Category Archives: Audio

Hidden Morse Code in Tubular Bells

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The link between The Exorcist, Amateur Radio and Alan Turing.

A quick look at how the movie The Exorcist from 1973 has links to the late great Alan Turing via Mike Oldfield’s album Tubular Bells, Scotland and Amateur Radio. It’s Halloween so figured why not throw some horror in the mix.

When Mike Oldfield recorded Tubular Bells in 1973 he had no idea his first album on Virgin Records would be chosen as the soundtrack to The Exorcist later that year. Neither did he know that recording with Virgin Records would have an unintended consequence of hiding a secret message which dates back to 1926, shortly after World War One.

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True directional speakers using modulated ultrasound

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Being able to direct sound is useful in many situations. Two examples are at a museum where people standing in front of two different exhibits can hear two different commentaries or at home if you don’t want to hear the crap someone else listens to.

This is where modulated ultrasound comes to the rescue – the ability to direct sound with an impressive 5 – 10° spread – that’s unheard of with any traditional loudspeaker.

field

Lets take a quick look at how this craziness works because it’s not your typical transducer, that’s for sure.

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What is a Decibel (dB) and why it simplifies calculations and graphs

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I’m going to try and explain what a decibel is and why it is used so often. For some reason it seems to confuse a lot of people, especially when used in sound engineering. As it happens the dB is actually really simple once you understand what it is and why it is used.

vu-meter-picture

The first concept you need to get your head around is a dB is nothing more than a ratio, just like saying a 2:1 ratio to mean two apples for every pear, in other words double the amount of apples for every one pear. Instead of linear scaling like this, in the land of dB’s everything is logarithmic. You don’t need to know what that means you just need to know that it’s a ratio. First off a bit of history.

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Build Pics: G-Sub High Pressure Subwoofer

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Buying speakers is boring, anyone with a credit card can do that. Building speakers is a lot more fun! A year ago a few friends and I decided to build a G-Sub. Here’s the build process in pictures.

gsub3

Before we start here’s a bit of background on the ‘G-Sub’. Speakerplans.com is a website run by speaker design guru Rog Mogale (Void Acoustics etc). The site contains free designs of various cabinets which anyone can utilise. The G-Sub is a twin 18″ reflex cabinet designed for high fidelity bass at extreme pressure levels. The drivers of choice were Fane Colossus 18XB which are industry standard 1kW (AES) drivers capable of 35Hz – 1kHz with 99dB (1w/1m) sensitivity.

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Mopify Behind Apache Reverse Proxy

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I’ll be writing a post about how great Mopify is shortly but essentially it’s a web plugin for Mopidy which provides a web front end to Spotify running on just about any machine. It means you can control Spotify running on a machine plugged into your HiFi without the needs for the Spotify App on your device. This is handy where you have other people in the house with their own accounts but still want them to be able to control the music on the main HiFi.

spotify-tile

Of course, an ideal host machine might well be a Raspberry Pi with a decent USB Soundcard.

Mopidy runs its own little web server which means Read More »