Screamin' Eagle Nightstick muffler
I know people post video from their phones of various mufflers all the time, but -- frankly, unless you're at the same distance with the same microphone, comparisons are really difficult to accurately judge.
I ordered the Screamin' Eagle Nightstick slip-on muffler because, frankly, my Street 750 sounded like a sewing machine. I wanted a beefier, deeper, throatier growl to it, more "Harley" and less "Singer" if you know what I mean. But, at the same time, I didn't want some obnoxiously loud fart cannon that disrupts the neighborhood and wakes up babies, or ruins the countryside rides for everyone else, y'know? Other folks may like loud pipes, to each his own, I'm just pointing out my particular reasons.
I also don't really give a hoot about maximum horsepower. To me, Harleys are all about torque, so - if the pipe maximizes torque, then that's a bonus, and that's what Harley says it will do. Harley advertises the Screamin' Eagle Nightstick as "Tuned by the factory for the ultimate combination of rich tone and legal sound levels". They also say "The high-flow design of the external diffusion discs produces plenty of low-end gutsť to get your bike away from the light, and a fat torque curve that gets you quickly around slow-moving traffic."
To me that sounded perfect. I listened to some youtube videos for what the difference in sound character is, as much as can be learned by that, and it sounded pretty good, so I ordered one; online price was about $275.
I decided I wanted to find out just how different the sound levels would be. I tested at three feet behind the pipe using a sound level meter. With the stock muffler, it was 73dB at idle, and 84 db at a constant 5,000 RPM.
I then installed the Nightstick, and immediately upon firing it up I thought that it definitely served the exact purpose I wanted. It definitely has a more characteristic Harley sound to it, although it doesn't quite get the full "potato potato" sound, but it's much deeper and throatier with a nastier growl. But is it actually any louder? And if so, how much?
I re-tested with the Nightstick. At idle it was 84dB. That's 11dB louder than the stock muffler, or almost exactly 4x as loud. Then, at 5000 RPM, it sat at 87dB. That's only 3dB louder, which translates to being 50% louder than the stock pipe.
So, take that for what it's worth. Harley said they tuned the sound levels; I don't know how they could get it so comparable at idle as it was at 5000, when the stock muffler is 4x louder at 5000 than it is at idle. The Nightstick is as loud, at idle, as the stock muffler is at 5,000 RPM -- but it sounds very different from the stock bike.
For the record, 85dB is the level at which sound can start causing permanent hearing damage, so the NightStick is right on (or just over) the limit -- although I measured at 3 feet behind the pipe, not at the rider position, which (being forward of the pipe) is almost certainly going to register a significantly lower noise threshold. But if you were standing behind the bike while it idles, you're going to be exposed to as much sound as your ears can take without needing ear protection.
In summary, I think Harley's advertising of the noise characteristics are accurate, and it suits my purposes nearly perfectly (still wish I could get just a little more potato-potato, but it may not be possible with the 60-degree angle of the Street's cylinders vs. the 45-degree angle of the Big Twins).