quote:

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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.

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Interesting that Dolby recommends a 45 degree angle. I don't think that's what the Dolby techs used with their mics.
 

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Posted by Michael Schaffer (Member # 1204) on 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?
 

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Posted by Antonio Marcheselli (Member # 373) on 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
 

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Posted by Oliver Pasch (Member # 1335) on 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.
 

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Posted by Antonio Marcheselli (Member # 373) on 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
 

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Posted by Michael Schaffer (Member # 1204) on 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.
 

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Posted by Antonio Marcheselli (Member # 373) on 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
 

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Posted by Oliver Pasch (Member # 1335) on 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)
 

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Posted by Antonio Marcheselli (Member # 373) on 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
 

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Posted by Manny Knowles (Member # 1171) on 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?
 

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Posted by Gordon McLeod (Member # 33) on 02-16-2003, 12:56 PM:
 
There are different types of mics and different characteristics
THe countrymans (USL and R2) aim at the ceiling
 

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Posted by John F. Allen (Member # 218) on 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
 

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Posted by Antonio Marcheselli (Member # 373) on 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 ]
 

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Posted by Manny Knowles (Member # 1171) on 02-22-2003, 04:43 PM:
 
What's involved with calibrating a mic?

Anybody got photos?
 

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Posted by Gordon McLeod (Member # 33) on 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
 

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Posted by Manny Knowles (Member # 1171) on 02-22-2003, 06:40 PM:
 
So calibration is for SPL sensitivity only?

Or does this also affect its "flatness" ?
 

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Posted by Gordon McLeod (Member # 33) on 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
 

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Posted by Manny Knowles (Member # 1171) on 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?
 

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Posted by Gordon McLeod (Member # 33) on 02-23-2003, 09:39 AM:
 
Yes it goes back to the manufacturer
 

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Posted by Justin McLeod (Member # 1329) on 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?
 

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Posted by Manny Knowles (Member # 1171) on 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.
 

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Posted by Justin McLeod (Member # 1329) on 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!
 

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Posted by Gordon McLeod (Member # 33) on 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 .
 

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Posted by Manny Knowles (Member # 1171) on 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 ]
 

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Posted by Gordon McLeod (Member # 33) on 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
 

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Posted by Justin McLeod (Member # 1329) on 02-25-2003, 08:03 PM:
 
I take it that if one uses a broom stick handle for a mic stand, they can still use a multiplexer, or am I wrong?
 

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Posted by Gordon McLeod (Member # 33) on 02-25-2003, 08:30 PM:
 
just need 4 mics and 4 broom handles and the later is a problem at some theatres:)
 

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Posted by Daryl C. W. O'Shea (Member # 1303) on 02-25-2003, 09:22 PM:
 
I use a broom handle once in awhile. It's just as sturdy as a mic stand if you stick the end down the side of a seat.

Most of the time I do use three legged aluminum mic stands, but that is because I mainly eq systems for live performances where I have mic stands readily available.

The advantage of using a broom handle is that you don't have to pay to transport a fairly bulky item (mic stand), albeit a light one, across the country.
 

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Posted by Antonio Marcheselli (Member # 373) on 02-26-2003, 02:03 PM:
 
Coming Back to the original topic (mic placement), I had a theory.

If the mic is designed to be straigt to the ceiling and I point it 45° with the screen instead, is it possibile that the "back surround" channel cannot be heard correctly by the mic?

I'm asking this because in many installation (where I saw the tech aim the microphone 45°) back surround sound is low, IMHO.

Perhaps it is a nonsense.

Bye
Antonio
 

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Posted by Manny Knowles (Member # 1171) on 02-26-2003, 03:49 PM:
 
Lately I've been doing all measurements with the element pointing straight up, but I would usually do surrounds with the element pointing up anyway (even back when I was still doing L/C/R with the 45-degree angle).

If you're using just one mic, you should move it to the centre of the aisle. In other words, not off-centre (like for stage channels).
 

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Posted by Antonio Marcheselli (Member # 373) on 02-26-2003, 04:13 PM:
 
Manny

Yes, I agree with you. I asked this because when few weeks ago I made my first equalization the theater (SR only) had no or very low surrounds. My PC said 77dB. I trim to 85dB and the result was correct, at my ears. Since many and many theater I've heard had very low surrounds, I thought that perhaps an incorrect mic placement and aiming can be the cause for the problem.

Bye
Antonio
 

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Posted by Tom Wienholt (Member # 1510) on 02-26-2003, 06:01 PM:
 
If the mic placement was the problem then wouldn't the back surrounds be to loud? If the mic is pointing toward the screen then it would not pick up the full signal from the back surrounds so they would have to be trimmed to a higher volume so that the mic would register 85db. So the result would be back surrounds that are too loud, not too soft. Isn't this correct?
 

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Posted by Manny Knowles (Member # 1171) on 02-26-2003, 06:33 PM:
 
I would have to agree with Tom. Assuming that there would be an audible difference, it would be a logical assumption that those surrounds would be too loud.

However -- in terms of SPL -- my hunch is that there would not be an appreciable difference. (Does anybody here know for sure?)

Still, it is wise to go into the theatre and double-check everything with your ears. If the SPL meter says 85dBC but it "sounds like less" then something isn't right.
 

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Posted by Antonio Marcheselli (Member # 373) on 02-27-2003, 10:32 AM:
 
Tom, Manny

I agree with you this time too!!
I've never understood why in some theaters surround are too low and why our EX installation has back surround too low...

I also agree with "ears" check before leave the theater.

Bye
Antonio
 

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Posted by Antonio Marcheselli (Member # 373) on 06-17-2003, 04:10 PM:
 
Gordon

Sorry if I resume this old topic but I had the chance to see R2 microphones and I would like to know what do you mean with "aim them at ceiling", I thought they were like "normal" microphones...

Someone has some photos?

Bye
Antonio
 

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Posted by Gordon McLeod (Member # 33) on 06-18-2003, 09:14 PM:
 
The countryman mics are basically small electrec condensor lapel mics that have calibrated SPL and response files made to correct the analyzers display to match the mic
They have a flat entrance point and they point upwards
there is a small windscreen over them
 

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Posted by Mark Gulbrandsen (Member # 72) on 06-19-2003, 07:19 AM:
 
Michael said...
"Has anyone worked with the screen luminance testing system?"
_________________________________________________________________

Yes, we have Serial nmber 001 USL Lightmeter at work and it is frequently used. Its used in all new installs , when installing a Phoenix kit, or general work if the lamphouse is far out of alignment.
Mark @ CLACO
 

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Posted by John Pytlak (Member # 331) on 06-19-2003, 10:07 AM:
 
Kodak also uses the USL PSA-200 in various lab applications.

http://www.uslinc.com/products/psa.htm

http://www.uslinc.com/products/features/psa200.htm
 

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Posted by Larry Zuverink (Member # 1483) on 06-19-2003, 02:19 PM:
 
Antonio,

If you don't think the mic placement makes a difference try EQing and then move you mic several times. No matter how well a theatre is designed it will have dead and hot spots. Also try this, point your mic at 90 degs from the speaker you are setting the spl on. Then move the the mic in every direction and watch the reading. You will most likely only see in increase and decrease when pointed straited on or straight away from the speaker. All mics will give a false spl reading if pointed to close to the speaker. You want the ROOM pressure not the energy hitting you. I use a swinging boom mic that we made ourselves. It swings the mic in a 8' arc. It's a cheap alt to a multiplexer and makes sure that we are not EQing in a dead spot.

Also be very carful not to over EQ the room. You can get any room to flatline but it will sound bad if frequencies are fighting each other to do it.

In general EQing is a art not a science. You need to learn how to interpet problems in the room and not fight them.

Just my two cents worth
 

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Posted by Philip Wittlief (Member # 1724) on 06-19-2003, 08:30 PM:
 
If the mic is an omnidirectional, like the behringer in the original question is, then 90 degrees or 45 or anything for that matter shouldn't make a difference. There are small changes in the responce to the mic at different points around it, as no mic is perfect. If you look at the spec sheet on the behringer website [URL=http://www.behringer-download.de/ECM8000/ECM8000_C_Specs.pdf ]here[/URL] you can see the response curve of the mic and notice that it is close to aproaching a circle (an ideal onni mic).

Looks like I can't figure out the UBB hyperlink thing. sorry
 

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Posted by Christopher Seo (Member # 7) on 06-20-2003, 12:51 AM:
 
Random incidence microphones do not have a flat response to sound in all directions, but rather are designed to have a flat response on average when the sound is coming from random directions. The face of the microphone creates direction-dependent pressure disturbances which affect the higher frequencies. This is why, for example, ANSI specifies a particular degree offset when making free-field measurements with random incidence microphones... it compensates for the directional variations since in a free-field the direction is not random.
 

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