Neat - thermal R&D's.... R&D process

[Clint Beastwood]

Sorry for redundant title, but after doing all the acoustic testing myself I became a big fan of thermal R&D because of the acoustic engineering they do. Same stuff I did, with mics and a laptop in the car mapping out resonance, etc. to calculate helmholtz chamber volume, etc. I haven't seen any other fiesta ST exhausts engineered quite the same way, so I am a fan even though I don't have one. Enough of my rambling, here's the video detailing their processes.

[video=youtube;j3iA_UtUWt4]http://www.youtube.com/watch?v=j3iA_UtUWt4[/video]

 

[Dpro]

Ya these guys know the science. It was definitely a deciding factor in my purchase. I can appreciate using Helmholz filters as I am a sound engineer.

 

[M-Sport fan]

Supposedly CP-E did this as well for their Nexus system, but I doubt that they take it as far technically/scientifically as Thermal does.

 

[Clint Beastwood]

Supposedly CP-E did this as well for their Nexus system, but I doubt that they take it as far technically/scientifically as Thermal does.

The CP-E isn't sized quite appropriately for the frequency range the FiST tends to drone with 3" exhaust, the thermal's spot-on. That's based on doing the math myself and eyeballing it, and pulling down recordings of both exhaust systems and running them through a spectrum analyzer.

I'm still trying to math my way to a perfectly sized chamber, but it's lead to:

1. I bought a welder. (I am garbage at it)
2. I bought a bunch of grinding/cutting tools.
3. I am taking welding classes.

This is how far I've gotten at this point:
Frequency 106.67 hz
Port area 0.0381 meters 1.5 inches
Port length 0.1016 meters 4 inches
Velocity of sound 343.4 meters/sec
Volume 9.97E-02 cu meters 333.2521 cu inch



http://www.onlineconversion.com/object_volume_cylinder_tank.htm
http://hyperphysics.phy-astr.gsu.edu/hbase/Waves/cavity.html
https://www.reddit.com/r/Acoustics/comments/38kyvn/helmholtz_resonance_calculation/

 

[dmb]

never tell anyone you know how to weld...

 

[Clint Beastwood]

never tell anyone you know how to weld...

Oh I definitely don’t lol, but I have an expensive new way to start small garage fires.

 

[Peter H]

...I became a big fan of thermal R&D because of the acoustic engineering they do...here's the video detailing their processes.

That video is the very reason I chose Thermal when I wanted to replace the cp-e catback on my 2016 FiST. I've had it on for about a month and love the way it sounds at WOT and the lack of droning when cruising.

 

[kivnul]

Frequency 106.67 hz

Is this something that is unique for each car? Like my FiST could be 106.44 or something? I do not know much about sound / resonator science.

 

[Dpro]

Is this something that is unique for each car? Like my FiST could be 106.44 or something? I do not know much about sound / resonator science.

Actually yes different engines will put out different acoustic frequencies depending on displacement and volume.
Its why the old V8 amd V10 F1 engines just screamed wonderfully at high rpm vs how the modern turbo 6 cylinders sound.
That means they may drone at different frequencies as well.

 

[Clint Beastwood]

Is this something that is unique for each car? Like my FiST could be 106.44 or something? I do not know much about sound / resonator science.

Well I think the most resonant frequency of the interior of the FiST is 120hz, but the most resonant frequency put out by a 3" exhaust appears to be 107hz, so when your exhaust drones you get a slight wah wah wah quality to it (oscillation?). There's math behind it, but essentially if your drone is ~3200rpm, thats 106.67hz, which I verified with a spectrum analyzer. I pulled down videos of a bunch of other people's exhausts and spectrum analyzed them as well, and the drone-y exhausts peaked around 107hz as well, the thermal had a hump there but it was much flatter.

I have a thread on identifying and eliminating drone where I go a bit more into my testing methodology and what I did to mitigate.