Portable Generators: Why Are They So Noisy?

Portable Generators – Why are they so Noisy?

It’s an interesting question.

Engines don’t need to be noisy. Just listen to your automobile. How quietly the engine runs is often one of the most emphasized selling points of any auto salesperson.

The only time you hear a loud noise coming from an automobile is usually when the exhaust has been seriously damaged, has fallen off, or when a “sports” exhaust system has been fitted by an enthusiast who perhaps likes to turn heads to marvel at their magnificent machine… Then the noise can be deafening.

So why are portable generators so noisy, especially those built with open frames? They are fitted with mufflers yet, considering the noise they make, these don’t appear to do much at all.

So let’s first go back to basics.

What’s a muffler for and why do I need one?

The muffler, also known optimistically in the UK as a silencer, is just one part of an engine’s exhaust system. According to Federal standards, a muffler must be able to safely expel exhaust gases away from passenger compartments (in vehicles) and meet Environmental Protection Agency (EPA) noise standards. For anyone interested, the Noise Control Act dating all the way back to 1972 can be found here COMPS-888.pdf (govinfo.gov), and a very brief summary of the act is here Summary of the Noise Control Act | Laws & Regulations | US EPA.

The exhaust system

While the exhaust system is designed to expel the gases produced by an internal combustion engine, the job of a muffler is to absorb and dissipate sound while the exhaust gasses are being expelled. We talk generally about noise and sound. It’s quite a complex subject.

The “problem” with a muffler, as far as efficiency is concerned, is that while it is designed to prevent excess emissions of toxic gases and sound, it also reduces the power and performance of an engine.

Federal and state legislation will often require the design of a muffler to be able to prevent “excessive or unusual noise”.  This harks back to the original 1972 Act, whose purpose was to promote an environment for all Americans free from noise that jeopardizes their health or welfare, and to establish the necessary institutional framework to coordinate Federal noise control research and activities, including the establishment of Federal noise emission standards.

In the case of vehicles, in some states, such as Kansas, a generally permitted noise level in most of its jurisdictions is between 80 and 90 decibels. Exceeding these levels can result in fines.

Of course, most vehicles don’t have exposed engines, and part of the sound deadening is performed with soundproofing material in the hood and body.

It’s also important to note that a proper functioning muffler and exhaust system will help to reduce the emission of the highly toxic carbon monoxide and other gases. We have more about the dangers of carbon monoxide.

Are there different types of muffler?

Yes, there are. Basically, good and bad ones.

You might have heard the noise sports and racing cars make, which is fundamentally down to putting efficient high performance in front of sound suppression. And if you’ve ever heard a Formula 1 or Indy race car you will be acutely aware of how ear-splitting the sound it makes, because to get the most power from the engine the exhaust system doesn’t include a muffler at all.

While you might not know it, there is a lot of science and technology involved in the design of a muffler not least because of emissions legislation which covers both noise and toxic gases. And be it for performance or noise suppression, the best mufflers can cost a lot of money owing to the materials used, while the cheaper ones with cheaper materials just don’t do a good job at all.

In terms of noise suppression, within the most modern mufflers are a selection of pipes which have been scientifically tuned to create reflected sound waves that cancel each other out in the process of their colliding. A pretty good explanation of all of this can be found here Backpressure and Other Types of Mufflers – How Mufflers Work | HowStuffWorks.

Now back to the question of noisy generators. Some say it’s down to cost and that manufacturers reduce theirs by fitting cheap mufflers. There is some evidence from owners to support this assertion, but it only comes from their personal experience rather than expert opinion.

But it also has something to do with the speed, or RPM, a generator operates at. Traditional models usually operate at a constant 3600 RPM, which is the speed needed to generate electricity at 60 Hz, and hence the sounds produced are louder than when the engine is idling.

Can you do anything to deaden the sound more?

Despite what manufacturers say about the noise levels of their products, you can measure the decibel levels yourself either with your smartphone or a dedicated sound measuring device.

For example, The National Institute for Occupational Safety and Health (NIOSH) have produced an App (for the iPhone) which has a tested and validated accuracy of ± 2 dBA. Dedicated equipment to measure sound include the Protmex MS6708, the most affordable and popular RISEPRO Decibel Meter, and the more expensive SM-130DB Digital Decibel Reader. Although none of these are NIST certified, they are probably good enough to do the job. NIST certification is, by the way, the calibration services of the National Institute of Standards and Technology, which are designed to help the makers and users of precision instruments achieve the highest possible levels of measurement. The certification is usually done for more sophisticated equipment, and their costs reflects that.

However, the answer is yes, you can take steps to reduce the noise level of your generator. But be aware that manufacturers often warn about trying DIY modifications to the generators they manufacture because this can, and probably will, void your warranty.

That being said, without making any physical change to the unit itself, the first and most simple step is look for a generator that is relatively quiet in the first place. For this, there is no better place to look than inverters, most of which have their engines in an acoustic enclosure. But unfortunately, none of these portable generators might meet your power needs if they are big. The most powerful in our selection is the Champion 100519. This model has a starting output of 6250 watts and a running output of 5000 watts, but it too has an open frame with a sound level of 68dB. For a reasonably quiet and powerful enclosed inverter, the Westinghouse iGen4500 is a good example if this model provides enough power output for your needs.

The second step is to place your open frame unit on sound absorbing material, and not on hard or wooden surfaces because those materials will act as sound amplifiers rather than suppressors.

And since the generator must be placed outside at least 20 feet away from your home because of dangerous carbon monoxide emissions, it makes sense to consider a well-ventilated enclosure. This could either be made by yourself or you could have a professional build it and in which you can install some soundproofing material. It needs to be well-ventilated to ensure the generator does not overheat and potentially catch fire.

But all your soundproofing efforts will be defeated if parts of the enclosure must remain open to aid air flow around the generator. A better, but more expensive solution, might be to look at installing sufficiently large but power efficient fans at each end of a well-sealed enclosure, one to pull colder air in from outside and the other to act as an extractor, pulling the hot air out.

What’s your experience been?

Noise in general is a controversial subject, and portable generators generate a high level of noisy opinions!

Nevertheless, we’d like you to share how you have approached and solved the problem of reducing the noise emitted by your portable generator. There are a lot of suggested solutions out there, but nothing beats actual experience of both success and failure.

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