This is topic Checking your R2 analyzer after calibration in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.
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Posted by John Walsh (Member # 168) on 12-29-2001, 04:40 PM:
Has anyone checked their R2 analyzer after being calibrated by THX? On the one I'm looking at now, there seems to be a 2db difference between two mics. This has happened twice before (2db off and another 3db.) After calling/talking to other R2 owners, they are finding similar differences.I'm not a big audio-guy, so I'm checking with a friend (who is) to be sure I'm checking them correctly.
But, in the meantime, I was wondering if anyone had any similar experiences.
Posted by Gordon McLeod (Member # 33) on 12-29-2001, 08:48 PM:
THX sells a calibrater to be used with teh BK calibrator
When you say they are off by 2 db what are you compareing them too?
Take the CEL SPL meter right beside the mic and compare it to what the mic says
Posted by Rory Burke (Member # 512) on 12-30-2001, 01:30 PM:
R2 Calibration consists of taking each one of those low diffraction condesor microphones and comparing them individually to a 1/4" precision mic in a controlled environtment whilst measuring pink noise and applying an offset via software to bring multiplexer mics to within a "tolerance" of the reference.
There have been good previous posts in reference to this topic. There is always room for error and while comparing an R2 to other analyzers <excluding price hehe> its stands out on top......some of the software provided analysis is unsurpassed and quite helpfull for analysis of structural nuances and acoustic farts! The R2 helps study a room let alone check SPL and EQ a room. 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!!!
Rory
Posted by Mark Gulbrandsen (Member # 72) on 12-31-2001, 09:49 AM:
With that much difference between mics it would be difficult to really get to thae required THX EQ tolerance. I would suggest you call them and perhaps send it back to them for further evaluation. It musta been a Monday morning or late Friday alignment job!
Mark @ GTS
Posted by Gordon McLeod (Member # 33) on 12-31-2001, 12:28 PM:
Mic 1 is the only one that spl level is really critical for as it is the one that the SPL measurement is based on
Posted by John Walsh (Member # 168) on 12-31-2001, 01:26 PM:
Thanks, guys... The unit was fresh back from THX; didn't even have time to knock it around dragging it from one theater to another!I know two other people who have similar problems. As I said before, I'm not 100% sure I'm checking the mics correctly (another thing I need to learn about!) If I find out anything interesting, I'll report back. 
Posted by Stefan Scholz (Member # 147) on 12-31-2001, 02:59 PM:
Any measurig reference must be checked with a known standard- and if neccessairy- readjusted before use. The R2 measuring tool refers to Mic 1 as the SPL reference, the others are only critical in frequency response characteristics, even though they should measure identical.
So get the BK calibrator, THX's adaptor and do the job prior to starting your measurements.AS beeing primarily a cellphone pro, working with microwaves, we are based on calibration standards, as otherwise measuremts will never be repetitive, and that's what makes troubleshooting easy.
(It may be different with DC... )
Posted by Rory Burke (Member # 512) on 01-03-2002, 01:26 PM:
John W.
Did you install the mic files that come with a newly calibrated kit by THX!! It probably came with a 3.5 floppy. These must be installed and verified thorugh the R2 software otherwise your testing is reflecting you old microphone calibration information. This will surely give you different readings. It consists of 8 files i believe. Mic1_s.adj thru Mic4_S.adj & Mic1_p.adj thru Mic4_p.adj and will have a number corresponding to your microphones serial number. This is critical!!!Anyone use their R2 for any other purposes cept for A-chain B-chain and EQ? Anyone perform Sound transmission testing on their building or any other procedure??
If anyone needs to know how to calibrate their microphones...please email me.....youll be surprised how simple it is although must be conducted very precisely!
Rory
Posted by Ray Derrick (Member # 1001) on 01-10-2002, 05:40 AM:
RoryOur 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.
------------------
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
Posted by John Walsh (Member # 168) on 01-10-2002, 07:57 AM:
I have not yet been able to talk to my friend about the mics on the R@ unit, so I'm still in the air about that...But Ray is right... you'd be crazy to trust anything from Radio Shack for exact readings!
Posted by Gordon McLeod (Member # 33) on 01-10-2002, 10:31 AM:
Cel instruments in the UK they have a US office in the new england states area is one of the best SPL meters
Posted by Mark Gulbrandsen (Member # 72) on 01-10-2002, 11:34 AM:
The R-2 mics are Countryman EMW condensers. Found that out when a carpet layer cut through two of my cables one day. Guess he didn't like the pink noise!! They run around 220.00 per mic if you went out to buy them. Essentially, they are as close as you can get to just having a mic element alone in free air and still have some durability to it. The Ulsra Stereo multiplexer uses the same type mics but its not as well calibrated and the other mics levels are not calibrated to mic 1. They have to be manually set(poo-poo!).
Mark @ GTS
Posted by Steve Guttag (Member # 268) on 01-10-2002, 04:07 PM:
The Ultra stuff is more wild than that...there is rather poor if any "calibration" to the system though you can set levels in them. There can also be loading interaction between your analyzer and the Ultra plexer. Often the upper frequencies are not a great representation.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
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"Old projectionists never die, they just changeover!"
Posted by Ray Derrick (Member # 1001) on 01-11-2002, 07:47 AM:
Actually Mark, the Countryman EMW lapel mic IS an electret. Mind you these days an electret mic is often referred to as an "electret condenser" because both electret and condenser mics rely on variations in capactitance to generate a signal. But old audio pros like myself have always regarded them as a "poor man's condenser". But I am waffling...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!!
------------------
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
Posted by Mark Gulbrandsen (Member # 72) on 01-11-2002, 02:42 PM:
I don't know what other techs are using for stands for their R-2 mics but I got 4 nice telescoping, variable angle stands with my R-2 when I bought it a long time ago. Anyone that doesn't have them shouldn't be doing this sort of work!!!! The stands are an important part of the system. Best of all the stands are telescoping and allow one to get them up high enough above the seat backs so there is not a hf pick up problem. The idea behind the Countryman mics is to have as much as possible, a mic element in free air that has no housing around it. This eliminates as much coloration as is feasable that a mic housing may introduce into the readings. They are normally used in a straight up position, and my results have been very good sounding, and very consistant doing it that way.
For placement it depends on if its stadium, usually rectangular pattern, or sloping floor, usually diamond, but staggered a bit. I have gotten the best results if I keep my mics within 8 feet of each other,a bit less in smallish rooms, and definately well away from side walls, usually about as you mentioned, 1/4 width. Of all the analyzers I have owned, the R-2 has given me the best, most consistant, and repeatable results.
Mark @ GTS
Posted by Ray Derrick (Member # 1001) on 01-11-2002, 06:54 PM:
Mark said "The idea behind the Countryman mics is to have as much as possible, a mic element in free air that has no housing around it. This eliminates as much coloration as is feasable that a mic housing may introduce into the readings".I can't say that I would agree with you on that one, Mark. I think you will find that the Countryman mics were chosen because they are relatively robust and inexpensive. (They were after all designed to clip on your lapel.) A set of true condenser analyser mics will set you back at least $10,000 and have to be handled with kid gloves. They wouldn't last 5 minutes being carted around from cinema to cinema.
The concept that these mics were chosen because they represent the closest thing to a mic element in free air sounds like one of those pieces of folklore (presumably originating at THX) to make people feel good about using cheap mics on an expensive analyser. (No disrespect intended to Mark or THX).
Yes, I have seen those neat little telescopic stands. Does anyone know who makes them?
------------------
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