Horn speaker

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Horn loudspeaker schematic.
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Horn loudspeaker schematic.

A horn speaker is a speaker that uses a "horn" to get more sound (volume) from the driving loudspeaker. The horn itself does not amplify anything, but rather improves the coupling efficiency between the speaker driver (typically made of paper or, more recently, more exotic materials such as titanium or mylar) and the air (which has a very low density). Since air is very light compared to speaker cones there is an impedance mismatch which leads to inefficient coupling of the speaker driver to the air, much as using a tractor to pull a bicycle trailer would not efficiently make use of the tractor's power. Horns couple the speaker driver to the air so that the driver appears to the air as though it were very large in surface area and very light (more like air), while the air appears to the speaker driver as though it were smaller in area and heavier. The small part of the horn next to the speaker cone "driver" is called the "throat" and the large part farthest away from the speaker cone is called the "mouth".

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[edit] How it works

In this sense some people have described a horn as an "acoustic transformer". Stated another way, it converts large pressure variations in a small amount of air into a low pressure variation (the human ear is very sensitive indeed to pressure variations — even quite loud sounds are actually very small pressure variations!) in a large amount of air and vice versa. It does this through the gradual exponential increase of the cross sectional area of the horn.

The most well known early horn speakers are those on mechanical phonographs, where the record moves a heavy metal needle that excites vibrations in a small metal diaphragm that acts as the driver for a horn. The horn improves the loading and thus gets a better "coupling" of energy from the diaphragm into the air, and the pressure variations then get smaller as the volume expands and the sound travels up the horn.

A modern electric horn speaker works the same way, replacing the mechanically excited diaphragm with a dynamic or piezo speaker.

[edit] Advancements on the basic principle

As usual, once a principle of operation has been defined, the technology can be adapted and improved almost without limit.

The horn should not just be a cone shape of fixed length, since this would resonate at the natural frequency of its length. Modern horn designs typically feature some form of exponential flare, such as the tractrix taper. Roughly speaking, the slower the flare rate, the deeper and lower frequencies the horn will reproduce. 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 ratio's as high as 10 to 1! The higher the compression the greater the horns ability to amplify, until the compression ratio is so high that it actually begins to limit and impede the ability of the cone to move. At this point the sound output power from the horn will begin to lower. As a proof, place a cone woofer face down on a concrete floor, the compression ratio is very high, however sound output from the back of the speaker is very low.

[edit] Applications

Horn speakers are used in many audio applications, since the usage of a horn reduces the need for the speaker cone to be as lightweight as possible. The drivers in horn speakers can be very small, even for bass frequencies where conventional speakers would need to be very large. Horn speakers can be designed to reproduce a wide range of frequencies using a single, small driver, avoiding the need for a crossover entirely.

Horn speakers can provide very high efficiencies, making them a good match for very low-powered amplifiers, such as single-ended triode amplifiers or other high quality tube amplifiers. Some audiophiles use horn speakers for audio reproduction, while others eschew horn systems for their harmonic resonances (finding them an unpleasant form of distortion).

Horn speakers can also be used to provide very high sound pressure levels needed for sound reinforcement and public address applications, although in these high sound pressure applications, high fidelity may sometimes be compromised for the sake of efficiency. Concert venues often use large arrays of horn speakers for high-volume bass reproduction ("bass bins"), in order to provide bass that concertgoers can not only hear but also feel.

[edit] Well Known

A few of the best & most used vintage Sound Reinforcement horns & new ones around the world are:

Peavey MB-1

CerwinVega Earthquake T-36, AB-36, SL-36, etc.. http://www.cerwinvega.com

Electrovoice W-Bins

Fane

Levan-Horn, http://www.acoustilog.com/disco1.html Levan Horn called like that by the DJ of Paradise Garage Larry Levan: http://www.acoustilog.com/disco4a.jpg

EAW BH882i ftp://ftp.eaw.com/Loudspeaker_product_info/Discontinued_loudspeakers/BH_Series/BH882iP.pdf now reemplaced by EAW DCS2, EAW LA400, BH822e or BH760 http://www.eaw.com/

JBL VS2210 Venue, New JBL HLA

the old http://www.adamsonproaudio.com

http://www.vikingaudio.com/

http://www.ramsdellproaudio.com/products/subs/WH1-DBL.htm

  • [1] Pyleaudio.com Pro PPM501

Electro voice MT4

many many more... for more info:

[edit] See also

[edit] External links

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