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 16th October 2007, 07:46 PM #1 diyAudio Member   Join Date: Jul 2004 Location: MTL please help me determine PONR for IB HT setup need to calculate the point of no returns for how many 18" i will be using in my HT setup ( could be 15" ..not 100% on that yet ) they will occupy most of the front wall in a "planar wave" type of array ( distributed equally over front wall area ) the room will be of 25' depth by 20' width by 8-9' height ( rear half is 8' for seats leveling ) How can we determine how many subs will yield the best \$\$\$ VS performance for this particular setup ? ( please don't suggest other loudspeakers config, my choice is already made on to this one ) rear wave will be evacuated to garage room ( 26' by 26' ) i was planning for 16 individual 18" drivers could also work with more 15" like the Dayton IB over at parts express if \$\$\$ and result are worth it so would like a way to calculate response vs number of drivers and possibility! thanks for your time!
 16th October 2007, 08:13 PM #2 diyAudio Member   Join Date: Jul 2004 Location: MTL also .. the number of drivers will have to be multiples of 4 for the planar wave system to work.
diyAudio Member

Join Date: Mar 2005
Location: Jacobsmountain
Quote:
 ...How can we determine how many subs will yield the best \$\$\$ VS performance for this particular setup ?...

Why not do most of the investigation works by your self? Make your choices and tell us to see if we can agree upon your driver/amp power demands/opinions of what is good performance for a HT set-up.
See 1(1) or go to: http://www.myhometheater.homestead.c...alculator.html

Added a 4 x driver DBA polar simulation for a room of 2.4 x 4 x 6 m where XO frequencies (LP= 12 dB/octave) is marked (black line) ensuring an acute (frontal, horizontal) wide enough initial planar (surge) wave coincident to both ears of any listener placed at the rear half of the room without any lateral velocity gradient occurring than caused by the main speakers (even at higher SPL when distortion often pops out from the subs randomly from the same but differently placed drivers) : 2(2).

b

1(2)
Attached Images
 115 db.gif (30.1 KB, 180 views)

diyAudio Member

Join Date: Mar 2005
Location: Jacobsmountain
2(2)
Attached Images
 dba-init-polar.gif (96.6 KB, 186 views)

 17th October 2007, 03:26 AM #5 diyAudio Member   Join Date: Jul 2004 Location: MTL woa! nice answer !!!! 2 things come out of this mainly for me : 1- could you please explain all of this, as this is seriously more advanced than my very very tiny limited knowledge now!! 2- i do not know exactly what i want/need as a result of this system, what i need right now is formulas or ratios ...stuff like that , that would permit me to determine and play with different values to see what can be achieved and what would be the best possible compromise to choose on the drivers and number of drivers on this system ( sub bass system ) this system will have to match very efficient floor to ceiling line arrays ( again ..should be very efficient as they will operate in nearfield and site not very far from the listening positions ) thanks again for your time!
diyAudio Member

Join Date: Jun 2003
Location: Chamblee, Ga.

Quote:
 Originally posted by JinMTVT they will occupy most of the front wall in a "planar wave" type of array ( distributed equally over front wall area ) How can we determine how many subs will yield the best \$\$\$ VS performance for this particular setup ?
Assuming an 80 Hz 4th order XO, then you ideally want the drivers < 1/4 WL apart at 160 Hz = ~13560"/4/160 = ~21.1875" c-t-c driver and to wall spacing. That's a lot of drivers and if 18"ers are used the wall will look like a giant's wine rack.

In reality though, unless you can damp the modes at the other end of the room this close spacing/large number of drivers will mostly be a waste of time/\$\$\$/effort IMO compared to distributing around the room. Sure will be impressive though, like a large Bessel Array for cinema apps, but with a large, long bass-horn's acoustic efficiency, so I imagine the cones will barely move at 'voice of God' LFs.
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 17th October 2007, 09:08 PM #7 diyAudio Member   Join Date: Jul 2004 Location: MTL impressive is what i am after ...
 17th October 2007, 11:07 PM #8 diyAudio Member   Join Date: Jul 2004 Location: MTL why do we need to space the drivers that close? why the 1/4 WL formula ? i would like to follow the " DBA" theory ( double bass array ) but minues the double ( rear reversed wave ) what would happen if i'd have only 16 18" drivers on the front wall of 20' by 9' high ? they would be positionned according to the "mirror" image effect ...
 18th October 2007, 01:43 AM #9 diyAudio Member     Join Date: Jun 2003 Location: Chamblee, Ga. Because you said you wanted "a "planar wave" type of array ( distributed equally over front wall area )" and to do this requires enough polar overlap between drivers to cover the BW. If you XO lower and/or use a steeper slope, then you can use a wider spacing/fewer drivers. Or you can do it anyway and accept the collapse of the planar wavefront at some lower frequency. Never having built a large one I don't have a clue at what point it might be obviously audible depending on seating location. __________________ Loud is Beautiful if it's Clean! As always though, the usual disclaimers apply to this post's contents.

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