Selective What?

So we’ve all heard of selective hearing, it’s the process whereby we listen in to things depending on whether we want to or not. I often remember being told by my mum that I only listened to things I wanted to hear and never when I was asked to do jobs around the house… (surprise surprise!) But is this actually a real thing?

Well in short yes, it is and is also known by some as the ‘Cocktail Party Effect‘ which is where we selectively pick out and listen in on the conversations we want to hear amongst a general background noise of many conversations. When I read about this, it reminded me of a story we were told at school in assembly once, which went something like this…

There were once two guys walking down the road together, trying to hear themselves and have a conversation over the noise of the cars going past. Then one of them stopped, turned to the other and said “Can you hear that grasshopper?”. “Of course I can’t! That’s crazy, you can’t hear that” replied the second man, “It’s far too noisy to hear something so quiet!” However, the first man knew he was right and replied “No, I did hear it and I bet you could hear it as well if you wanted, you just don’t want to”.

At this he pulled a small coin out of his pocket and dropped it onto the pavement below; as he did so several people around them stopped and looked down as if to check if it was them who had dropped their money. “See” said the first man, “They can all hear the coin, just like I can hear the grasshopper, the only difference is what we’re listening out for”.

This, although a very basic idea of what I’m talking about, does represent the theory quite well. The effect is something that is of particular interest to neuroscientists and also in the realm of psychoacoustics. It is linked to the brain’s capability to focus on particular information that it is interested in or can relate to (i.e. when you hear someone mention the name of the town you’re from). Studies have now been done in audio signal processing to create a program that can separate out different signals from a general noise (e.g. separating a piece of music from a signal that has talking over the top of it). This helps us to work  out how the brain works and also may have the potential to be used for security and data analysis in the further.

Coffee Shop

Because of this effect, people often find it hard to work when conversations are going on around them, which could be part of the reason why coffee shop noise is considered by many to be good for creativity. Background noise for many, is useful as it is so common now in our everyday life that a lack of it can often seem unnatural. With careful acoustic design through sound diffusion and by using large volume spaces (i.e. high ceilings) sound in these places can easily be dispersed giving a general background noise but where individual conversations are hard to pick out. Nowadays, as open plan offices are becoming more and more common, this knowledge is becoming more and more vital in order to create a creative and calm working atmosphere.

Where do you find it best to work, do you like the idea of open plan offices/coffee shops or do you work best with complete silence? Have a listen to Coffitivty and see if you find it easier to work to!


Stationary Falling

As it is currently half term, I have had several family members vising this week, meaning I have been out and about in Salford and Manchester, often visiting places I haven’t been before. One of these trips out was to Airkix, an indoor skydiving tunnel by the Trafford Centre, where I was lucky enough to be treated to a flight with my uncle and cousin.

It was such a surreal experience, falling in a vertical tunnel, yet not moving anywhere, whilst spectators sit around drinking tea and watching you. Despite my clear lack of skill, it is something I would definitely recommend if you ever get the chance.

Obviously, when doing activities like this there are many risks involved, hence why we had to fill in forms saying we were fit to partake. Apart from the obvious risks (dislocated shoulders, falling, or crashing into walls) there are other aspects that need to be taken into consideration; the main one of these, which you may have already guessed, is your hearing.

I don’t know if you’ve ever been on the phone on a stormy day, but it is often really hard work when all you can hear is the wind, making the conversation very hard. Now this is one thing, but imagine winds of up to 180mph (the speed that this tunnel can reach) and imagine not only how hard it would be to hear, but also the effect from pressure it would have on your ears. Thankfully, before anyone goes into the tunnel, they are given earplugs in order to protect hearing, but do these make any difference?

First of all I calculated the sound pressure of 100mph winds (about what it took to lift me) as around 1,200Pa, which when converted straight into decibels, is around 150dB. This initially does look extremely high (the human threshold of pain is around 120dB) even with the earplugs, which have around 30-40dB attenuation; however a few factors need to be taken into account first to understand how this is safe. This pressure is obviously needed to lift a person, but may not necessarily directly relate to sound pressure.

There may be a very high pressure at a stationary point in the tunnel, but the ears are covered by the helmet which are also facing outwards, not down, so most of the air goes rushing past. This leads to probably the main principle of acoustics, which is that you need something to vibrate in order to make sound. In the tunnel, if wind is rushing past at around 100mph, which may make a lot of noise due to the fans, the vibrating air particles are flying straight past you so fast that none of them are around enough to cause high Sound pressures. There is also quite a distance from fans to receiver and the way these fans work is shown on the Airkix website.

The duration of the flights are only 1 minute long (around 15 seconds longer than the free-fall when parachuting) which shouldn’t increase the Leq (the equivalent noise level if played constantly over a given time) excessively based on the whole duration of the visit to the centre. This is often why parachutists may wear earplugs for the noisy and longer plane journey up, but not for the flight down.

One final major factor could be the psychoacoustics of the noise, being the sound of wind, which is familiar meaning the flier feels less threatened and can be perceived as less. This could be linked to the frequency distribution of wind, which may be such that it does not affect the human ear so much. There are also likely psychoacoustic effects of giving out earplugs, whether they make much difference or not.


What do you think? Have you ever been skydiving or experienced high winds and noticed any effects on your hearing?