the science of sound: how the products you use every day are engineered for your ears - recommended air purifiers

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Squeaking, buzzing, ringing, beeping, chirping, chiming, whining, thum, bangs --
All kinds of noise come from the equipment and machines in our house, they are not just annoying.
In the long run, they will have a profound impact on you in ways that are not always obvious.
Public health experts have long warned that prolonged exposure to noise levels of 85 decibels or more can cause hearing damage (dBA)
Everything from building equipment to barking dogs is OK.
But experts have also seen evidence of the physiological and psychological consequences of noise exposure well below this threshold.
"About 40 decibels-
Louder Than a quiet office.
We're starting to see emotional confusion, "said Erica Walker, environmental health researcher at the School of Public Health at Boston University and director of the community noise lab.
"When we reach more than 65 decibels, we see high blood pressure, increased secretion of stress hormones, increased blood thickening and cardiovascular mortality.
"When we fall asleep, we may be more susceptible to noise.
Laboratory and field studies conducted by researchers from the Institute of Aerospace Medicine of the German Aerospace Center show that sound
Pressure above 33 decibels-
What would you experience 4 feet from CR
Recommended low air purifier-
Can disrupt the sleep cycle, resulting in impaired mental capacity and may lead to other health problems.
There may be nothing you can do about the noise you encounter in the outside world, but at your home you can control the volume.
Here you can make a decision about the product you have --
In some cases, their noise is very different --
And how you use them.
"Your home should be a shelter," said Maria Rerecich, senior director of consumer reporting product testing . ".
"We know that the sound of the product is very important to the consumer experience.
That's why we test noise in 24 categories.
"Podcasts: Product noise testing and design reports point out that many appliances now handle their basic functions well --
For example, the washing performance of almost all dishwashers in our rating is very good or very good.
In this type of product category, noise may be a feature that shapes how you feel about the machine that will be used every day.
"If you don't take a little time to think about the noise of the product before you buy it, you might spend a lot of time thinking about it after you buy it," she said.
The significance of measuring noise is basic and extremely complex.
By definition, noise is just unwanted sound.
But for the group of experts who try to measure, control it and look for it in the products we use every day, noise can be a problem that needs very hard work, complex instruments, occasionally there is a little imagination.
John Galeotafiore, an engineer in charge of overseeing Consumer Reports testing of outdoor power equipment, spent a lot of time installing sound meters in an interesting way to simulate the location of the human ear.
"When we test the mower, We clip the mcculpa on the baseball cap," he said . ".
"This is important because it captures what consumers will experience in their own backyard.
These instruments measure the sound pressure level "(
That is to say, the pressure difference between sound waves and ambient air pressure, expressed in decibels)
This is relative to where you stand.
Therefore, during the noise test, we often place the sound table at multiple distances from the product.
The meter measuring 3 feet from the blowing machine will tell us if you need to wear a ear guard, and the same 50 feet away will tell us if you decide to leave early on Saturday morning, what might your neighbor hear.
But other factors also affect people's perception of noise.
Like music, most sounds are not monotonous.
It usually includes many different levels of frequency.
Experts usually use terms such as "pitch", "loudness", "softness", "clarity", "roughness" and "tone" to define sound quality.
All these qualities together affect our response to different voices.
Some sounds make us feel relaxed. Others—
Especially high-
Low frequency of sound or sound
Frequency of "pounding" sound
Annoying us can cause stress
Produce hormones
"The decibel level or volume of the sound will not let you know the whole story," said Jim Nani, an engineer who oversees consumer reporting on large electrical testing.
"You can have a fridge that runs very quiet but generates a closed one
Sound when the compressor starts. A sound-
The level gauge alone will not tell us.
To assess sound quality, CR used experienced sound judges who sat for hours listening to the complete cycle of appliances such as dishwashers and washing machines.
We also send experts to the homes of CR members to see how they use the product and what factors are important to them.
We found that some people like the sound of the window air conditioner to put them to sleep while others wake up when the compressor starts.
Home appliance manufacturers know how noise affects how consumers react to their products.
Many companies have spent decades testing and improving their products to eliminate their noise.
Sometimes, noise becomes an engineering balancing act that requires a measure of product performance based on the consumer's sensory experience.
Other times, this is a mystery of the sound that requires a little detective work.
The case of the hissing compressorgabricerrato is a detective who sounds good.
She is an engineer working for the main sound company br ü el & kjr r. and vibration-
A measurement company founded by a pair of Danish scientists in the 1940 s-
Pioneer of the subject of sound measurement Per Vilhelm br ü el and Viggo kj r.
Bruel and Kaya are among the world's largest producers of sound
Measuring equipment;
It also consulted with manufacturers.
Cerrato, a trained theoretical physicist, most of her work is tracking noise in consumer products and then looking for creative ways to control, shield, decay, shield, redirect
In 2001, before she started with Brüel & kjr r, a large home appliance manufacturer called on Cerrato to help with one of its refrigerators.
Like everyone else on the market, it has a quieter compressor than the previous generations.
In fact, it is so quiet that consumers are starting to complain about more subtle noises.
Noise is not necessarily great for annoying.
"I can play metal and Beethoven music in the same range, but they sound completely different," Cerrato said . ".
Cerrato started her investigation by recording the device in the semi-quiet room.
Rooms with walls and ceilings covered by sound-
Absorbing foam wedges
This allowed her to isolate all kinds of taps, rumbling, hissing and squeaking from the refrigerator.
While looking at the chart that drew the frequency of sound, Cerrato and her team of engineers found a color thread --
Encoding diagram: narrow band-at about 2,350Hz-
Just that high-
The tone below your skin.
But she says she still needs to find a "source of excitement ".
So she installed the accelerometer on the individual parts, and when the refrigerator was working in the loop, she was able to determine that the compressor's discharge system was the cause of the problem.
Cerrato and her team, in collaboration with the compressor manufacturer, recommend redesigning two components in the exhaust silencer, which are designed to reduce the noise and vibration in the compressor exhaust line, and the unpleasant noise is no longer noticeable.
In the end, the improved fridge is no longer quiet but sounds better.
"Decibels have nothing to do with this issue," Cerrato said . ".
"This is pure sound quality.
"When assessing noise, the human factor, and sometimes the most effective test equipment, is the human ear --
Or better yet, a bunch.
The raw data of the sound meter can tell you how loud or quiet a machine is from a specific distance, however, it does not experience sound in a way that provides a background for consumers.
Dishwasher manufacturers, for example, may post a low decibel rating to support the claim that the model is quiet.
This number may be accurate on average, but by combining readings of long periods of silent drying cycles with noise spikes from machines full of water and drainage, the data may distort the noise of the machine.
"I can explode F-
16 fighter jet engine for a few seconds, then turn it off and let it sit down all the time-
The weighted average score is equal to 40-
DBA dishwasher, "said Larry Ciufo, a consumer reporting test engineer in charge of the dishwasher lab.
"But what you will remember is the noise from the engine in those seconds.
"In order to better reflect the consumer's experience with the dishwasher, Ciufo uses the CR's Voice judges who evaluate throughout the cycle of each model we test.
They will even listen to the loops of the reference models we keep in the lab to recalibrate.
"We heard the water splash, the soap dispenser opened and the solenoid clicked," Ciufo said . ".
"We listen to everything --
Except dry.
Like most major appliances, the dishwasher has become quieter in the last few decades
Part is the response to consumer feedback.
On 1996, Bosch appliances in Germany were consumers-
No, the study found.
The dishwasher owner complained about the noise. Bosch re-
The dishwasher was designed, the sound insulation layer was added, the base was strengthened to reduce vibration, and the built-in
In the food grinder with filter, if the filter is blocked, it must be removed and rinsed.
This reduces both convenience and noise.
20 years ago, all the tested dishwasher consumer reports were self-contained. cleaning.
Nowadays, they are relatively quiet with more than 90% artificial filters.
The dishwasher still sounds loud, but now that consumers have more options, you don't have to pay a high price to get a quiet dishwasher.
When manufacturers need to have a better understanding of the sound quality issues of the product, they use a hearing panel made up of ordinary consumers.
David Bowen, director of the Acentech noise and vibration Group, an acoustic and vibration consultancy based in Cambridge, Massachusetts.
Such teams often help companies solve noise problems or simply guide them in designing products that are more acoustic compliant.
Like Brewer and Kayar's Cerrato, Bowen is a bit of a voice detective who has looked at everything from electric toothbrushes to electric curtains --
He even helped a golf brand.
Adjust the sound of its titanium driver playing golf.
Bowen's panel listens to the sound played by the speakers and responds with numerical values.
Bowen said: "We introduced people and obtained quantitative answers to subjective attributes, such as 'acceptability, 'like 'How this particular sound from this particular product is accepted
Panelists were asked to rate the sound based on their subjective impressions of various attributes associated with the product's own features, and Bowen used these results to build a customer-aware data map.
In 2004, Bowen turned to such a group, involved in a project to optimize the sound quality of the vacuum cleaner, and voted on the acceptability of the isolated sound emitted by the machine to the members of the group.
With the help of his group, Bowen concluded that Gao
The harsh scream from the cooling fan annoyed the user
The frequency rumbling from the belt-
Driving a clean head gives them a reassuring power. The solution?
They kept the rumble and changed the geometry of the fan housing to reduce the screaming.
Finally, one of the things Bowen's panels and even the most complex instruments can't predict is how his work will affect the fate of the product in the market.
"I don't know if our changes have increased sales, but it's better to operate the machine," he said. ”Best Noise-
Canceled the principal in order to fight some noise in your own life? These CR-
Recommended headphones can quiet the world around you by producing sound waves designed to neutralize external noise
They can also make your music sound great.
Editor's note: The article also appeared in the February 2019 issue of Consumer Reports.
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