rullljud

Rullljud is a term that has appeared in some discussions of acoustic phenomena to describe a rolling, low-frequency noise produced by rotating or translating machinery. The concept is not widely standardized and may be used variably, but it typically refers to a steady, periodic rumble that arises from rolling contact between surfaces or from bearings, gears, belts, or rail-wheel interactions.

Etymology suggests it is a compound of the words for "roll" and "sound" in Scandinavian languages, with a neo-formation spelling that sometimes appears as rullljud in informal contexts. The term is relatively new and may be encountered mainly in technical or regional discussions rather than formal standards.

Characteristics include a dominant low-frequency spectrum, often under 150 Hz, with a strong periodic component corresponding to a mechanical rotation or rolling element, and possible harmonics. The sound can be amplitude-modulated when speed varies, producing a characteristic whooshing or pulsing effect. It is usually persistent under constant speed, but transient when loading or speed changes occur.

Measurement and analysis rely on conventional acoustic and vibration methods: spectral analysis to identify repetitive peaks, cepstral analysis to estimate periodicity, and time-domain envelope detection. Correlating with speed sensors or bearing diagnostics helps attribute rullljud to specific components.

Applications include industrial condition monitoring, noise-control engineering, and product design where rolling noises are undesirable. In audio and media contexts, rullljud can be an audible cue for mechanical realism or for sound synthesis, where it may be emulated or suppressed depending on desired effect. See also rumble, bearing noise, gear whine, rail corrugation.