Akabak vs Hornresp vs Real measurements

Here is a chart that shows the results from Hornresp vs Akabak when compared to the measurements of the actual real thing:

Black is the measured response of the 4" closed back midrange on S1. Red is Hornresp, green is Akabak.

S1 is a 60 x 60 point source horn:

Note: Pyle drivers shown are not what is being investigated here.

Here are the Hornresp parameters:

Included at the end of this post is the script for Akabak. I exported the script from Hornresp, so it was automatically generated.

You will notice an offet of the ports larger than built - 9.2cm was entered as it matches the first dip. The ports were located 8.6cm from the throat - a 7% difference. This could be related to the compression driver exit tube coming into play, or it could be related also to atmospheric conditions and the speed of sound which is  used to determine the port offset.

In this example it's interesting to see that Hornresp is actually more accurate where it matters most. In particular I'm interested in the top and bottom end roll off behaviour as it assists in choosing the parameters. Hornresp is closer with both. It estimates the first dip well enough to guide design decisions and then becomes very inaccurate at higher frequencies where the crossover takes over. In the bottom end, both fail to predict the peak and dip.


Akabak script generated by Hornresp:


|DATA EXPORTED FROM HORNRESP - RESONANCES NOT MASKED

|COMMENT: Celestion 4" single on S1

|========================================================================================================

|REQUIRED AKABAK SETTINGS:

|File > Preferences > Physical system constants:

|Sound velocity c = 344m/s
|Medium density rho = 1.205kg/m3

|Sum > Acoustic power:

|Frequency range = 10Hz to 20kHz
|Points = 533
|Input voltage = 2.83V rms
|Integration = 2Pi-sr
|Integration steps = 1 degree ... 1 degree
|Integration method = Cross

|========================================================================================================

Def_Const |Hornresp Input Parameter Values
{
|Length, area and volume values converted to metres, square metres and cubic metres:

S1  =     4.90e-4;  |Horn segment 1 throat area (sq cm)
S2  =   100.00e-4;  |Horn segment 1 mouth area and horn segment 2 throat area (sq cm)
S3  =  2500.00e-4;  |Horn segment 2 mouth area (sq cm)

L12 =     9.20e-2;  |Horn segment 1 axial length (cm)
L23 =    33.00e-2;  |Horn segment 2 axial length (cm)

Ap  =     2.50e-4;  |Chamber port cross-sectional area (sq cm)
Lpt =     1.80e-2;  |Chamber port tube length (cm)

Vtc =    34.00e-6;  |Throat chamber volume (cc)
Atc =    55.00e-4;  |Throat chamber cross-sectional area (sq cm)

|Parameter Conversions:

Sd  = 60.00e-4;  |Diaphragm area (sq cm)

Ltc = Vtc / Atc;
}
|========================================================================================================

|Network node numbers for this offset driver horn system:

|       0-Voltage-1
|                 |
|Radiator(1)-5-Driver-6-Chamber-7-Port-
|                                      |
|                            8-Segment-9-Segment-10-Radiator(2)

|========================================================================================================

Def_Driver 'Driver'

  Sd=60.00cm2
  Bl=6.49Tm
  Cms=3.01E-05m/N
  Rms=0.98Ns/m
  fs=444.4946Hz  |Mmd = 4.00g not recognised by AkAbak, fs calculated and used instead
  Le=0.60mH
  Re=5.69ohm
  ExpoLe=1

System 'System'

  Driver Def='Driver''Driver'
    Node=1=0=5=6

  Radiator 'Diaphragm'
    Node=5
    SD={Sd}
    Label=1

  Duct 'Throat chamber'
    Node=6=7
    SD={Atc}
    Len={Ltc}
    Visc=0

  Duct 'Port'
    Node=7=9
    SD={Ap}
    Len={Lpt}
    Visc=0

  Waveguide 'Horn segment 1'
    Node=8=9
    STh={S1}
    SMo={S2}
    Len={L12}
    Conical

  Waveguide 'Horn segment 2'
    Node=9=10
    STh={S2}
    SMo={S3}
    Len={L23}
    Conical

  Radiator 'Horn mouth'
    Node=10
    SD={S3}
    Label=2