RS Speakers MW 140.38 Fibonacci 5.5" woofer

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The RS Speakers MW 140.38 Fibonacci bass-midrange driver is a 5.5-inch driver that embodies Italian innovation and craftsmanship. With its unique, laser-engraved paper cone based on the Fibonacci sequence, this midrange driver offers exceptional resonance control and imparts a natural sound to any high-fidelity loudspeaker system. Designed for audiophile and professional applications, it combines patented technology, precision engineering, and high-quality materials to ensure uncompromising performance in home audio setups or advanced DIY projects.

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Highlights

• Patented special paper membrane with Fibonacci laser engraving for optimal resonance control
• Advanced double asymmetric rubber surround and progressive Conex spider for linear stroke
• High-performance 1.5" voice coil with fiberglass former for stability under extreme conditions
• Aluminum phase connector and equalization ring for extended frequency response and low distortion.
• Includes sealing gasket, mounting screws and thumb nuts for easy installation.

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Product details RS Speakers W 140.38 Fibonacci

RS Speakers MW 140.38 Fibonacci 5.5" midrange driver

The MW 140.38 Fibonacci features a specially developed diaphragm, a para-elliptical paper cone with a laser-engraved Fibonacci pattern. This patented process follows the mathematical golden ratio, reducing unwanted resonance modes and ensuring a balanced, natural sound signature. The diaphragm is further enhanced with an acrylic coating on the front and a damping layer on the back, creating a sandwich structure that perfectly balances stiffness and damping. The result is a midrange driver that reproduces music with clarity and precision, making it ideal for high-end loudspeakers and audiophile monitors.

Engineered for superior mechanical performance, this woofer features an NBR butyl rubber surround with Double Asymmetric Rolls technology, ensuring symmetrical excursion even at high levels. The progressive Conex spider is meticulously crafted to maximize excursion and minimize dynamic offset, guaranteeing accurate reproduction across the entire frequency range. The free-compression basket design with thin aluminum spokes eliminates back reflections from the cone, improving sonic purity and minimizing coloration—crucial in demanding woofer applications.

The MW 140.38 Fibonacci is designed for high power handling, featuring a 1.5-inch voice coil on a fiberglass former for high thermal stability and longevity. The vented ferrite magnet system is complemented by an aluminum equalization ring, which reduces inductance and harmonic distortion, resulting in clean, dynamic reproduction. The custom-designed aluminum phase connector extends the usable frequency range, making the crossover frequency to the tweeter particularly seamless and supporting detailed midrange and upper bass reproduction.

This driver is ideal for advanced DIY speaker kit builders and audio professionals who want to develop bespoke sound solutions. Precise Thiele & Small parameters, a robust design, and included mounting hardware allow for flexible installation in a wide variety of enclosures. Whether integrated into a sophisticated home audio system or used for custom monitor designs, the MW 140.38 Fibonacci offers a combination of innovation and sonic excellence that sets new standards for midrange drivers.

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Specifications

• Article number: MW 140.38 Fibonacci
• woofer series Fibonacci
• woofer type Woofer
• Nominal diameter 5.5" | 140 mm
• Resilience (QMW) 120 W
• Continuous Program Power 240 W
• Impedance (Z) 8 Ω
• Sensitivity (SPL at 1m / 2.83V) 87.8 dB
• Voice coil diameter 38 mm
• Weight magnet 515 g
• DC resistance (Re) 5.1 Ω
• Voice coil induction (Le) 0.45 mH
• Resonance frequency (Fs) 55.6 Hz
• Mechanical quality (Qms) 4.25
• Electrical quality factor (Qes) 0.49
• Total quality (Qts) 0.44
• Moving mass (mms) 10.4 g
• Suspension compliance (Cms) 788 µm/N
• Membrane area (Sd) 78.5 cm²
• Force factor (BL) 6.15 Tm
• Equivalent volume (Vas) 6.9 L
• Maximum displacement (Xmax) 4.0 mm
• Cone / Diaphragm Material paper
• Bead material Rubber
• Voice coil wire material Copper
• Voice coil mold material Fiberglass
• Basket/frame material Aluminum die-cast
• Magnetic material Ferrite
• Outer diameter 148 mm
• Total depth 72 mm
• Cutout diameter 113 mm
• Bolt Circle Diameter 138 mm
• Mounting holes 6
• Mounting hole diameter 4.2 mm