A horn loudspeaker 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.
Base on the Wikipedia explanation, now then I realized why the horn come with the minimum frequency spec. So if your speaker driver min freq is 2KHz and you need to lower that freq to 1KHz to cover the birds freq range, you need to consider getting a suitable horn.
Specifications: • Horn type: Exponential • Minimum frequency: 600 Hz • Nominal dispersion: 45° H x 45° V • Throat diameter: 1.0" • Mounting type: 1-3/8"-18 TPI •
Specifications: *Horn type: Bi-radial *Minimum frequency: 1,500 Hz *Nominal dispersion: 60° H x 40° V *Throat diameter: 1.0" *Mounting type: 1-3/8"-18 TPI *Dimensions: 6.34" W x 5.16" H x 4.16" D