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hornresp excursion plots

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roborg View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote roborg Quote  Post ReplyReply Direct Link To This Post Posted: 22 August 2008 at 2:31am
My mid-tops use two sn12-b's in a dual siamesed porn-horn sized horn & about 5 litres rear chamber (actually one hasnt been restricted yet hehe!)  I modelled them in akabak, hornresp is good for bass-horns but not for mid-range.
   For the sn12-b the response starts to become nicely flat 120-1.2Khz without EQ when using 2-4litres rear volume per driver.  Larger volumes allow for slightly higher low-output, at the cost of slight loss of higher frequency sensitivity. 
  At 3litres rear volume the simulated excursion is less than 3.5mm when being fed a 1.2Kw sine down to 100hz.  So basically around 3-5litres seems pretty optimal.  To be honest it's hard to get down to such small volumes without using a specifically moulded back chamber (i used polyurethane foam to restrict the rear chamber.)
  The smaller it is the more distortion from the rear chamber & the hotter it'll run too.
 
cheers,
  Rob.
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roborg View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote roborg Quote  Post ReplyReply Direct Link To This Post Posted: 22 August 2008 at 2:44am
The front chamber volume is almost not worth modelling as the comp-ratio in the porn horn is pretty low.  I've modelled 1 litre with my horns to represent the volume 'trapped' behind the phase-plug.
  The effect of modelling front-chambers is irrelevent for maximum excursion calculations, smaller front chambers only really give you more higher bandwidth.
 
A simple akabak script (google for akabak, its a free download) i used to model my mid-range horns to get parameters about right is this:
 
| 2x sn12-b DDR mid range horn with phase plugs
 
Def_Driver  'sn-12b'
  Meas_DoNotModify
  SD=530cm2  dD1=9.6cm  tD1=5cm   |Cone
  fs=50Hz  Mms=47.83g  Qms=4.32
  Qes=0.17  Re=5.4ohm  Le=0.79mH  ExpoLe=0.618
 
System  'DDR mid horn'
| the two speakers, defined as drivers
  Driver 'D1'  Def='sn-12b'  Node=1=0=25=5
  Driver 'D2'  Def='sn-12b'  Node=1=0=26=6
 
| the rear chambers of the speakers
 
  Enclosure    'rearchamber1'  Node=5
    Vb=3L  Qb/fo=10e-3  Sb=500cm2
    fb=100Hz  dD=2cm  QD/fo=.0001
    x=0  y=0  z=0  HAngle=0  VAngle=0
 
  Enclosure    'rearchamber2'  Node=6
    Vb=3L  Qb/fo=10e-3  Sb=500cm2
    fb=100Hz  dD=2cm  QD/fo=.0001
    x=0  y=0  z=0  HAngle=0  VAngle=0
     
  Horn    'top half'  Node=25
    STh=232cm2  WMo=60cm  HMo=41cm
    Vf=1L
    Len=70cm  T=1
      x=0  y=25cm  z=0  HAngle=0  VAngle=0
 
  Horn    'bottom half'  Node=26
    STh=232cm2  WMo=60cm  HMo=41cm
    Vf=1L
    Len=70cm  T=1
      x=0  y=-25cm  z=0  HAngle=0  VAngle=0
 
 
Cheers,
  Rob
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tommysb View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tommysb Quote  Post ReplyReply Direct Link To This Post Posted: 25 August 2008 at 2:05pm
Hey Rob, how is the phase plug defined here? Could you shed a bit more light/a bit more explanation please?

Tom
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roborg View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote roborg Quote  Post ReplyReply Direct Link To This Post Posted: 25 August 2008 at 8:20pm
Hi Tommy, The phase plug is implied by the area of the throat Sth being less than the area of the driver.  This is only a really simple script to get an idea of performance (IE low cutoff & bandwidth) of the horn.
  Any directivity information & a more accurate high frequency response would need the throat area & different parts of the horn to be modelled individually.  I've done this a few times, but get fed up with having to change the akabak scripts when i change my mind about the design.
  As i rarely array my mid-top designs, usually cos i only build two & want a stereo system! (they quite often get arrayed when in storage hehe!)  I'm not too fussy about constant directivity, more so with efficiency & wide dispersion.  I try to match up the -6db points with the lower & higher frequency sections tho,  so that the change in directivity varies smoothly down the stack.
  I'm a keen fan of keeping only 1 mid-top per side to keep to the ideal of a point source (or cylindrical source in this case) as faithfully as poss.
  You can really go to work with ducts in akabak, but it very quickly becomes hard work to make sure all the dimensions & areas are correct.
 
cheers,
  Rob.
 
PS I dont have a mid modelled as ducts & waveguides on the pc i've got with me here but i did have this approximation to the folding of an 1850 here.  This was a model i based the simulation of my smooth contoured 1850It uses ducts & waveguides to approximate the geometry in the 1850 horn:
 
Def_Driver  'sub800'
  Meas_DoNotModify
  dD=41cm  dD1=8.5cm  tD1=4cm   |Cone
  fs=30Hz  Mms=201g  Qms=10
  Qes=0.23  Re=5ohm  Le=1.5uH  ExpoLe=0.618
 
System 'better 1850'
    Driver 'D1'  Def='sub800'  Node=1=0=20=3
 
  Enclosure    'rearchamber1'  Node=3
    Vb=45L  Sb=2400cm2
   
| simulate v wedge with few ducts
 
   
  Duct    'Du1'  Node=20=21
    WD=60cm  HD=3mm  Len=4cm Visc=0
  Duct    'Du2'  Node=20=21
    WD=60cm  HD=0.5cm  Len=8cm
  Duct    'Du3'  Node=20=21  Visc=0
    WD=60cm  HD=0.7cm  Len=12cm
  Duct    'Du4'  Node=20=21  Visc=0
    WD=60cm  HD=1cm  Len=16cm
  Duct    'Du5'  Node=20=21  Visc=0
    WD=60cm  HD=1.5cm  Len=20cm
  Duct    'Du6'  Node=20=21  Visc=0
    WD=60cm  HD=3cm  Len=24cm
  Duct    'Du7'  Node=20=21  Visc=0
    WD=60cm  HD=1.5cm  Len=28cm
  Duct    'Du8'  Node=20=21  Visc=0
    WD=60cm  HD=1cm  Len=32cm
  Duct    'Du9'  Node=20=21  Visc=0
    WD=60cm  HD=0.7cm  Len=36cm
  Duct    'Du0'  Node=20=21  Visc=0
    WD=60cm  HD=0.5cm  Len=40cm
  Duct    'Du0'  Node=20=21  Visc=0
    WD=60cm  HD=0.3cm  Len=44cm
   
 
| first bend
 
  Waveguide    'bend1'  Node=21=22
    WTh=60cm  HTh=3.5cm  WMo=60cm  HMo=4.66cm
    Len=15.5cm  T=1
  Waveguide    'bend1'  Node=21=22
    WTh=60cm  HTh=3.5cm  WMo=60cm  HMo=4.66cm
    Len=22cm  T=1
  Waveguide    'bend1'  Node=21=22
    WTh=60cm  HTh=3.5cm  WMo=60cm  HMo=4.66cm
    Len=28.5cm  T=1
 
| first expo section
 
  Waveguide    'downpipe'  Node=22=23
  WTh=60cm  HTh=14cm  WMo=60cm  HMo=21.5cm
  Len=44cm  T=1
 
| second bend (three waveguides)
 
 
  Waveguide    'bend1'  Node=23=24
    WTh=60cm  HTh=7cm  WMo=60cm  HMo=11cm
    Len=30cm  T=1
  Waveguide    'bend1'  Node=23=24
    WTh=60cm  HTh=7cm  WMo=60cm  HMo=11cm
    Len=45cm  T=1
  Waveguide    'bend1'  Node=23=24
    WTh=60cm  HTh=7cm  WMo=60cm  HMo=11cm
    Len=75cm  T=1
 
| exit horn
   
  Horn    'top half'  Node=24
    WTh=60cm  HTh=32cm  WMo=60cm  HMo=60cm
    Vf=0L  Len=65cm  T=1
      x=0  y=0  z=0  HAngle=0  VAngle=0
 
 
What I cannot create, I do not understand
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