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Old 10-24-2012, 08:19 PM   #1
hmbrewd
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Member#: 298555
Join Date: Oct 2011
Chapter/Region: South East
Location: Asheville, NC
Vehicle:
2012 WRX
DGM

Default Cabin Noise / Drone - Hatch

Just wanted to share a few test results regarding the cabin noise of the Invidia Q300 v2 CBE (hatch model). For anyone complaining about drone with this exhaust under a hatch, and doesn't settle for the common response that it's all a matter of opinion...it has to do with what you like and what you don't like, I have provided some quatitative info below.

Would LOVE to hear if anyone eles has done this test with other exhaust systems.

Car: 2012 WRX Hatch
Downpipe: Cobb catted
Tune: AP OTS Stage 2 Tune
Other: Hatch filled with sound dampening rubberized matting directly on metal floor and medium density foam rubber stuffed into every hole it would fit under the rear compartment. Additional rubber matting on top of that.
SPL Meter: The tried and true audiophile reference RS Analog meter in driver's hand at chin level. In-cabin, windows up, seats upright all accessories off. (Note: This particular meter is said to need a +1.5 dB correction in the 60-120 hZ range which would add an additional value to the numbers below. The bulk of the exhaust frequencies fall into this range. The readings are not corrected, and are thus very conservative.)



IN CABIN:

Stationary Idle 82 – 84 dB
2nd gear light acceleration 2500-4000 RPM 96 dB
5th gear flat cruise 70 mph 95 dB
4th gear flat cruise cruise 50 mph 2500 RPM 96 dB
Interstate on ramp moderately aggressive acceleration 2nd-5th gears 20 mph-65 mph 95 dB
4th gear light acceleration from 2500 – 4000 RPM 100 dB
5th gear 65 mph cruise up a small incline 100 dB
Coast in 2nd gear 25 mph down hill 100 dB
4th gear coasting on off ramp 60 mph to 30 mph 102 dB
Ave commuter driving continual fluxuation between 96-102 dB
850 watt stereo system blasted until it’s uncomfortable beyond 10 seconds 110 dB


Noise comparison chart from Purdue University:

http://www.chem.purdue.edu/chemsafet...n/dblevels.htm

(Interesting to note that this exhaust regularly produces IN CABIN SPLs above that of a Bell Helicopter at 100 ft.)
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Last edited by hmbrewd; 10-29-2012 at 11:47 AM. Reason: spelling error
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Old 10-25-2012, 08:40 AM   #2
SubieCubed
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Chapter/Region: Tri-State
Location: Central PA
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2011 WRX Lmtd Stg2
Sexy Statin White Pearl

Default

I wish I would of read this a couple days ago. I just got the Q300 and I don't like the tone of the exhaust in the cabin. In my opinion, it doesn't sound loud but it just sounds too low around 2k-2.5k RPM. Anybody know how the SPT compares to the Q300?
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Old 10-25-2012, 11:44 AM   #3
hmbrewd
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Join Date: Oct 2011
Chapter/Region: South East
Location: Asheville, NC
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2012 WRX
DGM

Default

Just for clarification, all the above spl levels are C-weighted. A-weighted levels came in approx 18-19 dB lower. The basic difference is that a C-weighted meter attempts to measure amplitude of a sound wave in a linear fashion throughout the frequency range regardless of the human ear's ability to perceive these waves, whereas A-weighted attempts to create a mathematical model of the human ear's response to the levels since we don't hear all frequencies the same. So, for instance, the 102 dB C-weighted drone that is present in the car is actually perceived by the human ear around 80 dB (A). This is because the frequency of the exhaust note is very low. It is in a frequency range that we don't hear as well as say a high pitched scream, so 100 dB at 40hZ is not going to drown out 80 dB at 1000hz. This is why you can still have a conversation with a 102+ dB low frequency drone in the background. We're technically not "hearing" just how much sound pressure is being created at the lower frequencies. A c-weighted measurement is closer to actual spl levels whether we can "hear" those frequencies or not. C-weighted measuring of sound is most often used for higher amplitude (loud) noises when you want to find out just exactly how much sound pressure is striking an object (such as your inner ear or the bolts that hold your car together). Keep in mind we don't just hear sound, we also "feel" it, and it can affect us in strange ways even if our perception tells us that it's not technically all that loud. Hence, the inner ear "phenomenon." A 102 dB low frequency (40hZ or so) sound wave can assault your inner ear, make you dizzy, give you a headache, leave you a little "cloudy", and literally make you nauseous, though your sense of hearing only allows you to detect the sound level at a relative 80 dB, so you're having a conversation while all of this is happening.
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Old 10-25-2012, 02:11 PM   #4
SubieCubed
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Join Date: Jul 2006
Chapter/Region: Tri-State
Location: Central PA
Vehicle:
2011 WRX Lmtd Stg2
Sexy Statin White Pearl

Default

Wow,....you know lots about this. I learn something new everyday . The exhaust doesn't actually seem that loud. It just has a lower tone than what I'm use to. I had an N1 on my car prior and LOVED the sound but didn't like the way it looked. Some people like the low/deep toned rumble in an exhaust. I prefer something with a higher pitch.
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