Measuring exhaust ( in dB)

Hi,

Can anyone help me with any information on measuring my can, it's a blueflame tri-oval, baffles out, on my track SV.

I have borrowed a sound meter, just need to know distances etc. that they measure at.

I don't want to get somewhere and find out its too loud.

Thanks.

[Mr Speirs]

You'll also need to find out how the meter is weighted. In most applications they should be A-Weighted as this is the one that mostly resembles human hearing.

There was a post on another forum about a guy who had measured his can at 130db!!! Obviously with no weighting, then another guy posted that he thought his must be much louder and said his was 140db!!! Which is daft because although its a 10db difference that is actually nearly twice as loud.

differant places use different methods, but it should say on the track you wish to do how they do it

castle comb are noise nazis

Most aftermarket exhausts (even full race systems) should come in at under 105db - this being the 'normal' limit. Most race cans will meet 102 with a decent baffle.

Most places tend to test using the ACU regs:

Twin cylinder machines have to pass a static (as in not drive by) noise tets at 5000rpm. The noise test will be conducted with the microphone placed at 50cm from the exhaust pipe at an angle of 45° measured from the center-line of the exhaust end and at the height of the exhaust pipe, but at least 20cm above the ground. If this is not possible, the measurement can be taken at 45° upwards.

As a point of interest, the decibel scale is logarithmic. Doubling the noise intensity (often referred to as volume) requires a increase of around 3dB. However, to the human ear that 3db increase may not be perceived as twice as loud.

[Mr Speirs]

Originally Posted by phuk72

As a point of interest, the decibel scale is logarithmic. Doubling the noise intensity (often referred to as volume) requires a increase of around 3dB. However, to the human ear that 3db increase may not be perceived as twice as loud.

Quite right on an unweighted scale 3db is twice as loud however a percieved doubling in sound would need to be closer to 6-10db depending on Air Pressure and Temp.

Thanks guys, the meter I have as A or C Weighting? Anyone know which one to use?

[Mr Speirs]

As I said originally you need to use A-Weighting.

A-Weighting ignores low frequencies anything below 100Hz or around that area. This is because the ears naturally compress low-end frequencies and so doesn't interpret them to be as loud as they really are.

HTH

Cool, thanks for your help everyone. Just measured it at 102 dB. At 5k rpm.

Thanks again.

[Mr Speirs]

Jolly good. Sounds realistic not like the 140dB measurement that other fellow got

lol. Cheers. Judging by your avatar, you work with sound quite alot Mr Speirs!