It isn't that simple. It gets harder to keep up as frequency increases. Your number is true for a 20 Hz pulse. Not a sine wave or worse yet a 20 Hz square wave containing all odd order harmonics up to the crossover point of your sub filter. If you are crossing over at 80 Hz or higher the system will sound muddy and slow unless you calculate using higher frequency. The acoustic output of your speakers is real power, after efficiency loss. The relationship between the demand of your audio source material and the acoustic output of your speakers is far more complex than the RC time constant of the caps in the supply. The demand on the supply can only be calculated after you can account for the loss in the system. This is the hard part of matching a sub to the main system. Then to make it sound good, you need to adjust for energy that feeds back into the acoustic experience from room resonance. Not simple. -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Hfjord Sent: Thursday, September 20, 2007 11:51 AM To: [log in to unmask] Subject: [TN] SV: [TN] NTC:subwoofer Thanks Guy, According to your information: RIAA curve @ 20 Hz is 7,500 us My power supply Ri= 0.1 Ohm Backup caps on supply rails is 100,000 F Tau = R (Ohm) x C (F) > 0.1 x 0.1 = 0.01 s which is 10,000 us Not too bad! Near RIAA spec. Fine! I'm satisfied. Thanks again. Didn't realize it was that easy. /Inge -----Ursprungligt meddelande----- Från: Guy Ramsey [mailto:[log in to unmask]] Skickat: den 20 september 2007 17:00 Till: 'Hfjord' Ämne: RE: [TN] NTC:subwoofer On the output? You mean on the power supply rails? You can calculate how long it will take to discharge the caps if you know the output impedance of the amp and the speaker load. These act in series. With the RC time constant. http://en.wikipedia.org/wiki/RC_time_constant Compare the output impedance of the power supply to the audio amp. How long it will take to charge the caps. Then you need to decide what kind of sonic compromise you can tolerate base on the expected duty cycle imposed on the system by the music or sound track content. -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Hfjord Sent: Wednesday, September 19, 2007 4:57 PM To: [log in to unmask] Subject: [TN] NTC:subwoofer Audio techies, I've built a subwoofer with a 15" 400 Watt loadspeaker (4 Ohms). Bought a 200 Watt low frequency 12 V amplifier. For that one, I built a 12 VDC power supply with 15 A toroid, regulator, OP amplifier and a backup consisting of totally 100,000 uF on the output. What is your experience? Will these caps be enough to take the short power tops in Space War or the enormous sound effects in Matrix or Jurassic Park? Any thumb rules or maths? /Inge --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 15.0 To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 ----------------------------------------------------- --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 15.0 To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 ----------------------------------------------------- --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 15.0 To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 -----------------------------------------------------