Calculate box size using bass reflex alignments



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  1. Find out the Qts of your driver, by measuring it, or look for it in the data sheet.
  2. >>> If Qts is lower than 0.4, you will end up with a flat alignment.
    >>> If it’s higher than 0.4, the alignment will be non-flat.


  3. Find out fs and Vas of your speaker, by either measuring it or by looking it up in the data sheet.
  4. Choose a diameter for the port.
  5. Choose the alignment you would like, and go to the appropriate table.
  6. Use the radio button left of the Qts value to get all parameters and the results will be calculated.

  7. If you change the Thiele/Small parameters or the Port diameter , click the 'Recalculate' button

       QB3             SBB4             SC4       



Thiele/Small Parameters Alignments from table
Fs : Hz H :
Vas : liters a :
Port diameter : cm f3/fb :



Frequency Response







QB3

QB3 or Third-Order Quasi-Butterworth – is the most popular vented alignment, because it yields a smaller box and a lower f3. However, the transient response is not as good as SBB4 or SC4.

QL 3

QL 7

QL 15

Qts H a F3/Fs Peak  Qts H a F3/Fs Peak  Qts H a F3/Fs Peak
 0,1004,330331,29045,67090  0,1003,841634,39255,22330  0,1003,684135,47935,07150
 0,1103,937125,68245,14560  0,1103,494728,23414,73860  0,1103,349429,12864,60040
 0,1203,609621,41694,70690  0,1203,205823,54994,33370  0,1203,073224,29844,20690
 0,1303,332518,09744,33480  0,1302,961519,90463,99020  0,1302,839820,53923,87300
 0,1403,095015,46354,01500  0,1402,961517,01503,69490  0,1402,640017,55633,58590
 0,1502,889213,33863,73710  0,1502,571214,67843,43810  0,1502,457015,14983,33620
 0,1602,072911.59943,49320  0,1602,412912,76853,21260  0,1602,315813,18023,11690
 0,1702,550410,15813,27720  0,1702,274311,18553,01280  0,1702,182611,54782,92250
 0,1802,40928,95023,08440  0,1802,14959,85892,83450  0,1802,064410,17972,74880
 0,1902,28307,92802,91130  0,1902,03888,73612,67410  0,1901,95899,02182,59260
 0,2002,16947,05522,75480  0,2001,93937,77752,52890  0,2001,86408,03312,45120
 0,2102,06666,30412,61250  0,2101,84946,95242,39680  0,2101,77847,18222,32250
 0,2201,97335,65312,48240  0,2201,76786,23722,27590  0,2201,70076,44462,20450
 0,2301,88815,08512,36300  0,2301,69355,61322,16470  0,2301,62995,80102,09600
 0,2401,81004,58662,25280  0,2401,62545,06552,06200  0,2401,56525,23611,99560
 0,2501,73814,14672,15080  0,2501,56294,58221.96670  0,2501,50584,73751,90230
 0,2601,67193,75662,05590  0,2601,50544,15351.87780  0,2601,45124,29521.81530
 0,2701,61053,40901.96740  0,2701,45223,77141.79460  0,2701,40073,90111.73380
 0,2801,55363,09801.88450  0,2801,40293,42951.71650  0,2801,35403,54841.64710
 0,2901,50062,81861.80650  0,2901,35713,12231.64290  0,2901,31063,23141.58460
 0,3001,45122,56661.73310  0,3001,31452,84211.57320  0,3001,27032,94551.51590
 0,3101,40502,33861.66360  0,3101,27482,59441.50700  0,3101,23272,68671.45040
 0,3201,36172,13171.59780  0,3201,23762,36671.44390  0,3201,19762,45171.38800
 0,3301,32101.94321.53510  0,3301,20282,15941.38360  0,3301,16482,23761.32810
 0,3401,28281.77121.47540  0,3401,17021,96991.32580  0,3401,13412,04201.27050
 0,3501,24671.61361.41830  0,3501,13951,79641.27020  0,3501,10521,86291.12510
 0,3601,21271.46901.36360  0,3601,11061,63711.21670  0,3601,07811,69831.16150
 0,3701,18061.33601.31100  0,3701,08341,49051.16510  0,3701,05261,54681.10990
 0,3801,15011.21331.26050  0,3801,05781,35521.11530  0,3801,02861,40701.06020
 0,3901,12131.09991.21180  0,3901,03351,23001.06740  0,3901,00591,27771.01250
 0,4001,09390,99491.16490  0,4001,01061,11411,02140  0,4000,98451,15790,96720
 0,4101,06790,89741.11980  0,4100,98891,00650,97760  0,4100,96431,04660,92450,02
 0,4201,04310,80691.07630  0,4200,96830,90640,93620,01  0,4200,94520,94300,88490,08
 0,4301,01950,77251.03460  0,4300,94880,81310,89750,05  0,4300,92720,84640,84880,21
 0,4400,99700,64390,99470  0,4400,93030,72600,86180,14  0,4400,91010,75620,81620,43
 0,4500,97550,57040,95680  0,4500,91280,64450,82940,31  0,4500,89390,67190,78720,76
 0,4600,95500,50160,92100,02  0,4600,89610,56820,80010,56  0,4600,87860,59280,76181,18
 0,4700,93540,46720,88750,06  0,4700,88020,49660,77410,9  0,4700,86410,51850,73951,72
 0,4800,91660,37670,85630,14  0,4800,86510,42940,75101,32  0,4800,85030,44880,72022,36
 0,4900,89860,31990,82760,27  0,4900,85070,36610,73071,85  0,4900,83730,38300,70343,13
 0,5000,88130,26650,80140,45  0,5000,83700,30650,71292,46  0,5000,82490,32110,68894,04
 0,5100,86470,21610,77750,7  0,5100,82400,25030,69723,18  0,5100,81320,26250,67645,09
 0,5200,84880,16860,75581,00  0,5200,81160,19710,68354,01  0,5200,82100,20720,66566,33
 0,5300,83360,12380,73631,36  0,5300,79980,14680,67154,97  0,5300,79160,15470,65637,79
 0,5400,81890,08140,71861,77  0,5400,78860,09920,66106,08  0,5400,78170,10500,64839,56
 0,5500,80470,04130,70272,25  0,5500,77790,05400,65187,36  0,5500,77230,05770,641611,8
 0,5600,79110,00330,68832,78  0,5600,76770,01110,64388,87  0,5600,76350,01280,635914,7


SBB4

SBB4 or Super Fourth-Order Boom Box – is characterized by a large box, low tuning frequency (longer vent) and good transient response (which puts the term boom-box out of place).

QL 3

QL 7

QL 15

Qts H a F3/Fs Peak  Qts H a F3/Fs Peak  Qts H a F3/Fs Peak
 0,2001,00005,44443,54010  0,2001,00005,89803,36860  0,2001,00006,08443,29960
 0,2101,00004,90313,32550  0,2101,00005,33393,15180  0,2101,00005,51133,08180
 0,2201,00004,43553,12800  0,2201,00004,84572,95210  0,2201,00005,01492,88110
 0,2301,00004,02902,94540  0,2301,00004,42042,76740  0,2301,00004,58212,69550
 0,2401,00003,67362,77610  0,2401,00004,04782,59600  0,2401,00004,20252,52330
 0,2501,00003,36112,61860  0,2501,00003,71142,43660  0,2501,00003,86782,36330
 0,2601,00003,08502,47180  0,2601,00003,42862,28830  0,2601,00003,57112,21460
 0,2701,00002,83992,33470  0,2701,00003,16992,15030  0,2701,00003,30702,07640
 0,2801,00002,62132,20680  0,2801,00003,16992,15030  0,2801,00003,07081,94830
 0,2901,00002,42572,08730  0,2901,00002,73151,90310  0,2901,00002,85881,83010
 0,3001,00002,25001,97590  0,3001,00002,73151,79320  0,3001,00002,54481,79320
 0,3101,00002,09161,87240  0,3101,00002,37611,69220  0,3101,00002,46501,62220
 0,3201,00001,94841,68760  0,3201,00002,22331,60000  0,3201,00002,33841,53230
 0,3301,00001,81141,68760  0,3301,00002,08431,51620  0,3301,00002,19581,45140
 0,3401,00001,70021,60600  0,3401,00001,95761,44060  0,3401,00002,03571,37900
 0,3501,00001,59241,53130  0,3501,00001,84191,37280  0,3501,00001,94671,31460
 0,3601,00001,49381,46320  0,3601,00001,73571,25760  0,3601,00001,83751,31460
 0,3701,00001,40351,40140  0,3701,00001,63921,25830  0,3701,00001,73721,20710,01
 0,3801,00001,32051,34560  0,3801,00001,54841,21040  0,3801,00001,64471,16260,01
 0,3901,00001,24411,29520  0,3901,00001,46561,16790,06  0,3901,00001,55931,12330,16
 0,4001,00001,17361,24990  0,4001,00001,38901,13020,14  0,4001,00001,48031,08860,27
 0,4101,00001,10851,20910,01  0,4101,00001,31811,09660,24  0,4101,00001,40701,05770,41
 0,4201,00001,04821,17240,05  0,4201,00001,25231,06670,37  0,4201,00001,33901,03030,57
 0,4301,00001,99231,13940,12  0,4301,00001,19111,03990,37  0,4301,00001,27571,00590,73
 0,4401,00000,94031,10960,20  0,4401,00001,13411,01600,66  0,4401,00001,21670,98400,91
 0,4501,00000,89201,08280,30  0,4501,00001,08090,99440,82  0,4501,00001,16160,96431,10
 0,4601,00000,84690,05850,41  0,4601,00001,03130,97501,00  0,4601,00001,11010,94661,30
 0,4701,00000,80491,03650,53  0,4701,00000,98490,95741,17  0,4701,00001,06190,93051,50
 0,4801,00000,76561,01650,66  0,4801,00000,94140,94151,36  0,4801,00001,01670,91601,71
 0,4901,00000,72890,99830,79  0,4901,00000,90060,92701,55  0,4901,00000,97430,90271,91
 0,5001,00000,69440,98150,93  0,5001,00000,86220,91371,74  0,5001,00000,93440,89062,13
 0,5101,00000,66210,96631.08  0,5101,00000,82620,90151,93  0,5101,00000,89690,87952,34
 0,5201,00000,63180,95231.23  0,5201,00000,79230,89042,13  0,5201,00000,86160,86962,56
 0,5301,00000,60330,93941.38  0,5301,00000,76030,88012,33  0,5301,00000,82820,85992,78
 0,5401,00000,57650,92751.54  0,5401,00000,73020,87062,53  0,5401,00000,79670,85132,99
 0,5501,00000,55120,91651.70  0,5501,00000,70170,86192,73  0,5501,00000,76700,84323,21
 0,5601,00000,52740,90631.86  0,5601,00000,67470,85372,93  0,5601,00000,73880,83583,43
 0,5701,00000,50480,89682,02  0,5701,00000,64930,84623,13  0,5701,00000,71210,82893,65
 0,5801,00000,48360,88802,18  0,5801,00000,62510,83913,33  0,5801,00000,68680,82243,86
 0,5901,00000,46350,87972,34  0,5901,00000,60220,83253,53  0,5901,00000,66280,81644,08
 0,6001,00000,44440,87202,50  0,6001,00000,58050,82643,73  0,6001,00000,64000,81084,29
 0,6101,00000,42640,86942,66  0,6101,00000,55990,82063,93  0,6101,00000,61830,80554,51
 0,6201,00000,40930,85812,82  0,6201,00000,54030,81524,12  0,6201,00000,59770,80064,72
 0,6301,00000,39310,85182,98  0,6301,00000,52160,81024,23  0,6301,00000,57810,79594,93
 0,6401,00000,37770,84583,14  0,6401,00000,50380,82544,51  0,6401,00000,55940,79165,14
 0,6501,00000,36310,84023,3  0,6501,00000,48690,80094,70  0,6501,00000,54150,78745,35
 0,6601,00000,34920,834463,46  0,6601,00000,47080,79674,90  0,6601,00000,52450,78365,55
 0,6701,00000,33590,82993,61  0,6701,00000,45540,79265,09  0,6701,00000,50830,77995,76
 0,6801,00000,32330,82523,77  0,6801,00000,44070,78895,27  0,6801,00000,49270,77645,96
 0,6901,00000,31130,82073,92  0,6901,00000,42670,78465,46  0,6901,00000,47790,77316,16
 0,7001,00000,29990,81654,08  0,7001,00000,41330,78195,65  0,7001,00000,46370,77006,36


SC4

SC4 or Forth-Order Sub-Chebyshev – about the same enclosure size and f3 as the SBB4, but with different tuning frequency.
Somewhat degraded transients compared to SBB4.

QL 3

QL 7

QL 15

Qts H a F3/Fs Peak  Qts H a F3/Fs Peak  Qts H a F3/Fs Peak
 0,2501,00933,40802,60830  0,2501,03383,89612,22820  0,2501,04204,08902,30970
 0,2601,03223,23012,43910  0,2601,05343,67552,39490  0,2601,06013,85002,14770
 0,2701,05293,05162,28600  0,2701,07033,45512,07840  0,2701,07513,61191,99700
 0,2801,07032,87312,14730  0,2801,08423,23601,94390  0,2801,08713,37571,86470
 0,2901,07812,69522,02170  0,2901,09513,01931,82290  0,2801,09583,14291,74600
 0,3001,10042,51881,90780  0,3001,10282,80621,71370  0,3001,10112,91471,63910
 0,3101,11092,34471,80420  0,3101,10732,59771,61490  0,3101,10312,69241,54260
 0,3201,11872,17381,70970  0,3201,10862,39521,52510  0,3201,10162,47741,45490
 0,3301,12362,00691,62320  0,3301,10652,19971,44310  0,3301,09662,27111,37490
 0,3401,12551,84481,54370  0,3401,10122,01251,36790  0,3401,08842,07481,30160
 0,3501,12441,68851,47030  0,3501,09261,83471,29860  0,3501,88961,23421,23420
 0,3601,12031,53871,40230  0,3601,08101,66721,23450  0,3601,06261,71661,17200
 0,3701,11331,39611,33900  0,3701,06671,51091,17510  0,3701,04561,55671,11460
 0,3801,10341,26161,27980  0,3801,04981,36651,12000  0,3801,02651,41011,06150
 0,3901,09091,13561,22440  0,3901,03091,23431,06890  0,3901,00581,27791,01250
 0,4001,07581,01871,17230  0,4001,01031,11461,02150  0,4001,98401,15911,96750
 0,4101,05860,91101,12360  0,4100,98861,00700,97770  0,4100,96151,05350,92620
 0,4201,03940,81281,07780  0,4200,96620,91130,93730  0,4200,93900,96040,88840
 0,4301,01880,72381,03480  0,4300,94360,82660,90010  0,4300,91670,87870,85390
 0,4400,97700,64390,99470  0,4400,92120,75210,86600  0,4400,89510,80740,82260,01
 0,4500,97440,57260,95720  0,4500,89920,68580,83480.01  0,4500,87440,74530,79420.02
 0,4600,95150,50930,92220  0,4600,87800,62970,80640.01  0,4600,85470,76840,76840.03
 0,4700,92860,56330,88980  0,4700,85780,57980,78040.02  0,4700,85470,69110,76840.05
 0,4800,90590,40400,85970  0,4800,83850,53610,75670.03  0,4800,81870,60270,72390.07
 0,4900,88370,36050,83180  0,4900,82030,49780,73510.05  0,4900,80250,56660,70470.09
 0,5000,86210,32230,80600,01  0,5000,80310,46420,71550.07  0,5000,78730,53480,68730.12
 0,5100,84120,28850,78220,02  0,5100,78700,43450,69750.09  0,5100,77320,50680,67140.16
 0,5200,82120,25860,76010,02  0,5200,77190,40830,68100.12  0,5200,76010,48200,65690.20
 0,5300,80210,23210,73970,03  0,5300,75780,38490,66590.15  0,5300,74790,45990,64370.24
 0,5400,78380,20840,72080,05  0,5400,74450,36400,62000.19  0,5400,73660,44020,63150.29
 0,5500,76640,18720,70330,06  0,5500,73210,34530,62000.23  0,5500,72600,42250,62040.34
 0,5600,74990,16180,68710,08  0,5600,72050,32840,62750.27  0,5600,71620,40650,61010.39
 0,5700,73410,15080,67200,10  0,5700,70960,31310,61660.31  0,5700,70700,39210,60060.45
 0,5800,71920,13500,65790,12  0,5800,69930,29920,60650.31  0,5800,69840,37890,59190.51
 0,5900,70490,12050,64470,14  0,5900,68960,28650,59710.41  0,5900,69030,36700,59380.57
 0,6000,69130,10720,63240,17  0,6000,68050,27490,58830.46  0,6000,68280,35600,57620.63
 0,6100,67840,09840,62090,20  0,6100,67190,26410,58020.51  0,6100,67570,34590,56920.70
 0,6200,66610,08320,61010,23  0,6200,66380,25420,57260.57  0,6200,66900,33660,56260.77
 0,6300,65430,07230,61010,26  0,6300,65610,24490,56540.63  0,6300,66270,32810,55650.83
 0,6400,64300,63000,59060,29  0,6400,64880,23630,55870,68  0,6400,65670,32010,55080,90
 0,6500,64300,63000,59060,29  0,6500,64880,23630,55870,68  0,6500,66270,32810,55650,90
 0,6600,62180,04350,57260,32  0,6600,63530,22080,54650,80  0,6600,64580,30580,54031,00
 0,6700,61180,03430,56440,39  0,6700,62890,21360,54090,89  0,6700,64080,29940,53551,12
 0,6800,60220,02580,55670,42  0,6800,62290,29330,53550.92  0,6800,63600,29940,53111,19
 0,6900,59290,17500,54930,46  0,6900,61710,20060,53050,98  0,6900,63140,28760,52681,26
 0,7000,58400,00960,54230,50  0,7000,61160,19460,52581,05  0,7000,62710,28230,52281,33


Conventional and Assisted Alignments of Arbitrary Order and Box Quality Factor ( Ext. link )




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