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Is Your Dishwasher Quiet Enough?

Inside the appliance industry's quest for a quieter kitchen.

The interior of a dishwasher Credit:

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Ten to 15 years ago, dishwashers whooshed and washed and clunked and clanged with the vigor of a pile driver. It was annoying, but most people didn't know it was possible to wash any other way. Dishwashers were loud, a Bush or Clinton was running for president, and everyone was excited for the new James Bond and Star Wars films.

Over the past decade or so, things have changed—at least when it comes to dishwashers. While there are certainly some stragglers, most name-brand dishwashers on the market today are quiet enough to run in a library. Typically, they range from 45 to 50 decibels—roughly the noise level of typing on a keyboard, and just below the threshold needed to wake someone up.

Now compare that to dishwashers from the mid-2000s. Those machines averaged about 60 decibels—just below the sound level of a vacuum. So today's machines are much quieter, but the trend has had an interesting effect on consumers: Shoppers tend to overvalue the significance of the industry standard noise rating—the decibel A-weighting, or dBA.

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The dBA rating is complicated, but it basically boils down to this: Compared to straight-up decibels (dB), dBA puts emphasis on noises that we hear most clearly and de-emphasizes sounds that are harder to hear. The result is a rating that should, in theory, give shoppers a better idea of how much their dishwasher will annoy them.

But how did a quiet dishwasher become the envy of homeowners everywhere, and just how quiet is quiet enough?

Decibel Comparisons
Credit: Bosch

Once as loud as a vacuum, your average dishwasher is now quieter than a running sink.

A Quieter Kitchen

It was actually a German brand, Bosch, that first got Americans thinking about sound back in the early 2000s. The manufacturer already had a line of quiet dishwashers in the European market, so it had a leg up when it came to developing new models for quiet-hungry American buyers.

In short, Bosch anticipated a need that customers didn't know they had. Americans were starting to spend a lot more time in their kitchens, thanks the rediscovery of cooking via foodie culture and the growth of the "open kitchen" concept. Suddenly, a demand for quieter dishwashers was born.

The German giant met that need by fundamentally redesigning the dishwasher. Bosch engineers first incorporated a solid base made of heavy-duty plastic—the same material used in football helmets. They also installed a sensor-based drain pump that only ran when it detected the presence of water, eliminating much of the loud sucking noise heard during draining. Bosch also redesigned the hydraulic system, introduced a new filtration system to replace the hard waste disposer, and began using two motors instead of one to spread the work load.

(Not long after Bosch revolutionized the industry, a few retailers partnered with a sound lab to develop a standard measurement of dishwasher noise output. That's the reason for the ubiquitous dBA ratings you'll see in stores, in ads, and online—we'll explain those later.)

Dishwashers have gotten so quiet that the differences among them are hardly noticeable.

The result was a line of "SuperSilence" dishwashers that, today, operate in the range of 38-46 dBA. It also led to a race for the lowest possible sound rating. That's why Bosch's primary competitor, Miele, pushed hard to hit an impressive 37 dBA with its Futura Diamond model. Using a specific "Extra Quiet" mode, it limits mechanical action and prolongs the length of its wash cycles. In other words, it'll wash your dishes silently while you sleep, but it may take all night.

"Although there are peaks and valleys in measuring the sound levels during a wash cycle, we have managed to suppress even the portions of the cycle where the pump and drain noises are at their highest, turning them into a low-pitched hum," said Hiroko Kawaguchi, a product development manager at Miele.

Today there's a lot of one-upmanship between rival brands over decibel ratings, most of which fall between 40 and 50 dBA. But here's the thing: Dishwashers have gotten so quiet that the differences among them are hardly noticeable.

While there are certainly some noisy outliers—and our reviews make sure to point them out—pretty much every major manufacturer has gotten a handle on excessive noise. These days, you'd be hard pressed to find a dishwasher with a hard food disposer, let alone a noise rating over 55dBA.

Still, a lot of shoppers cite noise as one of their top concerns when buying a new dishwasher. In fact, according to Bosch, it's the second biggest driver for purchase—only after price. There are a couple of reasons why. One, quiet dishwashers were only introduced to the U.S. about a decade ago. Two, most consumers still own older, louder models.

"The average life of a dishwasher is 10 years, and 10 years ago an average dishwasher was around 60 decibels," explains Stephanie Hutaff, director of product marketing for dishwashers at Bosch. "The people who are buying them today are people who had a loud one."

According to Whom?

Though most manufacturers now make similarly quiet machines, there's a lot of mystery surrounding how noise levels are actually calculated. The dBA rating is designed to account for the level of stress human ears experience at different frequencies relative to their actual sound pressure. (It's important to remember that decibels don’t measure volume—they measure the intensity of sounds.)

Think of it this way: A 115 dB siren (high frequency) is a lot more abrasive than a 115 dB subwoofer (low frequency), even though they’re equally powerful with regards to sound pressure.

Acoustic Weighting Curves

The weighting of the dBA rating (blue) across the frequency spectrum

"When we hear a sound, what we're really hearing is the transmission of energy waves through the air," said Julia MacDougall, senior scientist at "Decibels quantify the energy being transmitted through the air over time. If a small amount of energy is being exerted over a given period of time, that noise will have a smaller dB value than a lot of energy being exerted over the same period of time. This is why it's easier to hear a lightning strike than it is to hear thunder."

The dBA rating attempts to compensate for this discrepancy by giving extra weight to high-frequency sounds and balancing sonic information regardless of the source's pitch, but it doesn’t perfectly account for the experience of human hearing. For example, our ears respond more sensitively to random, irregular noises, but the dBA rating is measured according to a flat, even tone.

Furthermore, dishwasher manufacturers measure sound levels in averages. That means they can lower their overall dBA scores by limiting the duration of certain loud or high-decibel activities. This makes for a quieter dBA rating, but it may increase wash times. That's one way Miele's "Extra Quiet" mode, for example, is able to achieve a rating of just 37 dBA.

But if you value peace and quiet—and still want clean dishes—that may be a reasonable exchange. As Kawaguchi points out, Extra Quiet will guarantee 37 dBA no matter how much of a mess you give it. "Miele machines will not increase their noise levels depending on the degree of soiling of the items in the machine," she said.

And that's an important point, as some third-party tests have shown that other machines produce a drastic spike in noise levels when washing heavily soiled dishes.

Dishwasher Rack
Credit: / Johnny Yu

What to Look For

In 2015, dishwasher noise need not concern you as much as it might have in 2005. Dishwashers, in general, just aren't that loud anymore, even if marketers try to tell you otherwise. That said, you shouldn't overlook the point entirely.

Dishwashers just aren't that loud anymore, even if marketers try to tell you otherwise.

Pay attention to the dBA rating, but remember that for the average dishwasher, a small dBA difference (say, the difference between Bosch's 38 dBA SuperSilence model and Miele's 37 dBA Futura Diamond) will be hardly perceptible to the human ear. Finally, dBA ratings do a poor job accounting for all those popping sounds and short, irritating bursts of noise that may occur from time to time.

So what rating should you aim for? Let's take a look at some examples:

  • Human speech in a quiet room typically ranges between 45 and 50 dBA. That means anything in that range is probably going to compete with a conversation between two people in your kitchen.

  • While much quieter, any dishwasher in the range of 40-45 dBA is going to at least be noticeable, but it's not going to force anyone in your kitchen to speak up.

  • If you really want a machine that can compete with the noise level of a fan, you'll have to look at some of the quietest models on the market (37-40 dBA). And don't pay attention to advertising claims that play up 37, 38, or even 39 dBA ratings. The difference between those particular ratings are virtually indiscernible to human ears.

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