Schott Borofloat Gobo Glass

Today I was interested in how glass gobos are made for moving lights.  I started with the Martin website and found the user manual for the Mac 2000 Profile II.  The manual specifies that the gobos be made with high temperature Borofloat glass or its equivalent.  It also specifies that the coating be dichroic or aluminum.

The Borofloat glass led me to a company called Schott.  Schott is in the business of manufacturing glass.  They make glass that is very resistant to breaking and heat.  Their website talks about the Microfloat process.  This process starts by mixing raw materials like borosilicate, and melting them.  This liquid glass is then spread onto liquid tin.  This creates the very flat surface needed in their glass.  It is then mechanically flattened to the desired thickness as it passes through an annealing stage.  Annealing is needed to reduce internal stress in the final glass product and toughen it.

Borosilicate glass also used in our HID lamps because of its strength and heat properties.  This type of glass is also marketed as Pyrex glass found in graduated bottles and cookware.  The Mac 2000 Profile II uses the OSRAM HMI 1200 W/S metal halide lamp, which has a maximum operating temperature of 450ºC.  Also, the glass that Schott makes for gobos has a long-term operating temperature of 450ºC.  This means that the gobo will operate in the temperature range of the lamp.

Finally, thin-film interference is the technique that is used to filter light in these gobos.  The glass is coated with thin layers of metals.  The metals are vaporized in a vacuum chamber with the glass gobo inside.  Through deposition, the vapor crystallizes on the glass in thin layers.  Since the range of visible light is from about 380nm to 740nm the metal layers need to be on this magnitude.  This is essential for thin-film interference.  The distances between the layers will determine which wavelengths reflect and which pass.  According to NASA, the vacuum deposition process for making dichroic glass was developed in the 1950s to protect instruments being sent into outer space.

The idea that the technology used in one application can be used creatively for another is really interesting.  I think it is important to remember that the future of entertainment technology likely exists in a precursor form right now.

OSRAM Arc Lamp

Replacing arc lamp bulbs is something that needs to be done routinely on moving lights with arc lamps.  I found a document online that gives information on how to replace the lamp for a MAC 700 Wash.  Summarizing what Martin recommends for lamp replacement was very interesting and taught me some useful information. 

The OSRAM SharXS HTI 700 W/D4/75 is the specific lamp for the MAC 700 Wash.  Some of the quick facts about the lamp are that it has an average of 750 hours of life and 700 watts of power consumption.  This can be counted in the fixture with a clock that can reset for lamp life, helping someone that services these fixtures at rental shops.  Martin actually says not to exceed 75 hours past the lamp life.  To help with lamp life it is recommended by Martin to let the lamp heat up for five minutes before dousing.  This means that if the lamp has been turned on by accident it is better to leave it running for five to ten minutes before rushing to turn it back off.

OSRAM is the company that makes these specific lamps.  In their documentation I found information like color temperature, which is 7500ºK.  In the Martin fixture there is variable color correction available.  OSRAM also specifies cooling of the lamp while operating to be forced air with a fan.  That seems pretty obvious but it is important to specify on a document describing the lamp.  Finally another interesting fact is that the cold strike for the lamp is 3,000 volts and the hot strike is 25,000 volts.  OSRAM says that the lamp is capable of hot re-strike so long as the fixture can provide the ignition voltage.

There are diagrams that Martin has online to replace the lamp.  Most importantly, time should pass after the lamp is off; 45 minutes is what Martin recommends.  The head of the 700 Wash can get up to 185ºF before a warning message appears.  This means that the lamp is clearly at a much greater temperature than that.  In fact, OSRAM specifies a maximum of 842ºF for the lamp.  Of course, Martin specifies cleaning the lamp with alcohol and polishing it as well.

The two documents were very interesting and straightforward.  They left little to the imagination on how to replace the lamp and what lamp to replace it with.  This is necessary for the correct and efficient operation of lighting fixtures.

http://www.martin.com/service/downloadfile.asp?name=UM_MAC700Wash_EN_D.pdf&cat=65

http://www.osram.com/_global/pdf/Professional/Display_Optic/Entertainment/SharXS_HTI/SharXS_HTI700D4-75-e.pdf

Elation Art SSC Lighting Controller

Elation just released a new product over a week ago.  It is called the Art SSC Lighting Controller.  It is a standalone DMX-512 playback unit with two universes.  It is about the size of two DI boxes next to each other.  It is intended for use in permanent installations where repeated lighting and show controlled devices work.  It has many features that appeal to the turnkey customer.

The input and output features are plenty in this small package.  It has DMX in, MIDI in and out, GPI and an RJ-45 port.  It has the ability to be programmed via an HTML page when connected to a computer.  The best part is the ability to connect a client's computer to it with custom interfaces made for them and password protection so they are locked out of advanced programming options.  This device also has an astronomical clock built in and a battery backup so that DMX and show control data will stay up and running through power interruptions.  The clock can be used to trigger events based on time, date or any other information an astronomical clock provides.

The DMX input port provides the ability to record up to 16 tracks of DMX data.  These recordings then can be programmed to play back as well.  I can imagine that a stream of DMX that a lighting programmer is good at creating, or is only capable of creating on their favorite console could be perfectly recorded and played back by the Art SSC.

The Art SSC can run as a standalone piece of hardware in an installation.  However, it is programmed with an external computer through an HTML page.  This leads me to believe that there is a tremendous advantage for clients and contractors.  The contractor can program a show, or whatever controls are needed with their computer, and the client can control what they need from day to day with their computer.  As long as both computers have a web browsing program and the right credentials to access the device, they can expect good operation.  The Art SSC has no moving parts making it more reliable than hard disk based show control found on computers.

http://www.plsn.com/product-news/8345-elation-art-ssc-dmx-lighting-controller-for-fixed-installs.html

http://www.elationlighting.com/ProductDetails.aspx?Category=&ItemNumber=1794

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.

Sound System Distortion

Tony Andrews in his May 20, 2011 article in ProSoundWeb speaks about crushing audio levels and the distortion associated with them.  Some of the things he mentions are interesting.  How machines are made to be run conservatively, how distortion is unappealing and damaging are some of the things that caught my ear.

Andrews' idea of fidelity stems from the meaning of the word.  He is talking about the degree of exactness in reproducing something, like sound.  In his article he mentions signal integrity, overdriving inputs and outputs, and overdriving loudspeakers.  It appears that he has experience with DJs, and other people who tend to desire unlimited system capacities.  I too desire a system with unlimited capacity, but like Andrews desire limited distortion in the end sound.

With the ability to work speakers and amplifiers past their conservative operating levels, there will be people who do so.  Andrews also talks about manufacturers lacking in their publishing of distortion figures at particular levels.  This does not help people who buy equipment.  The ability to change the point at which meters show the red LEDs may alleviate some distortion problems by tricking DJs or other users into thinking they are pushing a system to its limit when in reality it is in its conservative zone.  If we want more level at the same distortion value, the only thing we can do is make the system bigger or find a system that is bigger with the same distortion value.

Self-regulation is another point that Andrews hints at in his article.  This is very important to consider, because if we do not self regulate our industry, our industry will be regulated more by governments.  In these cases, blanket legislation will impede the normal operation of speaker and amplifier equipment we all use.  Susan Kelleher states it best when speaking about self-regulating the portable stage and tent business.  With the publicity of stage collapses and the stage collapses themselves, the portable stage business makes itself vulnerable to government legislation regarding the operation of outside staging.

Horrendous sound is also a concern for Andrews.  He makes a short note about fee-paying audiences in his article.  I think it is important to highlight the part about fee-paying.  It may be too easy to forget where the money to stay in business comes from.  It does not often come from audiences who leave a show with a subconscious dislike for distortion or loud levels.  It more often comes from audiences that consciously like and subconsciously like the whole entertainment experience.  This includes, the atmosphere, the food, the talent, the beer, the temperature, the lighting, and the integrity of the sound signal.  Andrews' point about fee-paying audiences matters to people in the business of sound.

What Andrews was talking about was not necessarily level so much as distortion.  The desire for unlimited level with very limited distortion is understandable.  If people can live with distortion and crushing levels, and people can make money doing it, then I will have to join them.  If hearing damage, audio fidelity, and audience experiences get worse due to distortion something will change.  I hope to be on the right side of the change if it comes.

http://www.prosoundweb.com/article/uncomfortable_audio_experiences_truths_about_sound_system_loudspeaker_disto