energia: Infrasound

Evidence: 100 • authority: 72

Infrasound, sometimes referred to as low frequency sound or (sometimes ambiguously) subsonic (subsonic being a descriptor for "less than the speed of sound"), describes sound waves with a frequency below the lower limit of human audibility (generally 20 Hz, as defined by the ANSI/ASA S1.1-2013 standard). Hearing becomes gradually less sensitive as frequency decreases, so for humans to perceive infrasound, the sound pressure must be sufficiently high. Although the ear is the primary organ for sensing low sound, at higher intensities it is possible to feel infrasound vibrations in various parts of the body. The study of such sound waves is sometimes referred to as infrasonics, covering sounds…

Evidence: 20 • authority: 88

Subjective comparison of single channel versus two channel subwoofer reproduction. Bass management has many advantages for surround sound listening, however there is still a question regarding audibility of two channel versus single channel bass reproduction. Many previous investigations have lacked rigor or been preliminary in nature. The study presented here includes strict control of nuisance variables and significance testing of results. A test is described wherein trained listeners compared four different subwoofer configurations in controlled listening tests, using a very sensitive triangle test, in a typical listening room. Methods of controlling nuisance variables are discussed. The…

Evidence: 20 • authority: 88

The rotary subwoofer: A controllable infrasound source. The rotary subwoofer is a novel acoustic transducer capable of projecting infrasonic signals at high sound pressure levels. The projector produces higher acoustic particle velocities than conventional transducers which translate into higher radiated sound pressure levels. This paper characterizes measured performance of a rotary subwoofer and presents a model to predict sound pressure levels.

Evidence: — • authority: 72

Audio crossovers are a type of electronic filter circuitry that splits an audio signal into two or more frequency ranges, so that the signals can be sent to loudspeaker drivers that are designed to operate within different frequency ranges. The crossover filters can be either active or passive. They are often described as two-way or three-way, which indicate, respectively, that the crossover splits a given signal into two frequency ranges or three frequency ranges. Crossovers are used in loudspeaker cabinets, power amplifiers in consumer electronics (such as Hi-Fi, home cinema sound and car audio), and pro audio and musical instrument amplifier products. For the latter two markets, crossove…

Evidence: — • authority: 72

A loudspeaker (commonly referred to as a speaker or, more fully, a speaker system) is a combination of one or more speaker drivers, an enclosure, and electrical connections (possibly including a crossover network). The speaker driver is an electroacoustic transducer that converts an electrical audio signal into a corresponding sound. The driver is a linear motor connected to a diaphragm, which transmits the motor's movement to produce sound by moving air. An audio signal, typically originating from a microphone, recording, or radio broadcast, is electronically amplified to a power level sufficient to drive the motor, reproducing the sound corresponding to the original unamplified signal. Th…

Evidence: — • authority: 72

A loudspeaker enclosure or loudspeaker cabinet is an enclosure (often rectangular box-shaped) in which speaker drivers (e.g., woofers and tweeters) and associated electronic hardware, such as crossover circuits and, in some cases, power amplifiers, are mounted. Enclosures may range in design from simple, homemade DIY rectangular particleboard boxes to very complex, expensive computer-designed hi-fi cabinets that incorporate composite materials, internal baffles, horns, bass reflex ports and acoustic insulation. Loudspeaker enclosures range in size from small "bookshelf" speaker cabinets with 4-inch (10 cm) woofers and small tweeters designed for listening to music with a hi-fi system in a p…

Evidence: — • authority: 72

A rotary woofer is a subwoofer-style loudspeaker which reproduces very-low-frequency content by using a conventional speaker voice coil's motion to change the pitch (angle) of the blades of an impeller rotating at a constant speed. The pitch of the fan blades is controlled by the audio signal presented to the voice coil, and is able to swing both positive and negative, with respect to a zero-pitch blade position. Since the audio amplifier only changes the pitch of the blades, it takes much less power for a given sound level to drive a rotary woofer than a conventional subwoofer, which uses a moving electromagnet (voice coil) placed within the field of a stationary permanent magnet to move a…

Evidence: — • authority: 88

Reproduction of wind turbine infrasound and low frequency noise in a laboratory. The use of large baffle speaker system to produce infrasound/low frequency noise from wind turbines for subject medical testing was found to have issues in reproducing the original recorded signal. Reproducing the original transient time signal was not achieved. The use of synthesised signals for subjective testing of infrasound was examined and is discouraged when compared to actual real world sound files. The results of the testing and recommendation to use medical studies in the field rather than laboratory testing is discussed.

Evidence: — • authority: 88

Physiological and content considerations for a second low frequency channel for bass management, subwoofers, and low frequency enhancement (LFE). Perception of very low frequencies (VLF) below 125 Hz reproduced by large woofers and subwoofers (SW), encompassing 3 octaves of the 10 regarded as audible, has physiological and content aspects. Large room acoustics and vibrato add VLF fluctuations, modulating audible carrier frequencies to >1 Hz. By convention, sounds below 90 Hz produce no interaural cues useful for spatial perception or localization, therefore bass management redirects the VLF range from main channels to a single (monaural) subwoofer channel, even if to more than one subwoofer…

Evidence: — • authority: 88

A laser pistonphone designed for absolute calibration of infrasound sensors from 10 mHz up to 20 Hz. Demand for calibration at infrasonic frequencies has emerged. It is supported by earth monitoring issues and particularly by the Comprehensive nuclear Test Ban Treaty Organization (CTBTO), which provides a global international coverage for nuclear testing ban, and requires for the IMS (International Monitoring System). In the presentation, a new laser pistonphone design is presented with the objective of establishing primary standards for sound pressure at very low frequencies down to 10 mHz. The piston is a modified accessorized loudspeaker driver whose diameter is equal to the diameter of…

Evidence: — • authority: 72

near- infrasound . Subwoofers designed to produce infrasound are capable of sound reproduction an octave or more below that of most commercially available subwoofers