it?
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Old 08-21-2014, 11:43 AM   #4
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I do not remember the brands but I have used intake silencers on stationary generators with great results. I think but am not sure but the name Maxim comes to mind.

The ones I used actually liked like a regular industrial exhaust muffler, and were made by muffler manufacturers.
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Old 08-21-2014, 12:01 PM   #5
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Walker AirSep? There is one on our Cummins and, combined with a high rise exhaust muffler and soundproofing, its pretty quiet.
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Old 08-21-2014, 12:02 PM   #6
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You might look at K&N filters first and see if you could remove that horn like filter housing you have now and replacing it with a large K&N. A lot of the noise may be due to the shape/nature of that housing.

What does it sound like if you run the engine without that house on it?
It is even louder without it. By the way, Yanmar refers to that piece as an "Intake Silencer" so I guess it does serve a purpose, but it is still awfully loud.

I ran across pictures of Yanmar stationery generators that had much larger Intake Silencers so at some level, it must be an issue that the engineers have addressed.
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Old 08-21-2014, 12:10 PM   #7
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Hello TF People,

First post.

I have the 3 cylinder version (3JH3E) of LarryM's engine and concur that the noise emanating from the intake is considerable even with the stock intake silencer (no filter) fitted.

Just last week I started experimenting with some homemade silencer ideas. Unfortunately, the first attempt was a complete failure at attenuating the problem frequency (low drone).

It is just a baffled box made of heavy weight foam rubber (1 inch thick). I suppose it might work better if the whole thing were encased in a hard shell that would minimize "druming" of the outer panels. Gut feeling tells me that I am on the wrong track. I will now abandon this first concept.

Here is pic taken just before I glued the lid in place. I look forward to finding the correct solution to this problem.

Steve

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Old 08-21-2014, 01:35 PM   #8
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a simple quick upgrade that may or may not work is Auto Zone or equivalent and find a cheap air filter you would consider as a permanent setup that has about the right sized intake opening...fins a piece of 90 degree hose that allows you to turn it down like the one post described. The filter and hose shouldn't cost $20.
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Old 08-21-2014, 01:40 PM   #9
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Greetings,
Mr. P. Welcome aboard.
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Old 08-21-2014, 01:44 PM   #10
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Installed a Walker AirSep on our previous boat on a 56HP Perkins. Didn't seem to make the least bit of a difference. I was very disappointed with the unit. It is also supposed to help reduce oil leaks by creating a negative pressure in the crankcase. Again, I noticed no difference, the venturi in the intake was so large for the size of the engine that it could not possible have created any vacuum.

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Old 08-21-2014, 01:53 PM   #11
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Installed a Walker AirSep on our previous boat on a 56HP Perkins. Didn't seem to make the least bit of a difference. I was very disappointed with the unit. It is also supposed to help reduce oil leaks by creating a negative pressure in the crankcase. Again, I noticed no difference, the venturi in the intake was so large for the size of the engine that it could not possible have created any vacuum.

Bob
Bob,

Thanks for the heads-up on the Walker AirSep. I would hate to spend $450 only to come to the same conclusion you did.

That is exactly the kind of feedback I was hoping for. Often, knowing what NOT to do or try, can be almost as helpful as an actual solution . . . .

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Old 08-21-2014, 02:08 PM   #12
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Hello TF People,

First post.

I have the 3 cylinder version (3JH3E) of LarryM's engine and concur that the noise emanating from the intake is considerable even with the stock intake silencer (no filter) fitted.

Just last week I started experimenting with some homemade silencer ideas. Unfortunately, the first attempt was a complete failure at attenuating the problem frequency (low drone).

It is just a baffled box made of heavy weight foam rubber (1 inch thick). I suppose it might work better if the whole thing were encased in a hard shell that would minimize "druming" of the outer panels. Gut feeling tells me that I am on the wrong track. I will now abandon this first concept.

Here is pic taken just before I glued the lid in place. I look forward to finding the correct solution to this problem.

Steve

Steve,

What a shame, that looked really promising! Baffling is often mentioned as an effective way to attenuate diesel intake noise.

Are you absolutely certain the 'drone' is emanating from the intake? The JH Yanmars with 3" exhaust can set up quite a resonance in the exhaust system that can be felt and heard throughout the entire boat.

I use the 'dB Meter Pro' app on my iPhone to measure the dBA levels. It would be interesting to know the before and after measured right at the intake on your diesel. Most of the research I have done indicates the intake noise is normally second behind exhaust. Third place is the injection and combustion noise, but I imagine this is highly subjective and very dependent upon the engine and how and where it is mounted.

Keep us posted on your trials and progress.

Larry
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Old 08-21-2014, 02:58 PM   #13
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Greetings,
Mr. P. Welcome aboard.
Thanks,

Good to be here. Hope the boat not being Trawler is OK. I do a lot of motoring if that helps.

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Old 08-21-2014, 03:12 PM   #14
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Just a somewhat remotely mounted automotive muffler connected by an accordion like tube of sufficient ID should work fine. One could paint the outside of the muff w POR-15 or whatever and replace it when needed.

Simple and cheap.
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Old 08-21-2014, 03:20 PM   #15
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.......Are you absolutely certain the 'drone' is emanating from the intake? The JH Yanmars with 3" exhaust can set up quite a resonance in the exhaust system that can be felt and heard throughout the entire boat.........
Larry,

I bet the noise is coming from multiple sources. I agree that the exhaust is definitely a big part of the problem.

The "test" that I did that convinced me that the intake is a significant noise source was to simply place my hand over the intake such that only a small slot (between fingers) remained. It was like night and day - no hand = drone, hand in place = drone gone.

Of course this "test" was performed with the sensing equipment (my ears) hovering right over the exposed engine. It is possible that the "drone" that I hear when seated in the pilot house is coming from another source.

I have noticed that things that are designed to be loud (megaphones, trumpets, horns, etc.) all have a long tract that gets wider the farther along the direction of sound travel. I also notice that the intake snorkel on my Yanmar silencer (and the air-cleaner on older automobiles) is built in the opposite way (long tract that gets narrower the farther along the direction of sound travel).

Next experiment will explore some sort of large cone. Basically just like what Yanmar has done - only larger.

I am sure that an acoustical engineer would save me a lot of messing around.

Steve
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Old 08-21-2014, 03:35 PM   #16
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Greetings,
Mr. P. "...Hope the boat not being Trawler is OK..." No problem from my end. The addition of a pilothouse had me thinking it was a motor sailor initially. You'll see the error of your ways eventually.....
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Old 08-21-2014, 03:35 PM   #17
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Just a somewhat remotely mounted automotive muffler connected by an accordion like tube of sufficient ID should work fine. One could paint the outside of the muff w POR-15 or whatever and replace it when needed.

Simple and cheap.
That would certainly be worth a try. Thanks.

Steve
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Old 08-21-2014, 03:43 PM   #18
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You'll see the error of your ways eventually.....
I suppose you are correct.

For now, it is all very clear to me:

Transportation = Engine (88% of the time).

Recreation = Sail.

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Old 08-21-2014, 04:57 PM   #19
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You might look in Grainger or McMaster Carr at compressor intake silencers, they come in all sizes and are specifically for silencing but have a pleated paper filter as well.

Like these Solberg | Filter Series Detail | FS Series 1/2"-6" Filter Silencers
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Old 08-21-2014, 05:04 PM   #20
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Greetings,


Recreation.
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