Earplugs for Commuters

Recently I have moved down to London for a placement role as an acoustic consultant over the next year (before I go back to uni and finish my degree). Since being here I have learnt many new things about my subject as well as been getting into the London life and that as a commuter in a working job. Because of this I have obviously been spending a fair amount of time on tubes and trains around the capital, and have been getting to know the tube map quite well. Anyway, it was as I was on one of these tube journeys the other day that I had a thought – should commuters wear ear plugs?

London Underground

It was as I was on the Jubilee line that I noticed high noise levels, so being the acoustician I am, I pulled out my iPhone and opened up the dB meter app. As I looked at the screen I was shocked to see levels around 90-100dB. If you are not aware of the scale of deciBels, this is about the same level as a klaxon or a nightclub. For workers, there are regulations set out to employers for daily/weekly exposures that employees can experience. These are 80dB as a lower limit and 85dB as an upper limit, whereby hearing protection should be provided for the lower limit and hearing protection is mandatory at the upper limit. Note, these aren’t maximum levels that can be experienced, but average levels over a whole working  day/week. Although saying this, if a commuter had an hour commute each day (to and from work) with an average level of 86dB during these periods, then they would have already reached the lower action limit of their daily noise dose! For occasional exceedances, there is a level of acceptability in this, however for continued exceedance, long term effects can occur.

The image below shows a noise map for Zones 1-3 on the tube produced by London Southbank University. These levels are averages, so theoretically higher levels are possible that what is shown.

Noise map of zones 1-3 of London underground, produced by London Soutbank University

Noise map of zones 1-3 of London underground, produced by London Soutbank University

With newer trains being introduced to the underground, these levels are being reduced to a more acceptable level (see the circle line above) however should we do something about it ourselves?

One option is for commuters to wear earplugs, however I don’t realistically see any chance that TfL may start handing out free earplugs or commuters wearing them any time soon! The alternative I see is simple and is already common to many commuters already – headphones. With headphones in our ears, even though we are adding extra noise, we are also reducing the background noise around us, thus reducing noise exposure (so long as we don’t have our music too loud – but that’s an issue for another day)!

From what I found by looking at various sources, I reckon that a standard set of headphones can reduce ambient noise by 20-30dB (depending on quality/type) with noise-cancelling headphones giving even more attenuation. Due to an acoustic phenomenon called sound masking, we can assume that anything that is more than 10dB less than the dominant level is not clearly audible, thus making the background noise from our commute seem no problem compared to our music. There will still be elements that we do notice however, mainly bassy rumbles and thuds, but this is because headphones do not produce low frequencies like this so well.

With the world around us getting noisier than ever, we need to protect our hearing as otherwise we will lose it later on in life. A daily commute is something that so many don’t even think to be a problem, when really it can be, but we’ve just learnt to live with it. What is your daily commute like, do you ever worry about it being to loud?

Notes

[1] London Southbank University Research

[2] Sennheiser Website

[3] Health and Safety Executive Wesite – http://www.hse.gov.uk/noise/index.htm

Silence is Golden

What do you think of when you think of holidays? Maybe sandy beaches, sunny greek islands or chilling by the pool with a piña colada… Well what about sounds? I mean what sounds remind us of summer and particularly of holidays?

As I was on holiday recently this was the question I suddenly found myself thinking as I was driving around the greek island of Kefalonia with the window down looking out and listening to the sights and sounds around me. I think we can often too easily take for granted the sounds that we get on holiday, when I think they are such an important part of it. Imagine sitting on a perfect scenic beach and all you can hear is road noise, a nearby factory or constant aeroplane noise, it’s not a nice thought is it? Now imagine the same scene but all you can hear is the smooth sounds of grasshoppers and the water lapping up on the shore of the beach – I know which one i would prefer! And yes sounds can be replicated but it’s not quite the same is it.

For me, those sounds of grasshoppers, birds, sea and otherwise silence is just something you can’t replicate anywhere else, it’s something you need to experience first hand. Each of these is something we have in the UK but we never get to fully appreciate them as there are so few places that are unaffected by noise pollution now.

The video below gives a couple of short clips I filmed on holiday of some of the sounds I heard and enjoyed.

What are your favourite holiday sounds? Are there ones in the UK that you appreciate that you don’t get abroad?

Solar Roadways

I love this clip and the concept of solar roadways! The idea behind the panels is so simple, yet the possibilities for what could be done with it are endless. The integration of heat and LEDs I think is brilliant and solves so many of the problems faced on our roads today. As a driver I look forward to this being introduced to the US and also UK, but as an acoustician I would be interested in some of the aspects of their design; let me explain.

The roads we have nowadays are smooth and even so, we get vast quantities of noise pollution near busy roads. This noise varies with speed: at lower speeds the noise is predominantly from the engine, however at high speeds it is dominated by tyre noise. Tyre noise is affected by the tyre material/texture depth and road surface as well as common factors to all noise such as Traffic flow, road gradient and percentage of HGV’s compared to normal traffic. Assuming all other factors would remain constant I wonder would the dimples seen on the design for the panels affect the noise created by the road? If so, I would then wonder why they would design it like that, specifically if it is meant to be designed for the future – to me making roads louder seems to be going back a step?

Maybe there is a reason behind the design, I’m sure on a project of such magnitude there would be a considerable amount of testing, of which noise would definitely come into. However, if dimples are really necessary, I would wonder if maybe they could be used creatively? This reminded me of another roadway project that had been created elsewhere, one which is a musical road! It works on the principle of grooves in the road and when cars drive over them, the grooves resonate and cause a tone depending on their spacing and traffic speed, which when put together can create a tune. Maybe they should try that as part of their new solar panel roads, I mean if the noise is less annoying then there is less chance of complaint, right?

There’s many interesting ideas for what could be done and where we could go with this concept and others for roadways of the future and I for one can’t wait to see them! What do you think of the solar panel road concept and the musical road? Would an increase in noise level put you off the idea of it?

“Fus Ro Dah”

Interesting Post this by my course mate Chris, where he asks the question of whether we could use acoustics as a form of weaponry. Deterrents such as the “Long Range Acoustic Device” (LRAD) and “The Mosquito” are possible and have been used in society, however unfortunately as Chris discovers, acoustic weaponry, like that classic “Fus Ro Dah” attack is but a nice feature on a game (see Robert Bungay’s post).

Notes:

[1] Could an Acoustic Weapon Make Your Head Explode? – http://cperryacoustics.wordpress.com/2014/04/10/could-an-acoustic-weapon-make-your-head-explode/

[2] See how many decibels it would take to tear apart the Universe? Have a look! – http://rbungay.wordpress.com/2014/05/06/see-how-many-decibels-it-would-take-to-tear-apart-the-universe-have-a-look/

CPerry Acoustics

Humans have an audible hearing range between 20Hz and 20000Hz, but sound waves do exist below and above this range. Sound waves below 20Hz we cannot hear, but we can feel. The pressure of the sound wave is still there but our ears are simply not equipped to hear it. This pressure can still affect our body though. The low frequency waves cannot just vibrate our ear drums but our entire bodies. This could potentially cause devastating effects when they are at very high levels.

There was a Russian born French researcher named Vladimir Gavreau who supposedly did research into the effects of infrasound (below our audible range) and has results which ranged from people being sick to having their internal organs liquefied when exposed to an infrasonic whistle for prolonged periods of time. However this is widely considered to be a conspiracy theory.

sonic-weaponssound_cannon

Theoretically, however, it is certainly possible to create…

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Pyracoustics

After seeing this video last week, it is definitely on my list of things to do this year! I’m currently unsure on my exact design, or whether I will create a Ruben’s tube instead, but nonetheless it is still a really cool idea (and probably the most interesting visualisation of acoustics)!

One of my current ideas is to create a few smaller Ruben’s tubes of varying lengths, each driven by a driver playing the same source. Because of their different lengths, they will resonate at different frequencies, each causing a different pattern of flames as the same source is played. If these were placed together (maybe in a stacked pyramid style) as music is played they would make a really cool music visualisation.

What do you think of the pyro board, have you seen anything like it before? If so, let me know or also if you have any other ideas for things I could try and build.

Doppler Effect

Today I received a Tweet with a question regarding a principle of acoustics, which I aim to answer in this post.

The effect that causes this pitch change is known as the Doppler Effect and regards the change in frequency of a sound source for an observer moving relative to its source. To understand how it works, a few basic principles must be underlined.

Sound is created by pressure changes in the air, which is caused via vibrations of an object (e.g. a speaker). As the speaker vibrates outward, pressure is increased in front of it and as it moves back inwards pressure is decreased again because it is compressing and decompressing the air particles in front of it. These pressure changes travel through air, away from the speaker, at a fixed speed of 344 metres per second. To play a lower pitch (or frequency) sound, the speaker vibrates slower (less vibrations per second). As the pressure variations (sound waves) move away from the speaker at the same speed no matter what frequency is made, there is a greater distance between the sound waves at lower frequencies (as the sound wave has had more time to travel further between the speaker vibrations).

Now back to that siren… As the fire engine travels, the sound it is creating from the siren, travels away from it in all directions. This next step best illustrated with a diagram:

Doppler Effect

Watch a video that animates this

The lines around the fire engine represent the sound waves travelling away from it. As the engine moves forward, the speed at which the sound waves travel away from it (in the same direction the engine is traveling) decreases because it is like the engine is ‘chasing’ the sound waves. This causes the distance between sound waves to decrease. This also means that the engine is ‘driving away’ from the sound waves travelling away behind it and, like said previously, a greater distance between sound waves relates to a lower frequency.

This means that if you are standing on the side of the road and an ambulance drives past with its sirens on, as it comes toward you, it sounds higher as the distance between sound waves is short, but as it has gone past the distance between sound waves increases and it has a lower pitch. This effect creates the classic sound we are used to when we want to recreate the sound of a car going fast, because the greater the speed of the vehicle, the closer its speed is to the speed of sound, the shorter the distance between the wavelengths in front of the vehicle and the more noticeable this effect becomes.

If you are in the vehicle however, this effect is unnoticeable because you are at a constant distance from the sound source (e.g. the siren/engine) meaning that the sound does not change relative to you. Also, if you are standing on a path and a vehicle goes past very slowly, it is not noticed as the difference between the speed of sound and the speed of the vehicle is so great that there is no noticeable effect.

As an aside, you may wonder what would be to happen if a vehicle did go faster than the speed of sound. This can happen, but only in planes as 344 metres per second is the same as 770mph. A sonic boom is created when this happens and is the sound of the shock waves as the object passes this speed.

Of course as some of you may be aware, the Doppler affect has been mentioned on TV before in the Big Bang Theory and I couldn’t really write a blog post on it without including the clip…

To Silence All The Gun Nuts…

This article was written by my course mate and good friend Dom Attwell, who writes about the perception, theory and practical effectiveness of gun “silencers”. A very good article worth reading, one of the best I’ve read for a few weeks!

DomJohnAttwell - Acoustics

The confession:
To begin, I must iterate that I am not a gun specialist. I have never even held a firearm that didn’t shoot BB-pellets or lasers. That said, my kill-death ratio on computer games is out of this world… literally (I mostly play Halo).

The Question:
I get a lot of questions concerning the efficiency and plausibility of gun silencers. Hollywood tends to take great artistic liberties with these ‘magical’ devices, with the explosive discharge of these lethal weapons sounding more like a kitten sneezing.

Handgun with SilencerMotorbike Silencer

Ever heard a gunshot at close range? You would definitely know if you had…

The Life Story: (if inpatient just jump to ‘The Gist’…)
Late last year, our course was given an ‘acoustic tour’ of the Halle Orchestra’s Bridgewater Hall in central Manchester. While there, we conducted an experiment to measure the hall’s reverberation time, which involved creating an impulse response. Due to the hall’s…

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