Do you do track days?

95 - 98 is the limit on most, 85 - 88 at croft.

 

Do you do track days?

95 - 98 is the limit on most, 85 - 88 at croft.

I do and am hoping to do more. I guess the question therefore is how loud is 90db, would it be noticably different to the 85 I have at the moment?

 

Thinking back to my science lessons at school (it was a good few years back ), increase by 1DB and it it twice as loud

 

An increase in 10db is 10x louder. Not 10%.

 

An increase in 10db is 10x louder. Not 10%.

Wow, is that for real or am I embarrassing myself with my lack of science?! Thinking about Goodwood the limit was 105 and the classic Mustang and Cobra that were close to that were like thunder so a 20db increase takes you from very quiet to ear-plug loud; maybe 90 will be plenty after all!

 

generally a stainless exhaust will sound 'sportier' than a stock equivilent.

 

An increase in 10db is 10x louder. Not 10%.

Wow, is that for real or am I embarrassing myself with my lack of science?! Thinking about Goodwood the limit was 105 and the classic Mustang and Cobra that were close to that were like thunder so a 20db increase takes you from very quiet to ear-plug loud; maybe 90 will be plenty after all!

Not exactly but pretty much. The ear can deal with massive differences in volume.
Just talking would be at about 60-70 db, loud music from a band or club would be around 110.

 

A lot of numbers being thrown around, but somehow they don't agree.

An increase of 3dB doubles the power of the sound, but our hearing doesn't work linearly and to make something sound subjectively twice as loud takes an increase of 10dB.

For comparison, the noise level you're allowed to be exposed to at work before your employer has to offer you hearing protection is only 80dBA. And if it reaches 85dBA there's a legal duty to use the hearing protection. Now that's for a full 8 hour day's exposure and louder noise can be allowed if the exposure is for less time. But remember that 3dB doubles the power, so for every extra 3dB you have to half the exposure time.

8 hours at 80dBA = 4 hours at 83dBA = 2 hours at 86dBA = 1 hour at 89dBA and so on.

Thankfully, few of us spend our time a metre away from an exhaust pipe.

 

Thanks Martin, as my grandma used to tell me 'you learn something new everyday'! To my mind an increase from 80 to 90 would be fairly marginal so shown how much I know.

Applying this to my exhaust it all suggests that 90bd will be an ample static reading but I guess static readings don't always translate into drive-by readings....

 

My 200 used to be 95db on static readings. when it was idling you had to yell to be heard if you were stood at the back.

 

Every three db is twice as loud.

 

What Martin says - but just to add that most DB measurements are taken with an A weighting which means that the readings are biased to what the human ear can actually hear. Just be mindful of the freqency of the sound - a bassy low frequency exhaust note might not in real terms sound as loud as one which is more raspy like a motorcycle exhaust for example but depending on the type of measuring instrument used they can actually produce the same or more dB on the gauge.

I used to do a lot of detailed sound level anaylsis on large electrical transformers.and there are lots of factors that infuence Db readings tremedously like the air pressure and relative humidity, etc correcting for all these varibles takes a lot of time money and effort. At best a handheld dB meter used on the track will be a ball park figure so don't assume you can fit a 90db exhaust to a car and pass a 90db noise test always err on the side of caution - Quality not quantity is the key!!

 

I wrote my dissertation on acoustics and psychoacoustics, dBs get banded about to mean all sorts of different things and are often taken out of context. The levels that are used for track limits are probably A-weighted, which is a flawed system anyway but an increase of 6dB in the SPL (p= pressure not power) equates to a doubling of the sound pressure (adjusted to an equal loudness curve) hitting your eardrum and is therefore in absolute terms, twice as 'loud', but it all depends on the frequency content as to whether it sounds twice as loud.
An increase of 10dB will certainly be noticeable, but not if you've just been listening to loud music for a long time...

 

Decibels get louder exponentially every 4db is a doubling of the volume as you hear it. So as said 10db is a lot more.

 

I want to second Martin Y, I did it acoustics at uni and this is exactly what they teach.