THE PURPOSE OF A HORN
What’s the functional difference between front loaded bass reflux cabinets and horn loaded speaker cabinets?
- They typically produce 10 times (10 dB) more sound power than a cone speaker from a given amplifier output.
- Horn loaded speakers will tend to be louder than their front-loaded counterparts, and will be more directional.
- A focus on the sound that would otherwise spread out in a wider pattern is dictated by the wavelength as well as the shape and size of the horn.
Why is Horn Loading used for Large Speakers
- Horn loading is used to increase the overall efficiency of the driving element(s)
- Improves the coupling efficiency between a speaker driver and the air
- Provides an “acoustic transformer” that provides impedance matching between the relatively dense diaphragm material and the less-dense air.
- The result is greater acoustic output power from a given driver.
- The narrow part of the horn next to the driver is called the “throat”
- The large part farthest away from the driver is called the “mouth”
- The angular coverage of the horn is determined by the shape and flare of the mouth.
Historically horn loaded enclosures have been used in large venues for reasons related to the differences outlined above:
- They can more easily reach a desired sound pressure level with less amplifier power than bass reflux designs.
- Horn loudspeakers can provide very high efficiency, making the power requirements for the same SPL as a bass reflux cabinet
- Horn loudspeakers can also be used to provide the very high sound pressure levels needed for sound reinforcement applications.
- With these high sound pressure applications, high fidelity is compromised for the efficiency.
- Concert venues often use large arrays of horn loudspeakers for high-volume bass reproduction.
- Multiple horn loudspeakers arrays provide the same benefits as a single horn with a larger mouth area
- Low frequency cut-off extends lower as the horn mouth gets larger.
- The speaker array using multiple drivers provides greater output power.
Loading of the Driver
The loudspeaker, which is a generator of pressure, has an internal source impedance and drives an external load impedance. The air is the ultimate load, and the impedance of air is low, because of its low density. The source impedance of any loudspeaker, on the other hand, is high, so there will be a considerable mismatch between the source and the load. The result is that most of the energy put into a direct radiating loudspeaker will not reach the air, but will be converted to heat in the voice coil and mechanical resistances in the unit. The problem is worse at low frequencies, where the size of the source will be small compared to a wavelength and the source will merely push the medium away. Increased loading of a driver over that of free air increases efficiency while concentrating the sound into a certain solid angle increases the output further.
Directivity is most important in sound reinforcement systems, where a large audience should have the same distribution of low and high frequencies, and where reverberation and reflections can be a problem. Increased directivity combined with high electric-acoustic conversion efficiency means that horn speakers are very easy to power, even with very small amplifiers.
Summary of Advantages:
- Increased sensitivity (Increase on-axis SPL/1W/1m)
- Increased efficiency
- Less power required for equal SPL of direct radiating
- Allows for more amplifier headroom
- Provides more dynamics and less low frequency distortion
- Better transient and less stress on the amp
- Increased directional characteristic
- Provides medium to long throw characteristics
- Decreased Excursion
- Reduced doppler distortion and lowers harmonic distortion
- Distortion proportional to diaphragm excursion magnitude
- Reduced Distortion