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Cato · 03-20-2014, 06:18 PM

Love my new BRZ Limited except for the sound generator, so I bought the Dynosty kit and removed it. I measured the cabin sound levels before and after removal, and I was pleasantly surprised by the large difference - 70 mph cruise sound level decreased from 88 dBA to 71 dBA on the same stretch of highway, and the sound level at full throttle in second gear (going from 35 mph to 55 mph) decreased from 97 dBA to 85 dBA.

This decrease is much greater than I have seen referenced in other posts, which generally looked like a 3-4 dB decrease. More on the methodology below, but, as they say, it isn't rocket science.

I have the data sheet from Car and Driver's test results on the 2013 Subaru BRZ Limited, and I noticed that my numbers after removing the noise generator were almost identical to C&D's numbers on the stock car (73 dBA at 70 mph cruise, 85 dBA at full throtle).

QUESTION: Did the 2013 Subaru BRZ Limited not have the noise generator? I don't have the date the C&D testing was done, just the PDF, and it could have been a pre-production version.

The moral of the story is that removing the noise generator will reduce the perceived sound level by over half (the actual acoustic power per unit of area is reduced by over a factor of ten).

METHODOLOGY: I used a Radio Shack Sound Level Meter on the A Weighting. For 70 mph cruise, I took six readings on the 70 dB range (I didn't believe the first three were so high) on the unmodified car and three on the modified car. The omnidirectional mike on the meter was not sensitive to the direction in which it was pointed. It was held by the passenger at 10 inches above the seat, pointed directly forward. These readings used the one-second average.

For the full-throttle, I took three readings for unmodified and modified, both on the 90 dB range, using the maximum value experienced in going from 35 mph to 55 mph.

The values for the modified car are similar to my wife's 2004 Miata, which I used for a sanity check. Miatas are not quiet cars, but they are quieter than the stock BRZ.

03-20-2014, 06:18 PM	#1
Cato Member Join Date: Mar 2014 Drives: 2014 Subaru BRZ Limited Location: North Carolina, USA Posts: 12 Thanks: 0 Thanked 0 Times in 0 Posts Mentioned: 1 Post(s) Tagged: 0 Thread(s)	Funny interior sound level numbers? Love my new BRZ Limited except for the sound generator, so I bought the Dynosty kit and removed it. I measured the cabin sound levels before and after removal, and I was pleasantly surprised by the large difference - 70 mph cruise sound level decreased from 88 dBA to 71 dBA on the same stretch of highway, and the sound level at full throttle in second gear (going from 35 mph to 55 mph) decreased from 97 dBA to 85 dBA. This decrease is much greater than I have seen referenced in other posts, which generally looked like a 3-4 dB decrease. More on the methodology below, but, as they say, it isn't rocket science. I have the data sheet from Car and Driver's test results on the 2013 Subaru BRZ Limited, and I noticed that my numbers after removing the noise generator were almost identical to C&D's numbers on the stock car (73 dBA at 70 mph cruise, 85 dBA at full throtle). QUESTION: Did the 2013 Subaru BRZ Limited not have the noise generator? I don't have the date the C&D testing was done, just the PDF, and it could have been a pre-production version. The moral of the story is that removing the noise generator will reduce the perceived sound level by over half (the actual acoustic power per unit of area is reduced by over a factor of ten). METHODOLOGY: I used a Radio Shack Sound Level Meter on the A Weighting. For 70 mph cruise, I took six readings on the 70 dB range (I didn't believe the first three were so high) on the unmodified car and three on the modified car. The omnidirectional mike on the meter was not sensitive to the direction in which it was pointed. It was held by the passenger at 10 inches above the seat, pointed directly forward. These readings used the one-second average. For the full-throttle, I took three readings for unmodified and modified, both on the 90 dB range, using the maximum value experienced in going from 35 mph to 55 mph. The values for the modified car are similar to my wife's 2004 Miata, which I used for a sanity check. Miatas are not quiet cars, but they are quieter than the stock BRZ.