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Author Topic: Mic placement Antonio Marcheselli Phenomenal Film Handler Posts: 1260 From: Florence, Italy Registered: Mar 2000 posted 02-15-2003 08:45 AM                        Hi everyone I hope this is not a FAQ question, I searched on the forum but I didn't found anything. I have a measurement microphone (nothing professional, it is a Behringer ECM 8000 here , omnidirectional). What is the correct placement of a microphone to perform a equalization in a theater? Since the microphone is omnidirectional I'd say perpendicular to the floor (parallel to the screen) so that the mic can analyze front, surround and room sound. Is it correct? Bye Antonio  |  IP: Logged Jeffry L. Johnson Jedi Master Film Handler Posts: 809 From: Cleveland, Ohio, USA Registered: Apr 2000 posted 02-15-2003 12:33 PM                        Microphone placement within the room and mouting height and angle of the microphone are defined in ANSI/SMPTE 202M, "SMPTE Standard for Motion-Pictures--Dubbing Theaters, Review Rooms, and Indoor Thaters--B-Chain Electroacoustic Response." The short answer is 2/3 back from the screen to the rear of the seating area and 2/3 over from the limit of the maximum width of the seating area, "and at a sufficient number of other positions to reduce the standard deviation of measured position-to-position responses to less than 3dB, which will typically be achieved with four positions...." The microphone should be mounted at normal seated ear height and: "that angle between the direct sound and the diaphragm for which the response is flattest. This angle is 90 degrees in typical 12.5 mm (0.49 inch) pressure measurement microphones, so they would normally be used pointed at 90 degrees to the direct sound."  |  IP: Logged Michael Schaffer "Where is the Boardwalk Hotel?" Posts: 4143 From: Boston, MA Registered: Apr 2002 posted 02-15-2003 12:58 PM                        For microphones set up in a diamond shape usually work best. I tried to draw this with lines and Xs, but it doesn`t work in the forum mask. The idea is to have two microphones in a straight line from screen to rear, and then two more at the height of half the distance between the two first microphones, on both sides. Or refer to the setup suggestion in the Dolby microphone multiplexer manual.  |  IP: Logged Antonio Marcheselli Phenomenal Film Handler Posts: 1260 From: Florence, Italy Registered: Mar 2000 posted 02-15-2003 02:12 PM                        Jeffry, "90 degrees to the direct sound" means that the mic should point to the roof? Thanks Antonio  |  IP: Logged Jeffry L. Johnson Jedi Master Film Handler Posts: 809 From: Cleveland, Ohio, USA Registered: Apr 2000 posted 02-15-2003 03:24 PM                        That's how I would interpret "90 degrees to the direct sound." Point the microphone straight up.  |  IP: Logged Christopher Seo Jedi Master Film Handler Posts: 530 From: Los Angeles, CA Registered: Jun 99 posted 02-15-2003 04:25 PM                     Antonio, You can download Ultra-Stereo's multiplexer manual from their website: www.uslinc.com There are helpful diagrams for multiple-mic setups. Also, most Dolby manuals have the usual diagrams for single mic setups in the B-chain section. For example, the CP65 Installation Manual says (hope I won't be sued for copyright infringement): quote: For a single microphone the recommended position is shown in the diagram — 2/3 of the way from the front speakers to the rear — but off the axis of the center speaker — 5 feet off the floor level — and angled 45 degrees upward toward the screen. Connect the microphone to the RTA. Interesting that Dolby recommends a 45 degree angle. I don't think that's what the Dolby techs used with their mics.  |  IP: Logged Michael Schaffer "Where is the Boardwalk Hotel?" Posts: 4143 From: Boston, MA Registered: Apr 2002 posted 02-15-2003 04:33 PM                        The handheld pink noise generator offered on the UltraStereo website might be interesting for Antonio. He talked about generating pink noise for a private installation. Has anyone worked with the screen luminance testing system?  |  IP: Logged Antonio Marcheselli Phenomenal Film Handler Posts: 1260 From: Florence, Italy Registered: Mar 2000 posted 02-15-2003 05:37 PM                        Thanks Christopher This is why I asked the question! I've seen make some equalization with mics pointed as you stated! Thanks for the link Antonio  |  IP: Logged Oliver Pasch Film Handler Posts: 53 From: Europe Registered: Jun 2002 posted 02-16-2003 04:42 AM                    I was a little worried about Dolby recommendations too: with all cinema processors until CP-500 and even SA-10 it was 45 degrees, but the CP-650-installation-manual all of sudden recommmends 90 degrees, so that's directly pointed to the ceiling. The dts-6ad-manual says nothing about this topic at all.  |  IP: Logged Antonio Marcheselli Phenomenal Film Handler Posts: 1260 From: Florence, Italy Registered: Mar 2000 posted 02-16-2003 05:09 AM                        Oliver, It seems more reasonable to point the mic straight to the ceiling. First because the mic is omnidirectional, second because if I point the mic 45° to the stage... what about the surrounds? What about R2's mics? Should they be angled 90° too or are they a different type of mic? Bye Antonio  |  IP: Logged Michael Schaffer "Where is the Boardwalk Hotel?" Posts: 4143 From: Boston, MA Registered: Apr 2002 posted 02-16-2003 05:59 AM                        Antonio, like Jeffry said, it depends on the microphone`s response characteristics. A microphone can not respond evenly to all frequencies from all directions, so there is a preferred direction in which it should be pointed for a response as flat as possible. Usually it is in the mic`s documentation from which direction the microphone`s response is flattest.  |  IP: Logged Antonio Marcheselli Phenomenal Film Handler Posts: 1260 From: Florence, Italy Registered: Mar 2000 posted 02-16-2003 06:41 AM                        Michael I understand qhat you want to say. But if the mic is not absolutely omnidirectional I balieve it is not suited for equalization purposes, do you agree? If a mic should be pointed, say, 45° to the sound field to be flattest, what about the surrounds eq? You have to change the position of the mic when equalize the surrounds? Am I saying nonsenses? Bye Antonio  |  IP: Logged Oliver Pasch Film Handler Posts: 53 From: Europe Registered: Jun 2002 posted 02-16-2003 06:48 AM                    Antonio, Michael, i have to give in still not beeing THAT sure about this issue. You're definitely right that the mics characteristics needs to be considered. But what about consideration of the characteristics of the human ear (or even brain)? I mean, human cognition of sound is perhaps not omnidirectional, well maybe the ear itself does but the brain puts in some priority to directionalizd sound - that's all about evolution and that real enemies for a human beeing use(d) to come from front and above, mostly not from the floor - kind of comparable to what visual cognition puts emphasis on. So i still think that the 45 degrees Dolby suggested for a very long time aren't that bad at all, well actually it might correspond more to what the human ear will hear after the alignment of the theatre - and i've never seen an audience lying on the floor of the auditorium pointing their ears and eyes to the ceiling)  |  IP: Logged Antonio Marcheselli Phenomenal Film Handler Posts: 1260 From: Florence, Italy Registered: Mar 2000 posted 02-16-2003 11:18 AM                        Oliver I do not agree with your analysis. Equalize a theater mean let that screen sound exactly as the recording theater. It is the mixer that decide how the film should sound. I believe that if I put the mic toward the floor both in recording theater and the movie theater the result in the movie theater is exactly the same of what the mixer thought... So the main question is: what is the standard procedure? How is the mic placed in the mixing theater? But despite this argumentation, I have to say that if the mic isn't in the sound filed of some speaker, it cannot read them and so the EQ and levels will be wrong. For example: if I angle the mic 45°, the back surround channels and partially the left and right surround will be out of the mic sound field... Am I wrong? The main reason we equalize a theater is let it sound in a standard way. How the movie has to sound is mixers' job. So, I think that (with an omnidirectional mic) the correct placement is toward the ceiling. What do you think? Bye  |  IP: Logged Manny Knowles "What are these things and WHY are they BLUE???" Posts: 4247 From: Bloomington, IN, USA Registered: Feb 2002 posted 02-16-2003 12:23 PM                     I just sent an email to Dolby inquiring about this (i.e. why they suggest a 45-deg angle). What about if you're using a multiplexer? How should those mics be aimed?  |  IP: Logged

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