Equation Icon  fcrit = -1-acrit aeq (382 ) 2πℓ aeq a0 ( )− 1∕2 ( )1∕2( ) −1∕4 = 5.6 × 10− 5 Hz ---ℓ---- ------H0------- 1-+-zeq . (383 ) 0.1 mm 72 km ∕s ⋅ Mpc 3200