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Testing in Variable Weather

Last updated on June, 2026

Sound is a pressure wave in air, so air temperature, humidity, and wind all act on a suppressor measurement in principle. At our reference microphone, one meter from the muzzle, the path is too short for most of that to register. Temperature and humidity fall out of the measurement. Two variables remain: the temperature of the ammunition, which changes the shot at the source, and wind, which acts on the microphone directly.

This article covers how temperature and humidity behave at one meter, why we still control ammunition temperature, and how we keep wind out of the data.

Key Info

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    Ambient temperature and humidity wash out at one meter, below normal shot-to-shot variation.

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    Acoustic-day corrections are a far-field tool; at the one-meter reference there is nothing meaningful to correct.

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    Ammunition temperature is the variable that matters: it sets muzzle velocity and port pressure and can move a load across the subsonic threshold.

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    Wind is controlled directly: logged per shot, capped near a 5 mph crosswind, within MIL-STD-1474E parameters.

Temperature and Humidity

Temperature and humidity change sound propagation, but the effects scale with path length. Humid air carries sound slightly faster than dry air; temperature shifts the speed as well; and the atmosphere absorbs the high-frequency content of a gunshot as the wave travels. Over one meter, none of these accumulate to a measurable degree.

This is what acoustic-day corrections address: standardized adjustments that normalize a reading for the day's temperature, humidity, and pressure so measurements taken in different conditions can be compared. They are built for far-field distances, tens to hundreds of meters. At one meter the correction is negligible. At 100 yards it is not: the same temperature and humidity swing changes how much signal the atmosphere absorbs over that distance, which is why a downrange observer can measure the same suppressor differently day to day. The physics is covered in detail in our piece on environmental humidity and acoustics.

Ammunition temperature is a separate matter and does affect the measurement. Propellant burn rate depends on the round's starting temperature, so cold and warm rounds produce different muzzle velocities and port pressures. This changes the source rather than the medium: it shifts the impulse and can move a subsonic load across the transonic threshold into a ballistic crack unrelated to the suppressor. We condition ammunition to a controlled temperature before firing. Ambient air is left uncontrolled at one meter; ammunition temperature is not.

ConsiderThe relevant temperature is the cartridge's, not the ambient air's.

Wind

Wind acts on the measurement at one meter, independent of distance, through two mechanisms. At the microphone, airflow across the diaphragm produces broadband low-frequency noise that raises the noise floor and can obscure the impulse. Between muzzle and microphone, a crosswind advects and refracts the muzzle blast, so a shot's reading varies with wind direction.

Wind is controlled directly. The working limit is a crosswind under roughly 5 mph; above that, distortion exceeds acceptable margins and testing stops. This keeps conditions within MIL-STD-1474E parameters.

Control is by measurement and timing. Digital weather sampling maps a wind reading to each shot, so any round fired outside the limit is flagged rather than averaged in. Wind socks at the line indicate direction and lulls, allowing shots to be timed to low-wind windows.

ConsiderAbove a light crosswind, the microphone increasingly measures airflow rather than the suppressor.

Mathematical Basis

MIL-STD-1474e defines the reference acoustic day standard at 59F and 70% relative humidity but it does not provide direct guidance on how to compute this correction factor when the test conditions diverge from this. For this mathematics we will have to look to secondary sources for an accredited mathematical basis to calculate this conversion.

We are going to compute the Standard Acoustic Day using both the XXX and XXX mathematic models for a 140dBa sound at 100deg F and 90% relative humidity for the distances of 1 meter and 100 meters. 140 dBa because it is in the range of a peak reading for a suppressed gunshot. 100degF and 90% RH to pick an extreme weather condition. 1 meter to show that our sampling distance eliminates the need for Standard Acoustic Day conversions and then 100 meters to show when the standard is relevant.

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