Engine air intake silencing ...some trials

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pcatterall

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Engine intake noise reduction- some tests


There has been some discussion aboutreducing the noise of marine engines by reduce the noise around theair intake.
One particular engine discussed was thePerkins 4108 many of which have no air box or filter fitted.
There have been quotes suggesting thatreductions of up to 8 decibels at cruising revs can be achievedequating to a real world situation where the noise from a heavy lorrybecomes equal to a quiet car!!


I decided to test some of the ideasusing an Eberspacher d4 heater which was set up on my bench
( clearly not a 4108 but some of theprinciples will apply!!)


I used a noise level indicator app onmy tablet to measure the noise so accuracy may be suspect but theindicated differences were my main interest.


My measurements are below


Ambient noise levels in shed 33db (outside 40db) Building is a well insulated brick built 'shed'


1) Near the heater no exhaust orintake silencers 60db

  1. Near the heater with exhaust hose ( led outside) 55db
  2. As above but with 5 feet of inlet hose fitted 50db
  3. At the inlet end of the inlet hose 54db
  4. As in 2 above and with the 'official' Eberspacher inlet silencer fitted 50db
  5. At the inlet end of the official inlet silencer 53db


Conclusion.....The inlet noise isconsiderable being, in this case the same as the non-silencedexhaust.
Fitting a long inlet hose moves aconsiderable sound source away from the engine though only to the endof the hose.
The official silencer has a realreduction in noise in the order of 3db.


Other observations.
People have commented that the long airinlet pipe will require sound insulation but other measurements weremade around the mouth of and then down the length of the pipe whichindicated that most of the noise generated was close to the sides andfront of the inlet mouth.


I also measured effects on the exhaustside of the heater



  1. exhaust off inlet pipes off 60db
  2. exhaust off inlet pipe on 58db ( looks small but significant)
  3. mouth of exhaust ( outside building) 60db then with steel silencer 56db (felt like more)


I wonder if the end of a long inlethose could be sited where the noise was less intrusive?
I wonder ( and will experiment) if abetter ( funnel?) shaped 'nose' on the inlet pipe would reduceturbulence around the mouth of the inlet pipe.

Clearly this is not a very comprehensive or accurate test but the figures are better than 'just impressions' and may stimulate some informed debate.

What else does one do on a wet bank holiday sunday!!??


 
Interesting,I have looking at methods of making my perkins perama a bit quieter. The noise in my wheelhouse with the engine running at 2000 revs is 85db,according to the noise meter on my phone. I have insulation in the engine box but that only reduced it by around 5db. The main noise is coming from the air intake which is just a straight box like pipe. Not sure of the accuracy of the db meter on my phone as even in a quiet room it reads 20 db.
 
chrishelen said:
Interesting,I have looking at methods of making my perkins perama a bit quieter. The noise in my wheelhouse with the engine running at 2000 revs is 85db,according to the noise meter on my phone. I have insulation in the engine box but that only reduced it by around 5db. The main noise is coming from the air intake which is just a straight box like pipe. Not sure of the accuracy of the db meter on my phone as even in a quiet room it reads 20 db.
Click to expand...
Your sound proofing reduction of 5db is actually significant 85 down to 80 is a large decrease ( don't forget the change is not linear)
the reading of 20 is very low a room with no outside noise penetrating.
You will find other threads where Perkins owners are fitting air boxes and filters from vehicles such as the Ford Ranger. This unit is big and I will struggle to find somewhere for it to sit but if I get a useful noise reduction then I will find somewhere.
 
Yes is suppose 5db is a result, it cost a lot of money for the sound proof sheets so I was expecting a bit more than that, but I guess where do you draw the line in soundproofing? I could have done under the decks and beyond. Plan b is to stifle the air intake.
 
The Eber study is a really interesting one, producing a big sound reduction for such a small change in set up. Do I dare remove the air filter box on the new engine and then out it back on to get a comparision? I'll see how quiet it is first!
 
I have a Nanni 4.150HE of 38hp. It also has no air filter, just an air box. Has anyone fitted an auto type air filter to one of these and experienced a noise reduction, without a loss of power?
 
100_5292.jpg

Here is a cheapo go faster filter I bought. I will try it on my perkins but bought it really for the reduction connector ( 75 to 60mm) and the solid bit of pipe with the short hose plugged in so I could just join this to my crankcase breather. I expect to be using those bits to help connect my Ford Ranger air box. I will report on the noise!! ( and how much faster we will go!!?)
 
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