E elec123 New Member Apr 18, 2005 #1 Hi, I need some help wit some calculations on filters.... For a woofer, simple L R circuit in series (taking the speaker as R). If the frequency transfer function: H=(V across R) / (V across L and R) So i get: H=IR/[I*(R+JwL)] Where Z=R+JwL R=8 Ohm L=2.5mH but am not given w so how do I work it out?!! Also, How do I find the break (3dB) frequency of the transfer function?? Any help would be great cheers!!
Hi, I need some help wit some calculations on filters.... For a woofer, simple L R circuit in series (taking the speaker as R). If the frequency transfer function: H=(V across R) / (V across L and R) So i get: H=IR/[I*(R+JwL)] Where Z=R+JwL R=8 Ohm L=2.5mH but am not given w so how do I work it out?!! Also, How do I find the break (3dB) frequency of the transfer function?? Any help would be great cheers!!
Roff Well-Known Member Apr 18, 2005 #3 You use the transfer function H=R/(R+j*w*L) to calculate the gain at any radian frequency w. w=2*pi*f, where f=frequency in Hz. The corner is at |H(3dB)| = |H|/2 (where |H| means 'the magnitude of H'), which occurs when w*L=R. So, let's say R=8, and you want the 3dB corner to be at 1kHz: solving for L, L=R/w, L=R/(2*pi*f) L=8/(2*3.14*1000) L=1.27mH
You use the transfer function H=R/(R+j*w*L) to calculate the gain at any radian frequency w. w=2*pi*f, where f=frequency in Hz. The corner is at |H(3dB)| = |H|/2 (where |H| means 'the magnitude of H'), which occurs when w*L=R. So, let's say R=8, and you want the 3dB corner to be at 1kHz: solving for L, L=R/w, L=R/(2*pi*f) L=8/(2*3.14*1000) L=1.27mH