Air Purifier, Quiet: Quietly Making Noise
Despite the universal, and often spurious, "silent" claim by air purification device manufacturers, “Noisy on the high speed” is by far the most frequent consumer complaint. Many resort to implying quietness: "Quietcaire." To be fair, the real issue is not how loud a purifier is on high, but how much sound does it make at the lowest speed which still produces meaningful airflow and air exchange rates. Several premium models are loud on high, but offer as many as six speeds for useful quiet operation. Sound is actually small changes in air pressure that move through the air. "Airwaves." Noise is just unwanted sound. Sound has two components: pitch and volume. Pitch is how quickly the air pressure is changing. Hertz (Hz) is the measure of pitch, we hear it as a scale from deep bass to tweeter treble. Volume is the size of air pressure changes, how loud we perceive a sound. The decibel (dB) scale measures volume. Sound measurement in decibels at 1-meter distance is considered standard, but it is easy to hide "at six feet" when posting air purifier test results. On the Decibel scale, each 10 points [dB(A)] added represents 10 times as much sound. The (A) means "A weighting", a compensation scheme for human hearing. For example; 70 dB(A), is not 17% louder, but ten times as loud as 60 dB(A). With many purifiers airing out in the low 70’s, louder than normal conversation, sound levels are a major consumer concern. Threshold of human hearing: 0 dB(A) Rustling leaves: 10 dB(A) Quietest air purifier: 15 dB(A) Soft whisper, peaceful living room: 20 dB(A) Good air purifier on low: 32 dB(A) Typical air purifier on low: 36 dB(A) Refrigerator: 50 dB(A)
Normal conversation: 60 dB(A) Dishwasher: 55-70 dB(A) Typical air purifier on high: 66 dB(A) Busy street traffic, Small orchestra: 70 dB(A ) Car interior on highway: 75 dB(A) Vacuum cleaner: 80 dB(A) Common home stereo listening level: 80 dB(A)
Lawn mower: 90 dB(A)
Front rows of rock concert: 110 dB(A)
The air purifier industry has no standards for sound emissions: only a few vendors voluntarily divulge actual decibel noise levels. Measurements are important, but they only tell half of the acoustic story, the listener is the other half. Many people will find equally loud purifiers are not equally distracting. This is because the pattern of pitches is different, mentally harmonious. When I was most ill, even minor sounds, which didn't normally bother me, became intolerable. The feeling we have that a quieter purifier produces reduced stress and better health is confirmed by scientific studies. Continued exposure to noise levels above 70 dB(A) in our airspace can cause hearing loss. Lower airborne sound levels affect learning, stress, and productivity. Noise levels greater than 50 dB(A) can make quiet conversation difficult. Other than the Ionic Breeze and its knockoff imitators, which produce little airflow, most air purifiers use a fan to move air. Despite vendor claims, nobody has found a way to clean air without moving it. Moving air makes sounds. Fans make noise. HEPA air cleaners with high internal purifying pressures require stronger fans, which may end up turned off.
We are encouraged to make a purchasing decision solely based on the room size an air purifier can clean. A larger capacity air purifier will clean the smaller room on lower speeds, often noiselessly. Many air purification buyers make the mistake of saving money by selecting a less expensive unit when the most powerful model in that same product line is maybe $20 higher. Within a given manufacturer's lineup, I almost always recommend the model with the highest clean air delivery rate (CADR) or fan strength in cubic feet per minute (cfm). A smaller unit must run on high continuously, and most smaller air purifiers are noisy on high. Notice again that absolute dB(A) noise levels are not useful without airflow data. If it isn't moving any air, who cares how "silent" it is? I try to cite a noise level with a related CADR or cfm rate. My IQAir HealthPro Plus, running on low, makes 44dB(A)@40 cfm air delivery. That is through a VOC filter. This is borderline inaudible, I sometimes have to look to see if the green lights are on. IQ Air Purifier HealthPro Plus Comprehensive Review The Blueair line has a reputation for quiet high performance (purifying particulate only). Blueair's 501 is a quieter air purifier (34.5 dB(A) @90 cfm) on low. The Blueair air purifier is a hybrid ionic near-HEPA machine. Blueair uses a relatively lighter electrostatic charge coupled with a slightly more porous HEPA-like charged media air filter to achieve HEPA efficiency. I like Blueair: efficient high performance without ozone emissions. Absence of VOC capability is the design drawback: no way can a big carbon filter breathe this fast. Blueair 401 is a seriously quiet bedroom particle remover! On low speed: 32 dB(A)@75 cfm, one of the quietest I have found. In second: 39 dB(A)@95 cfm, still very quiet. Third gear: 46 dB(A)@150 cfm, good. At top speed: 58 dB(A)@240 cfm. Blueair users report sleeping best with a 401. The Sharp FPN60CX operating in silent mode puts out a claimed 15 dB(A)@28 cfm. This is extraordinairly quiet. On high speed, with pure air CADRs averaging an acceptable 209, a claimed 40 dB(A)@212 cfm is also very impressive. These are the lowest published sound levels I have found. This unit is an ionizer advertised as not producing any ozone. I use this 12 Volt DC air cleanser as my closest air cleaner and ionizer, it is running now: my laptop is louder. Sharp Plasmascluster FP-N60CX Review The Friedrich C90a puts out an exceptional 55 dB(A)@365 cfm on high, but is known to make clicking static discharge noise and ozone that many buyers find annoying. In fairness, Ionic Breeze is nearly silent, and can work 24/7 without needing to be turned down. These air purifiers, placing most of the emphasis on the silence aspect, are still haunted by unresolved ozone issues. Air Purifier Design TradeoffsA poor quality fan and motor design is generally noisy. Well designed backward curved fan blades and sealed ball bearing motors are less noisy. They cost more. Noise can also develop when bushings wear out on cheaper motors, allowing side play of the fan shaft. When this slack allows fan blades to rub housings, noise and vibration increase. An air cleaner can be designed with additional mass to absorb noise. Weight is also a marketing issue for premium portable units. Too heavy, can't get it up the stairs, too light makes more noise. Central air purifiers, which sit in closets or basements with ductwork independent of the main HVAC, are a higher cost alternative for the noise sensitive.
Sound feeds on itself. The background level of our various air purifying experiments often has my wife and I yelling "I love you, now turn up the TV." Consider a typical home, with background noise around 45dB(A). The kids are napping. You watch TV at 60dBA, 15dB above background. Your air purifiers are running on high, making 66 dB(A), drowning out the TV. You turn up the TV and things are ok. When your spouse gets home and starts the dishwasher at 59dB(A), conversation is difficult. Your in-laws come over to watch the game, with their kids and dog. Your kids get up and start galloping around the house. The dog feels unloved and barks to get in. The TV gets turned up more… A sound absorber reduces noise in a room by absorbing a portion of the energy. Furniture, panels, fabrics, or houseplants can be arranged to channel noise without restricting airflow. The heavier an object is, the more sound energy it can absorb. Place extra mass between the noise source and you. Plants, with many reflecting surfaces, make good sound dissipators. I have five air purifiers in my 700 square foot apartment. In the living area where I work, two cute little Holmes HAP-242's chug away 24/7. These economy units have been torn down and sealed with scotch tape, and additional prefilter materials added. Also in the front room is a Honeywell 50250, a 14" round workhorse with an average clean air delivery rate (CADR) of 250. I also run a "poor-boy", a 20 inch box fan with filtration material duct-taped to the back, in this room. During the day the Holmes are both on high, "R2D2" (wife's nickname for the big round Honeywell) is adjusted to what I think particulate levels are at the time. It is important to realize that airborne particulate levels fluxuate dramatically, with foot and pet traffic across carpets and furniture a key impurity agitator. In the evening when my wife comes home, we may shut down the front room purifiers down while conversing or watching TV. My bedroom has another 14 inch round Honeywell, a 12520. It runs all day, generally on low. An hour before bed, it's time for pure burst mode in the bedroom. I turn my prized possession, an IQAir HealthPro Plus, on speed six (high), and the Honeywell to high, a ceiling fan also runs to stir up impurities. At bedtime, the living room goes on high and bedroom to low. My bedroom Honeywell goes off, and "Big John", the IQAir, is stair-stepped down to speed two or three, where it barely whispers through the night. My superquiet Sharp FPN60CX, in negative ionizer mode only (oxidizer off), runs on my nightstand. It blows across my face at night. I feel, but do not hear it.
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Here is a resource for the noise problem; White Noise Machines at Nature's Tapestry like the popular Sleepmate, plus BlueAir purifiers, educational toys like Magz, MagnaTiles and Zome Systems and unique gift ideas like SoapRocks, Bicalho wind ups and solar rainbow makers.
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There are also isolation duct kits, like the IQAir illustrated, which could be used to create a really noiseless air purifier installation. I think they are cost-effective only for the extremely sensitive.
