P.Audio SD-21

21.5" · 8 Ω · 1000 W · 98.8 dB · datasheet ↗

Thiele-Small parameters

Nominal size	21.5"
Impedance	8 Ω
Fs	41 Hz
Qts	0.412
Qes	0.43
Qms	9.89
Vas	200.6 L
Sd	1730 cm²
Xmax	5.7 mm
Re	5.3 Ω
Bl	31.6 T·m
Mms	315.1 g
Pe	1000 W
Sensitivity	98.8 dB

Alignment hint

EBP	95 · flexible
Sealed Vb (Qtc ≈ 0.71)	≈ 103.1 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
SICA 21 S 4 PL	38.7 -2.3	0.431 +0.02	229.8 +29.2	6.4 +0.7	100 +1.2	close	4 Ω vs 8 Ω: amp load changes	+
RCF LF 21N551	35 -6	0.331 -0.08	200 -0.6	7.7 +2	97.7 -1.1	usable		+
B&C 21 SW 115	32.5 -8.5	0.404 -0.01	268.7 +68.1	9.9 +4.2	99.2 +0.4	usable	4 Ω vs 8 Ω: amp load changes	+
Beyma 21SW1600ND	33 -8	0.382 -0.03	268 +67.4	8.9 +3.2	97.6 -1.2	usable		+
B&C 21 SW 152	32 -9	0.297 -0.11	198.2 -2.4	7.5 +1.8	98.9 +0.1	usable	4 Ω vs 8 Ω: amp load changes	+
B&C 21 SW 152 v2013	32 -9	0.297 -0.11	200 -0.6	7.5 +1.8	99.5 +0.7	usable	4 Ω vs 8 Ω: amp load changes	+
Beyma 21L50	33 -8	0.434 +0.02	300 +99.4	7.9 +2.2	97 -1.8	usable		+
P.Audio IMF HP-21W	36.4 -4.6	0.463 +0.05	384.4 +183.8	6.6 +0.9	99.1 +0.3	usable		+
B&C 21 SW 115 v2015	33 -8	0.353 -0.06	278 +77.4	9.3 +3.6	100.6 +1.8	usable	4 Ω vs 8 Ω: amp load changes	+
Ciare NDC 21-5	32.2 -8.8	0.344 -0.07	270.8 +70.2	8.8 +3.1	97.2 -1.6	usable		+

Compare the closest 3 against the SD-21 →

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.