I thought it was the second.
So, to inaugurate the earliest day of the second year of Atomic Fungus--commemorated in the second entry of the day--I will talk about my second 1995 Ford Escort a bit.
You see, once again it has been demonstrated that I know approximately dick about acoustics.
For several months the flexible coupling which connects the catalytic convertor downpipe to the rest of the exhaust system has needed to be reattached. There was about a 1/2-3/4 inch separation between the pipes, so that there was nothing connecting them at all.
You would think, wouldn't you, that the exhaust noise would escape through such a gap?
You see, the exhaust pulse has a longer wavelength than 1/2-3/4 inch. Much longer. My initial estimate would run somewhere north of ten feet, possibly as much as sixteen. The lowest wavelength the human hear can usually hear is something like 32 or 64 feet long (I can never remember which and I don't feel like looking it up, but the low "C" note hooked to a big pipe organ's lowest "C" pedal requires a pipe some 64 feet in length, and that is a low note). Regardless of what the wavelength is, it's huge, and the only cars that I've ever heard make a high-pitched hum were Indy cars whose engines rev up to 13,000 RPM.
Anyway, the point is, 0.75 inch is too small a band gap for the exhaust pulse to exit, so despite this gap in the exhaust system the car was mostly quiet--most of the exhaust energy would keep on going into the exhaust pipe. It did have a nice little rumble, and it would make a neat crackly backfire on deceleration when the ECM leaned out the fuel mix in response to a closed throttle. That's probably why I didn't fix it; it sounded cool.
Anyway, I took Mom to do some errands this morning; and when I started the car to drive home, VAROOM!!! --the pipe finally blew off, and when I drove it into the driveway I could hear the stupid thing dragging on the asphalt.
To be honest I didn't think the car had been that noisy before I put the last flex pipe in. But I went to AutoZone and got a new flex pipe, and I installed it, and the car purrs like a kitten, with no trace whatsoever of the "Hell's Angels" sound effects it was making this morning.
I'm glad, because I didn't feel like paying for a new catalytic convertor....