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Author
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Topic: Room Tuning w/ Multiple Microphones
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Manny Knowles
"What are these things and WHY are they BLUE???"
Posts: 4247
From: Bloomington, IN, USA
Registered: Feb 2002
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posted 02-27-2002 01:21 PM
I have an RTA with a calibrated microphone, but I've never been happy with the resultant "sweet spot."Does anybody here use multiple microphones and, if so, do you go through a mixer or a multiplexer? What's the ideal microphone spec for room tuning with multiple microphones? Is it true that multiple mics don't have to be calibrated to the RTA? ------------------
And, hey! Let's be careful out there. ~Manny.
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Manny Knowles
"What are these things and WHY are they BLUE???"
Posts: 4247
From: Bloomington, IN, USA
Registered: Feb 2002
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posted 02-27-2002 04:16 PM
This raises another question:I was taught that the mics were calibrated to the RTA and not to the multiplexer. Could someone clarify what is being calibrated? ------------------
And, hey! Let's be careful out there. ~Manny.
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Manny Knowles
"What are these things and WHY are they BLUE???"
Posts: 4247
From: Bloomington, IN, USA
Registered: Feb 2002
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posted 02-27-2002 05:52 PM
Thanks for the info...The USL MMP-10 Multiplexer looks good. I'll investigate cost.By the way, I downloaded the user manual and it says: "Each microphone is calibrated with its multiplexer to insure utmost accuracy." They are indeed Countryman lab grade test mics. ------------------
And, hey! Let's be careful out there. ~Manny.
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Steve Guttag
We forgot the crackers Gromit!!!
Posts: 12814
From: Annapolis, MD
Registered: Dec 1999
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posted 02-28-2002 10:11 PM
Gord,My tests do not back up yours. HF response using the USL plexer is totally dependant on the mic. There is no offset for frequency response. Furthermore, your analyzer can load the plexer and cause even more frequency anomolies, particualarly in the LF region. The USL system is a good tool and is better than a single mic but it is a far cry from a calibrated system such as the R2 where not only frequency response it calibrated but the levels across the 4 mics are normalized. For what its worth, the model number on the mics are not the same for the R2 as for the USL.... Steve
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Don Sneed
Master Film Handler
Posts: 451
From: Texas City, TX, USA
Registered: Aug 2001
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posted 03-01-2002 04:17 PM
Will, I use a R2 unit for my eq's, it sounds like the speakers were not aimed correctly, I use a sound pressure meter, pink noise, walk the aud. to get a overall response by sound pressure...I then have one of our techs to aim and tilt the speakers as needed, to give you an example, I just got finish doing a 10-plex All THX, the speakers were aimed as thje drawings called for, there was a 7-db difference from the front row seating to the rear, this is in a 700 seat aud. Sony 8.1 system, we reaimed the speakers position, speaker tilt we now have a 3db difference from front row to rear seating & side to side, now this took all day to get but we got a pretty good result by going the extra trouble...it sounds like the speaker you listen to was not properly aimed, tilted, & position....I know alot of techs do not go to this much length to get the speaker, freq. response, & coverage as they should....remember the "audience is listening"....
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Steve Guttag
We forgot the crackers Gromit!!!
Posts: 12814
From: Annapolis, MD
Registered: Dec 1999
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posted 03-01-2002 07:39 PM
Don makes an excellent point. The set up of a system is so important before the EQ begins. Making sure the speakers are as close to the screen as possible and properly aimed is very important to the overall response. Then there is the room itself. Even a great speaker with excellent electronics will sound horrible if the auditorium is not made well (acoustically speaking). I'm having a bit of trouble with a customer that contracts us to merely wire and tune their sound systems. While the R2 may say all is well, the actual performance varys all over the place. In some theatres he has 50% fiberglass on the walls, some 100% some have fiberglass above the ceiling tiles and some places none. The speakers are installed by the screen guy and are "safely" put nearly a foot behind the screen. He also uses a large varitey of speakers (both new and used based on availability) so consistancy is virtually impossible. One key thing about good sound systems is to get the room right first! It is a key part to a good sound system that is just overlooked once the wall drapes go up and the ceiling tiles are plopped into place. Then, install what you have as well as you can. Steve ------------------
"Old projectionists never die, they just changeover!"
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....can not totally blame the guy since the cinema owner doesn't pay enough for him to maintain a basic test set for his market.
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