SB Acoustics SB21SDC-C000-4 / Fabric Dome Tweeter

The SB21SDC-C000-4 is a 21 mm fabric dome tweeter from SB Acoustics, positioned as a balanced performer between compact size and excellent sound quality. It’s a great choice for high-quality 2-way designs, especially when you want a smooth, detailed top end without the harshness.

Features

• Large surround dome for increased acoustic output
• Dual balanced compression chamber for improved dynamics
• Copper cap for reduced voice coil inductance and minimum phase shift
• Saturation controlled motor system for low distortion
• Non-reflective rear chamber with optimized damping for improved dynamics
• Flow optimized vented pole piece for optimum coupling to rear chamber
• CCAW voice coil for low moving mass
• Long life silver lead wires
• Low resonance frequency

Specs

• • Nominal Impedance 4 Ω
  • DC resistance, Re 3.4 Ω
  • Voice coil inductance, Le 0.07 mH
  • Effective piston area, Sd 3.8 cm2
  • Voice coil diameter 19.1 mm
  • Voice coil height 1.8 mm
  • Air gap height 3 mm
  • Linear coil travel (p-p) 1.2 mm
  • Moving mass incl. air, Mms 0.22 g
  • Free air resonance, Fs 980 Hz
  • Sensitivity (2.83 V / 1 m) 88.5 dB
  • Mechanical Q-factor, Qms 6.45
  • Electrical Q-factor, Qes 1.50
  • Total Q-factor, Qts 1.22
  • Force factor, Bl 1.75 Tm
  • Rated power handling* 30 W
  • Magnetic flux density 1.24 T
  • Magnet weight 0.13 kg
  • Net weight 0.32 kg

  * IEC 268-5, high-pass Butterworth, 2600 Hz, 12 dB/oct.

✅ What Makes It Stand Out

• Exceptionally low Fs (~900 Hz) – allows for lower crossover points, even under 2 kHz.

• Integrated waveguide – improves efficiency and off-axis response.

• Smooth tonal balance – no shoutiness or harsh peaks.

• High sensitivity (91 dB) – can pair well with higher-efficiency woofers.

• Affordable with premium sound – high value in the DIY and OEM space.

🔧 Best Use Cases

• 2-way speakers with 5.25″–7″ woofers.

• Tower or bookshelf designs where wide dispersion and smoothness matter.

• Upgrades for midrange speaker builds looking to improve clarity.

🛠️ Crossover Tips

• Recommended crossover: 1.8–2.5 kHz (even lower possible with proper slopes)

• Pair it with:

  • SB17NRX2C35-4 (6.5″ woofer)

  • SB16PFC25-4 (5.5″ paper woofer)

  • Or similar drivers with a natural roll-off around 2–2.5 kHz

⚖️ Comparison: SB21SDC vs SB26STCN