B&C 21 DS 115 - 4

21.5" · 4 Ω · 1700 W · 103.3 dB · datasheet ↗

Thiele-Small parameters

Nominal size	21.5"
Impedance	4 Ω
Fs	30 Hz
Qts	0.196
Qes	0.2
Qms	11
Vas	274 L
Sd	1680 cm²
Xmax	6.9 mm
Re	2.2 Ω
Bl	29 T·m
Mms	406.4 g
Pe	1700 W
Sensitivity	103.3 dB

Alignment hint

EBP	150 · ported
Sealed Vb (Qtc ≈ 0.71)	≈ 22.8 L

EBP > 100: favours a ported (bass-reflex) 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
B&C 21 DS 115	30 =	0.234 +0.04	269 -5	7.6 +0.7	98.7 -4.6	usable	8 Ω vs 4 Ω: amp load changes	+
LaVoce SAN214.50LD vp	30 =	0.223 +0.03	250 -24	7.2 +0.3	98.4 -4.9	usable	8 Ω vs 4 Ω: amp load changes	+
18 Sound 21NLW9000C	29 -1	0.248 +0.05	257 -17	8.1 +1.2	100.5 -2.8	usable		+
B&C 21 SW 150	29 -1	0.261 +0.07	254 -20	7.5 +0.6	99.4 -3.9	usable		+
PD PDN 2151	31.4 +1.4	0.276 +0.08	303.4 +29.4	6.7 -0.2	99 -4.3	usable	8 Ω vs 4 Ω: amp load changes · 1000 W vs 1700 W: lower power handling · Xmax 6.7 mm < 6.9 mm: lower excursion-limited SPL	+
Precision Devices PDN 2151	31.4 +1.4	0.276 +0.08	303.4 +29.4	6.7 -0.2	99 -4.3	usable	8 Ω vs 4 Ω: amp load changes · 1000 W vs 1700 W: lower power handling · Xmax 6.7 mm < 6.9 mm: lower excursion-limited SPL	+
18 Sound 21LW400	28 -2	0.234 +0.04	385 +111	9.3 +2.4	99.5 -3.8	usable	8 Ω vs 4 Ω: amp load changes	+
RCF LF 21N451	30 =	0.239 +0.04	440 +166	8.9 +2	100.4 -2.9	usable	8 Ω vs 4 Ω: amp load changes	+
Beyma 21QLEX1600/Fe	30 =	0.281 +0.09	309 +35	8.4 +1.5	98.1 -5.2	usable	8 Ω vs 4 Ω: amp load changes	+
RCF LF 21N451 v2017	30 =	0.259 +0.06	375 +101	8.6 +1.7	99.3 -4	usable	8 Ω vs 4 Ω: amp load changes	+

Compare the closest 3 against the 21 DS 115 - 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.