Selasa, 23 Juni 2009

Horn Speaker

This Horn Speaker created by my friend and has been use in his bird house. Proven that horn speaker more better than PVC bazooka.

Below is article about horn speaker:

Horn speaker
From Wikipedia, the free encyclopedia

Horn loudspeaker with a sealed box driver mounting A horn speaker is a complete loudspeaker or loudspeaker element which uses a horn to increase the overall efficiency of the driving element, typically a diaphragm driven by an electromagnet. The horn itself is a passive component and does not amplify the sound from the driving element as such, but rather improves the coupling efficiency between the speaker driver and the air. The horn can be thought of as an "acoustic transformer" that provides impedance matching between the relatively dense diaphragm material and the air of low density. The result is greater acoustic output from a given driver.

The narrow part of the horn next to the speaker driver is called the "throat" and the large part farthest away from the speaker driver is called the "mouth".

Horns have been used to extend the low frequency limit of a speaker driver—when mated to a horn, a speaker driver is able to reproduce lower tones more strongly. The flare rate and the mouth size determine the low frequency limit. The throat size is more of a design choice. Horns have been known to extend the frequency range of a driver beyond five octaves.

Horns have been used to modify the directional characteristics of the produced sound waves. Horizontal coverage angle is the primary determinant of horn width, and vertical coverage angle determines horn height. On- and off-axis performance will differ depending on the shape of the horn. Compromises in performance such as distortions of the wavefront must be balanced against the design goal.

Acoustic horns convert large pressure variations with a small displacement into a low pressure variation with a large displacement and vice versa. It does this through the gradual, often exponential increase of the cross sectional area of the horn. The small cross-sectional area of the throat restricts the passage of air thus presenting a high impedance to the driver. This allows the driver to develop a high pressure for a given displacement. Therefore the sound waves at the throat are of high pressure and low displacement. The tapered shape of the horn allows the sound waves to gradually decompress and increase in displacement until they reach the mouth where they are of a low pressure but large displacement.

A modern electrically driven horn speaker works the same way, replacing the mechanically excited diaphragm with a dynamic or piezoelectric speaker.

Modern horn designs typically feature some form of conical, exponential or tractrix taper. Roughly speaking, the slower the flare rate, the deeper and lower frequencies the horn will reproduce for a given length of horn. For example, a horn area growth rate of 30% per foot will allow reproduction down to about 30 Hz; 1000% per foot (10 times area) per foot provides midrange reproduction; 100 times area per foot is used in high frequency horns.

Modern high output horns also make the throat area of the horn smaller than the cone diaphram area. This is called the "loading" or "compression" ratio of the horn. The compression ratio is the cone area divided by the throat area. Typically for bass and midrange frequency the compression ratio is from (1.5 to 1) low compression to normal compression (2 to 1) to high compression (3.5 to 1). High frequency tweeters sometimes have compression ratios as high as 10 to 1.

The higher the compression the greater the horn's ability to properly couple the diaphragm to the air at the horn's mouth, increasing efficiency, until the compression ratio is so high that it actually begins to impede cone motion. At this point the maximum sound output power from the horn (at a given distortion) will be reduced. To demonstrate this at an extreme, place a cone woofer face down on a concrete floor. The compression ratio will be very high, however sound output from the back of the speaker will be quite low.

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