Ciare NDK 21-4

21.5" · 4 Ω · 1500 W · 97.4 dB · datasheet ↗

Thiele-Small parameters

Nominal size	21.5"
Impedance	4 Ω
Fs	28.5 Hz
Qts	0.322
Qes	0.35
Qms	4
Vas	232.4 L
Sd	1662 cm²
Xmax	8 mm
Re	3.5 Ω
Bl	30.5 T·m
Mms	519.6 g
Pe	1500 W
Sensitivity	97.4 dB

Alignment hint

EBP	81 · flexible
Sealed Vb (Qtc ≈ 0.71)	≈ 60.8 L

EBP 50-100: works in either a sealed or ported alignment.

Rules of thumb from T/S parameters only. Verify against a real simulation before cutting wood.

Substitute candidates

Driver	Fs (Hz)	Qts	Vas (L)	Xmax (mm)	Sens (dB)	Fit	Notes	Compare
Eminence NSW6021-6	29 +0.5	0.304 -0.02	224.6 -7.8	10.3 +2.3	97.7 +0.3	close		+
Dayton Audio PSS545HE-4 VORTEX	28.8 +0.3	0.27 -0.05	212.1 -20.3	8.6 +0.6	97.8 +0.4	close		+
Ciare NDC 21-5	32.2 +3.7	0.344 +0.02	270.8 +38.4	8.8 +0.8	97.2 -0.2	close	8 Ω vs 4 Ω: amp load changes	+
RCF LF 21N551	35 +6.5	0.331 +0.01	200 -32.4	7.7 -0.3	97.7 +0.3	close	8 Ω vs 4 Ω: amp load changes · Xmax 7.7 mm < 8 mm: lower excursion-limited SPL	+
18 Sound 21NLW9000	29 +0.5	0.347 +0.02	304 +71.6	10.7 +2.7	96.4 -1	close	8 Ω vs 4 Ω: amp load changes	+
RCF 21LNW9000	29 +0.5	0.347 +0.02	304 +71.6	10.7 +2.7	96.4 -1	close	8 Ω vs 4 Ω: amp load changes	+
B&C 21 SW 152	32 +3.5	0.297 -0.03	198.2 -34.2	7.5 -0.5	98.9 +1.5	usable	Xmax 7.5 mm < 8 mm: lower excursion-limited SPL	+
B&C 21 SW 152 v2013	32 +3.5	0.297 -0.03	200 -32.4	7.5 -0.5	99.5 +2.1	usable	Xmax 7.5 mm < 8 mm: lower excursion-limited SPL	+
B&C 21 SW 150	29 +0.5	0.261 -0.06	254 +21.6	7.5 -0.5	99.4 +2	usable	Xmax 7.5 mm < 8 mm: lower excursion-limited SPL	+
SB Audience NERO-21SW1100D	32 +3.5	0.339 +0.02	312.6 +80.2	8.1 +0.1	98.6 +1.2	usable	8 Ω vs 4 Ω: amp load changes · 1100 W vs 1500 W: lower power handling	+

Compare the closest 3 against the NDK 21-4 →

Ranked on parameter similarity only (Qts, Fs, Vas, Xmax, sensitivity). Same nominal size required. A hint, not a simulation, model the swap before cutting or buying.

Used in enclosures (0)

No enclosure in the catalog uses this driver yet.