simulating "Deep Frame Dipoe" (DFD) Woofers, AkAbak?

[mige0]

Hi folks

After having arrived at a "new" speaker concept :

AMT sub - using dynamic woofer
(roughly down from posting #4)


I'd thought, it would be handy to have a somehow accurate simulation tool to have an easy look at possible variants and optimizations.
I've been advised to possibly give AkAbak a try, after Hornresp and AJHorn did not seem to be a good choice.

Needed is a possibility to simulate a *distributed speakers arrangement* in pipes - and possibly add dipole behavior.


I just download AkAbak:
Akabak

and had a look through a few pages:
Akabak Simulator

Thats the starting point.
Any input appreciated.



Michael

[mige0]

After some reading, AkAbak starts to make sense.
First, a most simple simu of the H-frame with only the front duct being modelled - looks definitely promising with respect to the measurements already taken (red trace):


Measurement:





Akabak simu:





This is the code used:

System 'H-Frame Part1' |Anything behind a line is for humans only


Def_Driver  '15PW5'
  dD=33cm   		|Piston
  fs=40Hz  
  Mms=84.6g  
  Qms=16.8
  Qes=0.41  
  Re=5.5ohm  
  Le=1mH  
  ExpoLe=0.618
  

Def_Const |This sets the units within to all be Meters
{ 			|Starts
Vrc= 9000.00e-3; 	|Rear chamber volume (litres)
Lrc= 1.00e-2; 		|Rear chamber average length (cm)

Sd = 860e-4; 		|Diaphragm area (sq cm)
Sdd = 1600E-4;		|Duct Outlet area (sq cm)
} 			|Ends 


Driver Def='15PW5''15PW5'
Node=1=0=2=3


Enclosure 'Rear chamber' 
Node=2
Vb={Vrc} 
Lb={Lrc}


Duct    'Du1'  
Node=3=33
dD=45cm  
Len=40cm  


Radiator 'DUCT outlet'
Node=33
SD={Sdd}
Label=2

Not too bad for a first lift off, I'd say


Michael

[soho54]

Interesting experiment.

I have a few ideas, but some questions first. Can you post the exact measurements of the test enclosure, external is fine, and wood thickness. Was the driver mounted as shown in the 3d shot? Where was the mic placed?

[soho54]

I got bored. Try this setup out for starters.

System 'H-Frame Full' 


Def_Driver  '15PW5'
  dD=33cm   |Piston
  fs=40Hz  Mms=84.6g  Qms=16.8
  Qes=0.41  Re=5.5ohm  Le=1mH  


Driver Def='15PW5''Driver'
Node=1=0=2=3

Duct    'Rear'  
Node=2=22    
WD=40cm  HD=40cm  Len=40cm |End Correction is not needed, as the attached Radiator handles it.

  Radiator  'Rear Outlet'  Def='Rear'    
  Node=22
  x=0  y=0  z=-40cm  HAngle=180°  VAngle=0
  WEdge=43.6cm HEdge=43.6cm
  Label=2 
 

Duct    'Front'  
Node=3=33    
WD=40cm  HD=40cm  Len=40cm |End Correction is not needed, as the attached Radiator handles it.


  Radiator  'Front Outlet'  Def='Front'    
  Node=33
  x=0  y=0  z=40cm  HAngle=0  VAngle=0  
  WEdge=43.6cm HEdge=43.6cm  
  Label=1

Just add "all" and labels 1 & 2 when simulating. Don't forget to play with the "mic/listener" distance as well.

[soho54]

You should end up with something like this, with the total FR, and both ends separately.

[mige0]

Originally Posted by soho54

Interesting experiment.

I have a few ideas, but some questions first. Can you post the exact measurements of the test enclosure, external is fine, and wood thickness. Was the driver mounted as shown in the 3d shot? Where was the mic placed?

Have arrived at something close to your script yesterday (except the "edge" diffraction statements I have not looked into yet) - but are still a little bit slow in verifying


Thanks for your input - very much appreciated!

regardig "wood thickness" : don't bother, there is no need to get "precise" results - all this simus are meant to just get the trend
regarding "driver mounting" : yes exactly like shown (I have added cone depth in my simu but it does not make the heck of a difference - as expected)
regarding "mic placement" : measurements (right a mouth) also were done just to catch the trend of different arrangements - so no claim to be "absolutely precise"

I will be back with some plots and specific questions soon...

Nice overlay plot BTW, I have to learn how to do this easily...

Michael

[soho54]

You're welcome.

This should be close enough then. I find that adding a conical diaphragm isn't necessary below ~1kHz.

The overlay is easy to do, look at the lower left corner here.


As you only have one System <all> and H-Frame Full are the same.

[mige0]

Well,I added conical mainly because it adds some un-symmetry in case of H-frame.

For doing the overlay "right", I'm not clever enough as it seems.

As far as I understood there is a max of thee traces to be overlaid. Works if I drag and drop from one plot into the other, but does not work to immediately simulate into one plot only and - also does not work to get / keep the colors of traces adjusted.


Another problem I've come across - seems if I simu close to mouth - approaching 40cm in above example - SPL level sky rocks to several 100dB. Any idea?

Michael

[mige0]

Originally Posted by mige0

For doing the overlay "right", I'm not clever enough as it seems.

Boy this took me time !

I always tried to *add* traces to a given plot window - better to just choose / select the scripted labels and every trace is then put into the upcoming plot at once...

Uff!

Michael

[mige0]

Why writing:

Driver Def='15PW5''Driver'
Node=1=0=2=3

and not :
Driver Def='15PW5'
Node=1=0=2=3

is there a difference?

Michael