We had an appreciative audience in the Kelvin Lecture Theatre at Savoy Place for the April IET Central London Evening Lecture to be enlightened by Kevin Madeja of Snelling Business Systems on the AV systems that illuminate and entertain. The refurbishment of Savoy Place was a major undertaking and the results are superb. The IET and Snelling are justly proud of their achievements which have been recognised with several awards.

Did you know that the BBC do live TV broadcasts from the roof - watch out for Carol's weather forecasts with the London Eye in the background! 


Kevin split his talk to cover the key components of the AV system:-


Projectors:

We had a reminder of AV in the 70's - chunky and low resolution - to now. The current projectors are based on 3-chip digital light processing (DLP) with a MEMS array of mirrors (one for every pixel). It relies on two of our physical attributes: persistence of vision (think of a "wobbly" pencil or Newton's disk) and colour vision. As per trichomatic theory, there is one DLP for each of  the three colours Red, Green and Blue (RGB). The mirrors can tilt 23000 times per second and give 1024 shades of grey through control of the duty cycle. The light source can be a filament lamp or a blue laser. There's a complex optical path of mirrors to bring the three colours together into the final beam.

Kevin was able to demonstrate this clearly and simply with his (much larger) simulation of a DLP. 


Screens:

The screen in the Kelvin Theatre is DNP Super Nova Screen Technology and is the largest in Europe at a width of 7m. The specification and performance is top class, including a low loss of 20% of incident light and a 170 degree viewing angle. Kevin explained brightness and the importance of a high contrast ratio.

To demonstrate how the black lenticular lens absorbs ambient light, as the house light levels were raised, a plain white board held against the screen became washed out, while the display screen remained visible with good contrast. 


Audio:

Sound is provided by line array speakers with a wide acoustic range of 80 to 20 kHz; 6 per side plus woofers for the bass (down to 40 Hz).

Looking back to The Beatles at Shea Stadium in 1965, the sound was very low-fi - the audience couldn't hear it. In the 1970's we got stacked systems which had volume but a muddy, non-directional sound. In the 1990's line array theory gave us hi-fi directional sound.

Kevin gave us a good Physics lesson on sound and how point source propagation is spherical with intensity governed by the inverse square law. Twice the distance reduces the level -6 dB. 

A fun hearing test let us experience what a dB change sounded like: 1 not much; 3 a little; 6 is "one step louder" (think of Spinal Tap going over the top with an amp setting of 11). 1 step is an acceptable step in sound within a venue. 

A dB Sound Pressure Level (SPL) of zero to 130 takes us from the threshold of hearing to the threshold of pain, spanning a very wide range of pressures.

The configuration of the speakers is key: a seven-point source produces a much flatter wave front that is directed straight out. The result in the Kelvin Theatre is a variation throughout of only ~ 4 dB.  


HDMI:

High Definition Multimedia Interface (HDMI) is electrically the same as DVI (Digital Visual Interface), but gives a better signal; a drawback is the short transmission distance - not suitable for system integration. Direct digital to digital, from frame buffer to frame buffer, eliminates the A to D converter and so improves quality at a lower cost. There's a surprising amount of technology in the cable - see Kevin's presentation for more details on what the 19 pins are used for and what TMDS is. 


After a fairly subdued Q & A session, we all continued at the networking reception in The Riverside Room. There, the attendees showed their interest and enthusiasm in the demo by Ian Baugh of the Panasonic Space Player projector, bringing a plain white oversized watch face to life with a stunning 3-D like video. There was also no rest for Kevin as many people wanted more of his demos and explanations.


This is a link to Kevin's presentation: http://bit.ly/2HI4UNL

And this is a link to a video of the Panasonic technology: http://bit.ly/2JVLsO3