formula for Q of Helmholtz resonator
 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
 14th September 2012, 02:18 AM #1 PeteMcK diyAudio Member   Join Date: Feb 2002 Location: Western Sydney formula for Q of Helmholtz resonator Can anyone point me to a formula for the Q of a Helmholtz resonator? TIA __________________ Impedance varies with frequency, use impedance plots of your drivers and make crossover calculations using the actual impedance of the driver at the crossover frequency
 14th September 2012, 02:48 AM #2 PeteMcK diyAudio Member   Join Date: Feb 2002 Location: Western Sydney Is it the second formula at (15) p5 in this paper?: http://www.itwm.fraunhofer.de/filead.../bericht10.pdf __________________ Impedance varies with frequency, use impedance plots of your drivers and make crossover calculations using the actual impedance of the driver at the crossover frequency
 14th September 2012, 02:52 AM #3 PeteMcK diyAudio Member   Join Date: Feb 2002 Location: Western Sydney found it halfway down this page: Acoustics/Flow-induced Oscillations of a Helmholtz Resonator - Wikibooks, open books for an open world __________________ Impedance varies with frequency, use impedance plots of your drivers and make crossover calculations using the actual impedance of the driver at the crossover frequency
 14th September 2012, 04:24 AM #4 PeteMcK diyAudio Member   Join Date: Feb 2002 Location: Western Sydney If the correct formula is Q=2pi SQRT(Vb * ((port length/port area) cubed)) then Q is proportional to port length and inversely proportional to the port cross section area, right? __________________ Impedance varies with frequency, use impedance plots of your drivers and make crossover calculations using the actual impedance of the driver at the crossover frequency
 14th September 2012, 06:03 AM #5 PeteMcK diyAudio Member   Join Date: Feb 2002 Location: Western Sydney what I'm thinking is that different port length/cross section combinations (for the same freq & box size) will give different Qs, thus having different effects on the bandwidth & level of bass freqs, yet changing the ratios of port length/cross section while keeping everything else constant in box sim programs doesn't have any effect on the freq response shown, what am I missing? __________________ Impedance varies with frequency, use impedance plots of your drivers and make crossover calculations using the actual impedance of the driver at the crossover frequency
 14th September 2012, 06:27 AM #6 picowallspeaker   diyAudio Member     Join Date: Apr 2007 I was to say 'group delay' but there are no speakers involved . Though a certain delay takes place in the process of resonance
 14th September 2012, 11:42 AM #7 sreten   diyAudio Member RIP   Join Date: Nov 2003 Location: Brighton UK Hi, The Q of a port treated as a hemholtz resonator has very little to do with the Q of a vented boxes bass alignment, as its a coupled resonating system, not one system. Basically the port "q" simply should be high enough not to matter much. The main damping in the system comes from the driver. Damped ports (e.g. drinking straws) are hard to model AFAIK, best done empirically. rgds, sreten.
 14th September 2012, 08:37 PM #8 PeteMcK diyAudio Member   Join Date: Feb 2002 Location: Western Sydney Re:'The Q of a port treated as a hemholtz resonator has very little to do with the Q of a vented boxes bass alignment" - so i guess I'm trying to quantify that 'very little' re:' the port "q" simply should be high enough' - don't you mean low enough? (I guess that could be a preference thing though, this is part of what I'm trying to explore), and again, it would be good to quantify 'enough'. (Just to make it clear, I'm not talking about the Q of a port as a resonating pipe, but the Q of the whole box/port combo) Perhaps I need to wade though those Thele/Small papers again, wish my maths was up to it... __________________ Impedance varies with frequency, use impedance plots of your drivers and make crossover calculations using the actual impedance of the driver at the crossover frequency Last edited by PeteMcK; 14th September 2012 at 08:44 PM.
 14th September 2012, 08:56 PM #9 PeteMcK diyAudio Member   Join Date: Feb 2002 Location: Western Sydney let me put up a hypothesis to be shot down (Subjective language warning): Ignoring the effects of port turbulence & reflections coming through the port, a short port giving a lower helmholtz resonance Q will sound more natural than a long port that results in a higher Q ...??? __________________ Impedance varies with frequency, use impedance plots of your drivers and make crossover calculations using the actual impedance of the driver at the crossover frequency
 18th September 2012, 02:12 PM #10 sreten   diyAudio Member RIP   Join Date: Nov 2003 Location: Brighton UK Hi, Again your equation only relates to a port connected to a closed box with no driver in it and has nothing to do with the Q of a vented boxes bass alignment. I haven't looked at it in detail as it does not matter. For a box port to work well its Q has to be high enough so it doesn't matter much, most of the damping and losses come from the driver. If you reduce the port Q, by adding port damping of some form most box sims simply can't handle it, and you'll get a response somewhere between sealed and "normal" vented. Aperoidic damping is a special case most sims can't handle either, where no phase inversion takes place in the port and it can reduce the Q of a sealed alignment, (by leaking out of phase bass that cancels with driver output). As you have noted, in Sims changing the port size keeping the same frequency has no effect on the small signal response / bass alignment. That is because the Sims assume the port is an undamped resonator, i.e. infinite Q, in practice port Q just needs to be high enough for the Sims to be accurate enough for the bass modelling they present. Port sizes are chosen based on the smallest total volume that works well with the large signal parameters of the driver, often port blocking is arranged to coincide with the driver reaching its excursion limits, compensating for increasing driver Q. rgds, sreten. Last edited by sreten; 18th September 2012 at 02:19 PM.

 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

 Similar Threads Thread Thread Starter Forum Replies Last Post hyperblaster89 Everything Else 22 10th December 2013 05:30 AM chairforce Multi-Way 6 26th June 2010 04:31 AM RyanW Multi-Way 17 2nd October 2007 11:08 PM TroelsM Multi-Way 5 29th September 2005 02:23 PM tade Subwoofers 6 17th August 2005 07:24 AM

 New To Site? Need Help?

All times are GMT. The time now is 04:33 PM.