61FIND

ENCLOSURE RECOMMENDATIONS: 61FINDX16-332A
Driver: 61FINDX16-332A (61FIND) — 6.5" ferrite mid-woofer, 16 ohm
Key T/S: Fs=130Hz, Qts=0.62, Qes=0.71, Qms=5.13, Vas=2.64L, Sens=92dB
Power: AES 150W / Cont 300W / Peak 600W
Xmax=2.3mm (linear), Xmech=10.3mm, Xprot=7.2mm
Sd=132.7cm², Bl=15.64T·m, Le=0.92mH, Re=14.9Ω
Voice coil: 50.8mm (2"), CCAW, TIL/Glass Fiber former (high-temp rated)
Cone: carbon fiber loaded paper (fire-retardant neck treatment)
Surround: fabric
Spider: Nomex (non-flammable)
Depth: 78mm | Baffle cutout: 144.5mm | Ferrite motor | Steel basket

APPLICATION CONTEXT — 16Ω MID-WOOFER FOR PRO 2-WAY SYSTEMS:
  The 61FIND is a cost-effective 6.5-inch mid-woofer intended for compact
  two-way professional audio products operating in the 150Hz–2.5kHz
  working band. The 16-ohm nominal impedance supports multiple deployment
  configurations:

    Single driver:        16Ω — used in 70V/100V distributed audio systems
                                 or with high-impedance PA amplifiers
    Parallel pair:         8Ω — standard professional amplifier load (2×)
    Parallel quad:         4Ω — high-current amplifier load (4×)

  Fire-retardant cone neck treatment, non-flammable Nomex spider, and
  high-temperature TIL voice coil former are specified to support UL
  listing of end products (luminaires, ceiling speakers, public address
  equipment, and similar). All steel parts are weather-treated, making
  the driver suitable for semi-exposed installation environments.

ENCLOSURE TYPE — SEALED ONLY:
  With Fs=130Hz and Vas=2.64L, the 61FIND is suitable for sealed
  (acoustic suspension) enclosures only. Vented (bass reflex) enclosures
  are not feasible: any useful Helmholtz tuning frequency in a box of
  1–10L requires port lengths exceeding practical limits (>500mm for
  even a 25mm tube). The driver's working band begins well above its
  resonance at 130Hz; in a two-way PA system, a system-level high-pass
  crossover at 80–150Hz (handled by the amplifier DSP or passive network)
  provides the necessary LF protection, and the driver's natural sealed
  roll-off provides transition between the LP and HP crossover points.

OPERATING BANDWIDTH:
  Lower working limit: 150–250Hz (set by sealed fc, below)
  Upper working limit: ~1.5kHz (cone beaming onset for 6.5" at wide
                       dispersion) to ~2.5kHz (Le rolloff at ~2580Hz)
  Typical 2-way crossover to tweeter/compression driver: 1.5–2.5kHz

INDUCTANCE ROLLOFF:
  Le = 0.92mH → f_Le = Re / (2π×Le) = 14.9 / (2π × 9.2×10⁻⁴) ≈ 2580Hz
  Clean, direct crossover to a tweeter at 2–2.5kHz with no Le
  compensation required. For wider dispersion below 1.5kHz, use
  a horn-loaded compression driver and cross at 1.0–1.5kHz.

DISPLACEMENT:
  Vd = Sd × Xmax = 132.7cm² × 0.230cm = 30.5cm³ (peak, one-way)

MAXIMUM SPL:
  Single driver (16Ω, 150W): 92 + 21.8 = ~114 dB at 1m
  Parallel pair (8Ω, 2×150W): 95 + 21.8 = ~117 dB at 1m
  Parallel quad (4Ω, 4×150W): 98 + 21.8 = ~120 dB at 1m
SEALED (ACOUSTIC SUSPENSION) ALIGNMENTS
  All Qtc values are above 0.707 (Butterworth) because the driver's
  Qts=0.62 requires an impractically large box (>8L) for Butterworth
  alignment in a 6.5" pro driver context. In a two-way PA system the
  rising bass shelf near fc is partially desirable — it compensates
  for the natural bass roll-off in compact enclosures and provides
  additional perceived warmth and body to the programme below 500Hz.
  System-level DSP can flatten the shelf if a neutral response is needed.
ALIGNMENT A — ULTRA-COMPACT (1.0 L net internal)
  Box volume:        1.0 L (net internal)
  Qtc:               1.18
  System fc:         248 Hz
  System f-3dB:      ~183 Hz
  System HP:         80 Hz, 12–24 dB/oct (amplifier or DSP)
  Application:       Column array speaker driver, ceiling pendant speaker,
                     ultra-compact PA satellite, under-seat fill speaker,
                     surface-mount 2-way cabinet.
  Notes: The smallest practical sealed enclosure for the 61FIND.
         At 183Hz -3dB the working band is approximately 200Hz–2kHz,
         appropriate for voice and mid-range programme reproduction in
         distributed audio and PA fill systems. The Qtc=1.18 produces
         a moderate bass shelf (+2dB near 248Hz) — warm and natural
         sounding for voice and music without sounding over-prominent.
         A 1L enclosure is approximately 100×100×100mm (external with
         panel walls) — easily integrated behind grilles in column arrays,
         ceiling tiles, or under furniture in installed audio. The HP
         at 80Hz protects the driver from sub-resonance frequencies that
         produce excursion without useful acoustic output.
ALIGNMENT B — COMPACT 2-WAY (2.5 L net internal)
  Box volume:        2.5 L (net internal)
  Qtc:               0.89
  System fc:         186 Hz
  System f-3dB:      ~155 Hz
  System HP:         80 Hz, 12–24 dB/oct (amplifier or DSP)
  Application:       Compact 2-way PA speaker, small-format stage monitor,
                     column speaker module, installed 2-way fill cabinet.
  Notes: The recommended general-purpose alignment. Qtc=0.89 provides
         a slight bass lift of approximately +1dB near fc — essentially
         flat from 200Hz upward with a gradual roll-off below 155Hz.
         The 2.5L enclosure at approximately 150×150×120mm external
         is a compact but practical format for a 6.5" two-way cabinet
         or column speaker module. This alignment is also compatible
         with a shallow back-can or in-ceiling format at 120–150mm
         internal depth. For distributed audio, a single driver in this
         enclosure at 16Ω matches standard 100V line transformer input
         impedances directly.
ALIGNMENT C — STANDARD 2-WAY (5.0 L net internal)
  Box volume:        5.0 L (net internal)
  Qtc:               0.77
  System fc:         161 Hz
  System f-3dB:      ~150 Hz
  System HP:         80 Hz, 12–24 dB/oct (amplifier or DSP)
  Application:       Standard compact 2-way PA or monitor cabinet,
                     small-format theatre fill, installed surface-mount
                     2-way speaker, 70V distributed audio wall cabinet.
  Notes: The largest practical alignment. At 150Hz -3dB and Qtc=0.77
         (near flat, slight +0.5dB shelf near fc) this alignment provides
         the flattest bass response and the lowest -3dB point achievable
         from the 61FIND in a practical enclosure. The 5L cabinet at
         approximately 180×180×180mm external is a standard small 2-way
         PA format. At this volume, the driver's working band of
         160Hz–2kHz provides full midrange coverage in a complete two-way
         product with a small-format compression driver or dome tweeter.
         A parallel pair of 61FIND (8Ω total) in this enclosure format
         with 300W AES combined delivers approximately 117dB at 1m from
         a compact 2-way cabinet — competitive with 8-inch single-driver
         designs at half the cabinet volume.
SYSTEM SUMMARY TABLE
  SEALED ALIGNMENTS:
  | Alignment       | Volume | Qtc  | fc     | f-3dB  | HP     |
  |-----------------|--------|------|--------|--------|--------|
  | A Ultra-compact | 1.0 L  | 1.18 | 248 Hz | ~183Hz | 80 Hz  |
  | B Compact 2-way | 2.5 L  | 0.89 | 186 Hz | ~155Hz | 80 Hz  |
  | C Standard      | 5.0 L  | 0.77 | 161 Hz | ~150Hz | 80 Hz  |

  Working band:     ~160–2500 Hz (enclosure-dependent lower limit)
  Crossover (HF):   1.0–2.5 kHz to tweeter or compression driver
  Sensitivity:      92 dB (1W/1m, 16Ω)
  SPL (150W, 16Ω): ~114 dB at 1m single driver
  SPL (pair, 8Ω):  ~117 dB at 1m parallel pair

  16Ω CONFIGURATIONS:
  | Config          | Impedance | Combined power | Max SPL |
  |-----------------|-----------|----------------|---------|
  | Single          | 16 Ω      | 150W AES       | ~114 dB |
  | Parallel pair   |  8 Ω      | 300W AES       | ~117 dB |
  | Parallel quad   |  4 Ω      | 600W AES       | ~120 dB |