Generator quieting

[Gdetrailer]

A while back someone mentioned looking for a quieter muffler to reduce the noise of their gen.

That question brought to mind that a video needs to be made which should clearly show that much of the generator noise does not come from the exhaust.

So, finally after a couple of months of super cold weather and lately several weeks worth of daily "monsoon" heavy rain we actually had a nice 50F day with no rain.. I have made a quick under 2 minute video.

Let me preface a few things..

1, this IS NOT A DEBATE as to why I and other folks do not spend the money for the super quiet gens.

The video of this gen IS FOR MY WHOLE HOME BACKUP SYSTEM so if you wish to debate, go somewhere else, I don't care about the noise and I can't hear it in my home and my closest neighbors are across the road and over 500ft away.

2, This is a demonstration that shows that most of the noise comes from internal vibration of the engine. No muffler will fix that.

3, this is a 8750W HF gen with 13 HP Chinese Honda clone engine, it IS louder than say a 6.5 HP Honda clone 4K gen but the SAME PRINCIPALS of where the noise comes from IS THE SAME.

4, While I can play the video on my PC using VLC player, playing it from Google drive you may need to download the file first because Google drive video player does not seem to like a MP4 video file?

5, Video starts out loud, turn down your volume, you have been warned.

6, Video is a bit shaky, newer digital camcorders do not have as nice of shake reduction of my old Sony Hi8 camcorder and I was holding camcorder and sound meter at the same time.

7, Distance for sound measurements was about 10FT, near the gen about 85 DB, exhaust was about 10FT and 70 DB, I don't have a lot of room between the out building and my house so 10ft was a compromise distance. Doubling the distance will reduce the noise level by 3 DB which is considered halving the noise..

That means at 20FT 70DB becomes 67DB and the 85DB becomes 82DB.

8, Building does not have any insulation, just wood siding covered in vinyl siding but does make a decent noise block.

9, Sound reduction via a box or shelter will be more effective than changing the muffler.

OK, now that we got that all squared away..

You can get the video HERE

[theoldwizard1]

pianotuna wrote:
Since a 1 square inch hole transmits as much sound as 24 square feet of gyprock, sound control for a generator is more about reflecting than containing.

I agree ! There are some materials that will absorb noise energy but the best require a lot of space.

If you can build an insulated box that sit OVER the generator with a 3-6" gap all around the bottom the noise has to bounce around before it can exit through this bottom gap.

Your second problem is HEAT ! Heat wants to go up, so you need a fan to push it down and out.

Where ever the exhaust comes out, you want extra space so that you can install a heat shield. A metal plate mounted on standoffs 3-6" from the side of the box. You probably need a top heat shield mounted on standoffs also. A short extension from the muffler into a 90 degree elbow and another short piece of pipe so that the exhaust exits downward and close to the ground will make a difference.

[SoundGuy]

SoundGuy wrote:
An Australian product ... and unfortunately irrelevant if not retailed and readily available here in N America.

pnichols wrote:
Hmmm .... I just received a $10 part for our RV from England that wasn't available here in the U.S..

Of course it took awhile to get here and the shipping costs were more than the part - but you know how it is - "anything for our baby". 😉

Sure, I can order from anywhere in the world, including Australia but even with the AUS$ and CDN$ hovering around par it still costs an arm & a leg, particularly for something large like these acoustic panels. :E Ordering from a US supplier and the cost in CDN$ can almost double from the advertised US price once it lands on our doorstep. :E :E Easy to say "order" but costly in reality. :M

[pnichols]

SoundGuy wrote:
An Australian product ... and unfortunately irrelevant if not retailed and readily available here in N America.

Hmmm .... I just received a $10 part for our RV from England that wasn't available here in the U.S..

Of course it took awhile to get here and the shipping costs were more than the part - but you know how it is - "anything for our baby". 😉

[SoundGuy]

SoundGuy wrote:
$300 US for 48 sq ft is dead cheap compared to $145 US for 12 sq ft of this purpose designed noise control barrier that will achieve maximum results when used to construct a correctly designed genset quiet box.

pnichols wrote:
This fireproof stuff may be a bit better - as apposed to being only fire resistant: http://www.megasorber.com/soundproofing-products/sound-absorbers/fireproof-acoustic-material

An Australian product ... and unfortunately irrelevant if not retailed and readily available here in N America. 😞

Here's another I can buy here in Canada - Acoustiguard. :B

[pnichols]

centerline wrote:
one only has to remove a panel from the housing of their generator when its running to see the proof of concept.... the exhaust is already exiting to the outside, with NONE of it exiting within the housing, but when an access panel is removed, the exterior noise nearly doubles... good sound deadening insulation in the box surrounding the generator and engine is the answer...

Exactly right ...so long as the sound deadening material still leaves enough room around the generator's top and sides for air circulation in accordance with the manufacturer's installation recommendations.

Also - at least with respect to Onan's "Micro" series of built-in RV generators - probably the bottom of them should be left completely open to the ground since they have a huge volume of cooling air circulating down there.

In addition one shouldn't neglect replacing most of the stock shock absorbing mounts with well engineered high end marine type ones of the recommended G-force ratings so as to stop all motion transfer into the RV's structure.

All of the above could easily be done by the RV manufacturer up front at only a modest adder to the purchase price. The owners of built-in RV generator's - and those camping close to them - sure would have a different overall opinion of them if the manufacturers had been doing this since day one.

It makes no sense to install a ~$3K-on-up built-in generator in an RV without also doing it right from the beginning. Solar is nice, but IMHO it should be backed up with outstandingly quiet, reliable, and convenient RV generator capability. (That is ... until propane fuel cells for RV's finally reach their full potential.)

[centerline]

one only has to remove a panel from the housing of their generator when its running to see the proof of concept.... the exhaust is already exiting to the outside, with NONE of it exiting within the housing, but when an access panel is removed, the exterior noise nearly doubles... good sound deadening insulation in the box surrounding the generator and engine is the answer...

[pnichols]

SoundGuy wrote:
$300 US for 48 sq ft is dead cheap compared to $145 US for 12 sq ft of this purpose designed noise control barrier that will achieve maximum results when used to construct a correctly designed genset quiet box.

This fireproof stuff may be a bit better - as apposed to being only fire resistant: http://www.megasorber.com/soundproofing-products/sound-absorbers/fireproof-acoustic-material

[SoundGuy]

MEXICOWANDERER wrote:
https://www.homedepot.com/p/Auralex-2-ft-W-x-2-ft-L-x-2-in-H-Studio-Foam-Wedge-Panels-Charcoal-Half-...

Not cheap!

Unsurpassed at blocking noise radiation

$300 US for 48 sq ft is dead cheap compared to $145 US for 12 sq ft of this purpose designed noise control barrier that will achieve maximum results when used to construct a correctly designed genset quiet box.

[Gdetrailer]

MEXICOWANDERER wrote:


https://www.homedepot.com/p/Auralex-2-ft-W-x-2-ft-L-x-2-in-H-Studio-Foam-Wedge-Panels-Charcoal-Half-...

• Not cheap!
• Not water resistant
• Horrible fumes if ignited
• Not petroleum resistant
• Unsurpassed at blocking noise radiation

Expensive? You bet.

Effective? You bet.

Unfortunately not ideal for conditions a RV would be in..

Yeah, one of my Companies products makes a LOT of noise (item uses air, vacuum, motors, gearboxes), for years they used simple 1/4" plexy as safety guarding to keep our customers from reaching into the belly of the beast (IT WILL KILL YOU! IT HAS NO FEELINGS AND WILL NOT FEEL SORRY EITHER)..

A couple of years ago, our engineers embarked on a project to dress it up and modernize it's looks but to also address the customers complaints of noise.

Very nice stainless steel skins were designed for the sides with small plexy windows and any surface on the inside that did not have a window opening got treated with sound control foam like you linked..

They even added a "roof" to the product which also had sound control foam glued to the underside..

The result was simply incredible from an obnoxious loud mix of motors, gearboxes, air and vacuum to barely even knowing it was running even up close..

[MEXICOWANDERER]

https://www.homedepot.com/p/Auralex-2-ft-W-x-2-ft-L-x-2-in-H-Studio-Foam-Wedge-Panels-Charcoal-Half-...

• Not cheap!
• Not water resistant
• Horrible fumes if ignited
• Not petroleum resistant
• Unsurpassed at blocking noise radiation

[road-runner]

pnichols wrote:
I think most of the sound from our RV's built-in Onan generator is NOT from it's exhaust. For example, when we're parked on soft ground running the generator it's quieter inside and outside the RV - since less sound from the generator's body is reflected upwards off the soft ground surface.

I agree totally.

[Gdetrailer]

pianotuna wrote:
Since a 1 square inch hole transmits as much sound as 24 square feet of gyprock, sound control for a generator is more about reflecting than containing.

Reflecting sound can be employed, however, the downside is it often can be reflected back via other hard surfaces like buildings or rocks that are in the line of where you are sending the noise..

Reflecting the sound up to the sky can work, just have to make sure your wall is higher than the gen. Too short and doubt it would help and taller than needed might make it difficult to make portable..

Yeah, I know, just get an expensive gen and be done with it..

But hey, sometimes the budget doesn't allow for it and one may need to make a few compromises..

Just trying to be helpful for those whose budgets don't allow for $2000 inverter gens..

[MEXICOWANDERER]

A lot of people associate noise with a sewerpipe megaphone exhaust note of a banger's 2015 Honda the one with 24" wheels. Or maybe the two thousand watt stereo the compresses the air inside to the point where their two eardrums touch each other.

[Gdetrailer]

MEXICOWANDERER wrote:
I believe a person will find COMBUSTION DETONATION is a major culprit of radiated noise. Example? Diesel. That knocking and clatter is an example and reduction of the noise because of water jacketing is a perfect example.

Because of "chain link association", my work with generators led me howling and fuming to problems with prime movers and it is impossible to isolate noise issues from customer complaints.

Take a 36-turn Wisconsin 37.5 horsepower 15Kw generator PM and compare it to an Onan 4cyl 36-turn 15-Kw generator.

The Wisconsin is deafening. The Onan is merely loud. The Wisconsin is air-cooled.

It's like a speaker. Only the voice coil actually is the origin of the noise -- the fabric is a sympathetic resonator. In an engine, cylinder combustion is the origin of BOTH exhaust AND resonating noise. The surface of the engine acts like the sympathetic resonator.

Water transmits noise, yes? But water in a chamber can also diffuse noise through an intricate physics of echo cancellation. Noise bouncing off a far side wall cancels frequency waves and this action is definitely selective.

I fiddled with sound proofing although I did not want to.

A thin foil of lead absorbs higher frequency emissions. Soft foam with pyramid protrusions is the most effective sound absorbsion for middle and low frequencies.

I had to deal with generator noise while building trawlers. It isn't fun. A diesel genset can turn the hull and bulkheads into giant resonators. Stick a stethoscope against concrete block of a generator shed and hear the effects of this.

Suppress sound. Then stick your stethoscope against the outside wall once again -- amazing eh?

It would cost a moderate fortune for me to clad the inside of my gen shed with 3" suppressor foam. Then there is the issue of flammability. Not feasible with auto extinguishing suppressors like Halon. Beyond my budget.

If you want real life examples of generator sound suppression, movie set tow trailer gen sets are perfect. A 20 Kw unit (diesel) is quieter with an ear a foot from the enclosure than a Honda 2000 watt inverter generator is at 10ft distance. Not bad for a DIESEL versus gasoline comparison. All's it takes is lots of money, lots of space and a significant reduction in engine efficiency due to increased exhaust back pressure. And keep in mind those movie set units have to deal with radiator cooling air flow.

Mex,

Yeah, in my haste to post..

I did omit the idea of the detonation in the cylinder as a plausible source of noise. What you have in a sense is a controlled burn, not exactly an explosion but a controlled burn in the cylinder which happens incredibly fast.

This spikes the pressure in the cylinder and head which slightly deforms the cylinder and head. In a nutshell the cylinder and head expand/contract with the pressure increase and decrease.

That vibration also can be transferred to the rest of the engine.

However, one should note that most of the "noise" is generated internally and radiated out through the engine case.

Air cooled engines do tend to be a bit noisier than water cooled, part in due to air cooled cylinders unlike water cooled are exposed.

Water cooled engines by design have a water jacket around the cylinder and head which can help dampen some of the harshness.

Sound control is a science all to it's self but in reality it comes down to dampening and absorption rather than trying to attack it with a huge exhaust muffler.

My video does clearly show a difference in the exhaust note vs the rest of the gen and that is what I set out to demonstrate in hopes that someone else on the wobbly web might bounce across my video before setting out going the wrong direction. 🙂