How can two speakers produce 3D effect?

Acoustic system of human being identifies space and direction of sound owing to its formation of ear, which can respond with different frequencies to sounds from corresponding directions. This mechanism of enabling human being acoustic system to change according to direction can be depicted mathematically with HRTF (Head Related Transfer Function). Again, brain of human being identifies space and direction depending on the changed frequencies. Classical sound record technology usually adopts microphone to record sound, which is different from human being ear in formation. Under this circumstance, although sounds from different directions can be recorded unanimously, microphone's lack of spatial and directional identification capacity disables it to authentically revive original sound field as recorded, when sound is displayed in classical two-way display system. Core of 3D technology is intended to remedy gap between microphone record method and human being acoustic system, i.e., is to extract, handle and revive original information of sound field by means of supplementing two-way display system with gap-remedial. With this technology, deserved width and depth in original sound field are played up, as well as a good resolution of point source, which is suffered by most general speakers of two-way sound systems. Thus, a broad and coherent sound field is formed, and surround effect, which is formerly only available with multiple speakers can be available by just two speakers now.

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What does active speaker's "active" mean?

Active speaker is a speaker consisting of signal processing circuit, regulating circuit and power amplifier. Active speaker can be directly matched with other common sound sources (walkman, CD player, VCD player, video player, and audio card of computer) to form a complete set of acoustic system. With help of active speaker, extra purchase of power amplifier is not needed and users can be exempt from trouble of rationally matching of amplifier and speakers. Active speaker enjoys very favorable cost/effect ratio. Owing to built-in amplifier circuit, active speaker has shorter and easier wire-linking, less interference, less background noise, and less space occupation than its peers do. Active speaker is easy to operate. There are only very few on-offs and knobs on the cabinet and some impractical knobs for operation had been removed, therefore with just "turn on" operation, everything can be OK for active speaker.

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Advantages of Wood-made Speakers

Classical cabinet of speaker usually adopts wood because wood is better for restoring sound and displaying timbre than other materials. A good speaker claims firm and tight-sealed cabinet. During course of operation, cabinet does not show harmonic resonance, otherwise, sound uttered by the speaker will be added with sound of harmonic resonance, which is called sound-staining. Many cabinets of speakers now available on market are made of flakeboard or plastic suffering inherent flaws due to lacking of certain strength and hermetic closure, and in turn are very inferior to speakers with wood-made cabinet.
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To authentically revive and restore sound, i.e. to achieve HI-FI (high-fidelity), sound signals output by the speaker should be primarily as same as the originally recorded without exaggeration or eclipse. Hearable frequency of human being's ear is between 20 Hz and 20KHz and circuit can satisfy this frequency range easily, what should be played up is the speaker, the sound output unit. Currently available speakers are unable to completely cover all hearable frequency of human being's ear, therefore sound display of entire gamut register should be sustained by many speakers collectively. One speaker sustains range from 20 Hz to 5KHz, and the other sustains range from 1KHz to 5 KHz, thus at range from 1KHz to 5KHz, both speakers will utter, which in turn can inferior timbre and resolution capacity. Frequency dividing circuit can be used to handle this problem. Of course, currently, there is a kind of speaker that can display entire gamut register with just itself solely. This kind of speaker is the so-called coaxial speaker (note to differ it from the sleazy dual-paper-basin speaker).

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Anti-magnet for Speaker

Speaker's magnetic field can severely interfere display screen of TV set or computer as well as distort or color-hybridize the screen. To avoid speaker without function of anti-magnetic of damaging display screen, anti-magnetic capacity is needed so high as even close neighboring to display of the TV set, interference will not occur. The method is very simple, that is to adopt anti-magnetic speaker.

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RMS & PMPO of Speaker

RMS (Root Mean Squared) is the most genuine indicator for power output of speaker. It refers to the amplifier's value of effective power in case when a consecutive sine wave signal is fed to it at a point where a specified distortion degree has been reached at a certain voltage output of the amplifier. Since the effective power is measured at a point of specified distortion degree, sometimes it is also called non-distortion power. PMPO (Peak Music Power Output) is a parameter indicating capacity of treatment of real musical signal. It refers to a peak power over a short constant time during a course of treatment of musical signal by musical frequency power amplifier. Value of the peak power is usually 8-10 times of that general effective power.

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Frequency Response of Speaker

Frequency response refers to output characteristics responding to changing frequencies of input signals of different frequencies, namely output range of power amplifier or sound frequency range displayed by speaker. It is very easy for power amplifier to approach a wide frequency range from 20 Hz to 20 KHz or more, while for speaker, the common range is from 40 Hz to 20 KHz.

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Classification and Features of 3D Technology

Two-way stereo only poses people with a flat sound field unable to authentically revive 3D features of sound field. To revive 3D spatial distribution of the sound field in the interest of enabling listeners to achieve more authentic spatial sensation and on-spot sensation, scholars have been devoting to research on 3D sound-restoration technology and during which they found that common two-way stereo's incapability of creating 3D stereo sound field had nothing with numbers of two sound tracks or two speakers, but had relation with microphone used to record sound, which lacked organs similar to human being's auricle and in turn was unable to embody features of frequencies from different spatial directions, but contrarily record sounds from every direction with only one frequency. Due to void of information of frequency range in the recorded signals required by brain to identify sound direction, human being can not feel 3D spatial sensation at display of the recorded sound. 3D-enhancement technology is to fulfill surround stereo with two speakers. Currently popular 3D technologies include SRS, Spatializer and Dolby Virtual, etc home and abroad. They are very similar to each other with common features of gigantic sound field, flamboyant effect, and vast information on surround and on-spot sensation (without it, sound field will become very flat). Spatializer and SRS have some subtle differences in sound quality and sound field from each other although they share common surround sensation. Concretely, the former has broad while concrete sound field owing to which dialogue between characters in the film can be located at a certain position of the screen and enhancement of volume and animation can also be secured. The latter adds a new control of set-at-middle in charge of subtle-adjustment of intensity of middle-set sound track and extension degree of sound field, but its transparency degree of sound field is inferior to Spatializer, and it is inferior to Spatializer in sound details due to over-increase of bass. Virtual Dolby technology is to emulate realistic multi-way surround with digital treatment technology. It can handle Dolby surround, Dolby Logic and Dolby AC-3 signals, or even some common stereo signals.

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