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Essay

In Which the Dreaded Leaf Blower Gets its Comeuppance

Ted Mitchell explains in painstaking detail exactly why you find leaf blowers so damned annoying.
By Ted Mitchell
Published October 27, 2010

Ideas

Ah, Indian Summer. Fall is simultaneously my favorite and most dreaded season. Cooler days awake the senses and invigorate the soul; but in an otherwise beautiful season, there is one sure thing that will wreck your day.

This Halloween, the most hideous monster is the one packing a leaf blower.

The last two decades have witnessed widespread increase in the use of leaf blowers and other cheap two-stroke lawn equipment. Accompanying this has been a stunning lack of concern for negative effect of nuisance noise and air pollution on quality of life.

Using a leaf blower suggests vanity, laziness, and disregard for peaceful enjoyment of the neighbourhood.

Vanity, because most of the work done by a leaf blower does not need doing, and nature reverses it quickly. Small amounts of organic debris do no harm, and can hardly be seen from beyond your sidewalk. Once a driveway is pristine, entropy is sure to cover it with more organic debris within a couple of days.

By the way, what do you think all those leaves blown onto the road look like? What does this say about you?

Laziness, because tasks accomplished by a leaf blower can be easily done with a rake or a broom in the same amount of time. Both manual tasks, done properly, utilize the large muscles of the trunk and can be done by people of nearly every age and ability. And there is no other power tool that is less effective in saving time and work.

Odds also favour your doctor having advised you to get more fresh air and exercise - rather than standing like a lump breathing particulates, hydrocarbons, mold spores, and inflicting same on others. Not good for the back, heart, lungs, brain, or soul.

Utter disregard for others, because - try relaxing in your back yard with friends or a good book in earshot of a leaf blower.

You might be the nicest person in the neighbourhood, but that all ends when you pull the trigger on a two stroke engine. Action speaks louder than words or intentions.

Most leaf blower operators don't intend to degrade their neighbours' quality of life, but it is a predictable consequence.


Three Observations

Aliens who landed on earth with no predisposed biases would notice three things about leaf blowers, in this order:

1. Noise. Far before you can see it, the noise is shockingly out of place in a residential neighbourhood.

2. Air pollution. In terms of smelly hydrocarbons and other pollutant byproducts of internal combustion engines, two-stroke engines are off the map, many times greater than those of automobiles with displacements 100 times bigger. Many people refuse to believe this, but try taking a two-stroke small engine for a drive clean test - the garage will refuse because it could damage their equipment.

3. Moving debris around, rather haphazardly. Aliens, being smart, would know that a cylindrical fluid jet loses its coherent flow at about 10 length/diameter units, or for a leaf blower, about half a meter. Beyond this distance, air movement randomly swirls, which makes the job of directing debris awkward and inefficient.


Quality of Life

Many factors affect quality of life, and your neighbourhood is an important one. Enjoyment of the neighbourhood physical environment can be described by the quality of what reaches your senses of vision, hearing, smell and touch.

Although many people might claim to be vision dominant, unless you are both deaf and unable to smell, these senses play an important role in our lives. This is especially true since you can close your eyes but not your ears, and holding one's breath is not a long term option.

A leaf blower's marginal benefit of visual flawlessness only accrues to you and your immediate hawk-eyed neighbours, but the noise and air pollution diffuses to hundreds of people in the neighbourhood (more on that number later).

Labour saving is similarly vastly outweighed by the lack of psychological, cardiovascular and muscular benefits of aerobic exercise and fresh air.

If you really want to remove leaves from your yard with minimum effort and time, a rake and 3m tarp will make quick work of a blanket of leaves. You can compost them at the back of your yard, or funnel into bags.

I am allergic to busy work, but this is satisfying because it is so effective. Often I marvel at why anyone would bother doing anything else.


Psychoscaping

If you claim that the only important thing is the visual aesthetic, chances are you are impressed by this trendy form of landscaping. Psychoscaping is my term for the construction of elaborate designs using rocks, trees, gardens, water and lighting to create a beautiful yard that is unused and mostly unusable. It is the HD, 3D version of '70s photographic wallpaper murals, and about as sterile for the soul.

While gardens are lovingly tended by hand by their happy keepers, psychoscapers use a battery of power equipment to maintain an unspoiled appearance. Those doing well enough to afford psychoscaping usually hire out the maintenance, which means industrial strength lawn and garden tools - and industrial strength noise. In the psychoscaping arsenal, the most effective weapon of mass quality of life destruction is the two stroke heavy duty backpack leaf blower.

Why so Noisy?

A blower is a device designed to move fluid at medium pressure and flow rates. Fans are better for volume, and pumps for pressure. Leaf blowers are centrifugal fans with multiple spinning blades that accelerate air from inside to outside and force it through an outlet. The blades are oriented perpendicular to the outlet and generate noise by a rapid change in air pressure. This generates something approximating a square wave, which is one type of spectral character ( timbre is the musical term, which seems inappropriate to describe this kind of noise!).
The fundamental frequency is determined by RPM / 60 times the number of blades, for example in the electric blower above, 1800 rpm / 60 seconds per minute x 13 blades = 390 Hz. A sine wave generates a pleasant, gentle tone. A square wave of the same amplitude generates sound perceived as relatively loud and harsh. This is due to multiple harmonics above the fundamental frequency. In the above example, f = 390 Hz, f2 = 780 Hz, f3 = 1170 Hz, f4 = 1560 Hz, and so on.

Add to this the sound from a two stroke engine, where exhaust gas is rapidly released through ports with a tiny muffler and you get a similarly percussive sound of rough waveform, but at a lower frequency. The fundamental frequency is RPM / 60, for example 6000 RPM / 60 = f = 100 Hz, f2 = 200 Hz, f3 = 300 Hz. Adding the complex harmonics from these two waveforms is what results in a noise that is like the bastard offspring of bagpipes and an air raid siren.

Why so Annoying?

Thanks to evolution, sounds in the frequency range of speech are preferentially amplified by the outer ear. Our frequency sensitivity is reflected in the A-weighted decibel scale. It is not coincidental to why I wrote this article that leaf blower frequencies are right in the middle of the sensitive range of human hearing. Spectral character is critical to annoyance, and our complex appreciation of this explains the richness of sounds in an orchestra. Tonal sounds have a dominant identifiable pitch. Noise analysts add 5 dB to any tonal sound to reflect the additional perceived annoyance. Oddly, there is no further correction for complex tones like those generated by a leaf blower, even though everyone would agree on increased perceived loudness. When these harmonics vary in pitch or come in unpredictable and impulsive fashion, such as a barking dog, it is yet more annoying.

Sounds that are similar in frequencies, tempo, and tonal quality of human speech will be the hardest to ignore. Our brains are hard wired for language, and cannot turn off our enhanced sensitivity to such input. These sounds will maximally interfere with activity, especially those involving language. Conversely, broadband noise, where sound is present fairly evenly at all frequencies, tends to be the least annoying and can mask sudden, disturbing sounds. Some people prefer to sleep with a quiet fan for this reason. If you wonder if these effects might be lessened in people with hearing impairment, you would be wrong. Reduced intelligibility of speech in the presence of competing similar frequencies is the first sign of sensorineural hearing loss .

A sound pressure level (SPL) meter is useful for measuring if sound is loud enough to cause hearing damage, to determine the need for limiting exposure time and/or wearing ear protection. However, an SPL meter is of little value in measuring noise, even when using the A-weighting filter. The spectral character of sound contributes more to annoyance than SPL does. I have found that a SPL meter measuring a clearly annoying level of noise such as that produced by a leaf blower 50 m away, will register only about 3-4 dB above background noise of wind, birds, and distant traffic. This is almost insignificant from a sound analysis perspective. But in that situation, you would find very few people who could sit outside without being seriously bothered by the noise. Even more amazing is the intrusive nature of blower noise: when I cut grass using a four stroke lawnmower at low throttle and wearing -30dB earplugs, the sound of a leaf blower 30m away penetrates clearly.


Non-Acoustic Factors

Many factors linked to annoyance have nothing to do with SPL or spectral character. People tend to be much less tolerant of noise produced without obvious necessity. Ability to control the noise source enables tolerance of much higher levels, such as with a vacuum cleaner. Context is important, especially when noise occurs in environments expected to be quiet. Activities requiring concentration or language processing will be much more disrupted than simple physical tasks in a noisy environment. Individual sensitivity can cause wide variations in perceived annoyance for the same source. Some people tolerate very little background noise, a feature which correlates with a psychological trait known as " chronic wide breadth of attention ". Such people also tend to score higher on creativity measures, and historical records frequently mention noise intolerance in famous writers, composers and scientists. Alternately, some individuals are almost imperturbable by noise.


The Noise Horizon

As a rough estimate, I've measured out 50m and 150m as subjectively important noise exposure distances in an average residential area. Really loud two stroke industrial backpack blowers can push those distances to 100m and 300m, and are easily audible at 500m on a calm day. With the Kirkendall neighbourhood as a test case, I identified two areas of low and high density housing. Using the Google Earth measuring tool, a 50m radius covers between 8 (low density) and 26 (high density) single occupancy houses around the blower operator. Within this distance, the noise level is high enough to drive anyone indoors if they have the ability to do so. Between 50m and 150m the sound is clearly identifiable as a leaf blower and constantly audible above background noise. You might not change your behaviour at this noise level unless engaged in conversation, but you would note it as unpleasant. In the two examples I tested, there were 60 and 250 houses within this radius.

Try this yourself. Pace out your own subjective annoyance thresholds, then go to Google Earth and count the affected houses in your own neighbourhood.

No Sanctuary

Although the SPL of leaf blower noise goes down drastically once you are in your house, the quality of sound actually becomes more annoying, because of the effect of frequency-dependent sound dampening on tonal components. Finnish researcher Pasanen has studied this.

Using Pasanen's data, let's look at two similarly loud power tools: a leaf blower and snow blower. This particular leaf blower source is 2 db louder than the snow blower, which is a barely perceptible difference. For the blower, there are spikes at the fundamental frequency (125hz) and several harmonics, which will be perceived as louder and more annoying than broad spectrum noise of the same power.
The ear is always drawn to the loudest peaks; they dominate the perception of noise. The snow blower is a more broad spectrum noise with no discernable peak frequency. In other words, you can't hum along with it.

Pasanen then applied a filter protocol to mimic the average residential wall. What you get on the inside of the house is clearly much quieter than next to the source, but the character is now different, one could say enhanced. The frequency filtering effect of obstructions such as walls and trees always let low frequencies pass relatively unscathed. The noise spectrum after filtering is startling: a 2 dB difference has now become a much more significant 7 dB difference. Also note that the peaks are exactly in the frequency range of human speech, While the snow blower spectrum retains its broad shape, the filtered leaf blower spectrum has relatively higher peaks in the lower harmonics as compared to the source spectrum. The spectrum generated by the snow blower after filtering is similar to brown noise (1/f) of the type found in nature. The human brain is good at ignoring such noises; they easily fade into the background. The harmonically complex leaf blower noise is much more penetrating than other power tools such as snowblowers and lawnmowers, even if they are similarly loud at the source. It is really only the peaks that matter in the energy spectrum. If those peaks occur in speech frequencies, your ear cannot stop hearing them any more than it can ignore English being spoken. It does not easily fade into background noise, and stays annoying down to the limit of perception.

The Golden Rule

Many religions have some form of the Golden Rule. My favourite is from Hebrew scholar Hillel : That which is despicable to you, do not do to your fellow, this is the whole Torah, and the rest is commentary, go and learn it. To get to the heart of this sentiment, you have to think from the perspective of the other; do not do unto others what is despicable to them. In other words, practice respect through communication and understanding.

Using a leaf blower has nothing to do with self-respect or respect for others. There are many sources of noise in modern life, and it is better to chill a bit than get all worked up over noise pollution. But the leaf blower crosses the line: its use is too trivial, labour saving insignificant, time saving nonexistent, and the cost to neighbourhood quality of life is hideous. If there is one big thing that cities can do to improve and protect the quality of life of citizens, it is to draw the line at leaf blowers.


Further reading

* NOISE EFFECTS HANDBOOK
* Right to Quiet Society, Vancouver BC
* Lorraine Sommerfeld, Leaf blower blew away last rays of summer, The Hamilton Spectator
* Bad Vibes test

Some of the material for this article was sourced from a mechanical engineering paper I wrote in 2007.

Ted Mitchell is a Hamilton resident, emergency physician and sometimes agitator who recently completed a BEng at McMaster University.

He is fascinated by aspects of our culture that are harmful, but avoid serious public discussion.
The full article can be found here

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