Underneath the arches

An interesting post from one of my future lecturers at the University of Salford

The Sound Blog

Soundwalking with balloons and a banjo

Some of the best sounds in cities can be found in places that at first might seem unlikely sites for an aesthetic wonder. For the Manchester Science Festival I took a group of people to explore underneath dingy canal and railway arches built at the height of the industrial revolution. This active soundwalk was inspired by Davide Tidoni, an artist I found out about while researching Sonic Wonderland / The Sound Book.

The reverberant arch

The reverberant arch [3] Start in the Castlefield arena and walk under the arch shown in the photo above and below. You need to make some sound as you walk under to notice how suddenly the sound changes. Tim played the banjo, and as I walked under the arch I could hear the sound reflecting and reverberating. As I entered under the arch, it was like someone…

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Amazing Acoustic Experiment with Water

The effect that you are seeing can’t be seen with the naked eye. The effect only works through the camera. However, there is a version of the experiment you can do where the effect would be visible with the naked eye. For that project, you’d have to use a strobe light. The key to this experiment is setting the camera’s FPS equal to the frequency you are playing in the water, i.e. 24Hz requires 24FPS.

The effect you see on the video is different to how your eyes perceive it, but on-screen you seemingly “freeze” the water mid-air. This is due to the wagon-wheel effect where, say, a propeller seems to be moving in a totally different manner than what it actually does. The effect is a result of temporal aliasing.

Wagon-wheel effect =====> http://en.wikipedia.org/wiki/Wagon-wheel_effect

 

Poles and Zeros

A technical post on poles and zeros from one of my peers, aimed at those specialising in digital signal processing.

SoundInTechnicolor

Poles and Zeros can be complicated if you have no where to start. I’m writing this guide to help out with the basics of Pole Zero plots for , which relate to filters. Hopefully you can gain some understanding!

Pole Zero Plot

So a pole zero plot is based around a circle. The circle represents frequency from 0Hz to 44100Hz, assuming that 44100Hz is the sampling frequency. Starting at the far right of the circle that is 0Hz, then we follow the line upwards to the top which would be 44100 * 0.25. And so on until we finish the circle to find that 0 and 44100 are at the same point. The plot represents the frequency response of the filter.

The Poles and Zeros come into play next. If a pole is on the circle it means that there is zero frequency response at this point. Conversely, a Pole means there’s is an infinite peak frequency response at…

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Audio Technica ATH-M50 Review

The Headphones

The Audio Technica ATH-M50s are professional studio headphones, designed to give the listers a true and accurate representation of the music they are listening to. This means they aren’t headphones designed with EQ (louder bass, louder mids etc..), they are designed to give a flat response. This is because they are studio headphones designed for monitoring and mixing. They have a collapsible design for portability, 180 degrees swivelling ear pieces, padded ear cushions for comfort and sound isolation, and a 1.2 -3m coiled cable with a gold plated mini plug adapter.

The Sound

The first thing you notice about these headphones is how incredibly detailed all the instruments you’re listening to sound across the entire frequency spectrum. Mid-high instruments cut through with a true sense of clarity that I haven’t heard in any other headphones. However this does not come at the expense of the bass, the bass still sounds full and rich. To those who think that you need excessive amounts of bass for headphones to sound good, these may not be the headphones for you. In my opinion the bass response is the best I have heard, but these are designed to have a flat frequency response so you get the perfect blend from all the frequencies. To get a better idea we can  compare the frequency response of the M50s to a pair of Dre Beats, not even in the same price bracket.

Monster Beats By Dr Dre currently (£189.99-£219.99)Beats

Audio Technica ATH-M50s currently (£89.99-£119.99)

ATH-M50 frequency response

Now sound quality is subjective, (I keep reminding myself), but even someone with no audio background should be able to look at these graphs and see which headphones are the best performance for your money. But it is up to you, if you want bipolar highs and a bass fat fat bass, Beats are definitely for you!

The Design

The headphones are very well built with a comfortable design for long lasting use (again subjective). Although these headphones don’t have noise cancelling technology, the noise isolation contributed just by the over-ear ear pieces is perfectly sufficient. They definitely aren’t the best looking headphones in the world, but by no means do they look bad. The priorities when designing these headphones were the best sound quality possible, and the comfort. The ear pieces fold away conveniently and also swivel in order to comfortably fit any sized head.

Summary

I have had these headphones for the best part of three years now and I am still absolutely content with them. They sound great and are definitely not delicate, they have been bashed about, dropped, squashed and even stood on many a time and they have pulled through. These are still definitely one of the best choices for sound quality in this price bracket, competing with headphones worth hundreds more, and some that are even worth thousands more.

Acoustic Levitation

At some point in GCSE or A Level physics you will have come across the standing wave experiment, the only experiment related to acoustics that you will study (well, it was with my curriculum). This not very inspiring experiment is actually very important and a lot of acoustics research is based purely on that principle! I feel that it isn’t a very fair representation of acoustics so I thought I’d blog about one of the many applications of standing waves, acoustic levitation.

Firstly if you need to remind yourself about standing waves and what they are, this video gives a great demonstration.

The important point to take from this video is about the nodes, these are crucial in the process of acoustic levitation. It is important to remember that with sound waves, the nodes will be points of minimum pressure and the anti-nodes are points of maximum pressure. Once this concept is grasped we can see how it is applied in acoustics levitation.

 

In the video you can see the droplets being suspended due to the characteristics of the pressure caused by the standing wave. A way to imagine it is to think of the air pressure as a river with rapids and points of still water. Objects placed into the river would settle in the points of still water (in theory). If this could be recreated in space the objects would settle in the nodes of the standing wave. However, on Earth we have gravity, and the objects levitate just below the nodes. This is because it is the point where the acoustic radiation pressure balances the pull of gravity.

Sadly, if you wanted to do this experiment yourself it isn’t quite as simple as just creating a standing wave and placing an object in the node. Firstly, intense sound is central to acoustic levitation, the transducers used in the experiment produce sounds in excess of 150 dB. Most systems use ultrasonic waves, which are above the human threshold. There are also a number of other factors that need to be taken into account.

  • The size of the object must be 1/3-1/2 of the wavelength. The higher the frequency, the smaller the diameter of the object.
  • The mass of the object, the density of the object is evaluated to determine whether the sound wave can produce enough pressure to counteract the pull of gravity.
  • Drops of liquid must have a suitable bond number, if the bond number is too low the drops will burst.
  • The intensity of the sound must not overwhelm the surface tension of the liquids.

Although this is a complex science the principle is very simple. This could be a huge step forward when it comes to manufacturing things such as microchips and electronic devices. This can even be used to simulate space environments by creating points that counteract gravity.