SICA 21 S 4 PL

21.5" · 4 Ω · 1000 W · 100 dB · datasheet ↗

Thiele-Small parameters

Nominal size	21.5"
Impedance	4 Ω
Fs	38.7 Hz
Qts	0.431
Qes	0.48
Qms	4.19
Vas	229.8 L
Sd	1661.9 cm²
Xmax	6.4 mm
Re	3.51 Ω
Bl	22.5 T·m
Mms	284.9 g
Pe	1000 W
Sensitivity	100 dB

Alignment hint

EBP	81 · flexible
Sealed Vb (Qtc ≈ 0.71)	≈ 135.8 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
P.Audio SD-21	41 +2.3	0.412 -0.02	200.6 -29.2	5.7 -0.7	98.8 -1.2	close	8 Ω vs 4 Ω: amp load changes · Xmax 5.7 mm < 6.4 mm: lower excursion-limited SPL	+
B&C 21 SW 115	32.5 -6.2	0.404 -0.03	268.7 +38.9	9.9 +3.5	99.2 -0.8	usable		+
Beyma 21L50	33 -5.7	0.434 =	300 +70.2	7.9 +1.5	97 -3	usable	8 Ω vs 4 Ω: amp load changes	+
Beyma 21SW1600ND	33 -5.7	0.382 -0.05	268 +38.2	8.9 +2.5	97.6 -2.4	usable	8 Ω vs 4 Ω: amp load changes	+
P.Audio IMF HP-21W	36.4 -2.3	0.463 +0.03	384.4 +154.6	6.6 +0.2	99.1 -0.9	usable	8 Ω vs 4 Ω: amp load changes	+
B&C 21 SW 115 v2015	33 -5.7	0.353 -0.08	278 +48.2	9.3 +2.9	100.6 +0.6	usable		+
RCF LF 21N551	35 -3.7	0.331 -0.1	200 -29.8	7.7 +1.3	97.7 -2.3	usable	8 Ω vs 4 Ω: amp load changes	+
LaVoce SAF214.50	30 -8.7	0.435 =	267 +37.2	11.6 +5.2	95.6 -4.4	usable	8 Ω vs 4 Ω: amp load changes	+
Ciare NDC 21-5	32.2 -6.5	0.344 -0.09	270.8 +41	8.8 +2.4	97.2 -2.8	usable	8 Ω vs 4 Ω: amp load changes	+
B&C 21 SW 152 v2013	32 -6.7	0.297 -0.13	200 -29.8	7.5 +1.1	99.5 -0.5	usable		+

Compare the closest 3 against the 21 S 4 PL →

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.