[in progress] identifying and canceling drone

[Clint Beastwood]

Would dynamat in spare tire area help dampen .... got MBRP 3” T409 installed literally an hour ago and drone is like hearing straight pipe.

Curious on sound dampening

It'll cure a small amount of sympathetic vibration but thats it. You really need to properly tune it to get rid of the drone.

 

[Clint Beastwood]

I wish I was smart enough to understand this thread

No worries!!! I'll try to give a quick breakdown.

A sound wave may look like this /\/\/\/\/\/\/\/\ - a muffler will dampen it, but if you stretch out that /\/\/\ you'll find that it's 10.5 feet long (in the case of a 107hz frequency that needs to be canceled) which means a muffler would need to be 10.5 feet long to help. The alternative is to generate an exactly opposite wave form. Active noise cancelling headphones, for example, constantly sample exterior sounds, then generate an opposite waveform inside the headphones, thus "actively" canceling the sound. With car exhaust, we can use quarter-wave, which means we can have a side branch that your exhaust noise goes down, hits a wall, and reflects back into the flow of sound. By calculating the frequencies carefully, you can tune it to generate an exactly opposite wave, which then cancels out the worst frequency.

Basically:

The initial sound wave /\/\/\/\/\/\/\
plus an exact opposite \/\/\/\/\/\/\/
results in a flat wave ------------ or "white noise"

 

[Clint Beastwood]

I know replies have been few and far between for me. Had some other stuff come up since covid hit, and now I've been handed the Dr's note that im gonna lose the use of my right arm almost completely, so barring any crazy advances in medical science I'll probably have to sell the FiST. When I have the time I'll have my assistant help me get the exhaust systems I've built, the couple intakes I've bought for the FiST, and other parts, and put them up for sale. I'll have to look for another cheap daily - maybe a BRZ or a Veloster N with DCT? If only they sold the FiST with the Fiat 500's aisin auto, that thing was excellent.

 

[Capri to ST]

I know replies have been few and far between for me. Had some other stuff come up since covid hit, and now I've been handed the Dr's note that im gonna lose the use of my right arm almost completely, so barring any crazy advances in medical science I'll probably have to sell the FiST. When I have the time I'll have my assistant help me get the exhaust systems I've built, the couple intakes I've bought for the FiST, and other parts, and put them up for sale. I'll have to look for another cheap daily - maybe a BRZ or a Veloster N with DCT? If only they sold the FiST with the Fiat 500's aisin auto, that thing was excellent.

Sorry to hear your news, good luck to you.

 

[SrsBsns]

I know replies have been few and far between for me. Had some other stuff come up since covid hit, and now I've been handed the Dr's note that im gonna lose the use of my right arm almost completely, so barring any crazy advances in medical science I'll probably have to sell the FiST. When I have the time I'll have my assistant help me get the exhaust systems I've built, the couple intakes I've bought for the FiST, and other parts, and put them up for sale. I'll have to look for another cheap daily - maybe a BRZ or a Veloster N with DCT? If only they sold the FiST with the Fiat 500's aisin auto, that thing was excellent.

Man... sorry to hear that. The BRZ or Veloster could be a nice option for you. Your contributions to the community have always been thoughtful and detailed. I hope things work out well for you.

 

[Clint Beastwood]

Man... sorry to hear that. The BRZ or Veloster could be a nice option for you. Your contributions to the community have always been thoughtful and detailed. I hope things work out well for you.

Thanks, I'm glad the info proved useful - I keep hoping someone will bring an exhaust to market other than the thermal using a quarter wave resonator (ron@whoosh?? lol) but it *is* significant extra fab work.