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PRODUCT CODE: 8FRX4-551A

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--- ENCLOSURE RECOMMENDATIONS ---

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ENCLOSURE RECOMMENDATIONS: 8FRX4-551A

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Driver: 8FRX4-551A (8FR) — 8" Full-Range (Hi-Fi / Open Baffle)

Key T/S: Fs=53Hz, Qts=0.378, Vas=36.8L, Sens=93dB 1W/1m

Power: AES 30W / Cont 60W / Peak 120W

Xmax=5.8mm (one-way linear), Xmech=11.8mm (protection at 9.8mm)

Sd=213.8cm², Bl=7.86T·m, Re=3.8Ω (4-ohm nominal), Mms=18.38g

Le=0.08mH (extremely low — wide-bandwidth motor design)

Voice Coil: 1.6" aluminum on Kapton former (17.6mm winding height)

Magnet: Ferrite with copper shorting cup | Basket: Aluminum

Cone: Bamboo fiber reinforced paper pulp with whizzer cone

Phase plug: Bullet style | Surround: Fabric

NOTE: This is a dedicated hi-fi full-range driver with a whizzer

(secondary) cone for extended high-frequency response to 15 kHz

and a bullet-style phase plug for controlled off-axis dispersion.

The extremely low voice coil inductance (0.08 mH) and copper

shorting cup ensure flat impedance and clean response through the

upper midrange and treble. Designed primarily for open baffle (OB)

applications, but also suitable for sealed and vented enclosures.

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  PRIMARY — Open Baffle (OB)

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Open baffle mounting is the intended application for this driver.

In OB, the driver radiates as a dipole — front and rear waves are

in opposite polarity and partially cancel at low frequencies. Above

the baffle frequency (fb), the response is essentially flat. Below

fb, the response rolls off at approximately 6 dB/octave due to

dipole cancellation.

BAFFLE FREQUENCY vs BAFFLE WIDTH:

  Baffle Width       fb (Hz)    Notes

  ──────────────────────────────────────────────────

  40 cm              273        Small desktop/nearfield

  50 cm              218        Compact stand-mount OB

  60 cm              182        Medium floor-standing OB

  80 cm              136        Large floor-standing OB

  100 cm             109        Very large statement OB

  Formula: fb = 343 / (π × baffle_width_in_meters)

RECOMMENDED OB CONFIGURATIONS:

  a) OB — Compact (50 cm wide baffle)

     Baffle Frequency: 218 Hz

     Dipole rolloff below 218 Hz at ~6 dB/octave

     Usable bass (no EQ): ~120–150 Hz

     With DSP bass EQ (+6 dB/oct shelving): usable to ~60–70 Hz

     EQ boost at Fs (53 Hz): ~12 dB

     Baffle suggestion: 50 × 70 cm minimum, 18–25mm birch plywood

     Notes: Compact OB for nearfield/desktop or small room use.

     Requires significant DSP bass boost to achieve flat response

     below 200 Hz. The small baffle allows excellent imaging and

     disappearing soundstage. Best paired with a dipole subwoofer

     (OB sub or H-frame) for full-range reproduction.

  b) OB — Standard (60–70 cm wide baffle)

     Baffle Frequency: 156–182 Hz

     Dipole rolloff below 156–182 Hz at ~6 dB/octave

     Usable bass (no EQ): ~100–120 Hz

     With DSP bass EQ (+6 dB/oct shelving): usable to ~50–60 Hz

     EQ boost at Fs (53 Hz): ~9–11 dB

     Baffle suggestion: 60–70 × 90–100 cm, 18–25mm birch plywood

     Notes: The recommended starting point for most OB builds.

     Moderate DSP bass boost achieves a musically satisfying

     full-range response. Good balance between bass extension,

     imaging, and practical room placement. Can work as a

     stand-alone full-range system in smaller rooms, or paired

     with a subwoofer for larger spaces.

     *** RECOMMENDED FOR MOST OB APPLICATIONS ***

  c) OB — Large (80–100 cm wide baffle)

     Baffle Frequency: 109–136 Hz

     Dipole rolloff below 109–136 Hz at ~6 dB/octave

     Usable bass (no EQ): ~80–100 Hz

     With DSP bass EQ (+6 dB/oct shelving): usable to ~40–50 Hz

     EQ boost at Fs (53 Hz): ~6–8 dB

     Baffle suggestion: 80–100 × 120–140 cm, 18–25mm birch plywood

     Notes: Large baffle provides the deepest bass without

     requiring excessive EQ. Less DSP boost means less excursion

     demand at low frequencies, improving dynamic headroom. The

     large baffle provides more acoustic loading but begins to

     narrow horizontal dispersion at higher frequencies. Best

     for dedicated listening rooms where room placement allows

     large panels.

OPEN BAFFLE DESIGN NOTES:

- Baffle should be made from acoustically inert material (birch

  plywood, MDF, or bamboo laminate — 18mm minimum, 25mm preferred)

- Bracing behind the driver cutout is recommended to minimize

  baffle vibration

- Driver offset from center (both horizontally and vertically)

  reduces edge diffraction artifacts

- Room placement: OB speakers require distance from rear wall

  (minimum 50–80 cm) to avoid comb filtering from rear wave

  reflections

- The dipole radiation pattern provides a natural, spacious

  soundstage with minimal room excitation compared to monopole

  (boxed) speakers

- The whizzer cone handles frequencies above approximately

  3–5 kHz; its integration with the main cone provides the

  wide-bandwidth single-point-source characteristic

- DSP bass equalization: a 6 dB/octave shelving boost below the

  baffle frequency restores flat response. Monitor excursion —

  the driver's 5.8 mm Xmax limits maximum output at low

  frequencies under heavy EQ boost

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  ALTERNATIVE — Sealed Enclosures

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For listeners who prefer a traditional boxed speaker, sealed

enclosures provide smooth, predictable rolloff and are simpler to

build than OB. The Qts of 0.378 produces overdamped sealed

alignments in practical volumes — the gentle rolloff integrates

well with room gain in domestic environments.

  d) SEALED — Compact (Qtc ≈ 0.7)

     Net Volume: 15 liters

     System Resonance (fc): 98 Hz

     Qtc: 0.70

     Response: Butterworth, maximally flat sealed response

     Notes: Most compact practical sealed alignment. The fc of

     98 Hz is relatively high — the speaker will roll off below

     100 Hz and rely on room gain for usable response into the

     70–80 Hz range. Best when paired with a subwoofer for bass

     support, or for nearfield desktop use where proximity gain

     assists low-frequency extension.

  e) SEALED — Balanced (Qtc ≈ 0.6)

     Net Volume: 25 liters

     System Resonance (fc): 83 Hz

     Qtc: 0.60

     Response: Overdamped, smooth gentle rolloff

     Notes: Good balance between cabinet size and bass extension.

     The overdamped response provides a natural, warm rolloff

     that sounds musical without excessive resonance. With room

     gain, in-room response extends usably to ~55–60 Hz. A good

     starting point for a full-range bookshelf or stand-mount

     speaker without a subwoofer.

     *** RECOMMENDED SEALED ALIGNMENT ***

  f) SEALED — Extended (Qtc ≈ 0.5)

     Net Volume: 50 liters

     System Resonance (fc): 70 Hz

     Qtc: 0.50

     Response: Heavily overdamped, very gradual rolloff

     Notes: Large enclosure providing the lowest sealed fc. The

     heavily overdamped alignment rolls off very gradually,

     providing usable response well below fc with room gain

     (estimated in-room -3 dB around 45–50 Hz). Suitable for

     a floor-standing full-range speaker in a medium to large

     room. The large cabinet volume makes this a substantial

     piece of furniture.

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  ALTERNATIVE — Bass Reflex (Vented) Enclosures

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Vented enclosures provide deeper bass extension than sealed in the

same volume, but introduce port-related artifacts (chuffing, resonance

at tuning frequency). For a hi-fi full-range driver, sealed or OB is

generally preferred for purity of reproduction, but vented is an

option where maximum bass extension from a compact enclosure is

required.

  g) VENTED — Compact

     Net Volume: 27 liters

     Tuning (Fb): 61 Hz

     Est. -3dB: 56 Hz

     HP Filter: 51 Hz (24dB/oct recommended)

     Round Port: 65mm dia × 51mm long

     Port Velocity: 14.3 m/s

     Notes: Higher tuning for stronger upper-bass output and

     compact cabinet. Good for a vented bookshelf-sized

     full-range speaker.

  h) VENTED — Balanced

     Net Volume: 31 liters

     Tuning (Fb): 55 Hz

     Est. -3dB: 51 Hz

     HP Filter: 45 Hz (24dB/oct recommended)

     Round Port: 65mm dia × 58mm long

     Port Velocity: 12.9 m/s

     Notes: General-purpose alignment with good extension

     relative to cabinet size. Usable bass response to ~50 Hz

     with room gain extending further.

  i) VENTED — Extended

     Net Volume: 37 liters

     Tuning (Fb): 48 Hz

     Est. -3dB: 41 Hz

     HP Filter: 38 Hz (24dB/oct recommended)

     Round Port: 65mm dia × 68mm long

     Port Velocity: 11.3 m/s

     Notes: Maximum bass extension, reaching into the low

     40s Hz anechoic. A compelling option for a vented

     floor-standing full-range speaker. Port velocities are

     moderate and well-controlled.

VENTED NOTE: Port lengths are short (51–68 mm) and velocities are

moderate (11–14 m/s), making port design straightforward. A simple

rear-mounted 65 mm round port is sufficient. Consider a flared port

for lowest noise in critical listening applications.

--- SUMMARY ---

The 8FRX4-551A is an 8-inch full-range driver designed for hi-fi applications where a single-point audio source is required, including open baffle, sealed, and vented loudspeaker systems. It features a lightweight bamboo fiber reinforced paper cone with an integrated whizzer (secondary) cone for extended high-frequency response to 15 kHz, a bullet-style phase plug for controlled off-axis dispersion, and a 1.6-inch aluminum voice coil on a Kapton former. The ferrite motor circuit with copper shorting cup and extremely low voice coil inductance (0.08 mH) provide flat impedance behavior and clean, wide-bandwidth reproduction from a single driver. At 93 dB sensitivity (1W/1m) with a moving mass of only 18.4 grams, the driver is efficient and fast, with good transient response across its full operating range.

The driver is primarily intended for open baffle (OB) mounting, where it radiates as a dipole source. On a standard 60–70 cm wide baffle, the dipole response is flat above approximately 155–180 Hz, with a 6 dB/octave rolloff below this frequency due to front-to-rear cancellation. DSP bass equalization (a shelving boost of approximately 6 dB/octave below the baffle frequency) restores flat response and extends usable bass to 50–60 Hz depending on baffle dimensions and EQ headroom. Larger baffles (80–100 cm) reduce the required EQ boost and provide deeper unaided bass extension. The dipole radiation pattern inherent to OB mounting provides a natural, spacious soundstage with minimal room excitation compared to conventional boxed loudspeakers.

For enclosed alternatives, sealed enclosures of 15 to 50 liters produce system resonances between 70 and 98 Hz with Qtc values of 0.5 to 0.7. A 25-liter sealed enclosure (Qtc 0.6, fc 83 Hz) is the recommended starting point, providing a smooth overdamped rolloff that integrates naturally with domestic room gain for in-room bass extension to approximately 55–60 Hz. Vented enclosures of 27 to 37 liters tuned between 48 and 61 Hz extend the anechoic -3 dB point to approximately 41–56 Hz with moderate port velocities (11–14 m/s). In all configurations, the driver is rated for 30 W AES / 60 W continuous power handling, which is appropriate for domestic listening levels given the 93 dB sensitivity.

This driver is particularly effective in hi-fi open baffle loudspeakers, single-driver sealed or vented cabinets, and full-range desktop monitors where point-source imaging, wide-bandwidth reproduction from a single driver, and natural tonal character are priorities. The bamboo fiber cone, whizzer cone extension to 15 kHz, and aesthetically refined design (exposed aluminum basket, distinctive colorway) support both high sound quality and modern industrial design integration.

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