MIGHTY DUB PASS MK2 (FSP-MDP)

Maybe vf is rendundance...but I think that akabak take care about shape and volume, if I correct hd wd and len because of the volume I change volume and shape...if I use vf I change only the volume.
I'll add acoucompliance to the script soon One question have I to add it on all the nodes right?

The first thing I'd try is to just remove the vf parameters and re-tune the ports for the frequencies listed on the spec. That should get closer I think.

The lumped compliances would replace the chamber volumes A B and C. It's debatable which is the most accurate. A approximates a duct quite well, so maybe it should stay as a duct. B and C are not so clear-cut.

using AcouCompliance only on chambers don't work....I don't think I make mistake on the definition of volume so I take c (sound velocity)=344 and roh (air density)=1.2 , just a copy and paste from akabak help.
Mantaining the same dimension of the first script I obtain a really different response, not good at all.
If I use AcouCompliance on all the ducts except port c I don't obtaing any response.
so AcouCompliance must be used on all the ducts except the throat chamber and port c. smiley20
edit:use duct defintion on chamber A

I think akabak is reaching its limit with this cab......

here's the script with acoucompliance
Def_Const |Hornresp Input Parameter Values
{

R1=50e-2/2; |radius chamber A
R2=30e-2/2; |radius port A
R3=17.5e-2/2; |radius port B
h4=60e-2; |cab width
w4=71.4e-2; |cab depth
R5=32.5e-2/2; |radius port C
thick=1.8e-2; |wood thickness
S1 = r1^2*pi; |duct area chamber A (sq cm)
S2 = r2^2*pi; |duct area port A(sq cm)
S3 = r3^2*pi; |duct area port B (sq cm)
S5 = r5^2*pi; |duct area port C (sq cm)
c=321; |sound velocity
roh=1.2754; |air density
rc=roh*sqr(c); |divide volume by this value

L12 = 26.50e-2; |depth A chamber (cm)
L23 = 3.6e-2; |depth A port (cm)
L34 = 110e-2; |depth B port (cm)
L45 = 76.5e-2; |depth chamber C (cm)
L56 = 65e-2; |depth port C (cm)

p34=l34/2; |depth port B into chamber C(cm)
p23=l23/2; |depth port A into chamber C(cm)
vd=11000e-6; |driver volume
vc=4500e-6;|cone volume
Lrc = 36.5e-2; |depth chamber B (cm)
Vrc = LRC*h4*w4-vd; |chamber A volume (litres)

Atc = 1892.00e-4; |Throat chamber cross-sectional area (sq cm)
Vtc = vc+atc*2*thick; |Throat chamber volume (cc)

|Parameter Conversions:

Sd = 1210.00e-4; |Diaphragm area (sq cm)

Arc = h4*w4;

Ltc = Vtc / Atc;
}

Def_Driver 'Driver'

Sd=1130.00cm2
Bl=23.50Tm
Cms=1.24E-04m/N
Rms=4.69Ns/m
fs=33Hz |Mmd = 190.63g not recognised by AkAbak, fs calculated and used instead
Le=1.9mH
Re=5.0ohm
ExpoLe=1

System 'System'

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

AcouCompliance 'chamber B'
Node=4=5
|wd={w4}
|hd={h4}
|Len={Lrc}
|vf={w4*h4*lrc-vd-s3*(l34-p34-thick)}
ca={(w4*h4*lrc-vd-s3*(l34-p34-thick))/rc}


duct 'Throat chamber'
Node=6=8
SD={Atc}
Len={Ltc}
vf={vtc}
|Visc=0
|ca={vtc/rc}

duct 'chamber A'
Node=8=9
sd={S1}
Len={L12}
vf={s1*L12-s2*(L23-p23-thick)}
|ca={(s1*L12-s2*(L23-p23-thick))/rc}


AcouCompliance 'port A'
Node=9=10
|sd={S2}
|Len={L23}
ca={(s2*L23)/rc}

duct 'second port B'
Node=4=10
Sd={S3}
Len={L34}
|ca={(s3*L34)/rc}

duct 'second port B'
Node=4=10
Sd={S3}
Len={L34}
|ca={(s3*L34)/rc}

AcouCompliance 'chamber C'
Node=10=11
| wd={w4}
|hd={h4}
|Len={L45}
|vf={L45*w4*h4-p23*s2-L12*(r1+2.5e-2)^2*pi-s5*(l56-thick)-(s3-thick)*p34*2}
ca={(L45*w4*h4-p23*s2-L12*(r1+2.5e-2)^2*pi-s5*(l56-thick)-(s3-thick)*p34*2)/rc}

duct 'port C'
Node=11=12
sd={s5}
Len={L56}
|ca={(s5*L56)/rc}

Radiator 'port C outlet'
Node=12
SD={S5}

and the best sim I can get from this script....thoughts?



edit: ops...too much things to do at the same time...sorry

Hi

The image appears to be a flyer for a roots/dub night about a year old. Shame, it looks like it was a fun night.

I still think all the Vf need to be removed. Just looked at the manual again - the description for the Vf parameter is not entirely clear, but the diagram figure 98 does show the Vf (Caf in the diagram, its the same thing) in shunt with the duct, which means the total volume of air Akabak is modeling is really the sum of Vf and Len*wd*hd, which is about twice as big as it should be.

The lumped compliance math looks correct.

The documentation for radiation is a bit confusing, but I an suspicious it might be simulating a single cab in 4pi, and that the only way to get 2pi would be to add a reflection. Not sure about this though.

Maybe I'll have a play with Akabak over the weekend.

:oops:

Note: don't do promotion when you're publishing sim smiley36

however.....
Imho Akabak use 2pi just because if I sim the same horn in HR at 2pi and export into akabak I have the same response.

As promised I've been doing a little Akabaking. I got the following script, based on bitzo's, with the following tweaks:
- Turns out AcouCompliance must be connected between a single node (which serves as input and output) and ground (= node 0)
- Changes to the dimensions of the ports to match the resonant freqs of 28, 57 and 95Hz, as per the plan
NOTE: These Akabak lengths will not match the reality, a prototype must be tuned by hand!
- All ports as ducts; A chamber as duct, B and C as compliances. No vf front chambers.
- Added a hack to model multiple cabs (see the "num" variable), and set number to 4, which is what I designed for.

Here's the code:

Def_Const |Hornresp Input Parameter Values
{
R1=50e-2/2; |radius chamber A
R2=20e-2/2;|30e-2/2; radius port A
R3=17.5e-2/2; |radius port B
h4=60e-2; |cab width
w4=71.4e-2; |cab depth
R5=40e-2/2; |32.5e-2/2; radius port C
thick=1.8e-2; |wood thickness
S1 = r1^2*pi; |duct area chamber A (sq cm)
S2 = r2^2*pi; |duct area port A(sq cm)
S3 = r3^2*pi; |duct area port B (sq cm)
S5 = r5^2*pi; |duct area port C (sq cm)
c=321; |sound velocity
roh=1.2754; |air density
rc=roh*sqr(c); |divide volume by this value

L12 = 26.50e-2; |depth A chamber (cm)
L23 = 20e-2; |3.6e-2; depth A port (cm)
L34 = 100e-2; |depth B port (cm)
L45 = 76.5e-2; |depth chamber C (cm)
L56 = 15e-2;|65e-2; depth port C (cm)

p34=L34/2; |depth port B into chamber C(cm)
p23=L23/2; |depth port A into chamber C(cm)
vd=11000e-6; |driver volume
vc=4500e-6;|cone volume
Lrc = 36.5e-2; |depth chamber B (cm)
Vrc = LRC*h4*w4-vd; |chamber A volume (litres)

Atc = (41.8e-2/2)^2*PI; |Throat chamber cross-sectional area (sq cm)
Vtc = vc+atc*2*thick; |Throat chamber volume (cc)

|Parameter Conversions:

Sd = 1210.00e-4; |Diaphragm area (sq cm)

Arc = h4*w4;

Ltc = Vtc / Atc;

|Number of cabinets stacked
num = 4
}

Def_Driver 'Driver'

Sd=1130.00cm2
Bl=23.50Tm
Cms=1.24E-04m/N
Rms=4.69Ns/m
fs=33Hz |Mmd = 190.63g not recognised by AkAbak, fs calculated and used instead
Le=1.9mH
Re=5.0ohm
ExpoLe=1

System 'System'

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

AcouCompliance 'chamber B'
Node=5=0
ca={(w4*h4*lrc-vd-s3*(l34-p34-thick))/rc}

Duct 'Throat chamber'
Node=6=8
SD={Atc}
Len={Ltc}

duct 'chamber A'
Node=8=9
sd={S1}
Len={L12}

duct 'port A'
Node=9=10
sd={S2}
Len={L23} | Warning: effective length

duct 'port B'
Node=5=10
Sd={S3}
Len={L34} | Warning: effective length

duct 'second port B'
Node=5=10
Sd={S3}
Len={L34} | Warning: effective length

AcouCompliance 'chamber C'
Node=10=0
ca={(L45*w4*h4-p23*s2-L12*(r1+2.5e-2)^2*pi-s5*(l56-thick)-(s3-thick)*p34*2)/rc}

duct 'port C'
Node=10=11
sd={S5}
Len={L56} | Warning: effective length

Coupler 'Multiple cabs'
Node=11=0=12
ratio={1/sqrt(num)}

Radiator 'port C outlet'
Node=12
SD={S5*num}

Sooo interesting at all. smiley20
Btw2 question...have you ever measured this cab? Only for getting the differences between reality and sim.

What do you think about "squareing" the ports and chamber A?

cheers

I expect the reflex port behavior to differ in reality. Neither my software nor Akabak can accurately simulate the "parasitic inertience" effects that tend to increase port inertience and reduce resonant frequencies. You have to measure the electrical impedance curve and then shorten the ports to match. Once this is done, additional cabs can just be copies of the first.

A square A chamber and square ports would probably be fine.

what about C ports?
Anyways...a quick sketch is better than thousand words, what do you think?