Longtime FoS Matt Calamari asks KC "Street riders love fitting aftermarket exhausts systems so we can all enjoy their noise together. Why does it seem like the smaller the bike the louder it is? The loudest bikes going my house are Honda Groms, followed by all the (horrible sounding) little parallel twin sport bikes. Four cylinder liter bikes seem whisper quiet by comparison. Why is that?"

“Why are small bikes so loud? Why are four-cylinder bikes …whisper quiet in comparison?”

There are more than one reason for this. First of all, the bigger the cylinder, the harder it is to quiet, requiring more muffler volume (this is also true of intake airboxes). Therefore Erik Buell put his muffler volume under the engine, where its size is less obvious. His sensible idea has since been widely copied for years.

Ever hear the 3900 rounds-per-minute anti-tank cannon on a ground attack aircraft? Because its firing pulses are so closely-spaced, what we hear is more like a harsh 65-cycle hum. A continuous drone is less startling or annoying than a series of bangs. One discharge from a high-velocity 30 mm is really loud and gets your attention.

Frequent pulses overlap so they form a tone, but fewer pulses per second are perceived as a series of spikes.

An amusing example of the problem of muffling a small number of large cylinders was Harley’s Sportster. The Styling Department loved its little sausage mufflers (“So fifties!") but the physical science types said there was no way those little cans could meet sound. Naturally, styling got their way, and the restriction necessary to pass sound with the sausages caused one engineer to joke, “After the rider switches-off, you expect to hear a long sigh as the back-pressure leaks down.”