8FHM

LOUDSPEAKER ENCLOSURE DESIGN REPORT
Driver: 8FHMX4-091
Generated: 2026-04-12
Application: Hi-fi two-way systems, studio monitors
DRIVER SPECIFICATIONS
Code             : 8FHMX4-091
Description      : 8" Ferrite Mid-Woofer — Carbon Fiber Nomex Honeycomb Composite Cone
Nominal Impedance: 4 Ω
AES Power        : 50 W
Continuous Power : 100 W
Peak Power       : 200 W

Fs               : 38 Hz
Re               : 3.6 Ω
Qes              : 0.41
Qms              : 12.9
Qts              : 0.39
Vas              : 32.1 L
Sd               : 206.1 cm²
Sensitivity      : 89.04 dB (1 W / 1 m)
Mms              : 31.5 g
Rms              : 0.58 kg/s
Cms              : 0.56 mm/N
Bl               : 8.19 T·m
Le               : 0.46 mH
Xmax             : 5.0 mm (one-way, peak)
Xmech            : 13.0 mm

Voice Coil       : 35.6 mm, CCAW, Kapton former
Cone             : 1K carbon fiber / Nomex honeycomb composite (sandwich)
Dustcap          : Hard-anodized aluminum
Surround         : NBR rubber (FEM-optimized)
Spider           : Nomex
Basket           : Aluminum
Magnet           : Ferrite
DERIVED PARAMETERS
Volume displacement
  Vd = Sd × Xmax = 206.1 cm² × 0.50 cm = 103.1 cm³

Inductance rolloff onset
  f_Le = Re / (2π × Le) = 3.6 / (2π × 0.00046) ≈ 1,246 Hz

Cone beaming onset
  r_cone = √(Sd / π) = √(206.1 / 3.14159) = 8.10 cm
  f_beam = c / (π × r_cone) = 34,400 / (3.14159 × 8.10) ≈ 1,352 Hz

Note on cone extension: The carbon fiber Nomex honeycomb sandwich
construction pushes cone resonance (breakup) modes well above the
conventional pistonic limit. The driver retains usable, low-distortion
output beyond f_Le and f_beam; the practical crossover ceiling is set
by cone directivity, not resonance artifacts.

Working band        : ~40 Hz – 1,250 Hz (conservative pistonic limit)
Tweeter crossover   : 1.5 – 3.0 kHz; carbon fiber composite permits
                      crossover placement up to 3 kHz before directivity
                      becomes the primary constraint.

Maximum SPL (anechoic, 1 m)
  At 50 W AES    : 89.04 + 10·log₁₀(50)  = 89.04 + 17.0 = 106.0 dB
  At 100 W cont  : 89.04 + 10·log₁₀(100) = 89.04 + 20.0 = 109.0 dB

Note on Qms: Qms = 12.9 is exceptionally high, indicating near-zero
mechanical losses. System damping is almost entirely electrical (Qes).
This results in very low harmonic distortion and highly controlled
cone motion — a key characteristic of this driver's hi-fi performance.
ENCLOSURE RECOMMENDATION
Qts = 0.39 → Both sealed and vented (bass reflex) enclosures
are viable. Sealed is preferred for studio monitor accuracy and
controlled transient response. Vented extends bass output and
reduces excursion at tuning frequency, suited to hi-fi floorstanding
and stand-mount enclosures where deeper bass extension is required.
SEALED ENCLOSURE ALIGNMENTS
Formula: Vb = Vas / ((Qtc / Qts)² − 1)
         fc  = Fs × (Qtc / Qts)
         f-3dB: u = [−(2 − 1/Qtc²) + √((2 − 1/Qtc²)² + 4)] / 2
                Ω = √u ;  f-3dB = Ω × fc

┌──────────────────────────────────────────────────────────────────────┐
│ Alignment │ Vb (net) │  Qtc  │   fc    │ f−3dB  │ Character         │
├───────────┼──────────┼───────┼─────────┼────────┼───────────────────┤
│     A     │   14 L   │ 0.707 │  68.9 Hz│  69 Hz │ Butterworth/flat  │
│     B     │   8.5 L  │ 0.85  │  82.8 Hz│  71 Hz │ Compact, warm     │
│     C     │   5.8 L  │ 1.00  │  97.4 Hz│  77 Hz │ Bookshelf / sat   │
└──────────────────────────────────────────────────────────────────────┘

--- Alignment A — 14 L sealed / Qtc = 0.707 (Butterworth) ---
  Vb = 32.1 / ((0.707/0.39)² − 1) = 32.1 / 2.286 = 14.0 L → 14 L
  fc = 38 × (0.707/0.39) = 68.9 Hz
  f-3dB = fc = 68.9 Hz (Butterworth by definition)

  Maximally flat sealed alignment; no bass shelf boost or hump.
  The ideal format for studio monitors and reference hi-fi systems
  where transient accuracy and flat frequency response are required.
  Deepest sealed bass extension for this driver at a practical volume.

--- Alignment B — 8.5 L sealed / Qtc = 0.85 ---
  Vb = 32.1 / ((0.85/0.39)² − 1) = 32.1 / 3.750 = 8.56 L → 8.5 L
  fc = 38 × (0.85/0.39) = 82.8 Hz
  f-3dB: 2−1/0.722=0.616; √(0.379+4)=2.093; u=(−0.616+2.093)/2=0.739; Ω=0.859
         f-3dB = 0.859 × 82.8 = 71 Hz

  Compact sealed format with mild low-bass warmth (~1 dB broad shelf
  around 80 Hz). Suited to stand-mount hi-fi speakers and compact
  two-way monitors where cabinet volume is constrained.
  A practical balance of box size, bass extension, and subjective warmth.

--- Alignment C — 5.8 L sealed / Qtc = 1.00 ---
  Vb = 32.1 / ((1.00/0.39)² − 1) = 32.1 / 5.575 = 5.76 L → 5.8 L
  fc = 38 × (1.00/0.39) = 97.4 Hz
  f-3dB: 2−1/1.00=1.000; √(1+4)=2.236; u=(−1+2.236)/2=0.618; Ω=0.786
         f-3dB = 0.786 × 97.4 = 77 Hz

  Very compact bookshelf or satellite format. Bass shelf boost (~3 dB
  around 90–100 Hz) subjectively full-sounding in small rooms.
  Mandatory high-pass filter at 60–80 Hz (DSP or passive) to prevent
  over-excursion below fc.
  Best deployed with a subwoofer crossed over at 80–100 Hz.

--- Notes for all sealed alignments ---
  • High-pass filter recommended: 30–60 Hz depending on alignment.
  • Zobel network improves passive crossover accuracy:
    R_z = Re = 3.6 Ω ; C_z = Le / Re² = 0.46e-3 / 12.96 = 35.5 μF
    → use 33 μF or 39 μF, 100 V non-polar.
VENTED ENCLOSURE ALIGNMENTS
Suited for hi-fi floorstanding and larger stand-mount enclosures
where extended bass and reduced mid-bass excursion are priorities.

Port: 50 mm round (Ap = 19.64 cm²)
  Port velocity limit: ≤ 17 m/s (hi-fi standard)

Leff = (Ap × c²) / (4π² × Fb² × Vb)
  c = 34,400 cm/s ; c² = 1,183,360,000 cm²/s²
  4π² = 39.478

Port velocity: v_peak = Vd × 2π × Fb / Ap
  Vd = 103.1 cm³ = 1.031 × 10⁻⁴ m³ ; Ap = 1.964 × 10⁻³ m²

┌──────────────────────────────────────────────────────────────────────┐
│ Alignment │ Vb (net) │  Fb   │ 50mm Port Length │ Port Velocity     │
├───────────┼──────────┼───────┼──────────────────┼───────────────────┤
│     A     │   25 L   │ 42 Hz │      133 mm      │  13.9 m/s  ✓     │
│     B     │   30 L   │ 38 Hz │      136 mm      │  12.5 m/s  ✓     │
│     C     │   40 L   │ 32 Hz │      144 mm      │  10.6 m/s  ✓     │
└──────────────────────────────────────────────────────────────────────┘

Port length calculations (50 mm round port):
  Alignment A: Leff = (19.64 × 1,183,360,000) / (39.478 × 1764 × 25,000)
                    = 2.323×10¹⁰ / 1.741×10⁹ = 133 mm
  Alignment B: Leff = (19.64 × 1,183,360,000) / (39.478 × 1444 × 30,000)
                    = 2.323×10¹⁰ / 1.710×10⁹ = 136 mm
  Alignment C: Leff = (19.64 × 1,183,360,000) / (39.478 × 1024 × 40,000)
                    = 2.323×10¹⁰ / 1.617×10⁹ = 144 mm

Port engineering note: All three vented alignments produce
near-identical port lengths (133–144 mm). This occurs because
lower Fb² is offset by proportionally larger Vb in the Helmholtz
equation. A single 50 mm × 138 mm port tube can serve all three
tunings with minor end-correction trimming.

--- Vented Alignment A — 25 L / Fb = 42 Hz ---
  Near-Fs tuning in a compact vented cabinet. Good mid-bass
  output and strong mechanical protection above port tuning.
  Suited to compact stand-mount vented enclosures where the
  driver replaces the sealed A alignment at lower excursion cost.

--- Vented Alignment B — 30 L / Fb = 38 Hz ---
  On-Fs tuning. Balanced response with extended bass to ~36 Hz
  (4th-order rolloff below Fb). The recommended general-purpose
  hi-fi vented alignment for two-way floorstanding or large
  stand-mount speakers.

--- Vented Alignment C — 40 L / Fb = 32 Hz ---
  Below-Fs tuning. Maximum bass extension into the low 30s Hz.
  Suited to two-way floorstanding hi-fi where sub-35 Hz reproduction
  is required without a separate subwoofer.
  Mandatory high-pass filter at 25–28 Hz to protect driver below
  the port rolloff (4th-order slope below Fb).
CROSSOVER AND SYSTEM INTEGRATION
Crossover to tweeter (acoustic target): 1.5 – 3.0 kHz
  f_beam = 1,352 Hz (cone directivity increases above this)
  f_Le   = 1,246 Hz (inductive rolloff onset)

The carbon fiber Nomex honeycomb composite cone pushes structural
resonance modes beyond 3 kHz. Crossover at 2.0–2.5 kHz is
recommended as the design point; 3.0 kHz is achievable where
off-axis directivity at the crossover frequency is not critical.

Recommended crossover order: 2nd-order (12 dB/oct) minimum.
  3rd or 4th-order preferred for controlled off-axis behaviour
  above 1.3 kHz at a 2.0–2.5 kHz acoustic crossover target.

Zobel network (for passive crossover flatness):
  R_z = 3.6 Ω (use 3.6 Ω standard, or 3.3 Ω nearest)
  C_z = 35 μF, 100 V non-polar (use 33 μF or 39 μF standard value)
  Place across driver terminals inside the enclosure.
IMPEDANCE CONFIGURATIONS
Single (standard) : 4 Ω
Pair in series    : 8 Ω (+3 dB sensitivity, standard amplifier load)
Pair in parallel  : 2 Ω (not recommended; exceeds most amplifier ratings)