Stock Exhaust Sound - dbA - of 91 NSX

ffffanman · 26 August 2005

Here are the sound readings taken 10 feet from behind the rear of my car.
I have 94,000 miles on this totally stock, engine & exhaust wise, car.
Car was stationary.
I just thought people might want to know and might use this as a reference.
Trev
The instrument used is as follows:
Bruel & Kjaer Precision Integrating Sound Level Meter Type 2230
Measurements where taken as SPL, RMS, A weighted, Frontal Sound Incidence.

RPM------10' OUT BACK-----INSIDE CAR AT EAR LEVEL
IDLE------61dbA------------51dbA
3000------74 dbA-----------60 dbA
5000------84 dbA-----------71 dbA
7000------93 dbA-----------81 dbA

netfreak · 27 August 2005

Cool. I'm pretty sure the legal limit for canada is 83dbA at 3000rpm. I'd be curious to see the numbers for some cat-less aftermarket systems.. I know on my honda it's over 120db

RP-Motorsports · 27 August 2005

I was told by someone once, that you are supposed to do readings at a 45 degree angle from the tip (may be a bit lower of a reading) for standard db testing. I am not sure.

ffffanman · 27 August 2005

I was doing some extensive readings during the day on a noisy paint booth fan and a Oskar welding fume arm system I supplied to a shop and found no real difference at what angle I was at but then again the noise was radiating out in all directions in a free field so............ Results could be a little quieter at 45 deg. for sure, but at ten feet, probably not much.
Trev

ATERPAK · 27 August 2005

At those readings, a stock NSX wouldn't pass the current 90 db max set at Laguna Seca for normal track schools. They're getting pretty lousy about making it that low so that even a stock car, and the NSX isn't the only problem car, can't pass the sound level they set. Now if you're IRL, or CART or a big name venue running an event, then those levels are never brought out. Seems money overrides any real concerns about noise control.

W · 28 August 2005

ATERPAK said:
At those readings, a stock NSX wouldn't pass the current 90 db max set at Laguna Seca for normal track schools. They're getting pretty lousy about making it that low so that even a stock car, and the NSX isn't the only problem car, can't pass the sound level they set. Now if you're IRL, or CART or a big name venue running an event, then those levels are never brought out. Seems money overrides any real concerns about noise control.

The microphones/decibel meters at Laguna Seca are probably more than 10 feet away from the car.

ATERPAK · 29 August 2005

They are but we are hearing that a lot more cars are having problems passing their sound restrictions lately. They're getting lower and lower with no real justification. :frown:

ffffanman · 29 August 2005

Double the distance and subtract 3 dbA!
So double from 10' to 20' and idle is 58.
Double 20' to 40' and idle would be 55.
Just a rule of thumb!
Dr. Tre

nis350 · 30 August 2005

Didn't know the OEM exhaust make much sound...

charlie640 · 23 June 2007

Anyone have any sound clips of a 100% stock exhaust? Can't find any with a search of the forums.

goldNSX · 23 June 2007

nis350 said:
Didn't know the OEM exhaust make much sound...

I think it's not the exhaust that makes the sound but the engine itself.

Very interesting measures. Do you have the SPL at ear at WOT?

ffffanman · 25 June 2007

Its the exhaust that makes the noise when I am behind the car for sure.
I only had the sound meter rented for that day and thats all I measured.
I since had cored out two stock exhaust with a increase in noise but nothing I was looking for.
I now have a flowmaster and its the bomb!!!
Trev

Daedalus · 25 June 2007

My stock exhaust got up to 106dba on the dyno. Nothing too scientific. I was holding the meter at hip level, standing just to the side of the car. Maybe 5' max tip to meter? I recorded in rough 1000RPM increments but I don't have the numers with me.

ffffanman · 25 June 2007

Cool, that would be the best place to test sound, on a dyno so the engine is under controlable and sustainable rpm and load.
And just like the different readings we get with different dyno's, testing sound is a strange thing in itself. So many different reading, setting and factors.
Post what you got when you get them.
Always interesting.
Trev

goldNSX · 25 June 2007

Daedalus said:
My stock exhaust got up to 106dba on the dyno. Nothing too scientific.

Don't you have very much noise of the wires on the dyno. I recall a dyno of a stock NSX where you coudn't hear the exhaust note at all.

Stock Exhaust Sound - dbA - of 91 NSX

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