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The saga cont. - RTA /SPL measurements

...OK chaps, as promised, I conducted the final segment of the World Finals-mock SPL and RTA testing in an attempt to get to the bottom of the controversy and lay to rest this topic as it concerned RTA lane 1, rookie lane, with Gord and Jamie judging/using the meter.

In previous posts, we stated and reiterated the proper procedure for testing frequency response using an Audio Control 3055 real-time analyzer step-by-step according to the IASCA sound quality competition rulebook. We also tested certain aspects of a sample car audio system trying to mimmick the scores obtained by some of the rookie cars at Finals and tested some of the "accusations" made that caused the retrial controversy at the event. THis final session of testing and results will address the last of the issues and/or possible explainations of the "low scores" in the supposedly otherwise "high-scoring" rookie cars...in otherwords, I am really trying to make our high-scoring truck score low in anyway possible to try to nail down the true cause of the low scores.

This is the itenerary this time>
1-Establish a baseline RTA measurement, following the exact RTA testing procedure outlined in the IASCA rulebook and further quoted here in another thread ( http://forum.elitecaraudio.com/showthread.php?threadid=135663).
2- Using the exact same system settings, I will add varying degrees of EXTERNAL FLOOR NOISE and measure it's effects with variances in ambient noise volume and record the scores.
3- Using the exact same system settings and highest REALISTIC ambient noise floor level, I will test to see if the noise floor being present has any affect on the Audio Control meter with regard to measuring system SPL.
4- I will then correct for this noise floor by re-tuning the parametric equalizers in said system to achieve the best possible RTA setting while said noise floor is present, then re-test the RTA section again and record the scores.
5- I will then test the SPL of the system with the NEW EQ SETTINGS after having corrected for the noise floor and record the data. THen we can all compare the findings.


>>>BASELINE MEASUREMENT-
-ambient IN CAB spl in my quiet garage is 62.2 dB , as measured in the standard RTA/SPL mic position in the driver's seat of said vehicle (see above link again)
- System eq set to RTA curve, proper IASCA RTA measurement procedure followed step-by-step (again, see http://forum.elitecaraudio.com/showthread.php?threadid=135663 ).
- Procedure repeated 5 times

Score 1- 29
Score 2- 29
Score 3- 30
Score 4- 29
Score 5- 30


>>> ADDING FLOOR NOISE
- using high-energy trance music set to repeat and bass control on test-bench head unit set to +5, I play the system in my garage at a normal listening level.
(a word about my garage system---it is my test bench/ building cars stereo system consisting of a Pioneer CD player, Autotek 4X50 mean machine amp running 3 channel, a pair of MB Quart coaxial surround mains, two Hollywood sound labs 12's in a 4th order bandpass enclosure. THis system has the mains mounted in the opposite corners of the ceiling, and the sub box is under one of my workbenches corner-firing off the wall. THis system gets just as loud, if not louder than, a good 100WPC home system. It all runs off an Astron power supply and an Optima battery.)
THis trance music has a lot of energy at 30-50 Hz to simulate the booming we had to deal with at Finals.

- With the truck system OFF, mic in test position, I adjusted the garage system to read in the range of 75.4-76.0 decibels ambient level INSIDE the closed truck....a gain of roughly 13.5 decibles over the ambient floor noise level with the truck in a "quiet" garage. Here are the findings>>>

>>>>+13.5 dB floor noise>>>SAME truck system EQ setting
(NOTE:- when setting the relative loudness of the system to 90dB, I ended up with a level of 90.4 dB playing the pink noise track. In the PREVIOUS testing when measuring the baseline, I had a level on the sensitivity adjustment of approximately +9 dB....THIS time, with the added floor noise, I should note that the sensitivity level adjusted was only about +6 dB)

Score 1- 27
Score 2- 28
Score 3- 26
Score 4- 27
Score 5- 26

Hmm, OK. Obviously, the added floor noise is causing the test system's scores to drop. Let's see what happens with MORE floor noise>>>>

>>> +20 dB floor noise over baseline>>> SAME eq settings. Ambient SPL level in truck with system off is 82.0 - 82.3 dB SPL>>>

Score 1- 27
Score 2- 25
Score 3- 25
Score 4- 26
Score 5- 25

Wow. Scores seem to be decreasing as floor noise increases. But wait! I remember someone stating that they *may* have seen the meter register 90dB at the show WITHOUT the competitor's system being on! OK. Let's test that>>>

>>> + 26 dB floor noise over baseline>>>SAME eq settings and measurement procedures. Ambient SPL level in cab with system off is 87.9 - 88.9 dB SPL>>>

Score 1- 24
Score 2- 24
Score 3- 25
Score 4- 24
Score 5- 24


HOLY MONKEYS! As the ambient noise floor increases, my otherwise high-scoring comp system's RTA scores DECREASE, and in this particular vehicle, by as much as 5 points!


PHASE TWO---SPL testing.
Please see http://forum.elitecaraudio.com/showthread.php?threadid=135675 for proper procedure and former findings in the SAME truck with the SAME eq setting

Scenario>>>

Noise floor present at 87.9-88.9 dB level in the truck cab with the system OFF. Check to see if the Audio Control meter microphone is affected during SPL testing by this noise floor. Here are the scores,...

Score 1- 134.4
Score 2- 134.4
Score 3- 134.0
Score 4- 134.0

Guess what? The meter is UNAFFECTED during SPL testing by any noisefloor present during the beginning or at anytime during the duration of the testing. To keep things constant, I double checked that setting the dB range selector to 90 dB (simulating a judge's error) as well as leaving the sensitivity at the RTA level of approx +6 (also simulating a judge's error) would have produced lower SPL scores...here are the results of both scenarios>>>

ALL 4 runs...Score OVR (recall this means "over", as the mic has reached saturation and the meter is set to an unuseable range- see other thread)

Findings indicate that both the presence of the noise floor AND the possibility of the judge's setting the meter incorrectly COULD NOT HAVE ATTRIBUTED to low SPL scores!


PHASE 3- Correct the system tuning via EQ adjustment to correct for the noise floor

>>>> By this time, I am getting a headache from hearing the same techno song over and over and over at high volume--LOL!! ARGGGGHHH! I am sure the neighbors think I have a rave going on in the garage!
OK, so I leave the garage system set at the same 87.9-88.9 dB measurement level, grab the meter, and re-tune a new EQ curve in the Hemimaddness. Takes about 10 minutes, but it looks good. Back to the mock comp lanes i go!

>>> System re-tuned while ambient noise floor present.
RTA testing as per protocol again, mic has not moved at all! Ambient noise floor via garage stereo system STILL going strong! Pink noise test level set to 90.0-90.3 dB spl, as per judging procedure.

Score 1- 29
Score 2- 28
Score 3- 29
Score 4- 29
Score 5- 29

AWESOME! Now I have retuned my system to score well on RTA with the roughly 89dB ambient noise floor! THis simulates the SECOND RTA/SPL run given out by IASCA at NOPI...with me so far?

PHASE 4- Test the effects of said re-tuning on the systems SPL scores using IASCA testing procedure.

System settings left as they were in phase 3 above, mic in same position, etc etc.

SPL score 1- 128.1
Score 2- 129
Score 3- 128.5
Score 4- 129

OK folks, I think this pretty much clears it up...my otherwise high scoring system capable of 134dB SPL all day long now, during it's mock-retrial run at NOPI ,gets better RTA scores after the re-tune BUT at the cost of precious SPL points!!!All this because of what??? That's right, Johnson! two precious little words I have been speaking of this whole time....NOISE FLOOR !!!


More to come...I am gonna go out there and check SPL measurements on the HI setting, even tho it is the LO microphone, as Matt suggested. BRB

Im BACK!! HOLY CHIT MANG!!!! I have a new World Record in an SQ car!!!! SWEET!!!!!

Oh wait a minute, it's the wrong SPL setting


>>>SPL testing again, original EQ setting, SPL mode set to HI, mic used in standard 136dB LO mic, same position as described...

With dB range set to 120 dB, I hit 194.4 dB!!!!!!
With dB range "left" at 90 dB, I hit "OVR" which I assume is either over 195 or 200 dB!!!

Obviously, this could not have been the cause of the low SPL scores at Finals either...but it sure could cause some excitement in such throbbing metropoli as backwoods, KY or Po-dunk, AL ! LOL!!!!

Stay tuned for a summation statement of all my Mock-Finals testing.

 

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