Tangential room modes, calculating frequency, propagation etc.
 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

 Room Acoustics & Mods A place to discuss measuring and modifying room Acoustics for better sound

 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
 Thread Tools Search this Thread
 25th February 2011, 09:28 AM #1 AllenB   diyAudio Member   Join Date: Oct 2008 Tangential room modes, calculating frequency, propagation etc. By my understanding, the travelled path of a diamond between the side walls and the front/rear walls (mode 1,1,0?) will be longer than any single axial dimension and yet, the frequency of a tangential mode appears to be higher. Does this have something to do with the propagation pattern...that it can't just be seen as a diagonal mode? I'm using this info to set up subs so I'd like to understand where the nodes would be and at what frequency.
 25th February 2011, 09:50 AM #2 sreten   R.I.P.   Join Date: Nov 2003 Location: Brighton UK Hi, As I understand they are lower not higher, take a 3x4x5 room - 3 main modes are related to 3, 4, 5 lengths. 3 double modes (pythagoras) related to 5, root 34 and root 41. Lowest triple mode is all three axis, root 50, very near 7. So if the three main modes are 60, 45 and 36 Hz, Secondary modes are 45 (again, not good), 31 and 28 Hz. The triple lowest mode is 25.5Hz. rgds, sreten. These are of course the fundamentals of each mode, adding in the harmonics does considerably complicate the picture. Last edited by sreten; 25th February 2011 at 09:53 AM.
AllenB
diyAudio Member

Join Date: Oct 2008
I've taken a screen shot of an online calculator that suggests otherwise. I became suspicious of a formula I noticed on another site but many calculators seem to be giving the same result.

(The tangential modes are the middle height bars on the graph.)
Attached Images
 mode.GIF (33.3 KB, 61 views)

 25th February 2011, 11:07 AM #4 JohnPM   diyAudio Member   Join Date: Oct 2008 It is not the overall path length that matters, but the distance between the surfaces along the path (the arms of the diamond).
 25th February 2011, 11:21 AM #5 AllenB   diyAudio Member   Join Date: Oct 2008 Hmmm, now I recall something. Is this because a pressure node must be found at a boundary in a standing wave, which therefore can only happen when there are at least four wavelengths in the round trip? EDIT: this still doesn't match the chart? Last edited by AllenB; 25th February 2011 at 11:25 AM.
 25th February 2011, 11:28 AM #6 speaker dave   diyAudio Member     Join Date: Nov 2009 Location: The Mountain, Framingham Thats the way the math works out. The Tangential and oblique modes are higher. In the case of the tangential modes the path length isn't from corner to corner, a longer dimension. It is more like bouncing from mid wall point to mid wall point, a shorter overall path. Hence frequences are higher. The math has a component: square root sum of the inverse of the squares of the 3 dimensions, so going from first length mode to first length and width tangential mode is a higher number or necessarily a higher frequency. Longer dimensions may lower frequency but adding consideration of width or height will raise frequency. David S.
 25th February 2011, 11:42 AM #7 AllenB   diyAudio Member   Join Date: Oct 2008 OK, so if i have L=7.2m and W=3.6m and, F = c/2 * sqrt( 1/L^2 + 1/W^2 ) then F = 53.4 So one wavelength would be 6.44m, but one arm of the diamond is 4.02m. It isn't clear where the nodes would end up.
 25th February 2011, 12:11 PM #8 speaker dave   diyAudio Member     Join Date: Nov 2009 Location: The Mountain, Framingham Yes, your math is correct. It isn't clear to me why the apparent "path" gets shorter when width is added. In the limit as the room gets narrower the tangential mode is the same as length. Boncing around the room mid points is the same path as the longest diagonal. Huh?
 25th February 2011, 01:32 PM #9 sreten   R.I.P.   Join Date: Nov 2003 Location: Brighton UK Hmmm...... So if its centre to centre distances I'm missing a 1/2 scale factor. The double and triple modes would be double what I said ..... rgds, sreten.
 25th February 2011, 01:48 PM #10 AllenB   diyAudio Member   Join Date: Oct 2008 I found this look at figure 5 In my example, the wavelength of 6.44m doesn't fit either the room diagonal of 8.04m or one side of the diamond at 4.02m

 Thread Tools Search this Thread Search this Thread: Advanced Search

 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 just a guy Full Range 14 26th August 2009 12:57 PM Yuihb Room Acoustics & Mods 22 18th March 2004 04:29 PM dtkky Multi-Way 0 3rd February 2004 10:01 AM

 New To Site? Need Help?

All times are GMT. The time now is 01:50 AM.

 Home - Contact Us - Advertise - Rules - diyAudio Store - Sponsors - Privacy Statement - Terms of Service - Top - Opt-out policy

Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 14.29%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio
Wiki