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?

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

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?

Denman Audio

Audio technology has come a long way since the early 1900’s and this can be seen by the size of the Denman horn, which is a massive 27ft long! When this horn was built, it produced incredible quality audio and it still does considering how long ago it was built. Even though it was built all that time ago when sound equipment wasn’t great, just a little knowledge of some basic acoustic principles meant that this horn could be made. Nowadays we have many ways in which we create high quality audio, particularly in  smaller and smaller enclosures, but the same basic principles used back in the 1930s are still in practice.

Horn loudspeakers work the way they do because they create a greater pressure around the speaker cone, which is the same effect of putting your guitar amp in a corner. When a sound source is placed on the floor, the area in which sound can propagate into is halved (assuming it propagates in all directions evenly and cannot propagate into the ground), meaning that the sound  pressure is doubled. This effect happens again when you place it against a wall and again when in a corner, hence if you want the best response (particularly bass) from your guitar amp, then stick it in a corner. As the horn surrounds the speaker, the sound pressure in massively increased and sound level becomes greater.

The gradual flaring out of the horn is used to slowly match the pressure around the speaker to that of the natural environment, reducing unpleasant audible effects that this could cause otherwise. As length of the horn increases, the  low frequency response increases, due to the longer wavelength of low frequencies (a greater distance between their sound compressions).

These methods can still be used today, but are altered into a smaller context, or are implemented in a different way, often taking advantage of the resonant frequency of a speaker enclosure, in an attempt to boost the signal. Nowadays a more common method is use of a vented box (a speaker with a hole in the front). Even though we no longer have to have a 27ft horn in our house to get high quality audio, there are still many things we can learn and use from audio methods of the past like the Denman horn.

What do you think of this, would you still want a music player in your house if it was the size of the Denman horn?

Notes

[1] BBC News Article – http://www.bbc.co.uk/news/uk-27483035

“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/

Beats by Apple

So those who know me will know that I like my tech, especially that which has a shiny apple on the back of it, which meant I was interested to read this week about Apple’s latest purchase. If you hadn’t already heard, Apple are currently in the process of buying Beats, the headphone brand that Dr Dre is co-founder of for $3.2bn. Generally speaking, this didn’t really surprise me, but deep down I kind of wish it had shocked me more… Let me explain.

Beats are a brand that can really split opinion (like Apple) and this opinion massively depends on who you ask. Ask most people on the morning commute and I imagine that most of them will like, or possibly own Beats, but ask any audio geek or tech fan and 9 times out of 10 they will probably have the opposite opinion. The brand is one that is very desirable and aesthetic based which, although is not a bad thing, can mean that you pay extra for the letter ‘b’ on each ear ‘can’. If this is compared to a brand like Bose for example, whose business strap line is ‘Better sound through research’, vast differences can easily be seen.

Bose (or Sennheiser for example) are both tech companies, based to create products with cutting edge tech that sounds great, whereas Beats do that with more of an emphasis on image (this is starting to remind me about the whole Apple vs Microsoft debate!). Headphones naturally are a more desirable accessory to own (as written about by a blog from Trevor Cox when comparing public perceptions for headphones vs loudspeakers), so I guess part of this comparison between companies could be to do with the background of the company.

Infograph of most common words associated with Headphones and Loudspeakers. Words nearer top related more to loudspeakers and vice versa. Words on right more commonly used than those on left. Credit Prof Trevor Cox

One major conflict of agreement will come when the quality of audio produced by Beats headphones is mentioned, some love it, some say it is awful. For me, I would prefer a pair of headphones by a tech company, but I can see that Beats do make some good sound. The main advantage to Beats audio quality is that there is bass and lots of it. The target market for these is primarily younger who listen to bassier music, which makes sense. Bass tones have the effect of making the user feel like that the sound is more immersive. This is to do with the wavelengths of bass sounds being bigger, hence it physically surrounding the listener more meaning they can feel the sound, not only through their ears. However, bass is not the be all and end all of audio quality; there are many more things to look out for in a good set of headphones (Comfort, Clarity, Sound Isolation, Frequency range, Price/Value for money…).

So if the quality is not so good, why do people buy them? To be honest, most people may not be able to notice the difference, or may not really care. One of my course mates wrote an interesting blog this week on whether we really care about the quality of our music, or whether we just go for convenience which I would recommend if you get a chance. One other main factor is again about appearance, if you’re going to spend £100-200 on some headphones, you want them to be noticed!

To me, Apple is a company of quality, yes with a big emphasis on image, but mainly focused on quality (more generally speaking and not when it came to audio!). Hence, when I saw they were buying Beats, I was kind of disappointed that they had opted for image over top end quality. Saying this though I can’t imagine them ever having bought a company like Bose or Sennheiser. When it come to brands (particularly those that make tech) people really buy into products, which is a factor that makes a huge difference (e.g. opinions of peers etc). Because of this I can imagine plenty of you will have different opinions to me! I would love to hear these if you want to comment below, alternatively click below which of the two options you’d choose!

Notes

[1] BBC News article – http://www.bbc.co.uk/news/blogs-magazine-monitor-27340356

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.

Dear @BASouthgate please could you explain to me why the siren sound changes pitch as a police car passes by. #neenor #blog

— Paul Southgate (@pablo_nwi) April 22, 2014

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:

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.

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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Seeing is Hearing

As kids we get taught about the 5 senses: sight, hearing, smell, taste and touch. They are each perceived by a different part of the body, i.e. sight with eyes and hearing with ears. But what if what we see clashes with what we hear, can we really hear with our eyes?

This short video is a really interesting view over an aspect of psychoacoustics looking into this. What makes this effect even better is that even when you know what’s happening, you can’t stop your brain from interpreting it as different.

Maybe we should stop relying on our eyes so much and start hearing with our ears, besides that was what we have them for!

Notes

[1] IoA SoundBites Spring 2014

[2] BBC 2 ‘Is Seeing Believing’ Documentary