RV Electricity – ABCs of generator noise

Dear Mike,
I really learned a lot from your RV Electricity article on generators last Sunday. But do you have a more basic version of it without all the math, sort of like generator noise pollution for dummies? —Lost in the numbers

Dear Lost,
All right, so here is the Cliff Notes version of Part I on Generator Noise Pollution without all the calculations. For those of you who want to see the mathematics behind it all, the full article is HERE. And no, the math isn’t terrible, but you may get a headache at first learning about logarithmic scales. However, no pain, no gain, right?

We measure loudness of objects with something called an SPL meter, which stands for Sound Pressure Level. And that measurement is made in a unit called a dB or deciBel. The more deciBels (dBs) you read on an SPL meter, the louder it is. Just know that a 50 dB generator is really quiet, one that’s 60 dB is starting to get loud, and a 70 dB generator is obnoxiously loud if you’re in a quiet area to begin with. So a generator in the low 50 dB range is hardly noticeable, while one in the upper 60 dB range can be heard from many hundreds of feet away. Just in case you have an SPL meter to try out, all generator SPL measurements are taken from 7 meters (23 feet) away using the A-Scale. (Read about SPL meter scales in my full article with the math – sorry.)

Here’s a video I made comparing the noise levels of two generators. The first one is a Honda EU3000iS inverter generator running around 52 dB SPL, and the second one is a basic 3,600-watt contractor generator making around 68 dB of noise. As you can plainly hear, the Honda generator is barely noticeable, but the contractor generator is really obnoxious.  Would you want that running anywhere near you in a campground? I didn’t think so….

There are two big reasons for the sound level differences. First of all, the contractor generator has the gasoline engine out in the open without any noise dampening around it. And it also has a cheap/noisy muffler that makes a lot of exhaust noise. Plus, it’s an AC generator, which means the gas (or propane) engine has to run at full speed all the time, even when the generator only needs to supply a few watts.

On the other hand, inverter generators from Honda, Yamaha and others are built with a lot of sound-dampening material around them. That kills much of the sound of the moving parts. Plus, they have really well-designed mufflers to dampen the sound from the exhaust. Finally, inverter generators really should be called “alternators” because they don’t make AC voltage directly. They really “generate” around 12-volts DC which is then stepped up to 120-volts AC by an inverter, just like you might have in your RV to make 120-volts AC from your house batteries. That allows them to throttle down to a slow idle when the generator doesn’t need to produce full power. And that not only reduces the noise level, that’s also why they’re easier on fuel than a contractor generator that needs to keep the engine running at a full 3,600 RPM all the time.

So are inverter generators worth the extra 200% to 400% price compared to a contractor generator? Well, I take noise pollution seriously, so if you plan to run your portable generator in any kind of campground or park I really feel you should be using a quiet inverter generator with a low 52 dB sound level, and not an open-frame contractor generator that makes maybe 68 dB of sound level (noise).  I don’t think that open-frame contractor generators belong in any campground setting.

What do you think? Please comment below, but be civil about it. This is not a flame war, just an intelligent discussion.

Let’s play safe out there….

Mike Sokol is an electrical and professional sound expert with 40+ years in the industry. Visit NoShockZone.org for more electrical safety tips. His excellent book RV Electrical Safety is available at Amazon.com. For more info on Mike’s qualifications as an electrical expert, click here.

##RVT852

18 Thoughts to “RV Electricity – ABCs of generator noise”

1. Richard

Mike, seems like diesel class A’s have variable speed generators which can be quieter than the gas class A’s which seems to run on one speed all out whether you have one a/c on or two or none. What exactly is the difference between these generators and why can’t the gas generators be variable speed?

1. Mike Sokol

To be able to run a generator engine at variable speed, there has to be an inverter in the system. Without that, any generator’s output frequency would vary from 60 Hz (or 50 Hz in Europe), which is a bad thing. The inverter adds significantly to the cost of these Inverter-Generators. And yes, lots of portable gasoline generators run at variable speed, the Honda EU2000iS being the prime example. I’m studying up on Class A generators for a future article, but for now I don’t know enough to venture a qualified guess.

1. Mark D. Hunsberger

Does it make a difference in sound volume if the generator is fueled by explosive Propane or gasoline instead of much safer non-explosive Diesel fuel?

1. I don’t think so. That’s because a diesel engine needs a much higher compression ratio to ignite the fuel (18:1 or so), compared to a propane/gasoline generator with a much lower compression ratio (maybe 6:1 to 8:1 I’m guessing). That’s one of the reasons that diesel engines in a vehicle are generally louder than their gasoline counterparts. But that’s certainly an interesting question which I’ll ask my contact at Cummins/Onan to verify.

2. Roy Ellithorpe

Hi Mike, sorry to go off topic, but I don’t know how else to connect with you.
I have a Travel Supreme with 2 Magnum 2000 inverter/chargers. First 1 stopped charging from the generator, then the other. They both still charge fine with shore power. I spent a couple of hundred dollars at my favorite auto electric shop and another \$300 at an RV repair shop. Any advice would be appreciated.
Thanks
Roy Ellithorpe

1. Mike Sokol

Roy, sounds like an interesting problem that I might be able to solve if I put some time into it. Unfortunately I’ll have to charge you for my time since I get a dozen emails like yours every week, and if I answered every one pro bono I would go broke trying. So everyone…. my standard consulting rate is \$250/hr but I offer a discount for RVtravel and No~Shock~Zone readers of \$125/hr. Contact me at mike (@) noshockzone.org to discuss how to proceed.

3. Chuck D

Yes Mike, the ones in Class A and Class C’s. They usually range from 3k to 5.5 K Watts. And regardless of the owners opinion, they are not super quiet.

1. Mike Sokol

More for me to test. Guess that will have to be Part III on generator noise pollution.

4. John Jung

I am confused when you say you are making a comparison of generators (or anything for that matter) and then say you are adjusting something. Maybe it’s just me, but a comparison should be the raw comparison of the two items. What am I missing here?

1. Mike Sokol

John, what I’m adjusting is the unknown gains of the two different microphones that were used to record each generator. Also, each video editing program tends to change the volume of the audio passing through it. So what I do is pick the louder of the two recordings, in this case the open-frame generator with a rating of 68 dBA at 23 feet, and make it my initial reference level. Then I take my second video recording of the quieter generator, in this case with a rating of 52 dBA at 23 feet. But I noticed that recorded level of the inverter generator was a lot quieter than the 16 dB difference I should be seeing on my meters. So I added about 10 dB gain to the inverter generator channel so the two audio tracks are only 16 dB apart, not the 26 dB that they initially started out as.

Now in a perfect world I would have both generators side by side, use the same microphone, same recorder, and same everything else including the distance. If I was able to do all that, then there would be NO gain adjustments needed and everything would be calibrated exactly the same. So as you can see, I adjusted my audio tracks to minimize the difference in levels between the two different generator technologies. Without that adjustment the level shift would have been much larger than you heard. Also, I tweaked the codec in my video editor while rendering the project to reduce video bandwidth while increasing audio bandwidth. That’s because I decided that the audio was more important than the video in this case. Finally, I uploaded the entire file to our own Word Press server because YouTube has all kinds of auto-gain adjustments for the audio, which would corrupt my original level calibration.

And the reason why relative levels are needed rather than actual levels is that your own computer has a volume control, so if I send you a track that was 68 dBA, then you can adjust your own computer level so it’s 50, 60, 70 dB SPL or whatever. That’s why you need to compare two different audio levels, not just one. Too many variables otherwise.

Does this make sense? Yes, it sounds like a hot mess, but this is the sort of thing I actually do for a living. If I could get a little budget and some test generators I could do a test that I could guarantee would be accurate within a fraction of a deciBel. Right now I’m sure it’s within a dB or so of the actual level differences.

Yes, I actually did calibrate nuclear missile guidance systems back in the 80’s, and I currently teach calibration of large sound systems. Too much fun. Yes, it’s geek fun, but it’s fun nonetheless.

5. Wolfe

Holy “Poop,” Mike… is THAT what most people think an open-frame genny *normally* sounds like? That’s pretty close to what my (~~70db?) LOUD 7500W (I/C, not RV) contractor genny sounds like, but seems much louder than 4KW “yellow” RV genny.

I may not sit on my 4KW as a bench while comfortably talking, but I can talk beside it without shouting… Out at the end of the RV’s normal cord, it’s quite reasonable to talk, and opposite RV side or if I use my extension cord, then it’s “easy to ignore.” My wife who watches TV at “whisper level” says “can tell it’s running, but nowhere near as loud as the [MS] video’s levels.”

Now I’m curious to try my own SPL measures with each of my gennies to see if I’m more deaf than I think or my cheapie genny is really that unusual. :-S

1. Mike Sokol

All generators have different volume levels. But the one in the video was listed at 68 dBA SPL at 23 feet, and I calibrated it relatively against a Honda EU3000iS running at 52 dBA SPL. While some “RV Ready” open frame generators might be a little quieter than 68 dBA to 70 dBA of a contractor generator, many of them are not. One of the things the manufacturers could do to reduce the dB level without breaking the bank would be to add a real muffler. And that could probably reduce the noise level by 3 to 6 deciBels, maybe getting the SPL down into the low to mid 60’s. But in any event, If we started up a quiet inverter generator next to yours for comparison, I’ll bet the level difference would be huge. Now I’m assuming you have a full-speed AC generator that needs to run at a constant 3,600 RPM to make 60 Hz. It’s possible that you have what’s commonly called an RV-Ready Hybrid open-frame generator, so it can throttle its engine RPM down to an idle when it doesn’t need to produce full power. Is that how your generator works? If so, then there’s nothing wrong with your hearing. A hybrid/open-frame generator with a good muffler could easily reach down to the low 60 dBA SPL range. If this all seems confusing, know that it seems to confuse the manufacturers as well, which is why my BIG article goes into all the detail.

6. ChuckD

Mike I do enjoy your articles even about the portable generators but are you going to cover the generators a lot of RVs have. I don’t think I have seen an RV without one.
Thanks

1. Mike Sokol

ChuckD, what brand and model RV generators are you referring to? Maybe you mean the built-in ones that are normally found in Class-A or Class-B RVs. Most these seem to be Cummins-Onan generators running on propane or diesel. I don’t know of any 5th wheel RVs with built-in generators, but a lot of Sprinter Class B’s have a built-in propane Cummins-Onan genny.

1. Mike Roberts

Mike, quite a few 5th wheel trailers are equipped with the Onan generators. Especially high end full time fivers and toy haulers. I have a 33′ fifth wheel (in today’s world a small 5th wheel) and had the option of a built in generator. When a generator is needed we have a Honda 2000 inverter/generator.

1. Mike Sokol

Casually looking around I see a lot of the 5th wheel toy haulers with built-in generators, and I’ve hung around at the drag race track a bit in my younger days and saw many 5th wheel car haulers with a built-in genny. The Cummins-Onan generators are very quiet, and have the extra benefit of being enclosed in a little generator compartment. I’ve not measured the dB Level on any of these yet, but that’s on list of things to do this summer.

7. Jim Anderson

Mike,
Your Cliff notes version is Perfect!
And the NPS has these regulations:
Generators must conform to National Park Service regulations pertaining to audio disturbances, which states that “motorized equipment or machinery cannot exceed a noise level of 60 decibels
measured on the A-weighted scale at 50 feet” (36 CFR 2.12).

1. Mike Sokol

That’s good info, Jim. So if you’ve read both the Cliff Notes and full-math version of this article you can easily see that a Honda generator that’s rated at 58 dBA SPL measured at 23 feet running full-throttle would be at least 6 dB lower at 50 feet. That suggests it might measure in the 51-52 dBA range. So it would pass the NPS test.

But an open frame generator running at 68 dBA SPL measured at 23 feet would only be down to 62 dBA at 50 feet. So it ain’t gonna pass. Plus as you can hear in my video the Honda (and Yamaha) inverter generators make much less high frequency noise than a contractor generator. The Honda sounds like a low rumble, while the open frame contractor generator sounds like a jack hammer.