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new QOTD

Discussion in 'Question of the Day' started by wolf825, Nov 24, 2003.

  1. wolf825

    wolf825 Senior Team Emeritus Premium Member

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    Couple new questions of the day for those still interested...

    SOUND:
    What is a VCA, what is its function and what is the difference between a VCA and a Subgroup?


    LIGHTS:
    What is the difference, if any, between a Stage Pin connector and an older Stage PLUG connector?

    General Stage:
    If you have a Double Purchase Fly System, and you have to hang 200lbs of lights on the pipe, how much counterweight can you estimate you will need to load the arbor with, to balance it? How much would you need if you had a single-purchase fly system?


    enjoy...
    -wolf
     
  2. MagliteL13

    MagliteL13 Member

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    Where shall we reply to the questions? Here?
     
  3. ship

    ship Senior Team Emeritus Premium Member

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    You might want to rephrase your stage pin verses stage plug question.
     
  4. wolf825

    wolf825 Senior Team Emeritus Premium Member

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    yup....this is for everyone to play and participate in...


    -wolf
     
  5. MagliteL13

    MagliteL13 Member

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    I'll start my answer with the general stage one. In high school we had 28 linesets, all single purchase except for the five electrics. If I remember right, you have to put twice as much weight on the arbor as you do the pipe (or is that modified double purchase???) I do remember that on our system you had to pull two feet on the working line for every foot the pipe moved. So, my answer would be 400lbs (plus pipe weight) on a double purchase system or 200lbs (plus pipe weight) on a single purchase.

    Stage plug? Wow, that's like from before I was born (maybe--I don't know when they were used regularly last). Don't they just have the two conductors--and are shaped differently?

    A VCA is a Voltage Controlled Amplifier. Briefly put, it uses an external controlling voltage to amplify or de-amplify a channel (or group of channels) assigned to it. The biggest difference between a VCA and a subgroub is the fact that a VCA doesn't have any jacks on the back (normally).

    My $.02 .
     
  6. wolf825

    wolf825 Senior Team Emeritus Premium Member

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    Houston we have a winner...correct on all. Good job and good descriptions! Yes--a stage plug is missing its ground..only two conductor. For those who don't kinow what one of those Stage Plugs looks like--think to the flick Back To the Future--Doc Brown used one to connect the cable on the lightning rod to the clock tower in the flick to power the flux capacitor on the DeLorean. That was the plug hanging from his pants leg as he dangled from the clock..thank you Steven Spielberg for being accurate in what was used back in the 50's.

    Now--since you won the question of the day, What did you win--you win the honor of posting the NEXT question of the day. :D

    Post away and pass on the honor of posting to the next winner who answers your question!

    -wolf
    (trying a new approach to the QOTD to revive it)
     
  7. MagliteL13

    MagliteL13 Member

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    As my knowledge and experience isn't quite that of wolf's (that's an understatement), here are my questions:

    Staging:
    What are teasers and tormenters?

    Lighting:
    How many Altman 360Q 6X9s containing a 750W FLK will fit in a 2.4kw dimmer if the dimmer is limited to 50%?

    Sound:
    What's the biggest difference between a monitor console and a front of house console?

    Enjoy.
     
  8. wolf825

    wolf825 Senior Team Emeritus Premium Member

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    Great questions!! Thanks for carrying the torch and posting some new QOTD. I look forward to seeing some folks answer these.

    Also--no persons knowledge or experience is any better then anyone elses. A key philosphy in life that I try to live by is that no one person can know everything (but its a fun goal to aim for)...and most important is that everyone, no matter of age or experience or ability IS a teacher and has something that they can teach or pass on, whether it be by example or whether it be a skill or knowledge or a viewpoint--every person is a teacher, provided you stop long enough to look at what they have to teach. I've learned some cool things from folks twice my age, and also from kids half my age. Even a 10 year old can teach an adult something. Age is just a number and has no meaning beyond linear time. Sometime the lesson isn't necessarily WHAT to do or how to be, but it could also be a valuable lesson of what NOT to do--and that could range from an action to the way another person lives or reacts to a situation. Sometimes seeing the way someone else thinks or see's life is a huge lesson. I mean think about it--how many kids say they will never do "this" or be like "that" when talking about their parents or friends--thats teaching..and they choose to look at the lesson. the rest is our CHOICE on what we DO with that lesson and if we make it part of our own lives, or pass it on to others, or keep that lesson handy to learn from in situations later on in life...

    thats my "zen"... Great questions and I hope to see some cool answers from anyone who would like to give them a try... Thanks!

    -wolf
     
  9. wolf825

    wolf825 Senior Team Emeritus Premium Member

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    Hmm..its been a few days--granted there have been holly-daze..but hmm. Now I KNOW someone wants to answer these questions and then post their own questions to challenge the readers....c'mon folks...let put the thinkin caps on or the QOTD may just fade away yet again..

    wolf
     
  10. cruiser

    cruiser Active Member

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    Let me clarify....

    With your lighting question, are you referring to a complete dimmer rack that is 2.4kw per channel so 12x2.4kw or are you saying you want to get as many fixtures onto 1 channel, so 1x2.4kw???
     
  11. DMXtools

    DMXtools Active Member

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    To me, "teasers" were always younger brothers and sisters and "tormenters" were always older brothers and sisters... but I'm in concert sound and lights, not theatrical production.


    Here's where I get serious. The fixture doesn't matter and limiting the dimmer to 50% doesn't matter - the lamp and dimmer wattage is what's important - 750W and 2.4KW (2400 watts). For safety, you should always assume a dimmer will be used at 100%, so three 750W lamps on a single 2.4KW dimmer.

    Here's why: Solid-state dimmers use an SCR or triac, basically an electronic switch, to turn power to the lamp on and off 120 times a second (assuming 60Hz power) or 100 times a second (50Hz power). This is so fast your eyes can't see the flickering. When a dimmer is limited to 50%, it means the lamp is on at full power, but for only half the time, so the average power the lamps will see is 375 watts each, or a total, for 3 lamps, of 1125 watts. The SCRs or triacs in the dimmer, however, are switching the full lamp power - 750W X3 = 2250 watts = 2.25KW - on and off.

    Start with location. The FOH console controls the speakers pointed toward the audience and (if you're lucky) is located somewhere in the audience (Front Of House) area, so the engineer can hear what the audience hears. The monitor console controls speakers pointed back toward the performers and is usually located somewhere in the wings, so the engineer can hear what the performers hear.

    Consoles designed for Front Of House usually are set up to mix everything down to one (mono) or two (stereo) main mixes. Really good ones allow you to mix selected inputs into sub-groups, but those sub-groups are then combined into the main mix(es). A good monitor console is set up as multiple mono mixers in the same box: each channel strip has a separate fader for each output channel.

    John
     
  12. MagliteL13

    MagliteL13 Member

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    Ding, Ding. Yup, the lighting and sound are correct. For lighting, I was taught always to assume the worst--hence the dimmers are at 100% all the time. Occasionally, I've broken that rule though. Sound, the way I always look at it, is a monitor board's main outs are auxes. When I mix monitors, I normally stick a wedge behind me so I can cue up the same sound that's going to the performers. Also, then I always cue it up when asked to changed something, so I can hear ringing quickly.

    Anybody got an idea as to what Teasers and Tormentors are?
     
  13. wolf825

    wolf825 Senior Team Emeritus Premium Member

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    FWIW, I'd say, with his question being "How many Altman 360Q 6X9s containing a 750W FLK will fit in a 2.4kw dimmer if the dimmer is limited to 50%?" he wants to know how many fixtures of that type you can put into a single 2.4kw dimmer. Now whether that means it is 50% capacity or 50% intensity is another question all together... ;)


    wolf
     
  14. MagliteL13

    MagliteL13 Member

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    Just trying to make things complicated now, aren'tcha? :wink:
     
  15. ship

    ship Senior Team Emeritus Premium Member

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    You guys do of course realize that the lighting question is innacurate don't you? Thus the question is a trick question. The answer is no fixtures with the non-existant lamp can be placed on a 2.4Kw dimmer. A FLK is a 575w not 750w lamp.

    On teasers:

    It's sexist, but I always remember the teaser as per a woman's skirt. It's horizontal and something easy to remember. Just a mental link for telling which was which.

    As for what ever type of 750w lamp is intended, EHG or GLD/GLE, I agree that three would be the maximum I would allow unless I can go into the soft patch and limit the dimmer to 80% which I would consider safe to be doing. It's a lot harder to funk with the soft patch than a fader so allowing higher wattage combinations on that level is safe. That's given you can deal with the amber shift.
     
  16. wolf825

    wolf825 Senior Team Emeritus Premium Member

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    Well now that ya let the fun out of the question--the real fun part is that a fixture won't fit physically INTO a dimmer as he originally stated...or will it if you disassemble it ;)

    I was hoping someone would answer it or try to... :D:D

    wolf
     
  17. DMXtools

    DMXtools Active Member

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    I hate to contradict you, Ship, but regardless of whether the dimmer is limited in "soft patch" or by simply telling people not to go above 50%, the maximum wattage of all lamps on a single dimmer should never exceed the rated wattage of the dimmer. It is NOT "safe." As a matter of fact, if dimmed to 50% (either at the fader or by "soft patch"), the triacs or SCRs in the dimmer are under greater stress for a given lamp load than if they are operated at 100%.

    A.C. Line current is a sine wave, going from zero to maximum positive voltage, back to zero, then to maximum negative voltage and back to zero for each full cycle. The dimmer controls power going into a lamp by turning the thyristor (the general class of semiconductors that includes both triacs and SCRs) on part way through each half-cycle (it turns off automatically when the voltage gets back to zero). But a thyristor doesn't turn on instantly - it may take several microseconds to go from completely off to completely on.

    Power is volts times amps. When the thyristor is completely off, the full voltage of the power line is across it, but there's no current, so no power is being turned into heat in the thyristor. When it is completely on, the current flowing through it is at its maximum, but the voltage across the thyristor junction is very low, so there's almost no power. It's only during the turn-on time that any appreciable power is turned into heat within the device. As the thyristor turns on, current increases and the voltage drops - at some point the thyristor sees half the voltage and half the current, and for that brief instant is turning a lot of power into heat.

    When the dimmer is set to 50%, the thyristor is turning on halfway through each half-cycle, just at the point when the voltage is at either the positive or negative maximum: the point where there will be the greatest amount of power converted to heat during the turn-on time.

    When the dimmer is set to 100%, the thyristor is turned on all the time. While current will be at its maximum, almost all the voltage is across the lamps, almost none across the thyristor, so almost none of the power is converted to heat in the chip- most of it gets to the lamps.

    John
     
  18. Inaki2

    Inaki2 Active Member

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    Ok, maybe I'm going off topic for this topic, but what exactly happens if you plug more power into a dimmer than it is intended for? I ask this because about a month ago some reard from work plugged 4k into a 2k dimmer and nothing happened.
     
  19. wolf825

    wolf825 Senior Team Emeritus Premium Member

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    You mean if you plug more draw then the dimmer is capable of? Well--if you plug in 4k into a 2k dimmer--the dimmer breaker will (or should) trip. Otherwise if it keeps going--and I've had this happen when I goofed on load balance calcualtions and plugged in 5 ministrips to one 2.4kw dimmer instead of 4, it will keep going BUT it will overheat. When it overheats, you run a fire hazard, you can burn up the chokes and brains of the dimmer, and overall you run an electrical shock hazard among other things....

    -wolf
     
  20. ship

    ship Senior Team Emeritus Premium Member

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    Nope, don't hate to correct me, by all means, do so. The day I become uncorrectable and not learning more is the day I should be put out of my misery.

    My specialties are not in how dimmers work nor it's electronics. I know what I have done and been tought in school - this soft patch was one of them for Lighting 101, but there is always more to learn and bad practices to correct for. Read all about dimmers at some point or another, know the basics but because I don't deal with them much, much less think about them I do apriciate standing corrected. I have done the soft patch 80% trick many times and never thought about the triacs overheating. I have also seen many dimmers that they were burned out on which have sloppy dimmer curves or just go on and off.

    This is a good point that without you pointing it out I will have never thought about it. Thanks. Explains a few things also at a time I'm ready to learn about it as opposed to reading about such things once or twice but not understanding.
     

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