Help with SPL calculation
 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

 Everything Else Anything related to audio / video / electronics etc) BUT remember- we have many new forums where your thread may now fit! .... Parts, Equipment & Tools, Construction Tips, Software Tools......

 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
 2nd August 2019, 08:42 PM #1 Conrad Hoffman   diyAudio Member   Join Date: Mar 2007 Location: Canandaigua, NY USA Help with SPL calculation From another thread, you can calculate SPL from driver diameter and peak excursion. (I also divide by 4, 2, 1 and .5 to account for radiation space due to baffle and wavelength.): p=Sd*Xmax*f^2*pi*rho0/(r*sqrt(2)) where p=sound pressure in Pa, Sd=eqv. piston area in m², Xmax=max peak excursion in m, f=frequency in Hz, rho0=1.2kg/m3, r=speaker-to-mic distance in m. The sound pressure p can be converted to sound pressure level: SPL=20*log10(p/0,00002) dB. Note that 0.00002 Pa = 0.0002 dynes/cm² I had access to a laser vibrometer and tested the equation with an actual driver. The results were within 1 dB, which is easily within the error of my meter and setup. What I don't understand is that the driver excursion is peak, one half of the peak to peak value, but the 0 dB reference is an RMS number, as is the SPL. How can unit be mixed like that? Can anybody explain why this equation works? Or should the driver excursion really be RMS? __________________ I may be barking up the wrong tree, but at least I'm barking!
 3rd August 2019, 11:55 PM #2 PRR   diyAudio Member     Join Date: Jun 2003 Location: Maine USA Too sticky here tonight to think (even bark), but asking....... What does the "sqrt(2)" in the bottom of the fraction do? Obviously "x/1.414" converts a Peak to an RMS. But I have not gone through the full formula to grok what it does.
 4th August 2019, 12:28 AM #3 rayma   diyAudio Member   Join Date: Apr 2011 The physical units are the same whether peak or rms, so either could appear in a formula in that sense. In this case, the (1/sqrt 2) factor does convert the Xmax peak value to rms in the SPL formula. Last edited by rayma; 4th August 2019 at 12:39 AM.
 4th August 2019, 04:00 AM #4 Conrad Hoffman   diyAudio Member   Join Date: Mar 2007 Location: Canandaigua, NY USA Ah, OK, simple enough. For some reason I though it was doing something else- thanks! __________________ I may be barking up the wrong tree, but at least I'm barking!

 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     Room Acoustics & Mods     Music     diyAudio.com Articles     Car Audio     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         Holton Precision Audio         CSS         exaDevices         Feastrex         GedLee         Head 'n' HiFi - Walter         Heatsink USA         miniDSP         SITO Audio         Twin Audio         Twisted Pear         Wild Burro Audio

 Similar Threads Thread Thread Starter Forum Replies Last Post kees52 Software Tools 4 7th February 2019 07:14 PM bigcatdairy Multi-Way 1 15th August 2011 05:14 PM bk7794 Multi-Way 7 6th July 2010 06:29 AM Ignite Multi-Way 17 9th April 2007 08:38 AM aguantesoda Solid State 5 31st December 2006 09:02 PM

 New To Site? Need Help?

All times are GMT. The time now is 06:36 PM.