RCF LF21N551

21" · 8 Ω · 2000 W · 97 dB · datasheet ↗

Thiele-Small parameters

Nominal size	21"
Impedance	8 Ω
Fs	35 Hz
Qts	0.33
Qes	0.35
Qms	6.2
Vas	200 L
Sd	1700 cm²
Xmax	15 mm
Re	5.2 Ω
Bl	39 T·m
Mms	434 g
Pe	2000 W
Sensitivity	97 dB

Alignment hint

EBP	100 · flexible
Sealed Vb (Qtc ≈ 0.71)	≈ 55.7 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
Lavoce SAN215.30	35 =	0.33 =	200 =	14.9 -0.1	95.7 -1.3	close	Xmax 14.9 mm < 15 mm: lower excursion-limited SPL	+
B&C 21SW152	32 -3	0.36 +0.03	200 =	15 =	96 -1	close		+
B&C 21SW152	32 -3	0.3 -0.03	200 =	15 =	96 -1	close	4 Ω vs 8 Ω: amp load changes	+
Fane Colossus Prime 21XS	35 =	0.339 +0.01	266 +66	14 -1	97.5 +0.5	close	1500 W vs 2000 W: lower power handling · Xmax 14 mm < 15 mm: lower excursion-limited SPL	+
18 Sound 21NLW4100	34 -1	0.4 +0.07	219 +19	15.2 +0.2	97 =	close	4 Ω vs 8 Ω: amp load changes · 1500 W vs 2000 W: lower power handling	+
B&C 21DS115	34 -1	0.27 -0.06	204 +4	16.5 +1.5	99 +2	close		+
Fane Colossus Prime 21NDXL	33 -2	0.36 +0.03	241 +41	14 -1	98 +1	close	1500 W vs 2000 W: lower power handling · Xmax 14 mm < 15 mm: lower excursion-limited SPL	+
18 Sound 21NLW9601	37 +2	0.29 -0.04	175 -25	14 -1	98 +1	close	Xmax 14 mm < 15 mm: lower excursion-limited SPL	+
Eminence NSW6021-6	29 -6	0.31 -0.02	224.58 +24.58	21 +6	97 =	close	6 Ω vs 8 Ω: amp load changes	+
18 Sound 21NLW9001	32 -3	0.31 -0.02	244 +44	14 -1	98 +1	close	Xmax 14 mm < 15 mm: lower excursion-limited SPL	+

Compare the closest 3 against the LF21N551 →

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.