Preping for a sound test.

[JnP]

Been prepping the car up for a sound test I have to pass for the French registration Wednesday next week (13th June).
In order to pass the car must not exceed 77dB

The test is as follows:




As indicated in the drawing the technician will be driving the car and arriving at 50KPH and will accelerate (floor it) for 20 meters (65') until he reaches the 2nd line.

He will be doing this 4 times in 2nd gear and 4 times in 3rd gear.
Now either they average the 8 results (minus 1dB) or they take the highest into account, not sure which.

The audiometer will be held at 1m20 (4') from the ground and at a distance of 7.5m (24')from the car's center


Started this weekend and will finish up next weekend.




Found a nice place to set up the test,



measured the whole thing and then we started the show



Passing one way,



Then the other,





And finally got the results...

Highest I got was 88.2 dB but the average was about 86.9

was 10 dB too high at the moment so I got some acoustic insulator and started fixing it around the engine bay and on the main bonnet.





The miss was helping out of course



Put the std cans back on too

I made two runs before the tape melted down and the insulator touched the engine and melted as well

Managed to get 85 dB which is still too high so I order heat proof double tape (120 C°) and better insulator as the ones I used are pretty cheap I must admit

On Sunday made two of these which decreased the sound level by a lot !!! But only used the audiometer at the end of the cans as i ran out of tape and couldn't fix the insulating foam again.



Fit them at the very end of the silencer.
I have a quick question as far as the "dB killers" are concerned, will it affect the engine/spark plugs or anything in any bad way ?
They will be on only for the tests as getting there will be with my other pair of cans

Looking forward to this weekend and let's hope that all together, it will be 77dB

[7 TVR]

Shocked that you put that stuff under the bonnet but not by what happened
I take my hat of to your dedication but would of thought it allot quicker and easier just to of stuck some quite cans on for the test!
Engine bay noise is rarely a factor its what comes out the back!
I hope you pass although thats got to be a good reason not to live in France? But i can think of plenty for not living in the UK as well

Edited by 7 TVR on Tuesday 5th June 01:24

[ajp70]

You learn something new every day because I didn't realise French cars had to go through that. Thanks for the explanation of the proceedure and thank God we don't have to go through a 77db test in the UK.

If you have a second set of cans then maybe you could get these repacked to really muffle the noise just for tests.

[JnP]

Since TVR had neither a European homologation for its cars nor a type approval I have to go through French national approval system which includes this test.

As far as the engine bay, in full throttle in 2nd gear it actually makes some noise, a lot less then what come out the exhaust but enough for me to make sure it's covered!

I'll look into quieter cans but the std over my other set is already a very significant change! Can't believe some still use the std :P

[slideways]

Just be very careful with that foam near the exhaust even if it is fire retardant it still catches fire it just take a bit longer

[LukeSi]

Don't suppose you could get away with track day silencers?

[JnP]

Thanks for the responses, I will be very careful with the foam and burning/melting it!

By track day silencers you mean cans that don't make too much noise ? If not I'm not sure what you mean :-D

[LukeSi]

Like so. http://www.actproducts.co.uk/silencing/trackdays/

[JnP]

Thanks for the info luke, email sent to ACT !

Will see what can be done !

[JnP]

Thanks for the info Luke, email sent to ACT!

Will see what can be done !

[LukeSi]

JnP said:

Thanks for the info luke, email sent to ACT !

Will see what can be done !

No problem. I imagine it can be done, it will be difficult simply due to the fact they make alot more than 77dB standard but I have no doubt that it is (just) possible. So glad there isn't a noise restriction in this country.

[JnP]

As they are custom made it will take approx 2 weeks to get it delivered, will have to go another route but their silencers seem pretty nice, might be helpful later on !

The UK is def great on that level! They love cars and aren't as restrictive as the French!!

[stopingby]

I have been there for my Cerbera. It will require much more work if you want to succed at UTAC but its a good start.

Good luck

[ridds]

As you've found the quick way to get through this is plug the intake and exhaust inlet and outlets as this is where most of the noise comes from.

Try and find a way of plugging the cold air feed under the car as you will get induction noise from this.

As for the exhaust plugs, they won't hurt the engine but I would remove them as soon as the test is complete as the increased back pressure levels will not so you exhaust any good. Try not to drive is at high revs too.

[JnP]

stopingby said:

I have been there for my Cerbera. It will require much more work if you want to succed at UTAC but its a good start.

Good luck

Thanks mate but I'd rather have pointers then a good luck :-) if that's possible...

[dnb]

If you are struggling, I think you need to be prepared to engineer to pass the test rather than make the car quiet. Eg - Measure the spectrum of the noise and then decide how to proceed. The test is probably measuring noise in dBA, so high audio frequencies are particularly damaging to passing the test, so target these first if they exist. Induction whistle for instance can be in the region of 10 to 15kHz. It's easy to get rid of this without foam, and it will be a big win due to the way dBA works. Of course if they insist on an unweighted scale you're a bit stumped...