Altec 421-8H

15" · 8 Ω · 150 W · 99.8 dB · datasheet ↗

Thiele-Small parameters

Nominal size	15"
Impedance	8 Ω
Fs	31.5 Hz
Qts	0.245
Qes	0.27
Qms	2.6
Vas	362.5 L
Sd	825.8 cm²
Xmax	1.3 mm
Re	5.5 Ω
Bl	16.5 T·m
Mms	67.3 g
Pe	150 W
Sensitivity	99.8 dB

Alignment hint

EBP	117 · ported
Sealed Vb (Qtc ≈ 0.71)	≈ 49.5 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
Cyrille Audio BM38ND76P	33 +1.5	0.236 -0.01	372 +9.5	1.8 +0.5	100.9 +1.1	close		+
Cyrille Audio BM38ND76P-2	33 +1.5	0.236 -0.01	372 +9.5	1.9 +0.6	100.9 +1.1	close		+
Eminence KAPPA 15C	31 -0.5	0.25 +0.01	329.9 -32.6	2.4 +1.1	98.1 -1.7	close	4 Ω vs 8 Ω: amp load changes	+
Altec 918-8A	32.6 +1.1	0.209 -0.04	372.7 +10.2	1.3 =	101.4 +1.6	close	35 W vs 150 W: lower power handling	+
Supravox 400 GMF PRO	32 +0.5	0.263 +0.02	370 +7.5	4.8 +3.5	99.4 -0.4	close		+
Altec 605 A	30.3 -1.2	0.248 =	405.8 +43.3	2.7 +1.4	97.5 -2.3	close	16 Ω vs 8 Ω: amp load changes · 35 W vs 150 W: lower power handling	+
Great Plains Audio 604-8H III	33.7 +2.2	0.254 +0.01	329.9 -32.6	3.8 +2.5	99.3 -0.5	close	100 W vs 150 W: lower power handling	+
Great Plains Audio 604-H III	33.7 +2.2	0.254 +0.01	329.9 -32.6	3.8 +2.5	99.3 -0.5	close	100 W vs 150 W: lower power handling	+
Focal AUDIOM 15	32.5 +1	0.236 -0.01	379.7 +17.2	6 +4.7	100.4 +0.6	close		+
Davis 39RPA15	31 -0.5	0.27 +0.03	340 -22.5	4 +2.7	99.3 -0.5	close		+

Compare the closest 3 against the 421-8H →

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.