Noise: A MO Investigation

It's everywhere you look!

story by Cheesebeast, Created Oct. 14, 2006
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..All the Who girls and boys
Would wake up bright and early. They'd rush for their toys!
And then! Oh, the noise! Oh, the noise! Noise! Noise! Noise!

- Theodor Seuss Geisel, How the Grinch Stole Christmas, by Dr. Seuss
New York: Random House, 1957.

The grinches at the National Institute of Health identify motorcycles, firearms and firecrackers as all sources of loud noise. Leave it to the NIH to write the prescription for fun. Perhaps as a motorcyclist you consider a hazard to your hearing trivial compared to the dangers presented by crack addled road clowns. Still, you can actually do something about this risk. I am sure you have been afflicted by the sneering self-righteous who examine your motorcycle and inquire: "So...do you wear a helmet?" I just soak up their venom, duct tape them to a chair and state: "Thank you for your concern. I wear a helmet. I also wear earplugs. Let me explain..."

A Fiend's Delight: The Sears Catalog of 1897 also offered Peruvian Wine of Coca for a mere $1.00 per bottle. inquire: "So...do you wear a helmet?" I just soak up their venom, duct tape them to a chair and state: "Thank you for your concern. I wear a helmet. I also wear earplugs. Let me explain..."

Part One: Sound - A Rustle In The Underbrush

Sound is a pressure wave. That pressure wave can be measured for intensity (watts/m2), and frequency (Hertz). For our purposes we will discuss sound intensity using decibels-which are in turn based on human hearing.

Human hearing has a surprising range to it. You can hear extremely faint sounds - from the threshold of hearing, or 0 decibels, all the merry way to the threshold of pain - 130dB. A sound at 130dB is ten trillion times more intense than a sound of 0dB. Unless you are Bill Gates or Carl Sagan, you are probably not comfortable flinging about billions, let alone trillions. Not a problem! The decibel scale is logarithmic and sops up all those pesky zeros.

Let's make this personal. Bob marinates in his cubicle, gazing lustfully at a Motorcycle.com bike review. Even with the background noise of the office (40dB) he becomes aware of an ominous sound. The sound in question comes from poorly fitted Italian loafers in the act of compressing carpet fibers (50dB). Suddenly Bob finds his cubicle besieged by the office annoyance. Cringing, Bob vainly pretends he is busy by wiggling his mouse. Too late, Bob. Too late.

"Oh, sorry Bob. Are you busy?"

Jumping from 40 Decibels to 50 Decibels represents 10 times the sound intensity- which means it is twice as loud! As with most blanket statements about sound, that is not truly accurate. Sound intensity is not the same as the perceived loudness of a sound. I am not done torturing Bob, though.

"Bob, you won't believe what happened to my cousin's neighbor. He had this motorcycle and..."

Bob tries to ignore the irrelevant story delivered at 60 dB. This is the level of "normal" speech. This means Bob is now being subjected to B.S. delivered with a million times more sound intensity than blessed silence (0 dB). At this point in the story a mythical motorcyclist has hit a mythical telephone pole. For a dramatic finale Bob's coworker rolls around on the carpet screaming out simulated death throes (120 dB). We will stop our murderous march up the decibel scale just south of the threshold of pain at 130dB. We certainly don't want to get to the Glock 19 (peak 150dB+) nestled in Bob's desk drawer, do we?

Bob's loud day continues when he gets home. The local garage band (Spankmonkey) is having a practice session. Bob puts his garbage can out on the curb and he watches as they close the garage door. This makes little difference. The low frequency of the poorly played bass and the frenetic drumbeats vibrate the walls of the garage and transmit right through. A window in the garage is opened to let smoke escape and that is when Bob is treated to frenzied shrieks and high pitched guitar wails.

The "music" follows Bob indoors. Bob knocks on his walls and discovers that they too vibrate at a low frequency, which is why he gets a free concert every third Thursday - at least the low frequency part. High frequency sound is more easily reflected - it is more "directional". This also explains why the neighborhood Harley acoustically saturates the neighborhood better than a weed whacker, even though they produce close to the same decibel level (and identical power on a dynamometer). Please be gentle with me - I bruise easily.

Review:

Too many zeros! Because of the human ear's sensitivity a logarithmic scale is used to measure sound intensity = Decibels.

Sound intensity is not the same as the perceived loudness of a sound, but look the other way for a moment while I state: If you increase the sound intensity by 100 times, or 10 decibels, then the sound will be twice as loud. Lower frequency sound is less "directional" than higher frequency sound. Lower frequency sounds usually transmit more efficiently into convents, churches, and daycare centers.

Part Two: Friends, MOrons, Countrymen, Lend Me Your Ears!

Your ears are designed to amplify faint sounds. What about really loud sounds - like motorcycles, for instance? The inner ear has a protective mechanism to handle loud sounds - it tightens muscles that limit the amount of eardrum vibration as well as the action of the three bones in the middle ear. This process does not work for sudden impulsive noises - like gunshots or a Bette Midler concert. When you shamefully ride your motorcycle without hearing protection you will probably experience this tightening effect in your ears. It is called a temporary threshold shift. I have forgotten to wear my earplugs on occasion. When the people in the office foolishly attempted to speak to me, the muting effect was obvious. Don't scamper off thinking this is a harmless thing, temporary at worst.

Exposure to loud sounds has a negative cumulative effect on your hearing. The damage done depends on a lot of factors - the level of sound intensity, time of exposure, personal physiology, hygiene....this means we get to play with one more type of math. Probabilities! Still, if you are likely to have caused damage, you are likely to have caused damage to the areas of the inner ear that allow you to figure out what the hell everyone else is prattling on about at the water cooler. Obscene gestures will only get you so far in this world and will not replace lost hearing. If I may be so bold to recommend the mohair Conversation Tube for a paltry $2.75?

Even if you can be helped by a hearing aid, there is a further penalty for damaging your hearing. You could develop tinnitus. Tinnitus is a "sound" only you can hear. It is essentially nerve damage. Constant ringing, buzzing, roaring...it depends on the individual. It never stops and there is no cure.

Part Three - Chinchillas that rock and lesser methods of testing sound.

In the 1970s a generation of darn kids put themselves at risk attending rock

Dasypus novemcinctusconcerts. To save a generation from itself local ordinances were hastily drafted, and scientists were asked to quantify the hearing damage caused by infernal rackets. In one inspired test six chinchillas were subjected to a live rock concert (placed one meter away from the loud-speakers). These chinchillas were then examined for hearing damage, and the results were mixed. It appears humans and chinchillas share a very similar sense of hearing (and varying susceptibility to hearing damage).(1) Regardless, when I discovered that chinchillas are used in acoustic animal studies I immediately hatched Plan A.

Plan A

Strap a chinchilla to my motorcycle. Expose it to the sounds of motorcycling. Manipulate the data. Report the results.

Flaws of Plan A

I would need more than one chinchilla to make this a statistically meaningful test. Chinchillas are expensive (150 bucks a pop!) - maybe I could get a bulk deal? I would hug them and love them and name them all Gabe. This could add confusion. I don't know how to test hearing loss in a chinchilla. My wife said no.

Plan B

I buy a commercially available sound meter and figure out how to mount it to my motorcycle.

Flaws of Plan B

Sound meters are not soft and furry. I still want a chinchilla. My birthday is coming up and I know she hasn't bought me anything yet.

In the end I purchased a Galaxy Audio CM-140 Checkmate Sound Pressure Level Meter and mounted it on my 2003 Buell XB9R. The bike was purchased second-hand,

I was too cheap to buy a cell phone so I mounted a cordless phone instead.and it came with a Jardine brand exhaust system. I did install a "quiet insert" into the muffler, and this does minimally decrease the sound output. Regardless, I am in the process of returning the bike to stock so please postdate your hate mail for at least a few months. The sound meter mount was constructed of aluminum stock bent to shape. It was secured to the bike using the rearview mirror attachment bolts. I needed to be able to see the test meter while keeping my hands free for sudden obscene gestures. Also, the meter can swivel, so the sound level can be tested from behind the fairing (this did not prove to make a significant difference).

 

Sound filters - dBA and dBC

The test meter can switch between two sound filters. We hear "more" at certain frequencies. The dBA filter more closely matches human hearing. The dBC filter takes more frequencies into account (particularly lower). Both dBA and dBC are important to motorcyclists. dBA is the filter that is used for noise enforcement. Don't recommend they change the sound meter over to the dBC filter, as the sound intensity level will significantly increase. This is because your motorcycle pumps out a lot of sound at lower frequencies (particularly <500HZ). The reason the dBC is useful to us is because this is how Noise Reduction Ratings (NRR) are determined for hearing protection.

This illustrates the difference between dBA and dBC readings. Both are taken at idle:


dBA: A reasonable volume
dBC: Putting it up to eleven

 

 

A proviso is in order. This test is meant only to demonstrate that a motorcycle is loud enough to cause hearing damage at operating speeds. I didn't test your motorcycle, which you might declare is a stealthy steed indeed. Here is my challenge to you - prove it or wear earplugs. Hint: if you have experienced a temporary threshold shift in your ears after you ride - you lose.

Speed (MPH) Gear
Engine RPM
dBA dBC OSHA Max Exposure (dBA)
75 4th Gear 111 120+ <1/2 Hour
75 5th Gear
4000 rpm
105 116 1 Hour

65

5th Gear
3500rpm
100 113.3 2 Hours
65 4th Gear
4000rpm
103.5 115 1.5 Hours
65 3rd Gear
5000rpm
110.6
<1/2 Hour
65 4th Gear
4000rpm
104.6
(behind
fairing)

1 Hour
55 4th Gear
3200rpm
102 113 1.5 Hours
55 4th Gear
3200rpm
101.6
(behind
fairing)

2 Hours
40 3rd Gear
3000rpm
97 111 3 Hours
0 (idle) 1000rpm 79.2 93.5 >8 Hours
0 3000rpm 95.3 107.2 <4 Hours
0 4000rpm 101.4 110.2 Depends on Police Response Time

Chinchilla Reference: 1 "Am I Too Loud?", Jour Audio Engineering Soc, V25, p126, Mar 1977. 

 

 

 

 

 

 

 

Do You Use Protection? All About Earplugs

Page 2 Do you lay awake at night wondering what differentiates a good disposable earplug from a mediocre disposable earplug? I certainly do. In a hoarding frenzy I collected 24 different pairs of earplugs. Deep in my basement I kept running my hands through my treasure, not wanting to share them with anyone. In a weak moment I wrote down my impressions of a pair of earplugs, and soon I just couldn't stop reviewing earplugs.

A pattern soon emerged. Most disposable earplugs are made either of PVC or Polyurethane Foam. The classic oil can-shaped PVC earplugs are what I used for years. I didn't see fit to try anything else, as I have a streak of my Great Uncle Jebidiah in me. He whittled his first set of plugs from a chestnut tree, and what was good enough for him is good enough for me. I was missing the boat. Polyurethane foam has made PVC plugs obsolete. I have seen the future and it is soft and foamy!

At the risk of losing the "G" rating of this review, the softness of the foam plugs makes insertion a bit trickier. I found the best approach was to reach over my head, lift the top of the ear slightly (which stretches open the ear canal), and then insert the properly rolled plug. This technique led to the most satisfaction.

There were criteria for picking the Top Five You Should Try. First, they had to

be comfortable. If they were not, then neither of us would wear them. Second in consideration was the NRR rating. They had to be equal to or greater than the PVC benchmark plug, which rates 29dB. Third, helmet use had to be determined - would the liner of the helmet compromise the earplug seal? I didn't consider the expense of the plugs, as this is frankly a trifle. You can afford a box of disposable earplugs. Stop supporting that plaintive waif in the Third World if you must budget something. You prefer the late-night lamentations of Sally Struthers? I thought not. Mail your pet waif some used PVC earplugs if it helps assuage your guilt. Then they don't have to listen to Sally Struthers either. The highly subjective test method was to ride my motorcycle to work (35 miles) wearing one set of plugs, insult my coworkers, change earplugs, and ride home. After twelve round trips I tabulated the results, threw the darts, drank the beer, lost the notes, and made it all up. The usual MO test process, in other words. (We seldom throw darts.-editor)

Comfort - what does that mean, exactly? Take this simple test for comfort. Insert

the earplug, and wait until the earplug is fully expanded. Now belt out Iron Butterfly's In-A-Gadda-Da-Vida at a lusty 110dBA. As your jaw moves up and down - you are singing, aren't you - you will notice the comfort of polyurethane plugs as opposed to PVC plugs. The PVC plugs rub my ear canals - the wrong way. Still not satisfied? The highest rated polyurethane plugs were comfortable enough that I soon forgot I was wearing earplugs. Now that is comfort.

Nothing is simple about sound, as you gathered if you survived the previous sections. You aren't naive enough to believe earplugs would be any different, are you? Remember that dBC numbers were used to determine Noise Reduction Ratings for hearing protection? I doubt you do. The math looks seductively simple. Your motorcycle produces 120dBC at 75mph. You take a set of earplugs with an NRR of 30. 120dBC minus 30dB equals 90dB...free and easy, hmm? Wrong!

You are probably not getting your full serving of NRR. The NRR of an earplug is determined in a laboratory setting. I would never be allowed near a laboratory setting, so you will have to use your imagination about what that constitutes. The "real world" performance of hearing protection is currently in debate. Let me cleave this Gordian knot: go with the best fitting earplug you can get - then factor in the NRR rating.

Earplugs are only part of your sound reduction strategy. I will go out on a limb (my natural habitat) and state a full face helmet will probably decrease your sound exposure - which in turn could buy you more exposure time. A helmet will not supplant earplugs, though - especially at the speeds you like to ride. Finally, and I am loath to mention this, but... you could make your motorcycle less noisy. Perhaps by reverting to the stock exhaust system? I know, I know. I am a dirty hypocrite. Look! A review of earplugs! Awesome! Wow!

The Top Five You Should Try

1. Howard Leight Max - NRR33 - Pink bell shaped polyurethane foam plugs. A most excellent plug - transparent comfort, excellent noise attenuation, and easy fit. Howard Leight shines on the competition (you hear me, E-A-R?) by stating the Max is: "The world's most-used polyurethane earplug." To which E-A-R probably responded: "You talkin' to me?" Bonus: They double as bath toys.

2. E-A-R Soft FX - NRR33. These are very soft tapered foam earplugs. They are lemon yellow in color. On the ride I could detect an intermittent whining sound emanating from the bike. I think it is cavitation in the fuel pump, but with the Classic 29dB PVC plugs the noise is a constant. The bottom line is that I can detect the difference between an NRR33 plug and a NRR29 plug. The roar of the exhaust is lessened by these earplugs enough I can also enjoy wind noise, helmet vent noise, fuel pump cavitation noise, and at slow speeds valve noise, the clicking of the turn signal cancellation button, the whine of the exhaust fan, and finally the CLUNK of the gear lever. Yes, I own a Buell.

3. Howard Leight LaserLite - NRR32. Pink and yellow in color. These plugs offer it all. I even made up a word to describe these: comfortabulous. I rapidly forgot I was wearing these, which really is a high complement. How good are they? Any better and they would be labeled a vice. Bonus: Shaped like an SR-71. A pink and yellow SR-71. Err....

4. MOLDEX Spark Plugs #6604 - NRR33. These polyurethane plugs go in as smooth as buttah. They are comfortable enough to forget you are wearing them and they block out as much sound as the other top poly plugs. I am not going back to PVC plugs. You can't make me. You could, however, bribe me into doing it. Bonus: They don't match - just like my socks.

5. Peltor Tattoo/Nitro - NRR32. These are softest urethane foam plugs in the top five, and they are quite narrow and rounded in profile. They are almost too soft, as you need some stiffness to get them into your ear canal. That softness delivers comfort, however. I can not discern a difference between an NRR32 rated plug and an NRR33 plug. If you have very narrow ear canals these may be the plugs for you. While I am not sure about the marketing soundness of associating barbed wire with ear canals, I dig the Tattoo pattern. The Nitro plugs are identical to the Tattoo, but differ merely in marketing savoir faire. Bonus: The Tattoo is badass, but in a feminine sense. Remember her? I do, and quite fondly. She had this tattoo...

6. E-A-R Soft Blasts - NRR33. Yellow with red flames. They are mildly stiffer than the Peltor Nitro/Tattoo plugs. They barely missed the top five - blame this on one of my moods, if you must. They work as well as the top five. I refuse to explain further.

7. Hearos Super Soft - NRR32. These are buff colored urethane foam plugs. They may not work for people with large ear canals - the plugs also live up to their name - super soft. I definitely had to lift the top of my ear to get these plugs to insert deep enough. The buff color could help hide the fact you are wearing earplugs, but not if you are not buff... colored.

8. MOLDEX Pura-Fit 6800 - NRR33. Lime green in color, simple tapered shape. Very soft and long - difficult at first to insert. Unfortunately it was raining when I tested these, so performance analysis was a tad cursory. Frankly I preferred the Peltor Tattoo and the Soft FX. These plugs, however, firmly established the dominance of urethane foam over PVC . PVC Plugs...are obsolete.

9. E-A-R EarSoft Grippers - NRR31. These yellow plugs are ribbed for your pleasure. They squish down quite well and the small tabs left on the end aid in removal - even if you are wearing gloves. They work great, but they remind me of an insect cocoon. The seeds of a quality urban myth these be...

10. Howard Leight Max Lite - NRR30. These are green polyurethane foam. They are very soft and expand a good deal. The NRR30 rating is, if anything, conservative. Comfort during the ride was absolute. Discomfort happened when I pulled the plugs out too quickly. They expanded to such a degree in my ear canal that I had pain in both ears. This could have been due to a pressure change? Bonus: If they were edible they would be low in calories.

11. 3M 1100 - NRR29. These are simple tapered foam earplugs. They are stiffer than the most of the other urethane foam plugs. Stiffness has its place. But not this time. This one is too soft...that one is too stiff. At least Goldilocks understands.

12. Peltor Next No-Touch - NRR29. The yellow stem is short enough it doesn't interfere with maintaining a seal once the helmet is on. I remain dubious about the stem, though. If you must have an earplug that you can remove while wearing your gloves, then these may be the ones for you. Very soft urethane foam.

13. Howard Leight Matrix - NRR29. I don't know what these are made out of. Urethane foam, with some kind of stiff core, perhaps? They were not as comfortable as plugs listed above. Bad news is best delivered quickly, with no pretense.

14. E-A-R Classic Superfit - NRR33. PVC conventional oil drum-shaped plugs. Same stiffness and required insertion force as the "classic" style plugs. They differ in that they are longer than the "classic" plugs, but that is the only difference I can detect. I don't know if I can insert them any deeper than the conventional plugs. I doubt it, so I find the NRR33 rating dubious. Bonus - racing stripes.

15. Peltor Next Triband Earplugs - NRR30. Another tired set of PVC plugs. I am over this phase in hearing protection, but I am partial to the Cat in the Hat color scheme.

16. Hearing Technologies - NRR29. These are generic PVC foam earplugs. They are indistinguishable in performance from the E-A-R "Classic" plugs.

17. Flents Quiet Please - NRR29. These are hexagonal in shape, which is cool. They are not one iota different in performance from the E-A-R Classic that I could tell. If you drop them they don't roll away as fast. That must be worth something to someone.

18. E-A-R Classic - NRR29

19. E-A-R Amigo - NRR29

20. E-A-R Grande - NRR33 These are three PVC plugs. The Classic is the benchmark plug for me - I have used them for years. They work well - but as of this test they have been made obsolete by urethane plugs. As for the three different sizes - the Amigo is a smaller diameter but the same length as the Classic, and the Grande is a simply longer than the Classic plug. I am dubious about the value of the longer plugs - and their claimed NRR rating. Bonus: Amigo and Grande plugs only - you can pretend to speak pitch perfect Spanish while wearing these plugs. Remember to trill your "Rs".

21. E-A-R Push-Ins - NRR30 with Grip Rings. Yellow with blue stems. The hard blue stems provide two problems, all in the same design. My ear canal is too narrow to let the earplug be inserted deep enough. Then the marginal seal is broken when my helmet is used as the stems drag against the helmet liner.

22.Custom earplugs made of clear silicone. I scored this pair of custom earplugs on the floor of a movie theatre. Unfortunately they didn't work very well. Wait a moment! Those are gummi bears!

23. Mack's Silicone Shooter's Putty - NRR22. These are odd blobs of silicone you roll into a ball and mash into your ear opening. You don't insert them into your ear canal - you plug the whole opening. I did not find them as effective in use as conventional earplugs, which is a shame. I haven't had this much fun with a pair of silicone blobs since....

24. SilentEar - NRR32 Reusable plugs. These are three different sized reusable plugs that seemed to hold great promise. Frankly I found them nowhere near as comfortable as foam plugs. The plugs are very rigid - they don't expand like a foam plug - instead they resemble small balloons. The rigid sizing posed a personal problem, as I had to go with two different sizes to properly fit my ear canals.

Ephemera

Wind noise: There is a lot published on how to mitigate wind noise inside microphones (a sound meter has an integrated microphone), but very little information is available if you want to measure wind noise. For continuity sake I left the small foam windscreen on the sound meter when I made these measurements. I did some test runs with the foam windscreen removed, and got an average increase of 3 dBA. However, the sound meter did have a larger variance in readings with the windscreen removed, particularly when cars passed by in the opposite lane producing a buffeting effect. Wind noise became the prevalent noise I experienced when I exceeded 65mph. Notice, however, that the engine rpm greatly impacts the amount of sound delivered.

Hey! My results vary! If you have the ambition to attempt to repeat these sound measurements....good luck. Variables include temperature, humidity, altitude, wind speed and direction, road surface type and condition, the type and configuration of the motorcycle, amount of refraction/reflection due to the surroundings, inherent accuracy of the SPL meter, current state of calibration of the SPL meter, zone of turbulence of the motorcycle in question, etc.

More on Noise Reduction Ratings: The NRR rating of a plug is not an accurate measurement of sound reduction. NIOSH (I won't decipher the acronym as it robs it of its mystic powers) recommends a decrease of 50 percent of the NRR for real world numbers. The 50 percent decrease may be suspect as well, for the test method they used is subjective. It included "naive subjects" (AKA idiots) who were only given what is on the hearing protection packaging as instructions. I am sure the scientists were distressed to see half of the test subjects with earplugs inserted in their nostrils.

Who is to blame for this NRR debacle? OSHA is frustrated with the EPA, who turn to ANSI, but ANSI is divided on deciding between S12.6 Method A and S12.6 Method B. ANSI's squabbles could be moot, as the EPA may turn to ISO to solve this mess. NIOSH is trying to stay above all of this, but it is no secret of what they really think of ANSI and their "methods". OSHA has resumed drinking in the broom closet and you know what happens when they partake of the grape. EPA in turn blames Congress for the lack of dough, and Congress blames the US taxpayer for being such a pack of parsimonious bastards. Essentially it is your fault and someone is going to have to drive OSHA home again.

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