Generator vibration and noise

cardude01 said:

You know it's funny, I am driving home now in my Tahoe, which I don't consider to be very loud, and using the same decibel meter on my iPhone going 70 miles an hour my Tahoe registers the same 88 to 90 dB.

Something about that generator noise just bothers me I guess. It's a much deeper noise than a normal road noise in the car.

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We both have sports cars and, especially with the top down, they're loud. Maybe next car will be a Tesla.

cardude01 said:

Good idea. Thanks.

Does 88-90db with the genny running seem loud to you? Maybe I'm just easily annoyed.

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Yes, that seems very loud for just a genset.

cardude01 said:

Is there such a thing as a big thick sheet of rubber I could slide under this pan then use some longer lag bolts on the same tabs?

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I don't think a rubber sheet would do much good. Look at the Soundown bushing. It has the deep rubber cone with grooves in it which gives it flexibility. You can't get the flexibility without depth.

David

85 db would require hearing protection at our plant. The threshold may be lower now because 85 still leads to long term hearing loss.

High Wire said:

85 db would require hearing protection at our plant. The threshold may be lower now because 85 still leads to long term hearing loss.

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OSHA has essentially set 85 as the limit for an 8 hour day. It's officially 90 but above 85 you have to develop a hearing protection program that is more trouble than complying with 85. NIOSH is at 85. OSHA allows 2 hours at 100 and NIOSH only recommend 15 minutes as the limit.

The charts I've used went something like this. 85 decibels for 8 hours, 88 for 4 hours, 91 for 2 hours, 94 for 1 hour and 97 for 30 minutes. I only remember because of the obvious pattern, cutting the time in half for every 3 decibels. That means 15 minutes at 100 and the pattern continues on up.

Dang, I didn't think my genset was THAT loud. [emoji15]

It's more of a low rumble, so that's why I'm thinking if I isolate that pan it could help. I looked at the genset engine mounts today between the engine and the pan (the two I could get to) and the rubber seemed OK I think.

Carpet bad idea. Fire hazard. Ceiling tile sound insulation possible for wall and ceiling. If this is a new sensation check engine operation

MVDarlin said:

Carpet bad idea. Fire hazard.

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Do you have carpet in your home or office/place of business?

Cardude:

i) Yes, that is the air silencer/cleaner. Induction noise is probably as low as it is going to get.

ii) You have four engine mounts. Might be worth while talking to the manufacturer to see if they recommend softer mounts. Be sure you need them as they will be something of a PITA to instal. The heat exchanger is a somewhat unusual arrangement, but I don't see it plays any part in your noise problem.

iii) Did you remove the end panel of the sound-enclosure? If not, where is it?

iv) You might consider adding Sound-Down or similar to the overhead and walls of the compartment and/or an accoustic blanket over the sound-enclosure. Be carefull not to block any vents.

v) Ski makes a good point about rigid components carrying noise. Exhaust hose can be one such. Is it touching where it should not?

Thanks!

Engine mounts-- you are correct, they are very hard (maybe impossible?) to get to.

I have the end panel of the enclosure. Just had it off while I looked around.

I actually bought some Soundown foam yesterday to mount to the ceiling and door to the "generator room". Maybe that will help.

I crawled to the back of the generator room and did notice the exhaust hose looked like it was touching a spot of the bulkhead cutout so I will try to isolate that.

I put my hand on the genset exterior sound enclosure while it was running and it vibrates quite a bit. I always assumed that was just normal but maybe not?

Sound attenuation pads need to be 'tuned' to the source. Simply shoving bits of this or that underneath may help a lot, but acquiring the correct pads will be far better. Do a little more research; your genset mfr probably sells everything you'd need. Comments above about aged pads are likely to be correct, particularly if the existing pads are over, say, 10 years old.

Sound attenuation is the result of dealing with the entire system: the source, structure-borne vibration isolation, air-borne isolation - air tightness of an enclosure, resonance elsewhere in the structure.

I've had peripheral, we had sound engineers, experience as an architect dealing with noise control in theater /symphony halls. The whole thing was fascinating. The sound isolators for the mechanical equipment were wonderfully complex: each isolator had springs of various rates, elastomeric pads etc.

My old 30' Hunter sailboat was factory equipped with a single horizontal cylinder (12HP) diesel engine. Vibrations were so bad that the lifelines vibrated up and down at least 6" in resonance with the engine. It was HORRIBLE! In later years I replaced that engine with a two cylinder downward thrusting pistons.

I was also involved in an engineering project at that time where some equipment I designed had to pass various vibration frequencies without vibration isolation. Piece of cake I thought. NO! It turned out to force our company to get a waiver from our customer....US Navy. So the follow on project we were quick to insist on using vibration isolators.

Vibration is almost a science unto itself. First, the isolator must be matched to the load, both in the vertical direction forces and horizontal direction forces. Horizontal forces would be important if the source was an engine turning a propeller for example. Isolators can really attenuate vibration frequencies but they must be matched to each particular application.

Now it gets better! All vibration isolators have their own resonant frequencies which means that if something has a resonant amplitude say about 1g at 100hz, if coupled with an improper islator that had a resonance at 100hz, the vibrations could soar to very high g forces.

So consider an engine turning at 1800RPM, that is 30 revolutions/second. THAT IS A DIFFICULT FREQUENCY TO ISOLATE! Now the OP already stated his engine mounts are difficult to get at but if he can get access to them along with knowing the engine weight he might be able to replace those mounts. The number of cylinders also impact the vibration frequencies.

If so, I suggest searching for technical data from vibration isolator manufacturers for replacements. Heck, call a few companies and speak to one of their engineers for help. Don't foolishly spend money without knowing it will help with this problem.

Foggy

DHeckrotte said:

Do a little more research; your genset mfr probably sells everything you'd need.

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Want to bet on that?

Just got off the phone with a pro at Soundown who is a TF member. He found some good isolator mounts for me to go between the pan and the deck, and some special barrier foam for my enclosure. Very helpful conversation.

cardude01 said:

Just got off the phone with a pro at Soundown who is a TF member. He found some good isolator mounts for me to go between the pan and the deck, and some special barrier foam for my enclosure. Very helpful conversation.

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The best sound proofing is lead sheeting. I have seen boats that the only sound was the cooling water splashing over the side.
Hoses and cables need to be flexible and not rigidly mounted near the enclosure.

Update:

A buddy of mine and I installed some isolation mounts I got from Soundown between the pan and the deck on the genset today. Vibration reduction was huge. We also installed some Soundown sound barrier foam on the genset enclosure which helped reduce the higher pitched noise. We also enlarged the hole for the exhaust hose through a bulkhead-- it is no causing the entire bulkhead to vibrate like a big speaker.

Overall a very successful project!

cardude01 said:

Update:

We also enlarged the hole for the exhaust hose through a bulkhead-- it is no causing the entire bulkhead to vibrate like a big speaker. Overall a very successful project!

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Hey, never gave that a thought! I bet that would help mine too, not that it's an issue, but quiet is better. Thaks for the tip.

healhustler said:

Hey, never gave that a thought! I bet that would help mine too, not that it's an issue, but quiet is better. Thaks for the tip.

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I feel really lucky to own our solidly built, 1977 classic Tollycraft tri cabin... in so many ways.

One way is the well mounted, gasoline powered, quite-sound 7.5 kw Kohler gen set. With thick base pad and thick Berber carpet there is lightly a whisper inside boat salon/stateroom when it's on. Can barely hear the exhaust stream into water about mid-ship on starboard side.

Hi, are you look vibration damber it is ok. vibration damber is At the end of the crankshaft, usually the pulley vulcan rubber.

Always happy to hear successful projects. As you noted plumbing and even wiring can carry vibration and need to be addressed as well as the source. Nicely done

cardude01 said:

Update:

A buddy of mine and I installed some isolation mounts I got from Soundown between the pan and the deck on the genset today. Vibration reduction was huge. We also installed some Soundown sound barrier foam on the genset enclosure which helped reduce the higher pitched noise. We also enlarged the hole for the exhaust hose through a bulkhead-- it is no causing the entire bulkhead to vibrate like a big speaker.

Overall a very successful project!

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remplace old engine mounting bloc on generator can help a lot (need to inspect)
very ofter to foam isolation and generator canopy are very often dead can be remplace by better quality.
and in your boat that also depending what is under you generator sometime that empty place and the surface where the generator is bolted are not dense enough and the under place make crate of resonance, one of the solution is to instal hard steel plate under generator that absorb vibration and sound (that optional on some brand)

101TUG said:

remplace old engine mounting bloc on generator can help a lot (need to inspect)
very ofter to foam isolation and generator canopy are very often dead can be remplace by better quality.
and in your boat that also depending what is under you generator sometime that empty place and the surface where the generator is bolted are not dense enough and the under place make crate of resonance, one of the solution is to instal hard steel plate under generator that absorb vibration and sound (that optional on some brand)

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You just mentioned an item regarding one reason why our gen set is so quiet... the mount area has hard steel plate that absorbs vibration and sound.

Mr. Robert Merland Tollefson (better known as "Tolly" - the originator of Tollycraft boats and its owner till he passed at age 100, on 5/13/2011) had spent years during WWII as tugboat and mine sweeper captain for U.S. Navy. Tolly really understood many of the intricacies in boat design/building. He and his several knowledgeable associates built over 6,500 really good pleasure boats during the existence of Mr. Tolly's boat building company.

Art said:

You just mentioned an item regarding one reason why our gen set is so quiet... the mount area has hard steel plate that absorbs vibration and sound.

Mr. Robert Merland Tollefson (better known as "Tolly" - the originator of Tollycraft boats and its owner till he passed at age 100, on 5/13/2011) had spent years during WWII as tugboat and mine sweeper captain for U.S. Navy. Tolly really understood many of the intricacies in boat design/building. He and his several knowledgeable associates built over 6,500 really good pleasure boats during the existence of Mr. Tolly's boat building company.

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I know we don't see a lot this solution but that a good one.
Problem you need thick plate and best to have no rust stainless steel so expensive, I never saw but lead plate can by better and may be cheaper

Art said:

I feel really lucky to own our solidly built, 1977 classic Tollycraft tri cabin... in so many ways.

One way is the well mounted, gasoline powered, quite-sound 7.5 kw Kohler gen set. With thick base pad and thick Berber carpet there is lightly a whisper inside boat salon/stateroom when it's on. Can barely hear the exhaust stream into water about mid-ship on starboard side.

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Art--

I also have a 7.5KW Kohler (4 cyl, 1800 RPM) generator. Mine is quite! I agree with your assessment.

Cardude,

Did you take a new Db noise level reading after the fix?

Even if the number didn't go down a lot, "sounds" like you attenuated the frequencies that were annoying. Glad to read that your solution worked, these can be tough problems to solve on boats.

I did take a reading, and the decibel reading was only slightly lower than what it was before the mods. Maybe the "rumbling" was not registering on the iPhone DB meter?

Bruce B said:

When I installed a generator in our sailboat, I read every manual Fischer Panda had on the the model we chose.

One thing that became clear was that everything counts when it comes to sound attenuation. They cautioned against mounting on a platform that might vibrate and thus broadcast that noise.

The other suggestion was to use a second set of motor mounts between the generator enclosure and the beds.

Here is a picture of my installation. It was not silent but it was far better than other 3600 rpm small generators I have experienced in sailboats. With the door to the aft cabin closed and the air conditioning on the air was louder than the generator...

Bruce

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Bruce

I got the mounts installed but I need to put a piece of channel beam or something (flat bar?) that will span under the pan from tab to tab. The mounting tabs on my pan are offset off the pan not directly under it, and as someone else posted it's causing my mounts to "squat" to one side a bit-- much of the load is one one side of the mount and not directly over it. I need a beam of some sort like the one shown on your pic but I don't have much room to spare. Not sure I even have 1" of room left I can jack it up. The beam shown in your pic would straddle my mounts and cause the genset to rise hardly any at all. What is that beam?

Too bad the tabs and frame didn't cover enough of the mount top. I went back and looked at what Bruce had and it looks like U channel used upside down and cut away towards the mounts, a very clean installation. If you could do this across the short direction between two mounts it would probably solve the problem of evenly loading the mounts very nicely