Understanding Sound and Suppression

A critical relationship to understanding suppression as hearing safety device and suppression as a device for concealing muzzle report down range is understanding the difference in how a suppressor sounds to the shooter and how it can stand to someone standing nearby in the environment.

When a semi-auto firearm is shot, there are two competing sound sources, ignoring bolt/cycling noises. The loudest and expected blast at the muzzle and the smaller but very much at play, blast at the ejection port called "port pop". This port pop blast is the gasses used to cycle a semi-auto firearm escaping out the chamber. This blast at the ejection port is orders of magnitude smaller than the one at the muzzle, but is on a few inches from ones face instead of feet away and propagates towards the shooters ear instead of down range.

When we stack these two pressure waves in the environment, the port pop is drowned out by the muzzle report making a near imperceivable impact on perceived noise. But that same sound as heard by the shooter, is comprised in a very perceivable way, by the port pop. so much so that the ear nearest to the ejection port hears more noise and incurs hearing damage at a high rate than the opposite ear.

Putting a high-backpressure suppressor on an untuned semi-auto increases the gas volume used to cycle the action, and pushes that excess gas out the ejection port. A high-flow-rate can sends those gases downrange instead of right next to your ear. This is why, a high flow rate suppressor, even if it is louder in the environment, might be the superior safety device for the shooter.

The Huxwrx Flow 556K illustrates the tradeoff. Bystanders in an enclosed range describe it as loud and boomy, and compared to its contemporary (the now-discontinued SilencerCo Saker 556, long praised for its quiet muzzle signature), it sounds like a step backward. But when Pew Science published the numbers, the Flow 556K decisively outperformed the Saker on shooter's ear measurements, which is the metric that actually matters.

To many who have shot both the Saker 556 and the Huxwrx Flow 556K, the Saker still sounds quieter, despite its measurably higher noise hazard. This is because our ears are poor at differentiating a noise that will injure you from one that is merely perceived as loud. When a shot is fired, you first hear the brief initial blast wave, followed by the boomy echoes of that wave moving through the environment, bouncing off walls and changing tone as it hits your eardrum for seconds after. Much of the hearing damage incurred (environment dependent) happens in that brief fraction of a second where the port pop and muzzle blast first combine to hit you with the highest-amplitude wave of the many to follow. Your ear will hear and feel this first wave, but it is quickly muddled and concealed by the smaller, duller waves that follow, leaving your brain unable to distinguish a soft echo from a shrill snap. Those dull echoes are what constitute the pleasant tones a reviewer might report back to you, and sure, they can sound nice, but they are no substitute for proper risk analysis. This is where spending time with Pew Science sound reports will give you a much clearer picture of how your suppressor actually functions as a safety device in a measurable, empirical way.

We don't want to leave you critical of people who talk about tone. Despite what we said above, tone can still be directionally correct. A measurably louder can will often have a subjectively better tone. And a lot of the fun in suppression is making your suppressor sound cool. Some of my favorite cans have mediocre risk profiles and relatively higher decibel readings, but their tone just sounds good. Short, fat cans tend to sound thumpy and satisfying regardless of their readings. Many of my friends still run their ancient Surefire RC2s because that's what a suppressor is supposed to sound like to them. Used within their limitations, most every suppressor paired with proper PPE can become safe for an intents and purposes.

We encourage you to go see the Hazard Maps on PewScience that take a deep dive into this topic, ripe with visual aids and hard numbers to back them.