User Name Stay logged in? Password
 Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read Search

 Parts Where to get, and how to make the best bits. PCB's, caps, transformers, etc.

 Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
 16th April 2003, 08:16 PM #1 JDeV   diyAudio Member   Join Date: Oct 2002 Location: Hemel Hempstead About dB's I am bussy with a corespondence course in electronics and got the following question in an assignment. It sound a bit wrong to me (the uninformed one) and want to know if it make sense and what would the answer be? I don't grasp the dB thing yet, so please excuse silly questions (Maybe somebody can give me a "dB for Dummy's" explanation. ) Q: Determine the dB level from a given sound power of 15dB, and a reference sound power of 20dB. (Don't you measure sound power in Watts?) Thanx for all help.
 16th April 2003, 08:32 PM #2 SY   On Hiatus     Join Date: Oct 2002 Location: Chicagoland I think the text writer needs the "dB For Dummies" course more than you do. Or at least a writing course. Sound power is given in watts OR in dB referenced to some standard power level. Here's the entire course: For power ratios, dB = 10 log (P1/P2) Since power = V^2/R, and log (x^y) = y log x, then for a voltage ratio, dB = 20 log (V1/V2) That's all there is, there ain't no more. If the dB quoted in the question are both referenced to the same standard power level, the answer is -5 dB. __________________ "You tell me whar a man gits his corn pone, en I'll tell you what his 'pinions is."
 16th April 2003, 08:39 PM #3 dhaen   diyAudio Moderator Emeritus     Join Date: Jun 2002 Location: U.K. dB's are a logarithmic scale. They are not absolute, and can be referenced to any point. In this case they have told you the reference point (20dB). The magic formulae I keep in my head are: 10*Log (P1/P2) (for power) and 20*Log (V1/V2) for voltage (and other non squared values) In other words, the dB figuer is describing the ratio between the 2 voltages, powers, or whatever... You'll need to do some substitution... Cheers,

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is Off Forum Rules
 Forum Jump User Control Panel Private Messages Subscriptions Who's Online Search Forums Forums Home Site     Site Announcements     Forum Problems Amplifiers     Solid State     Pass Labs     Tubes / Valves     Chip Amps     Class D     Power Supplies     Headphone Systems Source & Line     Analogue Source     Analog Line Level     Digital Source     Digital Line Level     PC Based Loudspeakers     Multi-Way     Full Range     Subwoofers     Planars & Exotics Live Sound     PA Systems     Instruments and Amps Design & Build     Parts     Equipment & Tools     Construction Tips     Software Tools General Interest     Car Audio     diyAudio.com Articles     Music     Everything Else Member Areas     Introductions     The Lounge     Clubs & Events     In Memoriam The Moving Image Commercial Sector     Swap Meet     Group Buys     The diyAudio Store     Vendor Forums         Vendor's Bazaar         Sonic Craft         Apex Jr         Audio Sector         Acoustic Fun         Chipamp         DIY HiFi Supply         Elekit         Elektor         Mains Cables R Us         Parts Connexion         Planet 10 hifi         Quanghao Audio Design         Siliconray Online Electronics Store         Tubelab     Manufacturers         AKSA         Audio Poutine         Musicaltech         Aussie Amplifiers         CSS         exaDevices         Feastrex         GedLee         Head 'n' HiFi - Walter         Heatsink USA         miniDSP         SITO Audio         Twin Audio         Twisted Pear         Wild Burro Audio

 New To Site? Need Help?

All times are GMT. The time now is 11:58 PM.