Beatmag’s regular technical columnist James Spectrum (AKA Jari Salo of Pepe Deluxe)

One of the most arduous, frustrating and challenging tasks known to man is opening a stuck jar lid. Unless you’re the strongman of the local circus, you do benefit greatly from the fact that steel heats much faster than glass and steel’s thermal expansion coefficient is about 40% greater than that of glass. This means that you can heat the lid (for example with hot water), and this causes the metal to expand enough to make it come off easily. The same procedure in reverse, when applied to producing strong joints between two pieces of metal is called shrink-fitting [http://www.alliedpipefreezing.co.uk/shrink-fitting.htm]. Cooling causes one piece of slightly oversize metal to contract, and it is then inserted into the other. When the cooled metal returns to the original temperature and size, it produces interference and pressure which holds the two pieces together mechanically.

The thermal expansion phenomenon is also a constant source of tricky engineering challenges. During the days of fast intercontinental flights the designers of Concorde had to take into account that the heat created by friction with air would cause the aircraft to expand 15-25 centimetres. The cabin was put on rollers in order to isolate it from the body, thus preventing the stretching from ripping the plane apart. The body was also painted with a special paint that could accommodate the changes and dissipate as much heat as possible. Rollers and gaps are also common with steel bridges. For example the Golden Gate Bridge, spanning at 1280 m between 2 towers, can expand up to 50 centimetres on a hot day. That would be enough to cause severe structural damage if the construction wouldn’t allow any variation.

Heat not only expands metals, but also affects their electrical conductivity. This effect is actually much stronger than thermal expansion: the resistance of the metal filament of 100-watt bulb increases to approximately 20-fold when it’s switched on. As a result of this, the bulb actually regulates itself when power is applied. When resistance increases as the bulb heats up, it is limiting the current going thru the filament, and this in turn reduces the heating effect and stops the bulb from burning out. Using this knowledge, some clever speaker manufacturers have actually employed miniature light bulbs, wired in series with speakers, as a simple means of speaker protection. The bulb acts like a ‘compressor’ by heating up and turning down the power spikes caused by loud peaks in music. Hi-fi purists are very offended by the potential effects of bulbs on audio quality… a reason good enough for Men-In-White-Lab-Coats, a.k.a Team Deluxé to work on, not merely another protected speaker, but the World’s first standalone compressor based on miniature bulbs!

As usual, we started with a name, finally settling for ‘Imperator’ as in ‘One compressor to rule ‘em all’ (modesty is the lowest and most uninspiring of the seven holy virtues [http://en.wikipedia.org/wiki/Seven_virtues]. And as usual, we had a few setbacks when working on the first prototype, basically a row of bulbs in series plus one power resistor to drop the voltage from speaker level back to signal level. With our little (read: no) knowledge of electronics we ended up burning lots of bulbs, fingers and one power amplifier channel, until we actually took some time (gasp!) to figure out all the whys and wherefores of the basic system. Armed with new hope and confidence, the basic idea was soon taken many steps further… but that’s something we will bat around next issue. In the meanwhile, here’s a short demo of the first Imperator: unprocessed drums followed by same drums going thru the whole nine lamps…

LISTEN HERE

Filed under: Life, Pepe Deluxe Gets Technical by Flexmaster Nylon
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2 Responses to “The Red Light District”

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