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Author Topic: Mic placement Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 02-16-2003 12:56 PM                     There are different types of mics and different characteristics THe countrymans (USL and R2) aim at the ceiling  |  IP: Logged John F. Allen Film Handler Posts: 54 From: Newton, MA Registered: Nov 1999 posted 02-16-2003 01:12 PM                     This is a most interesting thread. It points out how technicians have been trained to think about measurements and equalization. It is truly unfortunate that so many have been mislead for so long. The result of this misunderstanding is that theatres all over the world are mis-equalized and do not have natural tone. I have been working on this problem for over twenty years. As a result of this study, I have developed an understanding of the problem that, I think it is fair to say, exceeds that of the prevailing conventional wisdom. I have been able to build a very large group of sound systems that do have the same NATURAL tone from room to room and system to system. Larger systems and larger rooms do, of course, sound bigger. I am referring to tone -- something I never hear anyone talk about. Knowing that there will be some that are so certain of their long held beliefs that they will strongly disagree, there are a few comments that I would make. First, is that this old measurement system does not work. We are not measuring what we hear. This is because all of the room's reverberation is included in the measurement. Our brains suppress most of this reverberation. What technicians end up doing is adjusting the frequency response of the direct sound -- used by our brains to determine what the tone really is -- with the inverse of the frequency response of the reverberation of the theatre. When this happens, technicians end up with a sound system that measures great and sounds terrible. As I have said, these misunderstandings are a major contributor to the problems seen in the way movie theatres sound today. After all, this method is a very primitive 30 year old technique, long abandoned by just about every other branch of the sound industry. To say that such an approach will duplicate the sound characteristics of a good sound dubbing stage, is naive -- not to mention completely impossible. This is because the sound systems in the best dubbing stages are not tuned in this manner, but by ear. As a chief engineer of the best facility in Hollywood once confided: The mixers record the materials. When they don't hear the same tone in the room, they fix the sound system. The reason that we generally have the same tone in most mixes, is because the mixers are trained to hear analytically. They are a talented bunch that seem to hear pretty much alike. While it should be said that not all dubbing stages sound the same, the mixers do compensate for these differences when they work. This is how we end up with mixes from all over the world with a consistency that allows them to be played in movie theatres without the need to readjust the theatre's equalization for every picture -- a remarkable achievement if you ask me. For further reading about this topic, I have written several articles over the years. Three of these can be downloaded at: http://www.hps4000.com/pages/special/missing.pdf http://www.hps4000.com/pages/general/the_mythical_x_curve.pdf http://www.hps4000.com/pages/general/toss_meters.pdf In answer to the question of where a measurement microphone should be placed and how it should be aimed, it really doesn't matter. This is simply because this entire approach to sound system measurement is so flawed. There is no way at this time to measure what something sounds like. You could place the microphone in the lobby and get as useful a measurement as anywhere else. In other words, do not believe ANYTHING you see on a real time analyzer measuring airborne pink noise in a room the size of a movie theatre. John F. Allen  |  IP: Logged Antonio Marcheselli Phenomenal Film Handler Posts: 1260 From: Florence, Italy Registered: Mar 2000 posted 02-16-2003 02:08 PM                        Manny I believe that the mic position does not change if you're using a multiplexer or a single mic. I believe that the mic should be in the best position that it can "hear" ALL speakers in the theater. I've read the USL manual and I understand why did you make the question!! Perhaps their mics are different made... Antonio [ 02-16-2003, 05:04 PM: Message edited by: Antonio Marcheselli ]  |  IP: Logged Manny Knowles "What are these things and WHY are they BLUE???" Posts: 4247 From: Bloomington, IN, USA Registered: Feb 2002 posted 02-22-2003 04:43 PM                     What's involved with calibrating a mic? Anybody got photos?  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 02-22-2003 05:55 PM                     Mic position for a multiplexer is to produce a diamond shaped array in the seating area the rule of thumb is Mic1 is 2/3rds back off centre (as the old single mic was) it is the SPL reference Mic 2 is on the left hand side about under 1/2 way Mic3 is offset of centre (opposite to the centre line than one) in the front 3rd of the seating Mic 4 is on the opposite side of 2 but in front of the centre To calibrate a mic one uses a calibrator that encapsules the microphone and feeds it a precise tone (114db in the case of cell) and the meter is then adjusted to reed that value For the R2 mics a offset is introduced in the software  |  IP: Logged Manny Knowles "What are these things and WHY are they BLUE???" Posts: 4247 From: Bloomington, IN, USA Registered: Feb 2002 posted 02-22-2003 06:40 PM                     So calibration is for SPL sensitivity only? Or does this also affect its "flatness" ?  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 02-22-2003 07:00 PM                     SPL on a daily basis but the analyzer and mics for the R2 should be recalibrated for response yearly  |  IP: Logged Manny Knowles "What are these things and WHY are they BLUE???" Posts: 4247 From: Bloomington, IN, USA Registered: Feb 2002 posted 02-23-2003 01:27 AM                     Oh, wow! I suppose that you have to send the RTA and its mic back to the manufacturer -- or somewhere else -- for the frequency response re-calibration?  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 02-23-2003 09:39 AM                     Yes it goes back to the manufacturer  |  IP: Logged Justin McLeod Film Handler Posts: 93 From: Oklahoma City, OK, USA Registered: Jun 2002 posted 02-23-2003 11:47 PM                     Here is a situation I witnessed. A tech used a particular mic ( I don't know what kind of mic was used) that was aimed at the screen tied to a broomstick handle that was lying against a chair. The mic didn't seem like a omnidirectional mic. It looked like a standard mic ( one you talk into ). The system didn't improve, sound wise. Was this tech doing something wrong?  |  IP: Logged Manny Knowles "What are these things and WHY are they BLUE???" Posts: 4247 From: Bloomington, IN, USA Registered: Feb 2002 posted 02-24-2003 10:29 AM                     I've seen the broomstick technique and I don't like it because you really don't have much control over (a) how high off the ground the mic is, or (b) the angle used in the measurement taking. I've also known the broomstick method to be unstable, meaning that the mic tends to move around. The broomstick can roll over, inverting the mic and taking it out of position. That's probably not too terrible, but then I have also seen situations where the contraption will fall out of balance and teeter-totter its way out of position so that the mic winds up at knee-level in the next row. The slightest disturbance of the cable can wreak havoc with the mic placement. Microphones don't really like to get banged around. Having seen techs do that in the past (and having heard the results of their work) I would resist that method at all costs; my measurement mics are too valuable to my work. If you treat them badly, your work will eventually suffer. Also, this comes down to priorities and attitude towards the job. A microphone stand costs next-to-nothing when compared to the test equipment. There's really no excuse for cutting the budget there. If you're going to do a job, you owe it to whoever is paying you -- and to yourself -- to provide quality service, and that necessitates having the right tools, the right skills and the right attitude.  |  IP: Logged Justin McLeod Film Handler Posts: 93 From: Oklahoma City, OK, USA Registered: Jun 2002 posted 02-24-2003 06:07 PM                     Thats very intresting to know, since I know nothing about EQ. If I ever do get a chance to EQ in the future, I would like to know the basics. That info will help out alot, Thanks Manny!  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 02-24-2003 10:30 PM                     A mike stand is an expensive and heavy item to be toteing around in the baggage I used to always tape the mic to a broom handle and never had one drop or droope .  |  IP: Logged Manny Knowles "What are these things and WHY are they BLUE???" Posts: 4247 From: Bloomington, IN, USA Registered: Feb 2002 posted 02-24-2003 10:34 PM                     I don't mean to be contradictory. Not on purpose, anyway. My experience has been different, that's all. FWIW, my mic stand cost $12.00 here in The Bahamas. If you're living in the U.S. or Canada you can get one for about $10.00. It weighs less than five pounds. It collapses and can travel in a tube. It's nothing terribly special. I got it at a music supply store. [Edit: I just saw a pic of Gordon's tool kit (Currently in a Sneak Preview of the Galeria installation in London) and his kits are kind-of on the HUGE side compared to some that I've seen.] [ 02-25-2003, 01:14 PM: Message edited by: Manny Knowles ]  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 02-25-2003 01:22 PM                     Manny next week I fly to western canada to do routine service at about 15 different complexs before I return home. Each has differnt brands of consoles projectors amps processors so as such a lot will be travelling with me (about $300.00 in excess baggage cost) But when you are in rural areas fedex doesn't even deliver so one is very judicisious of what is packed  |  IP: Logged

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