How do exhausts physically control sound?
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From: Glendale/Burbank/LA
How do exhausts physically control sound?
I've recently been inspired to research what it takes to up the pitch of my exhaust by quite a good deal in order to achieve a more F1-like sound. I'm curious as to whether anyone has a head start on the specific physical knowledge of how pitch (and sound in general) is controlled using exhaust piping, resonators, mufflers, and the like? Any info is much appreciated, especially if it's S2000-specific! 
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From: San Diego
Check out David Vizard's classic exhaust article. Not so much on the aesthetics of exhaust sound, but on minimizing them without sacrificing power. A good read.
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Well, you see, it's like this: There's these little Japanese men with curled up shoes inside your exhaust system. In sequence, they all yell "VROOOOMMMMM BOOOOOMM BOOOOOMM!" repeatedly when you push down on the gas peddle. Since normally, they have very deep voices and you want a higher pitched sound, you need to castrate at least 90% of them and increase this by a percent at a time till you get the desired pitch.
Sorry Steve, I just couldn't help myself. Seriously, you need to look up stuff dealing with acoustics engineering or something like that.
Sorry Steve, I just couldn't help myself. Seriously, you need to look up stuff dealing with acoustics engineering or something like that.
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From: You wish
Steve,
There is a lot of information on exhausts, so I'll try and just address the sound issue.
First of all, you should understand that any given engine outputs a lot of sound energy across a pretty wide frequency spectrum.
An exhaust system essentially acts like an "equalizer" does on a stereo system. Except that the exhaust rarely increases the amplitude of a given frequency. Of particular interest to OEMs, especially those who make inline 4 engines, is the elimination of the higher pitched, "tinny" sounds.
Another item that needs to be considered is that while any given engine puts out a lot of sound across many frequencies, the type of engine (I4, V6, V8, etc.), displacement, and other factors determine where that energy is concentrated - IOW, which sounds are most prominent.
Specific to your desire to make the sound higher pitched, and more F1-like, is that the the primary frequencies outputed by the F20C are not conducive to such an exhaust note. Why? Here are some reasons:
1. Engine configuration. The F20C has a 180 degree, or flat crank. This means that every 180 degrees of crank rotation will see a combustion event, which will therefore create an acoustic pulse through the exhaust system. So, at 9000 rpm, you have 18,000 exhaust pulses per minute, or a primary frequency of 300 Hz. Now, take a look at the typical F1 engine. Its usually a 72 degree V10 (or something close to that). This means that every 72 degrees of crank rotation there is a firing event and an exhaust pulse. So, for every crank rotation there are 5 firing events. At 9000 rpm there would be 45,000 exhaust pulses/minute, or a frequency of 750 Hz. A 2.5 times higher frequency.
2. Engine speed. Clearly, this is an obvious one, but spinning close to 18,000 rpm means that the F1 motor will further double its primary frequency to 1500 Hz (1.5 KHz). A frequency 5 times that of the S2000!
3. Exhaust system design. The F1 motor uses 5-1 exhaust headers. This means that each pulse reaches the collector in about the same amount of time and then goes directly to atmosphere (with a reflected pulse travelling up the other head pipes). Conversely, the typical S2000 header is a 4-2-1. Therefore you have a more complex set of reflections and interactions in the exhaust system, even before you get the tailpipe.
In the end, you'll really never get a true F1 type sound. However, with proper header design and careful tweaking for the higher pitched harmonics in the exhaust note, you could get something a little higher pitched and sweeter. However, it would probably sound more like a NASCAR shorttrack engine, or maybe a Ferrari flat crank V8 (F355/F360). And even then, it would be a rougher sound, because the V8s will have more firing pulses per revolution, smoothing out the sound. The problem isn't so much that you don't have some of those frequencies in the sound profile, its just that they're a relatively small part of it and muffling everything else enough to hear them would probably kill performance.
UL
There is a lot of information on exhausts, so I'll try and just address the sound issue.
First of all, you should understand that any given engine outputs a lot of sound energy across a pretty wide frequency spectrum.
An exhaust system essentially acts like an "equalizer" does on a stereo system. Except that the exhaust rarely increases the amplitude of a given frequency. Of particular interest to OEMs, especially those who make inline 4 engines, is the elimination of the higher pitched, "tinny" sounds.
Another item that needs to be considered is that while any given engine puts out a lot of sound across many frequencies, the type of engine (I4, V6, V8, etc.), displacement, and other factors determine where that energy is concentrated - IOW, which sounds are most prominent.
Specific to your desire to make the sound higher pitched, and more F1-like, is that the the primary frequencies outputed by the F20C are not conducive to such an exhaust note. Why? Here are some reasons:
1. Engine configuration. The F20C has a 180 degree, or flat crank. This means that every 180 degrees of crank rotation will see a combustion event, which will therefore create an acoustic pulse through the exhaust system. So, at 9000 rpm, you have 18,000 exhaust pulses per minute, or a primary frequency of 300 Hz. Now, take a look at the typical F1 engine. Its usually a 72 degree V10 (or something close to that). This means that every 72 degrees of crank rotation there is a firing event and an exhaust pulse. So, for every crank rotation there are 5 firing events. At 9000 rpm there would be 45,000 exhaust pulses/minute, or a frequency of 750 Hz. A 2.5 times higher frequency.
2. Engine speed. Clearly, this is an obvious one, but spinning close to 18,000 rpm means that the F1 motor will further double its primary frequency to 1500 Hz (1.5 KHz). A frequency 5 times that of the S2000!
3. Exhaust system design. The F1 motor uses 5-1 exhaust headers. This means that each pulse reaches the collector in about the same amount of time and then goes directly to atmosphere (with a reflected pulse travelling up the other head pipes). Conversely, the typical S2000 header is a 4-2-1. Therefore you have a more complex set of reflections and interactions in the exhaust system, even before you get the tailpipe.
In the end, you'll really never get a true F1 type sound. However, with proper header design and careful tweaking for the higher pitched harmonics in the exhaust note, you could get something a little higher pitched and sweeter. However, it would probably sound more like a NASCAR shorttrack engine, or maybe a Ferrari flat crank V8 (F355/F360). And even then, it would be a rougher sound, because the V8s will have more firing pulses per revolution, smoothing out the sound. The problem isn't so much that you don't have some of those frequencies in the sound profile, its just that they're a relatively small part of it and muffling everything else enough to hear them would probably kill performance.
UL
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