I'm not a big audio-guy, so I'm checking with a friend (who is) to be sure I'm checking them correctly.

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Hint
As far as mics being off......these may not apply to you. there can be many reasons for that..........how bout poor calibration? <doubtful>, poor packaging, maybe, the flight? I always thought taking the sensitive mics 30,000 feet for 6 hour flight etc has got to affect them somehow. I always meant to make a point to try and ship them via ground only but never got around to it. A handy calibrator such as the one mentioned by Gordon is always helpful in for any situation...good idea. And remember you cant drop those microphones even when they are in those foam spongy covers. they dont do squat cept make those microphones look bigger!! Check all multiplexor connections. Those odd assigned <1&3, 2&4? male/female connectors sometimes go loose and can affect a SPL reading <seen it happen> Make sure they are fully seated even though they have a spot where they snap in but check it twice. Wind up that black canon plug chord properly over top over under blah blah....one, its a decent cable and two,the jugular to the R2....alot of folk have probably already cracked their ends by now or bitten off some of the casing on their pelican cases or theater door/port window ...haha make sure those are seated in properly as well. Never unplug anything while the R2 is on. Make sure its off....The R2 is able to convert most power sources by moving a little card and swtich next to the power cord plug and thus very sensitive....Its a pain to open it up to have to change a fuse or IC chip! Buy a cheesey Radio Shack SPL meter to double check what the R2 reads...in case its starts to read different for what ever reason, your Radio Shack SPL will confirm this. Make sure you have updated R2 software installed and dont use Window's shell for DOS!!! Just dont! This software was written for 386's it can only be so resilient without finding something to coflict with modern day Windows.

Your problem with mics being 2 db off...well lets see. I think we need a little more confirming information just to be sure. I hate assuming! Are those two microphones right next to each other or are they measuring 2db off while being in their typical testing positions?
When you recieved the R2 from THX did you check to make sure the correct mic calibration files <offset to reference mic> were installed onto your computer and registerd on the R2 software <not too hard but tricky still>??
Id also call THX and ask them to what db tolerance they calibrate the mic to or is it strinctly a frequency response tolerance they calibrate. I am assuming its both.
Lastly make sure the cleaning guy isn't sweeping/vacumming right behind you. hehe sometimes its just that. HAHA!
Much luck to your SPL mic problem!!!

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Our service guys use Linear-X analysers rather than R2's so I am not an expert of R2's but I was under the impression that the R2 mics are electret, not condenser. Small point I know, but significant in terms of microphone technology. Am I mistaken?

Also, I would be wary of using SPL meters from Radio Shack (Tandy in this part of the world) for anything other than rough checking. We bought a bunch of these a while back and found that out-of-the-box the calibration varied from one to the next by up to 3dB! You only get what you pay for. I would suggest that the only true and accurate way to calibrate an analyser is with B&K calibrator.
Even then, the calibrator needs to be sent back to B&K periodically for alignment.

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FWIW, the model number on the Ultra Mics is different than that from the THX mics though that may have to do with what ends or length of cable is attached more than with any properties of the mic element.

Steve

I am interested in how the resident Filmtech techs set up their microphone arrays in cinemas. We have found using four mics in a tilted rectangle, centred about the main seating area (usually about 2/3rds back), but with the edges of the rectangle no closer to the side walls than about 1/4 of the width, produces the best results. The rectangle ends up covering four seat rows. I have seen some THX guys stick their mics all over the place including near side walls and the rooms always end up sounding pretty ordinary. So what is the general consensus on this?

Also Linear-X supply neat little pencil mics which, with the help of small piece of foam can be mounted on the seat backs angled up at the preferred angle of 45 degrees. I am wondering how R2 users manage to get those tiny Countryman lavaliers sufficiently high above the seats to avoid excessive losses at the HF end. I have seen metal brackets used, but relections from these would almost certainly have a detrimental affect on the readings. I've also seen the mics just drapped over the seats -- wooaa!!

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Ray Derrick
President
Panalogic Corporation Pty Limited
44 Carrington Road
Castle Hill NSW 2154 Australia
Phone: 61 (0)2 9894 6655 Fax: 61 (0)2 9894 6935