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Old 06-27-2003, 04:51 PM   #1
AcquaCow
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Default Anyone have a noise / SPL meter for calibration?

I finally tracked down good RTA software...Just need to calibrate a mic so I can start tuning with it. If anyone in Fairfax Co. has a meter that I can borrow I'd appreciate it. If anyone has one to sell...that works too =)
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Old 06-28-2003, 11:41 AM   #2
Jakezor
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I'm in MN and have an Audiocontrol SA3055 in my temporary possesion.

Sorry can't help ya on the other stuff.
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Old 06-29-2003, 04:15 PM   #3
AcquaCow
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so, can't sell it eh?
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Old 06-30-2003, 02:29 AM   #4
ldivinag
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what RTA s/w?

what are you trying to do?

if you just need to make an IASCA curve, the RTA should take of it.

it should have the meter built into it or it wouldnt be an RTA.

anyways, bought a digital SPL meter from radio shack for like $50, if not, the analog meter is like $10 cheaper.
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Old 06-30-2003, 11:04 AM   #5
AcquaCow
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I'm using "Realtime Analyzer Lite" A decent program I found and have found to be very useful. I haven't seen spl meters at the shack...I suppose there's one in the catalog though =P

I just need the spl meter to flatline the response curve of the mic. Thats all.
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Old 06-30-2003, 11:09 AM   #6
AcquaCow
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>if you just need to make an IASCA curve, the RTA should take of it.

What?

How does the International Auto Sound Challenge Association have anything to do with a sound curve?

>it should have the meter built into it or it wouldnt be an RTA.

Do you know what an RTA is? Yes, it has a meter built into it, a meter that reacts to input. Problem is tuning that input as any given microphone's sound curve will not be a perfect flat response. Thus you need the noise meter and a few test tones to tune the program around the mic to compensate for the mic's sound curve.

hardware RTA's have calibrated Mic's built in, plus calibration that you can change if you use an external mic.
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Old 07-01-2003, 03:17 AM   #7
ldivinag
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Quote:
Originally posted by AcquaCow
>if you just need to make an IASCA curve, the RTA should take of it.

What?

How does the International Auto Sound Challenge Association have anything to do with a sound curve?

>it should have the meter built into it or it wouldnt be an RTA.

Do you know what an RTA is? Yes, it has a meter built into it, a meter that reacts to input. Problem is tuning that input as any given microphone's sound curve will not be a perfect flat response. Thus you need the noise meter and a few test tones to tune the program around the mic to compensate for the mic's sound curve.

hardware RTA's have calibrated Mic's built in, plus calibration that you can change if you use an external mic.
it's been a while since i competed and read the rule book, but IASCA RTA curves at not really horizintal flat from 20hz to 20Mhz

but rather a max of 3db deviation from one band (usually 1/3 octave) to the next.

back when, lowest band on the AC 3055 was 25 hz. say your system hits at +12db. the next 1/3 octave band would be 31.5hz. if your system deviates more than 3db, plus or minus +12db, you would be deducted points.

so a gentle sloping down curve was the thing to aim for during IASCA RTA portion of the judging. this was early 90's to around 1998.

dont know what the rules are now. going for a flat "curve" didnt sound that good either.
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Old 07-01-2003, 03:29 AM   #8
ldivinag
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Quote:
Originally posted by AcquaCow


I just need the spl meter to flatline the response curve of the mic. Thats all.
okay... now you've lost me...

if i were to tune a car, this is the minimun thing to use:

SPL meter
source softwware to playback on the system at known frequency and known levels.
equalizer for the system
paper and pencil

usually, i would start out by listening to the system with ACTUAL music that the owner will listen to.

if the owner likes to listen to hard rock, i wouldnt put in classical. and visa versa.

now, first thing is to bring all controls (both head unit and EQ) to flat or 0.

let's assume that we will leave the head unit BASS and TREBLE controls to flat or 0 for the entire testing. we will only use the EQ.

also, it is best to find test tones that are closest to each band on the EQ.

so again, let's make up center frequencies on the EQ: 30hz, 60, 90, 120, 250, 500 1000, 2000, 4000, 8000 and 16000.

so cue up the track which plays a 30 hz tone. keeping the SPL meter's mic at a predetermined location, record the level. most places i've seen says to use C-weighted and SLOW response on the radio shack type SPL meters.

write down reading and repeat for the all of the bands of the EQ.

ON A PERFECT SYSTEM, when you plot all of the points on a X-Y graph, there should be a flat line.

but we dont so it will look llike a series of peak and dips. this is where the money is to made.
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Old 07-01-2003, 03:35 PM   #9
AcquaCow
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I did that with the mic yesterday infact. but I tuned the mic around my RTA software at home on my home speakers (more room to setup)

I generated and corrected the mic's response curve at the following points (all in hz): 30 50 70 80 90 100 200 300 400 500 700 1000 1500 2000 3000 4000 5000 7500 10000 15000 and 20000

Now my noise meter and RTA software report almost the exact db level for any tone that they hear (its off by 1 or 2db at certain freqs.).

Step 2 today is to get in the car with the pink noise track and point the mic at the speakers. I want as flat a response as possible from the system. Now that the mic is tuned properly I can get a more accurate image of the sound spectrum. I can visibly see where I have too much midbass or treble. I know I'm lacking on the bass, so I'm not concerned about that. I'm really worrying about 500hz-2000hz (most sensitive range of human hearing). If I can flatten that out nicely I'll be happy.

-- Cow
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Old 07-01-2003, 06:55 PM   #10
ldivinag
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best advice i got?

dont let the RTA be the final judge. let your ears be the deciding factor...

tuning can be a bitch. good luck. and if you get at a wacky bump or a peak, dont forget to check your crossover points. you can use them fine tune...
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