Quietening Exhaust

[AdamR]

Hi guys,

I'm looking to book a track day next week so bought a cheapo sound meter from eBay... however, being a 'tard I ordered a C-weighted meter when MSV use A-weighting. I had a Google to see if there is any relationship between these two but it doesn't seem easy to convert. At approx 5000hz (5000rpm - I assume 5000rpm means 5khz sound frequency?) the A and C weightings look very similar, but wondering if anyone knows from experience how close they are/what sort of relationship these two have at that sort of frequency? From my searching is looks like dB(C) is about 1.3 'louder' then dB(A) at that frequency which leaves me in a bit of a pickle - Oulton Park have a max dB(A) of 105 and my car seems to be around 107 dB(C).

Secondly, any ideas of how to quieten it down a little? I heard some bodgetastic stories of wire wool held in place with steel wire (which sounds right up my street, lol), but is there anything 'proper' that can be done too, such as a muffled tip or something? My exhaust is a Milltek stainless with dual tail pipes, not sure of the diameter though...

Many thanks in advance for any help!
Adam

[Wayne]

Might be worth seeing if you can get a extra silencer welded in or maybe switching back to a Jetex 3 box system.

[AdamR]

Thanks for the info - an extra silencer might be the way forward in that case since I don't have the original exhaust to hand. Thanks again!

[DubSociety]

Ive got 3 silencers in my 16v but it hasn't made much of a difference. Its just quieter in the 'higher' rev range making motorway driving tolerable.

[AdamR]

Yeah, there was very little difference in sound level between tick over and 5k! If it can be made quieter at high revs then that's what I need, the noise test is conducted at 3/4 full revs. Thanks again.

[TDIgadge]

Might be worth seeing if you can get a extra silencer welded in or maybe switching back to a Jetex 3 box system.

Yep, jetex would pass looking at their info.  I swapped my milteck for a jetex, no way would i swap back

[Jimp]

Milltek's mk3 exhaust is known to be loud, a lot louder than their mk4+ systems. Can't suggest much apart from an extra silencer or swapping to a quiet system like Jetex.

[AdamR]

Thanks for the replies and info guys, much appreciated. Would really rather not get a whole new exhaust as this car was meant to be a bit of 'cheap fun', not a money pit (although it seems to be heading that way, lol), so I'm gonna explore other avenues.

I found some info on a TVR forum regarding A and C weighting for those interested:

http://www.shpub.co.uk/tvrbooks/faq_noise.html
http://www.sengpielaudio.com/BerechnungDerBewertungsfilter.pdf
http://www.sengpielaudio.com/calculator-dba-spl.htm

Seems that at the frequency most cars are tested at (4.5-6kHz), C weighting gives a reading approx 1.8dB higher than A weighting would, so I *might* be ok!

Still gonna look at something like this though: http://www.merlinmotorsport.co.uk/p1527/JETEX-UNIVERSAL-DECIBEL-INSERT-2/product_info.html - they had decent reviews on the TVR forum (~5dB noise reduction and no noticeable loss in power).