Overview

The Coral Flat-6 is a vintage 16cm full-range speaker driver manufactured by Coral Audio Corporation from approximately 1973-1980. This double cone design features a duralumin dome center in a white paper cone, with a diaphragm constructed from pulp mixed with chemical fiber. The driver employs specialized molding techniques and was priced at 24 USD during its production era. Coral Audio Corporation, founded in the 1950s, was a respected Japanese manufacturer that ceased operations in the mid-1980s.

Scientific Validity

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Limited measurement data exists for the Coral Flat-6. Official specifications list frequency response at 45-20,000 Hz with 8Ω impedance and conflicting efficiency claims ranging from 92-98 dB/W/m [1][2]. Advanced parameters from DIY community testing show Qts of 0.402 and Vas of 31.346L, with resonance frequency (Fo) at 68Hz [3]. No published data exists for THD, IMD, crosstalk, or dynamic range measurements. The absence of modern measurement validation and conflicting efficiency specifications prevent confirmation of scientifically audible performance improvements over contemporary alternatives.

Technology Level

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The Flat-6 represents industry-average technical implementation for its 1970s era. Design features include proprietary duralumin dome center with specialized pulp and chemical fiber composite diaphragm molding using contemporary advanced molding machines [1]. The double-cone configuration with lightweight alloy dome aims to improve ultra-high frequency directional characteristics. However, the analog-only mechanical design lacks modern digital integration and employs technology that contemporary manufacturers can easily replicate. Construction quality reflects Japanese craftsmanship standards of the period without Computer Aided Design tools [4].

Cost-Performance

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Current market pricing shows the Coral Flat-6 at 229 USD per driver. The Dayton Audio PS65LP-4 provides equivalent-or-better performance with superior frequency extension and modern construction at 129 USD per driver [5]. Equipped with comparable 6.5” diameter, equivalent frequency range (45-20kHz), and superior 99 dB efficiency versus the Coral’s 92-98 dB specification, the Dayton offers equivalent full-range functionality at significantly lower cost. CP = 129 USD ÷ 229 USD = 0.6.

Reliability & Support

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Coral Audio Corporation discontinued operations in the mid-1980s, eliminating official warranty and support infrastructure [4]. Vintage units lack manufacturer backing and commonly experience cloth surround degradation requiring restoration with sewing machine oil treatments [3]. While some units demonstrate remarkable longevity over 25+ years [4], the absence of parts availability and repair support significantly compromises long-term reliability expectations.

Rationality of Design Philosophy

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The Flat-6 reflects 1970s design approaches emphasizing analog construction and Japanese craftsmanship without scientific measurement transparency. The conservative analog-only methodology lacks modern innovation or functional integration with contemporary audio technology. While materials quality demonstrates period standards, the design philosophy does not align with measurement-focused approaches that achieve transparent performance levels.

Advice

The Coral Flat-6 serves primarily as a collectible vintage driver rather than a practical modern audio solution. Enthusiasts seeking historical Japanese craftsmanship may appreciate its construction, but those prioritizing performance and support should consider contemporary alternatives like the Dayton Audio PS65LP-4. The lack of measurement validation and discontinued manufacturer support makes this driver unsuitable for critical audio applications requiring verified performance specifications.

References

[1] Audio Database. CORAL Flat-6. https://audio-database.com/CORAL/unit/flat-6.html. Accessed 2025-09-04. [2] HiFi Wiki. Coral Flat-6. https://hifi-wiki.com/index.php/Coral_Flat-6. Accessed 2025-09-04. [3] DIY Audio Forum. Coral Flat 6 Parameters Discussion. https://www.diyaudio.com/community/threads/coral-flat-6-question.59879/. Accessed 2025-09-04. [4] DIY Paradise. Coral Speaker Drivers. https://diyparadise.com/w/coral-speaker-drivers/. Accessed 2025-09-04. [5] Parts Express. Dayton Audio PS65LP-4 6-1/2” Ultra Efficient Low Profile Full-Range Driver. https://www.parts-express.com/Dayton-Audio-PS65LP-4-6-1-2-Ultra-Efficient-Low-Profile-Full-Range-Driver-4-Ohm-295-348. Accessed 2025-09-04.

(2025.9.4)