18 Sound XD125 – Integrated Polyethylene Driver with 90°×60° Constant Directivity Horn
The 18 Sound XD125 has been designed for 2-way or 3-way systems. It will deliver an unmatched combination of extended linear frequency response and very high efficiency. This is the integrated horn counterpart to the standalone HD125 documented earlier in this session, sharing that driver’s exact diaphragm technology and named succession claim — the major advancement in the XD125 compression driver consists in a new innovative diaphragm assembly made in proprietary treated polyethylene material, maintaining the minimum resonance frequency point value at 1600 Hz, extending the frequency response in the mid region when compared to the previous compression driver model, the XD120.
The design of the diaphragm and surround in polyester material allows better control in terms of movement and mechanical stress. Radial ribs increase stiffness, avoiding uncontrolled vibration modes in the usable frequency range — identical construction language to the HD125, confirming both products share the same driver platform, here integrated permanently with a purpose-built horn rather than sold as a standalone throat-mount unit.
Design and Construction of the 18 Sound XD125
An edge-wound aluminium voice coil, wound on proprietary treated Nomex, completes the diaphragm assembly. The proprietary treated Nomex former, thanks to its physical properties, shows a 30% higher value of tensile elongation at working operative temperature (200°C) when compared to Kapton. This plus is capable of keeping proper energy transfer control to the dome in real working conditions, and 18 Sound’s proprietary Nomex former is suitable to work also in environments with higher moisture contents.
The polypropylene phase plug is the result of a meticulous design exercise. Its shape assures the correct acoustic impedance of the radiating dome, reducing distortion levels across a very wide range of frequency. Final result is a smooth coherent wavefront in the horn entrance, high thermal stability, and manufacturing consistency. The compact and lightweight ceramic magnet assembly has been designed to obtain 16 kGauss in the gap — matching the HD125’s exact flux density figure.
The XD125 pressure die-cast polyurethane foam horn maintains constant nominal 90° Horizontal × 60° Vertical pattern control, providing consistent on-axis and off-axis frequency response from 2 kHz to 16 kHz in the horizontal plane and from 2.5 kHz to 16 kHz in the vertical plane. Horn directivity is constant from 2.5 kHz. Computer Aided Finite Element Analysis and extensive testing were used to obtain the horn contours. The horn is designed to be free of resonance and vibrations, assuring maximum strength.
At 1.1 kg, the 18 Sound XD125 carries the combined mass of both compression driver and integrated horn — genuinely more than the HD125’s standalone 0.8 kg, but comparable to sourcing a separate driver and horn independently.
Performance and Applications for the 18 Sound XD125
The 18 Sound XD125 delivers 109 dB sensitivity across a 2.0 – 18 kHz frequency range, with a recommended crossover of 2.5 kHz using a 12 dB/octave or steeper high-pass filter — matching the HD125’s exact sensitivity and bandwidth, confirming both products share the identical driver platform behind their differently packaged HF loading.
The 90° H × 60° V coverage pattern is genuinely wider than the XD110’s 60° × 50°, offering broader horizontal and vertical dispersion appropriate for different room coverage and system design requirements. Directivity constant from 2.5 kHz upward gives system designers a well-documented, predictable coverage pattern across the driver’s usable range.
For 2-way or 3-way systems requiring a pre-matched driver-and-horn combination with wider 90° × 60° coverage than the XD110, the 18 Sound XD125 delivers a complete, engineered HF loading solution.
Conclusion – 18 Sound XD125 Integrated HF Assembly
The 18 Sound XD125 is the integrated horn counterpart to the standalone HD125, sharing its exact treated polyethylene diaphragm technology and quantified improvement over the named XD120 predecessor, here paired permanently with a wider 90° × 60° constant directivity horn made from pressure die-cast polyurethane foam.
This completes this session’s exploration of 18 Sound’s integrated XD-series HF assemblies alongside the XD110, giving builders two distinct coverage pattern options — 60° × 50° or 90° × 60° — both built around 18 Sound’s proven phenolic and polyethylene diaphragm technology respectively.
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About 18 Sound
18 Sound products are proudly made in Reggio Emilia, Italy, combining advanced technology with Italian craftsmanship. Known for their high-performance professional audio components, 18 Sound is a trusted name in the global audio industry. Their state-of-the-art manufacturing and strict quality control ensure exceptional reliability and sound clarity. 18 Sound products are designed to meet the demands of speaker builders and audio professionals, 18 Sound offers premium products with outstanding value and performance worldwide.
