Why do we sound different in our heads?

So there is nothing worse than hearing yourself back on a recording… but why is it that we sound so different?

The sounds we hear are waves of pressure that move through the air, when these sound waves reach our ear they travel down the ear canal and strike the ear drum, this starts to vibrate. The vibrations travel to the inner ear where they are translated into electrical signals which are sent to the brain.

So why is it so different? The inner ear as well as processing sounds from outside the body, it can also be stimulated by vibrations that travel through the body. So when you talk you hear both sets of vibrations, you hear the sound from your mouth combined with the transmitted vibrations that travel from your vocal cords. Bones in the neck, and your skull help to enhance low frequencies, so in most cases you tend to sound deeper in your head than on recordings.

So how do they cancel all that noise?

If you listen to music through headphones you will know all to well that external noise can seep in, be that of aeroplane engine noise or just the drone of everyday life passing by. So what has been done to fix this? Well you will probably of heard of the noise cancelling headphone, but how do they make everything so quiet except for your music?

Noise cancelling headphones come in two variations, passive, and active. Passive cancelation refers to an actual barrier that is in place to stop unwanted sound entering the ear canal, think big clumsy over ear type headphones. They are so big as they are packed full of dense absorbing materials, much like big ear protectors. But these passive methods only reduce sound by around 15-20dB[1] which is a bit useless considering the drone of an aeroplane engine can reach 80dB within the cabin.

So here we have the active cancelling headphone, their structure and design is similar to the passive design, meaning it already has a good start on cancelling the high frequency noise. But they actively remove the lower frequencies… so how?

They create their own sound waves that mimic the incoming noise, however these emitted sound waves are 180 degrees out of phase with the incoming sound. The image below shows how the technology works;

Active noise cancelling allows the noise to be cancelled by a further 20dB, which translate to around 70% of ambient noise being reduced to realm of silence! Thats not too bad!

References:

[1] – http://electronics.howstuffworks.com/gadgets/audio-music/noise-canceling-headphone3.htm

To Silence All The Gun Nuts…

GUNS GUNS GUNS!!!!

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

Wow this is cool, the McGurk effect!!

Pretty Sound

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

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Wobbly Wob!

making the invisible, more invisible.

Check this out! interesting!

Sounds interesting!!!

Trevor Cox a lecturer at the university of salford has spent some time traveling the globe to discover the most interesting sounds that the world has to offer. His book ‘The sound book’ documents these weird and wonderful noises, here are a few that he has disused in interviews…

Whispering galleries are a strange acoustic phenomenon where sound is propagated over a curved surface, if a person is to talk into the wall at one side, the sound will travel on the surface and the opposite side will emanate the sound, and will sound as though the wall is whispering. Whispering galleries are generally not a planned aspect of the construction, and can occur in the most normal of places, for example the New York underground infrastructure, and St Pauls Cathedral in London, to name a few[1]. There are also purpose built whispering galleries for the enjoyment of the public for example there is a whispering gallery in the museum of science and industry in Chicago. 

Figure 1 – How a whispering gallery works

Professor Cox (Trevor not Brian) also mentions a world record breaker… and that is for the longest reverberation in the world. Reverberation is measured using an impulse, in this case a shot was fired. The time it takes for the sound to decay by 60dB is measured. The location was an old oil storage site in Scotland, and remarkably the reverberation last for 112 seconds… … … … … Professor Cox remarked “My initial reaction was disbelief,” he said. “The reverberation times were just too long.” [2]

Figure 2 – A Long tunnel with a long reverb time

These are just two example of the sonic wonders found in our world, I hope this entices you to discover some unique sounds for yourselves. Also check out The Sound Blog for more interesting articles by Trevor Cox.

References:

[1] – http://www.npr.org/2014/02/10/274717997/sounds-intriguing-the-worlds-most-interesting-noises

[2] – http://www.bbc.co.uk/news/uk-scotland-highlands-islands-25757937

 

Hearing for the First Time

Pretty Sound

You may have seen this video during the week, it’s a lovely story of a lady called Joanne Milne (40) who was deaf from birth and her hearing was restored with a cochlear implant. This video shot by her Mum shows the moments when she hears for the first time, in tears as the nurse recalls the days of the week to her. Watching this made me appreciate how much of a difference my ears make to the world I experience everyday. I mean some people (including myself) have recently been talking about the sounds of F1 and how they don’t sound as nice as previously, but imagine that with no sound at all and I think it really puts it into perspective!

It is said that if you have shortfalls in one aspect of life then you more than make up for it in another and this is certainly true in this…

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Aircraft are undeniably loud!

Here is something of interest, aircraft are now 100 times quieter than there counterparts from 40years ago.

The noise we here from an aeroplane is mostly produced by the engines, this happens because there is a difference in air speed between air being exhausted out of the rear, compared to the air passing around the engine. However aeroplane designers use a design that allows cool air to be bypassed through the engine, and this allows it to be exhausted at the same speed as the combusted air. This causes an attenuation in noise (the hot air is enveloped). Applying a larger fan can also be considered which allows more cool air to be bypassed, increasing attenuation.  Some noise is also produce by the body of the aircraft, for example, sharp changes in airflow lead to unnecessary noise.

So, aircraft engineers are constantly working on the survival of our ears. But what are they doing? Research in the way the air is expelled, research and application shows us that shaping exhaust gas leads to attenuation. Also looking at the wings of birds has lead to improvements of wing design, as the feather design that birds use, has a reduced noise compared to scale models of aircraft.

References:

http://www.sciences360.com/index.php/why-are-airplanes-so-loud-17217/

 

 

OOO Peace and quiet

Where do you think is silent? alone in a field? reading a book before bed? an awkward silence? well true silence comes in the form of a specially designed room, called an anechoic chamber. Here you experience background noise levels of -12.4dB [1]  comparing this to the noise levels described in my previous post, this is damn quiet  and as close to silence as it gets. So much so, you start to realise that your own body is a noisy bit of kit, making noises you probably didn’t realise it made.

Why is it quiet?

The room is this quiet due to its special design features. These include the room being built on springs with a low natural frequency, which prevents vibrations from being transmitted from the outside world. Once inside, it has a very specific design feature, this is that all the walls, ceiling and floor are covered with large foam wedges. These wedges are designed so no sound is reflected back to the listener. This is achieved by the sound entering both the foam material and areas in between the wedges, dissipating sound through friction.

The point of these rooms is for measurements, measurements such as loudspeaker response, microphone response or ear protection [1]

Here is a test subject in Salford universities anechoic chamber;

References:

BBC Manchester 27/08/09, The quietest room in the world [online], BBC News, P.1,  Available from: http://news.bbc.co.uk/local/manchester/hi/people_and_places/newsid_8224000/8224555.stm [Accessed: 9.3.2014]