Andrew Dixon

Thinking of doing a track day or two over the summer, and the organisers tell me that entrance is subject to the my car producing less than 105 dB of noise. This is a standard 'race' noise limit they say.

I have a MY97 Turbo with K&N induction kit, straight-through Magnex centre section, and Scoobysport backbox.

Is my car going to be too loud?

If so, what should I put back on in order for it to meet the noise limits?

Thanks in advance!

Andrew

johnfelstead

Andrew, you will be fine on that setup IMHO. Most track days run at 98DBa which is the legal maximum for a vehicle on the road.

Your setup should be below 98Dba unless it is old and has had the packing material burned.

Andrew Dixon

Cheers John. The system is less than 6 months old, so (fingers crossed) should be okay. From what little I know about decibels, 105 db is considerably louder than 98 anyway.



A.

Andy H

When i used to grasstrack with a class 9 special we had to be below 105 to pass noise test and i have yet to hear any scooby that comes anywhere the noise a open mounted pinto with tiny exhaust made and it allways passed.

Andy H

[This message has been edited by Andy H (edited 16-05-2000).]

johnfelstead

yep, DB's are a logarithmic scale. 105DBa is very loud. 6DBa doubles the noise level. We just get 105Dba with our race esprit and that is Loud.

DavidRB

I should have known! The one that was considered "too loud" by the people living near MIRA!

johnfelstead

AH, my old 350BHP 2wd cossie, now that was a fun, LOUD car.

Havent got a clue how loud that thing was, thats why i mentioned the packing material, as my flame outs melted all mine.

It was quiet until i started to use full throttle at 7200RPM, sounded quiet in the car though

My westie has a repackable silencer for when i melt that one

DavidRB

How loud was that Cossie then John?

johnfelstead

which cossie david?

robski

John,

thought it was generally thought of as 3DB to double sound pressure level?

10 decibels is 10-fold increase, but that works only for 10, the base of the decibel system. 20 decibels is 100-fold (10x10), and an increase of 5 decibels is an increase by a factor of the square root of 10.

Your handy pocket formula
for power: 10 log(P2/P1)

although Im confused as to how you actually work that one out!

robski

johnfelstead

robski,

I have heard that said many a time about 3DB being double.

However i worked for years using ultrasonic high acuracy testing equipment on aircraft engines and in the nuclear industry and a 6DB gain is always classed as double the energy when using ultrasonics.

So either there is a different scale for ultasound to sonic (which i doubt) or there is some duff info out there?

johnfelstead

OK, its been bugging me so i did a bit of research. We are both right in some ways robski.

In audio apps 3DB is double the sound energy.
The reason i was confused on this issue is that with the kit i used, it was using voltage power as a reference, in this app a 6DB gain in amplifier power gives double the energy.

As all my instrumentation used high energy ultrasonic probes driven by amplifiers. The instruments scaleing is done in 6DB gains.

So i have been going around for at least 15 years with the wrong scale in my head for audio power levels.

we learn sommat new every day.

[This message has been edited by johnfelstead (edited 17-05-2000).]

robski

John,

I think you want this one!

for voltage: 20 log(V2/V1)

still dont know how to use them tho!

robski