PLSN on the VLX Wash Fixture

While looking through the PLSN website I found an interesting article about a wash light by Vari-Lite.  It is called the VLX Wash and it is being used for the televised sporting competition on MTV called Bellator.  According to the article this light has some unique characteristics for television.

The VLX Wash light is being used as a wash fixture for the sports event.  More precisely it is being used for the main light source for the broadcasts.  The light can be mixed to have any color temperature.  According to the Vari-Lite website the temperature on the VLX3 Wash which is comparable to the VLX Wash can dial from 3000ºK to 9000ºK.  This is very useful for television cameras and their engineers.

The light source in the fixture is LED.  The article says that the VLX Wash merges the colors completely before the light exits the fixture.  The Vari-Lite site says that the color mixing is free from color shadowing found in typical LED lights.  This is another advantage when used with television cameras and multiple fixtures.  When the wash is dialed into full wash, or from a 15º beam to a 55º beam, the color temperature in the field is consistent, helping video engineers.  Automated lights tend to not have even fields when light level is considered.  The VLX Wash gives a flatter field from the center to the edge of the beam.

Finally, the Vari-Lite site had some interesting figures on the VLX3 Wash.  This is not the same as the VLX Wash talked about in the PLSN article, but it is comparable.  The site says that the LED chips last for 10,000 hours at a guaranteed 70% output level.  That is really nice for lamp replacement, maintenance and for rental houses.  It also has the typical pan and tilt control found in other moving lights, and is of course uses the DMX512 protocol.

The following URL is to the PLSN article described above.

http://www.plsn.com/news/21-news/8194-vlx-wash-enters-the-cage-on-mtvs-bellator.html

Shure Axient Wireless Microphones

Shure has a site dedicated to its wireless system called Axient.  It is a wireless microphone software system that manages UHF at its receiver and transmitter.  It has the capability of automatically managing networked devices and indirectly managing legacy wireless or incompatible devices.

The system also uses two frequencies per transmitter and receiver for what I call a dual redundant wireless microphone.  Shure calls it frequency diversity.  The site says that when one of these frequencies is interfered with the other is a backup.  Another frequency is then used for the interfered one within, what Shure says, is milliseconds using interference avoidance.  Interference avoidance can be used with frequency diversity.  That makes for a wireless signal that will never be interrupted as long as there are open frequencies.

The interference avoidance feature works by using the spectrum analyzer.  The analyzer finds clean RF and ranks the best ones.  You could manually switch to the better RF or have Axient do it for you when interference in detected.  Shure shows that this automatic switch can be done almost instantly from the time interference is detected.

Axient transmitters use lithium-ion batteries.  The way Shure describes how the batteries work is similar to how a modern computer battery works.  The batteries have a gauge that reports hours and minutes of life remaining within about fifteen minutes.  This information is also transmitted to the base station.  The batteries can be taken out of the microphones and charged in docks.  The batteries then have charge time, cycle count and battery health information just like modern Apple laptops.  The transmitter and receiver display the battery time remaining, giving peace of mind to a performer and sound technician.  The advantages of using manageable batteries seem to outweigh the advantages of fresh alkaline batteries for every show.

Axient also uses software called Wireless Workbench.  It has features like, storing spectrum scans, TV frequency database for locations, and listing open RF.  This software can also have non-networked device frequencies entered in, or it can find open frequencies for other wireless devices like communications.  This system can manage RF for all networked and non-networked devices.  The networked devices automatically adjust, but the non-networked devices have to be entered manually from a list provided by the Wireless Workbench software.

ShowLink is a trademark for the technology that transmits information in two directions on the Axient system.  Shure says that it can be used to control all the transmitter parameters.  This feature did not have its own page on the website but it was mentioned and alluded to.  It is used to control parameters and receive information on the transmitter.  Things like RF output level, preamp gain in the transmitter, and transmitter frequencies can be adjusted wirelessly.  The battery status is also transmitted.  Apparently this information is either embedded into the frequencies or on the edge of the frequencies being used.

The advantage of using a system like Axient is that the wireless components, whether networked or not, can be managed with software and hardware.  The Axient devices have the added ability of zero downtime, barring power failure or running out of clean RF in a venue.

Amplifier Power Rating

John Meyer wrote a paper on amplifier ratings called "Making Sense of Amplifier Power Ratings".  He said that since companies like Meyer are producing self powered speakers the issue of how to compare them with amplifier ratings arises.

Peak power is a term that I have heard about.  This paper clarified it for me.  Meyer talks about the need to measure power ratings as the ability of the amplifier to reproduce signal at the speaker in a duration, with a particular amount of distortion.  He appears to recommend that the distortion and voltage sag at peak durations be negligible.  The distortion should not be significantly coloring the signal.

The way amplifiers are tested is by loading them with resistance like a speaker or another load.  They then put a sine wave into the amplifier which drives the load.  I gather that when the amount of tolerable distortion is reached that information is recorded.  The sine wave is unique in that it is a signal with a crest factor of three decibels.  This means that the heating power or average power compared to the peak power produced by a sine wave has a two to one ratio (three decibels).  Meyer goes on to say that amplifiers need to make short bursts of square waves sometimes.  The amount of time they need to be able to do this is a concern.

In the example John Meyer gives about their 18" subwoofer system, he says that the peak power was tested with a drum note for 40 milliseconds as a peak.  When this happened the voltage sagged in the amplifier.  This is not just true for amplifiers, it is true for electrical systems when demand goes up in a peak like way.  This sag produces an unintended compression effect of this subwoofer system at this testing level.  At lower testing levels there is not the same distortion.  This leads me to the idea of conservative operation of equipment to gain desirable results.  In my opinion certain amplifiers and speakers could be underrated in order to better their distortion specifications and their power ratings.  

To put these ideas of how long amplifiers should sustain output into a usable rule, Meyer found a solution.  The goal is to not compress the signal in the amplifier.  They say that the sine wave should be able to reach its peak without significantly sagging the peak of the line voltage over half a second.  This makes sense to me in that we should strive for a rating that does not include a significant sag during half a second.  Hopefully the peaks that are demanded are no longer than half a second.  If they were, that signal (or song) might not be listenable anyways.  

Here is my way of understanding the rating concern.  At the 40 millisecond rating, the amplifier says, "Yeah, I can handle that peak".  When the same amplifier is asked to peak for 500ms it might say, "Okay, but I will distort, compress and sag in voltage".  That is why this amplifier should be derated, so that it more accurately reflects its peak capabilities.

The power rating should reflect real use with little distortion if that is desirable.