Generator noise ratings matter more than you think

At first glance, you might not be particularly concerned about generator noise ratings. After all, if it’s quiet enough to put up with, it must be quiet enough already. Right? It ain’t necessarily so. With increasing emphasis on “keeping nature natural,” it shouldn’t be surprising to hear that visitors to the nation’s parks may get a bit sensitive about noise. And while the National Park Service may not “have an app for that,” they most certainly do have a rule for that. If you’re shopping for a generator, you do really need to be concerned about noise ratings.

National Parks make it a rule

As far as U.S. parks are concerned, noise is an issue set down in writing. Here’s the specific item: “Audio disturbances. (a)The following are prohibited: (1) Operating motorized equipment or machinery such as an electric generating plant, motor vehicle, motorized toy, or an audio device, such as a radio, television set, tape deck or musical instrument, in a manner: (i) That exceeds a noise level of 60 decibels measured on the A-weighted scale at 50 feet.” (36 CFR § 2.12). [Italics ours]

The technicalities of sound (and its measurement) can run deep. We’ll try and make it as simple as possible. In essence, if a park ranger stood 50 feet from your generator and used a sound level meter, it should read at 60 decibels (dB) or less—or you’re in violation of the code. What’s 60 dB equivalent to? As you can see from the chart, it’s louder than a dishwasher in the next room, but quieter than a conversation at three feet.

Do published noise ratings really count?

When evaluating generators to buy, noise ratings count. Or do they? Our Firman generator, purchased at Costco a couple of weeks ago, is rated at 56 dB. We should be in the clear, right? Well, here’s where consumers can easily be misled. One generator retailer admits, “No real standards exist for measuring portables. Manufacturers usually take measurements from 21 feet away in all directions and publish the lowest noise level.” Well, the term “usually” in connection with how far away the measurements are taken is evidently at the whim of the manufacturer.

For example, Cummins, the parent company of those good old “Green Generators” with the Onan label, takes their measurements at 3 meters, or a smidge over nine-and-a-half feet. Firman tells us that our generator was tested at 25 feet. But a host of manufacturers don’t tell you the distance when they tested for noise levels. Some don’t even tell you noise level specifications at all. For example, some “RV generator review” sites mention some of the DuroMax brand as being great for RVers. Checking on the DuroMax website reveals ZERO information about their generator dB ratings. The same is true for most of the generators marketed under the Champion brand.

We did have to hand it to Honda and Wen—they were both clear as to the noise levels of their machines, and also at how many feet away their measurements were taken: Honda at 23 feet, and Wen at 22. But even armed with this information, it’s still not clear how things stack up at that mandated 50-foot measuring rule for National Parks—which includes campgrounds.

Putting it together for a sound decision

Here’s where we’ll try and simplify the nature of sound. Let’s take a Honda EM4000SX. Honda says this generator cranks out 61 dB at 23 feet. That’s a dB more than the law allows, right? Well, no. Because sound levels drop as you move away from the source. Here’s the rule of thumb: As you double the distance, the dB level is reduced by 6 dB. So that 61 dB would drop to 55 dB at 46 feet—well within the limit.

But hang on, there’s one more little detail. Our retail industry source says, “Manufacturers usually … publish the lowest noise level.” Again, kudos to Honda. On a chart we obtained, the company provided not the lowest noise level, but gave two figures. For the generator we mentioned above, two figures appear: 61 – 63. The lower number is for a generator operating at a 50% load, and the higher one, at 100% of load. One of their louder generators, the EM6500 SX, which posts noise ratings of 63 – 66, would still be “legal” at full load. 66 dB at 23 feet would probably “read” 60 dB at 46 feet – even less at 50 feet.

We reached out to Champion, who makes both open-frame and inverter generators. While their web site doesn’t provide the information on distance measurements and load, when we put in an e-mail request for more information, they responded. They mentioned they tested at 7 meters (around 23′), and that,  “Inverter generators are measured at a 25% load and open frame generators are measured at a 50% load as is the general rule.”

In general though, many manufacturers aren’t particularly inclined to cut loose with the “real” information. This leaves the consumer on the dirty end of the stick. Pull into a National Park and fire up your new generator to cool off, you could actually find your noise level is above the limit. If somebody complains and you “test bad,” you’ll surely be told to shut your generator down, or even tossed be out of the campground.

Inverter versus “contractor” generators

What’s the consumer to do? If there’s any question as to how much noise, at what distance, and at what power level of use it’s created at, demand answers. You (like us, so far) may not get them. It may be time to take a walk and find a manufacturer who is more willing to come clean on noise ratings. This much is clear, however. Of the two types of portable generators, “inverter” and “contactor” or “open frame,” you get less noise for your dollar with the inverter generator. There are two reasons for that.

First, an inverter generator set for “ECO” mode turns only the amount of RPMs needed for the given load. The fewer the RPMs, the quieter the generator. Open frame, contractor generators are designed to operate at the same speed, regardless of the amount of load. And that translates to much more noise for the same maximum power output compared to an inverter generator. Second, inverter generators are designed to insulate the engine and exhaust noise from the outside environment. Yes, inverter generators are ghastly more expensive when comparing the initial purchase price. However, they burn far less fuel than an open frame unit of the same power output.

Test your own generator

Finally, if you’ve already bought your generator but aren’t sure how it stacks up noise-rating wise, there’s still something you can do. Go out to your smartphone or tablet’s “app store” and look for a dB “sound level meter” app. We use SPL Meter by Keuwlsoft. You’ll need to calibrate it. The suggestion is often made to find a known good SPL (sound pressure level) meter and calibrate against it. But in a pinch, find a quiet room and have someone read to you from three feet away. The average dB level of a conversation is 60 dB. Calibrate your meter against this, and you shouldn’t be too far off.

Meanwhile, we’ll hope that more generator manufacturers come clean on real-world generator noise ratings.

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