Acoustic Horn Design – The Easy Way (Ath4)

One recent design I made - 1.4" throat, approx. ⌀23" x 10".

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bmc0

Member
2019-08-26 2:09 am
Here's my attempt at an extremely simple compression driver model (1 inch exit):

Code:
Def_Driving
  Value=2.83 IsRms

Def_Driver 'Drv1'
  dD=44mm
  Mms=1.0g
  Cms=25e-6m/N
  Rms=3.5Ns/m
  Bl=8.0Tm
  Re=6.3ohm
  fre=35kHz ExpoRe=1
  Le=0.1mH ExpoLe=0.618

System 'S1'
  Driver 'D1' Def='Drv1' Node=1=0=10=20
 
  // Rear enclosure
  Enclosure 'Eb'  Node=20
    Vb=50cm3
    Qb/fo=0.1

  // Phase plug (simplification)
  Waveguide 'W1' Node=10=300
    STh=3cm2  dMo=20mm  Len=22mm  Conical

  // Conical section between phase plug and exit
  Waveguide 'W2' Node=300=400
    dTh=20mm  dMo=25.4mm  Len=22mm  Conical

  RadImp 'Throat' Node=400 DrvGroup=1001

I don't really know what I'm doing and most of the parameters were wild guesses, but it seems to give sane results. It's based on the "Horn Expo 400" example included with ABEC3. First three images are the bare driver in free space and the next three are with the waveguide in this post.

The driving voltage is 2.83V and the measurement distance is 3m (add 9.5dB to get the 1m equivalent).
 

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Last edited:
That's just perfect! I think we don't need more at the moment.
Very nice. So the compression ratio is simply expressed as the mismatch between Drv1.dD and W1.STh? That would be very elegant.

BTW, the Waveguide 'W2' could be already easily moved to BEM side, so to fully simulate the conical exit section of the driver as a part of the waveguide.
 
Last edited:

pelanj

Member
Paid Member
2008-07-17 8:47 am
Hořovice
The high loading version on axis FR shape looks exactly like my DE500 in an ES-800 horn by Joseph Crowe. I wanted to compare it with the 10" waveguide, but my second print of the waveguide failed (it is soft and brittle due to partially clogged nozle:( ) and I need to make a new one.
 

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The one thing that seems missing in the CD model is the air gap between the diaphragm and the phase plug. This gap forms a volume that attenuates the response at HFs. I don't see where this effect is in the model. If the gap is very small then this effect is pushed out-of-band, but larger and it has a substantial effect.

The plot below shows this effect on the volume velocity for some rather large gaps - on a PWT.
 

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