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Thread: Engine noise abatement

  1. #71
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    Default Re: Engine noise abatement

    Oh. Yeah, I don’t know how the mics would compare on the two iPhones. Mine is an SE, I like the small form factor.

  2. #72
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    Default Re: Engine noise abatement

    Any consideration for a directional microphone to try and locate the source?

  3. #73
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    Default Re: Engine noise abatement

    Okay, I bought some stable mats. My pilothouse is about 5’x8’ so I got two 4x6 mats. Now comes the work. These things are a nightmare to handle. First I’ll make a pattern including the cutouts for the stack, chair pedestal, focs’l companionway, etc. Then some serious cutting, (like Favorite said, these things are 3/4” of recycled tires), then wrestling these things down the dock and into the pilothouse. Another problem is I have to be able to access the engine thru a floor hatch. So this mat has to have a seam where I can hopefully roll it away from the hatch. But I think the idea is correct and I expect an improvement. It’ll be a few days before I can get to it, but I’ll post some results when I do.

  4. #74
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    Default Re: Engine noise abatement

    This morning I made the patterns and got about half of the stable mat cut, but not yet on the boat. The good news is that this stuff is easier to work with than I expected. It cuts very easily with a jig saw with a fine carbon blade (Blu-Mol 10 tpi) as long as the material is well supported. I put 2x2s under each side of the cut, and then a couple more 2x2s 10-12” away so it would not sag away from the cut. It also drills nicely with forstner bits and hole saws for larger openings. The sawdust is course granular with no flying dust. And the material does not heat up or try to melt, I used one blade all day with no clogging or filling. Adjacent cut edges lay tightly against each other so as a result I felt I could cut a section over the engine access hatch. I cut interlocking keys so they will stay in position. Because the material is black, it is hard to mark cut lines, I ended up just spraying a little white paint along the edges of the pattern which worked well. So about half of the pilothouse floor is ready to take to the boat, but I’m too beat to do that now. Looking forward to getting it all installed and bringing out the decibel meter again.

  5. #75
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    Default Re: Engine noise abatement

    The results are in. I finished installing the stable mat on the pilothouse floor today. It was a much bigger project than I expected mainly due to the cutting and fitting around fittings and furniture, couple with the weight and immobility of the material. As explained earlier, I used several different decibel meters that varied widely. I decided to settle on two that are accepted by the industry. So the results as follows:

    SPLnFTT meter: Before mat = 80.0, after mat = 76.5
    NIOSH meter: Before mat = 82.4, after mat = 78.5

    So the average improvement is about 3.7 dB quieter. Not a great deal to shout about, but any improvement is good. And when you realize that decibels are measured on a log scale, 3.7 decibels is better than nothing. I took a lot of care to reduce the variables in my testing so I’m confident in the improvement even tho it was not as much as I hoped for. The material was about $100, the rest was just aches and pains of this old body.

  6. #76
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    Default Re: Engine noise abatement

    The 3/4” stable mat cuts pretty easily with a jig saw. The trick is to support the material on both sides of the blade. Also hole saws and forstner bits work well.

    D6051C74-5FA9-4D2B-8666-D1ED0BD19DE0.jpg

    Here is about out half of the mat cut into manageable sections and holes for the stack, chair pedestal, and various other required openings.

    4B223CA4-B391-4181-8353-BC592F6CCCB6.jpg

  7. #77
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    Default Re: Engine noise abatement

    Is a 3-4 dB reduction enough that you can detect it by ear? I would think so. Anything helps when stretched over a long day motoring I'm sure.

  8. #78
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    Default Re: Engine noise abatement

    Quote Originally Posted by J.Madison View Post
    Is a 3-4 dB reduction enough that you can detect it by ear? I would think so. Anything helps when stretched over a long day motoring I'm sure.
    It is slightly noticeable, but it’s more like the type of sound changed. It just seems a bit more mellow.

  9. #79
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    Default Re: Engine noise abatement

    Quote Originally Posted by ron ll View Post
    It is slightly noticeable, but it’s more like the type of sound changed. It just seems a bit more mellow.
    That's a key piece IMO - not just the level, but the type of sound. Glad to hear (so to speak) that it made at least some difference!
    "If it ain't broke, you're not trying." - Red Green

  10. #80
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    Default Re: Engine noise abatement

    As a coincidence, I had a hearing aid appointment with my audiologist today. She offered to check the calibration of my decibel meters in a sound booth. Turns out my SPLnFTT iPhone meter app is the most accurate. It’s also the one that reads the lowest improved level of 76.5 dB, which she says is a pretty safe level.

  11. #81
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    Default Re: Engine noise abatement

    When you run the engine at the dock, do you notice a checkered rippling of the water? Where that water feature starts points to where the vibration is transferred to the hull, and by extension, to the house.

    If you have a couple of 5 gallon buckets fill on with water and experiment with placing it at different points on top of the wheelhouse roof. If it shows some improvement, add the second bucket. It has the effect of deadening the drumhead. If you notice a difference you can install lead or other material to absorb the sound short. A lot of old trollers the size of Snoose noticed big differences in cabin noise once fishing gear or life rafts were placed on top of the roof.

    But at the end of the day, they call them a screaming jimmy not a whispering jimmy...

    Chris
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  12. #82
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    Default Re: Engine noise abatement

    3-4 Db ...

    Quote Originally Posted by ron ll View Post
    It is slightly noticeable, but it’s more like the type of sound changed. It just seems a bit more mellow.
    Similar here ... but in practice, I think the reduction is larger than it appeared. For instance, I can talk on the phone now, and hear the vhf. Before, I could not. It still seems loud but no longer gives me a headache. You may (I hope) find the new Snoose Noise Level similar.

    http://www.asiproaudio.com/soundproo..._reduction.htm

    I've got a box around a goodly portion of the engine, plan to damp that with the same material ... if I could get another 4 dB I'd be pretty happy.

  13. #83
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    Default Re: Engine noise abatement

    Thanks Favorite for all your help. The stable mats were a good idea. Of course I was hoping for a bigger drop in dB but in the real world it doesn’t work that way and that table you linked to shows why. But overall I’m happy with the result and in spite of my grousing about the work, it really wasn’t that much and fairly cheap. So far I’ve only tested at the dock, but I hope to get a sea trial in in the next few days.

    @Chris-on-the-boat, thanks for the ideas. The water buckets on the roof will be an easy test and especially now that I have a good baseline and trustworthy meters. I had never thought about watching the vibration in the water, I’m anxious to try that.

  14. #84
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    Default Re: Engine noise abatement

    I'm glad to hear that you are making progress on the noise abatement problem, Ron. Regarding the buckets on the roof, per my suggestion in post #10, flat & heavy on the roof will do a great deal to reduce the resonant-frequency noise in the wheelhouse. The stable mats are a good substitute for more expensive marine sound dampening mats.
    Hope for the best, but plan for the worst.

  15. #85
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    Default Re: Engine noise abatement

    Quote Originally Posted by mmd View Post
    ... per my suggestion in post #10, flat & heavy on the roof will do a great deal to reduce the resonant-frequency noise in the wheelhouse.
    For me, and maybe Snoose is similar, the biggest noise-transmitting area now seems to be the forward bulkhead of the wheelhouse, which is in direct contact with the engine room. Unfortunately there's all kinds o stuff bolted to it, like all the electrical But I would not be shocked if that area was the next most productive place to attack.

  16. #86
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    Default Re: Engine noise abatement

    Michael, yes I neglected to mention the others on this thread who suggested the weight on the roof, my apologies. I certainly have been thinking about it, just haven’t tested it yet. Initially I kind of dismissed it because two years ago I added epoxy bedded 1/4” plywood and glass on that roof and it didn’t seem to change much. Of course that may have just contributed to a more resonant drum head. Also now with the calibrated meter and reduced variables, the testing will be more informative. As far as the stable mat just being a cheaper alternative, I already have 2” lead-lined foam under the floor, and 1/4” lead/rubber sound mat on top of the floor. But neither of those cover the entire area as I did with the stable mat. And I still have several leaks I can do a better job with.

    Favorite, on Snoose the forward bulkhead is not that connected directly to the engine room and doesn’t seem to be generating the noise as much. The next project for me will be more barrier between the engine room and aft cabin.

  17. #87
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    Default Re: Engine noise abatement

    Quote Originally Posted by J.Madison View Post
    Is a 3-4 dB reduction enough that you can detect it by ear? I would think so. Anything helps when stretched over a long day motoring I'm sure.
    It's a logarithmic scale. A 3db reduction is a halving of the noise energy IIRC, across the entire bandwidth of the sound meter - which will be better than your Mk1 eardrum!
    The way an individual perceives the noise reduction will depend a bit on how much of the noise energy is contained the band of frequencies that you personally can hear, which depends in part on how much hearing loss you've suffered over the years.
    I am pretty sure some sound level meters can be set to either respond to everything, or alternatively, mimic an idealised human hearing capability.

    Pete
    Don't underestimate the power of stupid people in large numbers!

  18. #88
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    Default Re: Engine noise abatement

    Most sound meters I have been using are set to dBa by default, which weights the human hearing range.

  19. #89
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    Default Re: Engine noise abatement

    Back in the day, sound measurements referenced to human hearing perception rendered these as 'psophometrically weighted' in ITU (Intl. Telecomms Union, Geneva) jargon ....the USs AT&T referred to the same as 'C-Weighted'.....just as an aside...

    Your determination at reducing engine/drivetrain noise in your boat is commendable.

  20. #90
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    Default Re: Engine noise abatement

    Ok, an update here. I'm up in Blaine today and had a chance to test the noise level on Skookum Maru. Using the NIOSH meter on an iPhone X I get about 76.5 dB. Assuming that we can compare readings from the same app between our phones that makes Skookum Maru a bit quieter than Snoose but not dramatically so. The thing I notice though is that the noise is not at all unpleasant. It's just a rumble that tends to blend in after a while. Which opens up an entirely new area of investigation - sound quality versus volume. A couple of examples come to mind.

    There is a law office in my building that regularly shreds large numbers of documents. They hire a company that parks a truck right under my office window every few weeks and runs that d****d shredder for a couple of hours straight, right when I'm trying to concentrate. It's not really that loud but something about the noise just crawls under my skin. I use noise cancelling headphones when it's running bue even so. It's a public nusiance.

    Then back when I had an office downtown by the Pike Place Market, one summer there was a guy learning to play the saxophone who would practice in the park every afternoon. Again, not all that loud and we were a full block away from the park, up a steep hill and on the fourth floor of the building, but something about the arrangement of the buildings created an acoustic corridor that piped that sax right into the office. Same scales over and over and over and over. It went on for weeks.

    Have I mentioned that I'm sensitive to noise?

  21. #91
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    Default Re: Engine noise abatement

    I too have noticed the difference in the sound quality on Snoose since installing the stable mats. While the decibel difference is relatively minor, for some reason it is just not quite as annoying. The other thing that both Kathy and I noticed is that there now seems to be a bigger difference when donning the Bose noise cancelling headphones. Not sure why that would be but the difference now seems more dramatic.

  22. #92
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    Default Re: Engine noise abatement

    Quote Originally Posted by ron ll View Post
    I too have noticed the difference in the sound quality ...
    The throaty rumble of Skookum made me wander over while Chris was checking sound levels ... I'm thinking that at this point, your distress must be more frequency-oriented than volume-oriented. If Snoose's 76 Db is the same as Skookum's 76 Db (I don't know how accurate iPhone testing is !), it must be the quality rather than the quantity, because Skookum is quite pleasant. I am green with envy when he fires up.

    When I was researching this, the next best material was suppsed to be either carpet or cork. THICK cork, as in 1" thick. And the carpet had to be high thread count with an open weave in back, placed over something absorbent rather than reflective. Persian carpet was the best

    The complaint of sound engineers with cork was that it absorbed the higher frequencies but didn't do as much for low frequencies. For their purposes that was not acceptable but seemed like it might be pleasant on a boat. I wish Favorite sounded more like a locomotive, a low rumble. Maybe cut a 6-110 in half to make a 3-110

    Anyway, thick cork is available, not too expensive, and a lot lighter to handle than the stable mat. I bet it doesn't work as well, either, but perhaps for absorbing the higher frequencies, it would do what you want ?

  23. #93
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    Default Re: Engine noise abatement

    Thanks to an idea PM’d to me by Favorite, I opened on of the pilot house windows while cruising the other day. The decibels dropped by about 3 points. That was only one window out of nine that will open. It’s not very practical to steam with all windows open, but it points to a source of the problem. If only someone made sound absorbent glass.

  24. #94
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    Default Re: Engine noise abatement

    Switch to polycarbonate or better yet PETG.

    Bed it (or your glass) in something shock absorbent like Sika or butyl tape.

  25. #95
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    Default Re: Engine noise abatement

    Quote Originally Posted by Gib Etheridge View Post
    Switch to polycarbonate or better yet PETG.
    Just did a little looking .... studio people recommend against plexiglass and for heavy thick glass, two pieces with an air space, the two pieces of different thickness and possibly one or both of them slanted in relation to the rest of the surfaces.

    Not very practical, maybe

    Bed it (or your glass) in something shock absorbent like Sika or butyl tape.
    Possibly the problem is that the noise is being generated *inside* the wheelhouse. In a recording studio the noise is in the room, you want the glass to damp transmission into the booth. But if our noise is in the booth, we're screwed.

    Thicker glass is maybe a good idea regardless, tho.

    Kind of interesting that dropping just one window makes so much difference. I noticed the same thing. All the noise isn't escaping through that window like a confused starling .... something is going on here, and I don't know 'zackly what it is, Mr Jones.

  26. #96
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    Default Re: Engine noise abatement

    Quote Originally Posted by Favorite View Post
    Just did a little looking .... studio people recommend against plexiglass and for heavy thick glass, two pieces with an air space, the two pieces of different thickness and possibly one or both of them slanted in relation to the rest of the surfaces.

    Not very practical, maybe


    Possibly the problem is that the noise is being generated *inside* the wheelhouse. In a recording studio the noise is in the room, you want the glass to damp transmission into the booth. But if our noise is in the booth, we're screwed.

    Thicker glass is maybe a good idea regardless, tho.

    Kind of interesting that dropping just one window makes so much difference. I noticed the same thing. All the noise isn't escaping through that window like a confused starling .... something is going on here, and I don't know 'zackly what it is, Mr Jones.
    I would think it'd be reflection, as sound will reflect off hard surfaces after all. When the surfaces are parallel, the sound would bounce back & forth. Drop a window & it breaks the "cycle".
    "If it ain't broke, you're not trying." - Red Green

  27. #97
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    Default Re: Engine noise abatement

    Opening the window changes the resonant frequency of the enclosed space, causing some frequencies to cancel each other out, robbing the sound of its energy.
    Hope for the best, but plan for the worst.

  28. #98
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    Default Re: Engine noise abatement

    Quote Originally Posted by mmd View Post
    Opening the window changes the resonant frequency of the enclosed space, causing some frequencies to cancel each other out, robbing the sound of its energy.
    Quite likely. But the trick is, how to do this in the winter months without freezing your ass off

  29. #99
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    Default Re: Engine noise abatement

    Quote Originally Posted by Favorite View Post
    Quite likely. But the trick is, how to do this in the winter months without freezing your ass off
    https://voltheat.com/products/5v-hea...RoCpbsQAvD_BwE
    "If it ain't broke, you're not trying." - Red Green

  30. #100
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    Default Re: Engine noise abatement

    How very... literal.

  31. #101
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    Default Re: Engine noise abatement

    Quote Originally Posted by cstevens View Post
    How very... literal.
    I was just trying to be helpful Chris!
    "If it ain't broke, you're not trying." - Red Green

  32. #102
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    Default Re: Engine noise abatement

    Sounds like (sorry; excuse the pun) you have to change the resonant frequency of the cabin volume. While I agree that the glass is probably a large contributor to the problem, isolating or insulating them will be problematic. The other problem is that the best sound attenuator is weight. Any chance of being able to insulate one (aft, maybe?) or several wheelhouse bulkheads with that stable mat stuff? Or at least temporarily fit some to a bulkhead to see if it makes a difference?

    I am sure that this is an instance in which you wish that you weren't a good example, but you are now finding out just how pernicious a problem noise is aboard a boat. As a cautionary tale for others, this is why noise control needs to be addressed prior to beginning construction.
    Hope for the best, but plan for the worst.

  33. #103
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    Default Re: Engine noise abatement

    Quote Originally Posted by Garret View Post
    I was just trying to be helpful Chris!
    And you were! In a very literal way

  34. #104
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    Default Re: Engine noise abatement

    Quote Originally Posted by Garret View Post
    I was just trying to be helpful Chris!
    I wonder how much heat those can produce ? What's USB power, about three milliwatts ? You could probably make more heat eating beans and lighting the methane

    At this point, if I were wealthy and Snoose's owner, I'd look into those lead-lined blankets they put over diesel engines. Stop the noise before it gets into the wheelhouse ... won't do much for structure-borne vibes but has to help with the airborne ones.

    And open a window

  35. #105
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    Default Re: Engine noise abatement

    Here's another little progress report - I don't have an iPhone so no Apple sound meter but ...

    There's one area of the forward bulkhead in the wheelhouse that is shared with the engine room. It's about 12" x 36". Double wall, tongue and groove each side with about a 2" space between that the windows drop down into. After matting the floor, I noticed the buzziness from the forward bulkhead. Previously it was too loud to hear that

    Anyway, matted that area inside the engine room, so not really damping the vertical surface of the wheelhouse itself, just a wall that was connected to another wall. What the heck, can't hurt to try, right ?

    I went out today with a friend who brought along an infrared heat meter to check my temp gage (luckily the gauge or sender is bad, was not looking forward to thermostat replacement) and I thought he was running about 1200, where I run it. Seemed quieter, was happy. Came up and looked at the tach, we were running 1350 and it was still quieter than it hade been at 1200.

    So maybe anything you can do to damp the vertical surfaces of your wheelhouse will help. I used screws and silicon caulking to give the mat some adherence to the bulkhead. I'd have tried green glue if it were easier to get.

    No miracles promised but something else to try ...

    (I'm still going to line the engine box, too. Have 20 ft2 of mat hanging around, may as well try. The steel engine room sole would be the next logical place to damp but I like the red diamond plate too much
    Last edited by Favorite; 05-15-2019 at 12:43 AM.

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