Why does an undersized horn mouth sound "honky"?

If a horn mouth is cut short before reaching wavelength circumference, the expanding sound wave hits a sudden acoustic boundary step. Sound reflects backwards toward the throat, creating standing wave resonances that the human ear perceives as a nasal, hollow "megaphone" or "honky" timbre.

Why should the high-pass crossover frequency be set above fc?

Never cross over a compression driver right at the horn cutoff frequency (fc). At fc, phase distortion is high and driver cone excursion quadruples. Always set the electrical crossover high-pass filter at 1.25x to 1.5x fc to protect the fragile titanium diaphragm.

What is the acoustic advantage of a Tractrix horn over an Exponential horn?

A Tractrix flare terminates at the mouth at exactly a 90-degree angle to the horn axis. This eliminates diffraction glare at the mouth boundary, providing a smoother high-frequency dispersion and superior stereo imaging.

Free Acoustic Horn Flare & Cutoff Frequency Calculator

📢 Driver Throat & Cutoff Target

Compression Driver Throat Exit

Acoustic Cutoff Target (fc in Hz) Horn ceases to load below fc

Horn Flare Profile

Coverage Space / Radiation

Crossover Recommendation

📊 Acoustic Dimensions & Flare Geometry

Minimum Mouth Perimeter 22.5 Inches 57.2 cm circumference

Axial Horn Depth 9.8 Inches 24.9 cm front-to-back length

Flare Expansion Rate (m): 0.0223 in⁻¹ (8.78 m⁻¹)

Minimum Mouth Width × Height: 7.2" × 7.2" (Square / Round)

Driver Throat Area (St): 0.785 sq.in (1.0" exit)

Acoustic Impedance Match: Reflection-Free Termination

✅ Reflection-Free Mouth: Mouth circumference matches the 600 Hz wavelength (22.5"), ensuring acoustic energy transitions into room air without mouth mouth reflection notches.

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The Acoustic Physics of Horn Loudspeakers

An acoustic horn functions as an acoustic impedance transformer. A raw loudspeaker diaphragm is a high-mass, high-pressure, low-velocity device trying to push ultra-low-density air. Because of this massive impedance mismatch, a direct-radiator speaker converts less than 2% of electrical power into sound.

A horn gradually transforms high-pressure air at the small throat into low-pressure, large-volume air movement at the wide mouth, boosting electro-acoustic efficiency from 2% to over 25% (a +10 to +15 dB gain in sensitivity!).

The Flare Constant and Wavelength Rule

In an exponential horn, cross-sectional area expands according to (S(x) = S_t imes e^{mx}), where the flare rate (m) is strictly tied to the lowest cutoff frequency (f_c):

m = (4 × π × fc) / c

Below (f_c), acoustic radiation resistance drops to zero and the horn provides zero acoustic loading.

The Critical Mouth Perimeter Dimension

To prevent sound waves from reflecting back down the horn from the mouth (which creates severe comb-filter phase notches and honky coloration), the mouth perimeter must be at least equal to one full acoustic wavelength at cutoff (( ext{Perimeter} ge lambda_c = rac{c}{f_c})).