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Thread: Engine noise abatement

  1. #36
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    Default Re: Engine noise abatement

    Quote Originally Posted by ron ll View Post
    The results of the first test, not encouraging. I ran 3 tests at 1250 rpm as is, and 3 tests after putting carpet on the overhead. The meter averages the levels, and then I further averaged the averages of each three tests. Without the carpet, the average was 95.87. After tacking up the carpet, the average was 94.57. So a reduction of about 1.3 decibels. Not very significant a reduction at those levels. But carpet is just a test, a permanent application there would be 2” acoustic fiberglass panels, which should improve the results over carpet, but not sure if it would be enough to suffer the ugly factor.

    Yes, I agree the biggest culprit is the hard mounting of the engine as Paul and others point out. Maybe it’s time to really study the soft mounts. It’s overwhelming and beyond my personal abilities, but maybe I should price the task by others.
    The carpet would have worked if it were simply ambient sound reflecting off of the overhead but that's not what's happening. which is why I suggested spraying in expanding closed cell PU. It would completely alter, and probably pretty much eliminate, the vibrating of the diaphragm. The trouble with that is that if it didn't work and you wanted to get rid of it it would be a mess to deal with.

  2. #37
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    Default Re: Engine noise abatement

    Quote Originally Posted by ron ll View Post
    The results of the first test, not encouraging. I ran 3 tests at 1250 rpm as is, and 3 tests after putting carpet on the overhead. The meter averages the levels, and then I further averaged the averages of each three tests. Without the carpet, the average was 95.87. After tacking up the carpet, the average was 94.57. So a reduction of about 1.3 decibels. Not very significant a reduction at those levels. But carpet is just a test, a permanent application there would be 2 acoustic fiberglass panels, which should improve the results over carpet, but not sure if it would be enough to suffer the ugly factor.

    Yes, I agree the biggest culprit is the hard mounting of the engine as Paul and others point out. Maybe its time to really study the soft mounts. Its overwhelming and beyond my personal abilities, but maybe I should price the task by others.

    Those mid 90's decibel readings are way too high to tolerate. You know that's damaging. Something must be done. Meanwhile, wear muffs or earplugs.

    Jeff

  3. #38
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    Default Re: Engine noise abatement

    The intake (blower) on a Detroit can be a large part of the noise.
    It might be worth talking with these guys...

    http://www.walkerairsep.com/product_detail.asp?id=647

  4. #39
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    Default Re: Engine noise abatement

    Quote Originally Posted by Stiletto View Post
    Check out post #28.
    I neglected ot mention in my post (#26) that we did have a before and after reading with a meter and the difference was significant in both the reading and the perceived noise level. Sorry I cannot remember what the readings were, but we were amazed at the change in numbers. Worth a try. They used to have a video on their website, probably there somewhere.

  5. #40
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    Default Re: Engine noise abatement

    Quote Originally Posted by jpatrick View Post
    Those mid 90's decibel readings are way too high to tolerate. You know that's damaging. Something must be done. Meanwhile, wear muffs or earplugs.

    Jeff
    yup. Bose noise cancellers for both of us.

  6. #41
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    Default Re: Engine noise abatement

    Post 33 (the tractor) is a good illustration of post 19 (describing noise transmitted through the structure). You already have lots of soft material to absorb the air borne noise, and you've checked for gaps/holes where sound might leak. Since both of these seem ok it appears the problem is elsewhere, and one possibility is noise being transmitted through the structure. If the engine is soft mounted it can't transmit as much noise to the structure in the first place. The alternative is to create a break in the structure elsewhere by say having your whole wheel house floating on rubber pads... (which is sort of how sound proof studios are built for radio broadcasters) but that seems a lot more difficult than adding something soft at the engine mounts. If you feel that the engine mounts might be implicated, but are daunted about the job, maybe post a picture of the existing mounts here. Someone may have some simple advice on dealing with them.

  7. #42
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    Default Re: Engine noise abatement

    Quote Originally Posted by ron ll View Post
    I ran 3 tests at 1250 rpm as is, and 3 tests after putting carpet on the overhead. The meter averages the levels, and then I further averaged the averages of each three tests. Without the carpet, the average was 95.87.
    96 decibels ?! At 1250 ?

    Hokey smokes, Alfie. I don't think I saw that at 1600, even before the stable mat. The Navy experiment referenced above was mostly in the 80's, with end results in the low 70's at 1800-2100. Favorite is somewhat pleasant at 1200 ... (and Skookum is very quiet, also hard-mounted. So it can be done ... )

    After tacking up the carpet, the average was 94.57.
    Yes, I was not that enthused about carpeting. Most of the resources say carpet is wonderful but we all knew guys that practiced in a garage with carpets all over the walls and you could still hear them six blocks away. Not sure about cork, either. And I am certain that egg cartons don't do diddly

    The stable mat tho, is pretty cheap and easy to try. Did make a measurable difference here. What I noticed was a drop in overall levels then a change in the character of the noise and also a change in where it was coming from. Half the engine is underneath the wheelhouse. Before, the floor was making a racket. After, I could hear the racket coming from the forward bulkhead.

    I do have an Airsep, not sure that makes much difference tho ? The Navy had the air intakes coming in through baffled wooden inlets, that would be fairly easy to do if you have room.

    I did find one place that makes lead-lined engine blankets. They are not cheap. Not sure they work but I guess if they don't and they cost real money, then people would not buy them ? It does seem that if you can kill the airborne noise at the source, that should help. You'll still have the structure of the boat vibrating but ... hmm.

    My engine mounts are one hefty-ass solid thingamajig, like everything on this boat. That might be helping. But 95 db, yikes.

    I would grab a stable mat and throw it down on your wheelhouse sole. It should help some with the noise, and even if it doesn't, it's really nice to stand on, slightly anti-skid, a bit cushy on the legs and knees. Can't hurt and won't be money wasted, unlike $1.50 a square foot cork or cheap carpet.

    If all else fails, the turbos are quieter than the normally-aspirated, so you could add a turbo

    If you ever feel like a trip up north, bring your meter and we can do some comparison tests ....

    Make sure to snag that Navy research paper which DaveMN so kindly found. It has a lot of real test information. Real numbers, real instruments, scientifically-derived information.
    Last edited by Favorite; 04-08-2019 at 12:22 AM.

  8. #43
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    Default Re: Engine noise abatement

    Any chance that the dry stack or heat shield is touching the overhead or bulkhead?
    How is it flashed/waterproofed where it goes outside?
    R
    Sleep with one eye open.

  9. #44
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    Default Re: Engine noise abatement

    I was also surprised at the 95 reading so I did some meter testing. First of all, these are not professional meters but rather apps on my iPhone. The one I was using seems to consistently read 5 or 6 decibels higher than others. Still, even 90 decibels is too high to live with, but at least it gave me a carpet/no carpet comparison.

    @Favorite: good point about your boat and Skookum Maru both being hard mounted and quieter. I think it is time to try the stable mat. Part of the reason I’m resisting it is because it is already really difficult to get to the engine hatch and that will make it a lot more difficult. At some point I might have to redesign the access entirely. And I will definitely study the Navy report. And I need to invest in an Airsep as well. I have what is called a Turbo Silencer, but it is old and decrepit.

    @Ron Williamson: the dry stack is the quietest part of the whole pilothouse. I’ve got a new exhaust stack with two silencers and it has all been professionally wrapped. Wish I could get the inside of the pilothouse as quiet as the outside.

  10. #45
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    Default Re: Engine noise abatement

    Just talked to the Airsep guys, they say they can’t help with noise on a naturally aspirated engine. Their noise abatement is designed for the high pitch whine of a turbo. Bummer.

  11. #46
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    Default Re: Engine noise abatement

    On further testing I’m finding the meter I was using is closer to ten decibels high. So my pilothouse readings at 1250 rpm were closer to 85 decibels. That’s a relief.

  12. #47
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    Default Re: Engine noise abatement

    If you find that the stable mat works that will imply a certain amount of stable genius somewhere on this thread.

  13. #48
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    Default Re: Engine noise abatement

    Quote Originally Posted by ron ll View Post
    I was also surprised at the 95 reading so I did some meter testing. First of all, these are not professional meters but rather apps on my iPhone. The one I was using seems to consistently read 5 or 6 decibels higher than others. Still, even 90 decibels is too high to live with, but at least it gave me a carpet/no carpet comparison.

    @Favorite: good point about your boat and Skookum Maru both being hard mounted and quieter. I think it is time to try the stable mat. Part of the reason I’m resisting it is because it is already really difficult to get to the engine hatch and that will make it a lot more difficult. At some point I might have to redesign the access entirely. And I will definitely study the Navy report. And I need to invest in an Airsep as well. I have what is called a Turbo Silencer, but it is old and decrepit.

    @Ron Williamson: the dry stack is the quietest part of the whole pilothouse. I’ve got a new exhaust stack with two silencers and it has all been professionally wrapped. Wish I could get the inside of the pilothouse as quiet as the outside.
    I recall the thread from a couple of years ago and was thinking that there might be a hard contact conducting noise,at or near head height. Something like a mounting bracket or the exit fitting/flashing on the overhead.

    Our dust collector(10 hp,10' off the floor) needed bearings a few years ago,so when we re-installed it,to align the pipe,I drove a cedar shingle under one corner.

    The next day, my accountant came down from her office complaining about a terrible noise,enough that she had to leave. Standing in her door opening, I heard nothing out of the ordinary, but 30" into the office,it was truly unbearable.

    Since nothing else had changed,I took out the shingle and the noise went completely away.
    100' apart on the same side of a wood building.
    R
    Sleep with one eye open.

  14. #49
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    Default Re: Engine noise abatement

    You remember correctly. But since then the exhaust stack has been completely rebuilt.

  15. #50
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    Default Re: Engine noise abatement

    Right. Post #28 for Paul's comments about sound deadening paint. Thanks.

  16. #51
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    Default Re: Engine noise abatement

    Some observations based on my short experience with Skookum Maru that may help, or not.

    1. Skookum Maru is not exactly quiet, but the noise is not at all objectionable. I ran 13 hours straight from Seattle to Blaine back in September and had no issues with the noise level at all. I don't even remember thinking about it. Noise reduction isn't on my list.

    2. Same engine as Snoose (3-71) running same rpm (~1250) and also hard mounted. But SM's Detroit has low compression "S" kits. I don't know if that would make any difference in noise, but just something to note.

    3. Skookum Maru has a much larger engine compartment. Maybe 12' x 10' x 4', so there is a very large box to dissipate sound before it reaches any cabin space. The engine is also mounted well aft of the helm, but it's not that noisy even standing right above it.

    4. There is sound proofing underneath the salon sole, lining the tanks on each side of the engine and on the aft bulkhead. Standard foil-faced stuff like the Sounddown product. Total thickness under the sole is 3" or so. There is also a rubber pad and a carpet covering the sole right over the engine.

    5. There is a short muffler mounted under the cabin sole immediately after the outlet from the manifold. It's covered by a blanket so I can't determine the type, but it looks like the right size to be a Cowl-type spiral muffler (https://www.miratechcorp.com/cowl-silencers/). I'd note that one of the resources I found *strongly* recommends (insists actually) that a muffler or expansion chamber should be mounted as close to the manifold as possible to control noise from a Detroit.

    6. The engine compartment is very well sealed off from the living space. The overhead extends out to the hull and there are four large air ducts leading to vents on the cabin top for air supply.

    7. The dry stack runs up through the salon in a wooden trunk. It's not very large - maybe 12" x 12" - so there can't be much in the way of sound proofing inside. There is no muffler in the stack as with Snoose. There is the muffler in the engine compartment and then (reportedly) another one in the funnel although Paul says it's in poor condition.

    So, some ideas:

    - Obviously there is nothing you can do about the size of the engine compartment on Snoose or the location of the engine in relation to the helm. But anything you can do to increase the sound deadening between the engine and the living spaces can only help. I'd throw down a couple of layers of stable mat on the sole just to see what it does, and generally double down on layers of insulation wherever possible.

    - You already have external air ducts but they have less than 1/4 of the total area of the ducts on Skookum Maru so it might be worth trying to enlarge them and add baffling and absorbent coating on the inside. There may be sound escaping through the ducts and it comes out pretty close to where people are standing in the pilothouse. I can imagine that sound is being transmitted from the ducts to the pilothouse bulkhead and contributing to the noise you are getting at the top of the house. Not a simple change, I know. I wonder if there is some way to add temporary ducting of some sort to see if it makes a difference? Maybe run a large, temporary duct out through the aft cabin and block off the current ducts behind the pilothouse just to see if if has any effect on noise in the pilothouse?

    - I would also try adding some heavy sound dampening material to the overhead. Can't hurt. Might help. Again I like the stable mat here as a cheap way to experiment before designing something permanent and better-looking.

    - If you have room I think a second muffler in the engine compartment ahead of the muffler in the stack would be worth doing, assuming that you can keep back pressure at reasonable levels.

    Just throwing out ideas...

  17. #52
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    Default Re: Engine noise abatement

    Thanks Chris. That’s a lot of good info for comparison. Seems like I’ve been fighting this for a while now, doesn’t it?

  18. #53
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    Default Re: Engine noise abatement

    Quote Originally Posted by ron ll View Post
    Thanks Chris. That’s a lot of good info for comparison. Seems like I’ve been fighting this for a while now, doesn’t it?
    Well...yes.

  19. #54
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    Default Re: Engine noise abatement

    Is there a flex coupling between your engine and the stack?

    http://www.flexicraft.com/Metal_Expa...SAAEgJfgfD_BwE

  20. #55
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    Default Re: Engine noise abatement

    Quote Originally Posted by Canoeyawl View Post
    Is there a flex coupling between your engine and the stack?

    http://www.flexicraft.com/Metal_Expa...SAAEgJfgfD_BwE
    Yes.

  21. #56
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    Default Re: Engine noise abatement

    Just for reference here is the earlier thread on replacing the old dry stack.

    http://forum.woodenboat.com/showthre...aust-on-Snoose

    Unfortunately all the photos went in the PB debacle but it's still useful info.

  22. #57
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    Default Re: Engine noise abatement

    Just to save Detroit's reputation a little, there's a guy down the dock with a glass boat that has a Cummins 555. It's almost as loud as the 6-71. Maybe louder, but I'm farther away so it's not as objectionable

    Good to hear that your sound meter is less than wonderful. I was amazed that a 3-71 could be that loud ! Or that you could stand it

  23. #58
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    Default Re: Engine noise abatement

    Have you steel or SS fuel tanks each side of the engine room?
    I found to reduce engine noise in the pilot station directly above the engine, I had to cover the inside surface facing the engine with 25 mm foam and lead sound deadner.
    Glued it on and it worked well at noise reduction. I presume it stops the sound waves doing 5 laps of the engine room before busting out the top!

  24. #59
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    Default Re: Engine noise abatement

    Quote Originally Posted by Garret View Post
    @ Favorite: Site timing out? I haven't seen that - when & where & while doing what?
    Since you're in the biz and this might do some good .... I actually have a woodenboat upon which I spend a lot of time. Planning to spend more and be in more remote places. Internet is via tethered t-mobile. I don't care if it's slow, but this site must poll to see if you are still connected. If your lovely data connection doesn't answer in 2 seconds or less, it decides you are logged off. That means answering any thread is a total pita.

    You might think that on a boating site, they'd assume some people would be on boats. You'd be wrong.

  25. #60
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    Default Re: Engine noise abatement

    Quote Originally Posted by Favorite View Post
    Since you're in the biz and this might do some good .... I actually have a woodenboat upon which I spend a lot of time. Planning to spend more and be in more remote places. Internet is via tethered t-mobile. I don't care if it's slow, but this site must poll to see if you are still connected. If your lovely data connection doesn't answer in 2 seconds or less, it decides you are logged off. That means answering any thread is a total pita.

    You might think that on a boating site, they'd assume some people would be on boats. You'd be wrong.
    Well - first off, the forum is hosted on one of the most common forum software packages around - vBulletin. There are others & many are newer - but that's not necessarily good. The vast majority of software people I talk to look at me like I'm from Mars when I say "But what about when you don't have a good internet connection?" Folks living in/near population centers don't get that there are people who live in places that have zero or one bar cell coverage & no cable.

    So - newer software tends to assume a good internet connection & older software won't run on newer operating systems. Additionally, WB doesn't have a big IT staff to deal with all this - it's basically Scot.

    I use my AT&T phone as a hotspot often and as long as I get 2 bars it's just fine. One bar can be iffy. I have no experience with TMobile as around here it's completely useless (few towers). Maybe a booster would help? Some people say they make a big difference - google "cell phone antenna" or "cell phone booster"
    "If it ain't broke, you're not trying." - Red Green

  26. #61
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    Default Re: Engine noise abatement

    I started a new thread to address the timeout issue here:

    http://forum.woodenboat.com/showthre...ng-to-a-thread

  27. #62
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    Default Re: Engine noise abatement

    Decibel meter calibration seems to be an issue. I have five iphone apps, and one hand held dedicated meter. Of the apps, The National Institute for Occupational Safety and Health (NIOSH) looked at 130 iphone apps, and 62 Android apps. Of those, only four iphone apps were considered dependable enough to be used in the workplace. I purchased one for my iphone that they liked best, SPLnFTT meter, and downloaded another free one on their list, the NIOSH Sound Meter. I then tried all meters at our kitchen range exhaust hood running on high with the following results:

    Hand held Goldline meter = 73.0 dB (a 1970s style dedicated box meter with digital screen, not a phone app.)
    Ashlogic Decibel meter = 73.1 dB
    dB Meter = 71.0 dB
    Decibel X = 74.5 dB *
    SPLnFTT = 67.5 dB (approved by NIOSH study)
    NIOSH Sound Meter = 68.2 dB (approved by NIOSH study)

    *The Decibel X meter was the one that was giving me abnormally high readings on the boat. After downloading a newer version of it, it now seems to be more in line with the others, but still the highest readings.

    Interesting to me that the two NIOSH approved apps read quite a bit lower than the non-approved apps and the stand alone meter. Any meter should be professionally calibrated, but I don't have the means to do that. Later today I'll go to the boat and repeat my tests at 1250 rpm with the meters listed above. I'll post the followup results.

  28. #63
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    Default Re: Engine noise abatement

    Quote Originally Posted by ron ll View Post
    Decibel meter calibration seems to be an issue.
    Seems to be How is it on repeatability ? that is, try the garbage disposal at noon, then go try some other stuff, then come back and see if it at least reads the same ?

    I bet Fluke makes something ... ah well, next life, when I win the lottery

    Later today I'll go to the boat and repeat my tests at 1250 rpm with the meters listed above. I'll post the followup results.
    If you ever get north, you could check Skookum's quiet 3-71 and my louder 6 at the same time. Maybe check around in different areas of those boats to see where and what is doing the most effective damping ?

  29. #64
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    Default Re: Engine noise abatement

    Quote Originally Posted by Garret View Post
    The vast majority of software people I talk to look at me like I'm from Mars when I say "But what about when you don't have a good internet connection?"
    Developers should be forced to do their work on a Pentium 90. That way the useless barstadges would see what it's like for normal people. Every cute little jumping bunny rabbit they think up gobbles extra cycles and on paid-for data plans, costs someone money.

    And I thought the [blink]blink tag[/blink] was bad

  30. #65
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    Default Re: Engine noise abatement

    One issue with two-stroke Detroits that matters more than with other engines is dealing with intake noise. The blower adds quite a bit of noise to the mix. 71 series is better than 53 series in this regard as the 53 has straight lobes vs the helical of the 71, but it still is a source for noise that almost all other engines don't have. One can't directly do much about the gear drive part of it, other than making sure all is well in the gear drives(particularly in the blower case), but the path back out the intake tract upstream of the blower is a point of mitigation that can provide significant gains in noise suppression on a Detroit.

    Ken

  31. #66
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    Default Re: Engine noise abatement

    Quote Originally Posted by IHWillys View Post
    One issue with two-stroke Detroits that matters more than with other engines is dealing with intake noise. The blower adds quite a bit of noise to the mix. 71 series is better than 53 series in this regard as the 53 has straight lobes vs the helical of the 71, but it still is a source for noise that almost all other engines don't have. One can't directly do much about the gear drive part of it, other than making sure all is well in the gear drives(particularly in the blower case), but the path back out the intake tract upstream of the blower is a point of mitigation that can provide significant gains in noise suppression on a Detroit.

    Ken
    Would you have any suggestions on how to best muffle the intake? Presently I have what is called a Turbo Silencer on it, but it is pretty simplistic and doesn't seem to do much. When I talked to the guys at AirSep, they said their products are made mostly for turbo charger high frequency noise and don't do much for naturally aspirated engines. The other thing that has been mentioned here is to put a baffled intake plenum to the outside, not sure where on the outside I could run that tho.
    Last edited by ron ll; 04-10-2019 at 03:28 PM.

  32. #67
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    Default Re: Engine noise abatement

    Okay, back from the boat with the results of the new decibel meters tests at 1250 rpm, (no load) as follows:

    Hand held Goldline meter = 85.5 dB (a 1970s style dedicated box meter with digital screen, not a phone app.)
    Ashlogic Decibel meter = 78.0 dB
    dB Meter = 76.0 dB
    Decibel X = 95.4 dB *
    SPLnFTT = 80.0 dB (approved by NIOSH study)
    NIOSH Sound Meter = 82.4 dB (approved by NIOSH study)

    So we can see the wide variation in different meters. The outlier of course is the Decibel X meter which is the one that origianlly scared me to death with the 95 dB readings. The ones I would trust most are the SPLnFTT and the NIOSH, the only ones approved by the National Institute of Occupational Safety and Health. So it would appear that Snoose's pilot house at ear level is about in the low 80s (1500 rpm isn't much different than 1250 rpm). I still want to make it quieter, but at least it isn't killing me.

  33. #68
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    Default Re: Engine noise abatement

    So two questions come to mind at this point:

    1. Does the NIOSH meter register the same on two different devices?

    2. What is the noise level in Skookim Maru at 1250 rpm?

    I just installed the app on my iPhone X and it says my office is a peaceful 44-47dB depending on traffic. If I can make it out of town and onto the boat this week (still to be determined, client demands being what they are) I'll test it out on SM and see what it says.

  34. #69
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    Default Re: Engine noise abatement

    Quote Originally Posted by cstevens View Post
    So two questions come to mind at this point:

    1. Does the NIOSH meter register the same on two different devices?

    2. What is the noise level in Skookim Maru at 1250 rpm?

    I just installed the app on my iPhone X and it says my office is a peaceful 44-47dB depending on traffic. If I can make it out of town and onto the boat this week (still to be determined, client demands being what they are) I'll test it out on SM and see what it says.
    Not sure I understand your question #1. I have two apps that are approved by NIOSH. One is the NIOSH app and the other is the SPLnFTT app. If you get a chance to test Skookum Maru, I held the iphone kind of upside down at about a 45 degree angle, so the mic was pointing up and forward at about ear level when standing at the helm. I ran the engine at 1250 rpm in neutral, tied to the dock. All meters were set to read at the dB(A) scale, the default setting.

  35. #70
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    Default Re: Engine noise abatement

    By same device I meant if your phone and mine were side-by-side would they show the same reading on the NIOSH app? Easy enough to check. And I’ll try to duplicate your test as closely as possible.

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