Spreadsheet for Folded Horn Layouts...

[soho54]

From David McBean he is actually gone past AkaBak in computaional accuracy. His programis just a bit more limited. I can attest to it's acuracy as can Brian. It is really close to what you will measure in the real world if you actually make the box well.

Mark

I am not putting HR down at all, but when it comes to really checking out your finished design you need more inputs than HR will allow.

 

[soho54]

No, not yet. I'm an absolute noob wrt Akabak.

Ok, I'll see what I can do.

Can you verify the accuracy of this sketch-up model to your finished build?

Also the exact distance from the edge to the drivers center, or mounting edge lip to the throat end if you have it. Mouth to driver hole cut-out with correct cut-out size will work too.

Also any bracing that you might have added. I don't see any in the pics, but I thought I remember you saying something about it. Maybe not.

 

[Brian Steele]

Ok, I'll see what I can do.

Can you verify the accuracy of this sketch-up model to your finished build?

That looks about right.

The driver's center is located 20 cm down the sloping portion. The driver is top-mounted through the panel.

The bracing didn't make any difference to the measured impedance minimum, so I suggest not bothering to include it in the model.

 

[Kravchenko_Audio]

Once I can work out other foldings, I'll include them in the spreadsheet.

Sweet!

Now that would be a truly awesome program. Can't begin to explain how much time I take folding horn designs into the smallest space.

I am not putting HR down at all, but when it comes to really checking out your finished design you need more inputs than HR will allow.

I agree. But Horn resp will export AkaBak scripts and you can do an apples to apples comparison. I do it all the time. But what I find when measureing the box is that Hornresp and AkaBak are usually very close, Hornresp being the closest.

I find AkaBak on the arcane side of intuitive. It was and is a great program. And for what it can do it is still quite powerfull. It's just that Hornresp is much easier to work with.

Mark

 

[Don Snyder]

HornRes v28 now does parabolics, no need to specify conics. The error is small, but the reported volume in the schematic window is much more
accurate. Now, if we could only get more segments.

 

[Brian Steele]

It looks like the best correlation between predicted and measured results occurs when the path length through the folds is somewhere between the centerline method (Lc) and the centerline/arc method (Lca).

I also found a small bug in the spreadsheet's calculation of L. I will deal with that shortly.

In the interim, I modified the graph to show the centerline of the path (dotted red line), the longest lenth (in black) and the shortest length (in green).

For the TH I built:

Centerline method gives 242.2 cm (dotted red line in the graph)

Centerline method with arcs gives 225.6 cm (not illustrated)

Sqrt method gives 241.4 cm (long length in black, short length in green)

Measurement of the build TH suggests that L is somewhere around 233 cm.

(The 0.7 method is going to give a value for L that's longer than the centerline method, which actual measurement suggests is too long, so I did not consider it in this exercise)

It looks like the geometric mean between the centerline method and the centerline/arc method gives the closest approximation to the measured results, so I'm going to redesign the spreadsheet either around this or the centerline/arc method (for a bass horn, I think perhaps it might be best to err on the side of the horn being slightly too long rather than the horn being slightly too short).

 

[soho54]

Brian Steele,

I have a preliminary AkAbak model set up. The first thing I noticed is that the HR model posted here is a bit different than the base numbers from the Excel sheet from there. I'll look into it more later.

This is just a starter model with the extra mass and resistance of the bends not included, the path length has just been approximated. The next step would be to remove the corner sections and replace them with Acoumass/resistance components to take the edges off the peaks and displacement.

Here is a pic of the AkAbak model on the left, and the original HR sim on the right.

System 'DEMO1'

Def_Driver 'Driver'
dD=26cm dD1=11cm tD1=6.5cm |Cone
t1=1.1cm
fs=39Hz Vas=92L Qms=7.5
Qes=0.31 Re=5.2ohm Le=0.37mH ExpoLe=0.618


Def_Const
{
S1 = 4.8e-2;
S2 = 6.3e-2;
S3 = 8.2e-2;
S4 = 9.6e-2;
S5 = 10.9e-2;
S6 = 10.1e-2;
S7 = 10.1e-2;
S8 = 11.8e-2;
S9 = 13.1e-2;
S10 = 12.1e-2;
S11 = 12.1e-2;
S12 = 14.5e-2;
S13 = 17.1e-2;
S14 = 16.1e-2;
S15 = 17.3e-2;
S16 = 15.8e-2;
S17 = 13.6e-2;
S18 = 13.6e-2;
S19 = 14.8e-2;
S20 = 13.4e-2;
S21 = 11.8e-2;
S22 = 13.6e-2;
S23 = 16.3e-2;
S24 = 15.3e-2;
S25 = 16.3e-2;
S26 = 17.7e-2;


L1 = 20e-2;
L2 = 26.7e-2;
L3 = 2.5e-2;
L4 = 3.3e-2;
L5 = 2.0e-2;
L6 = 33.0e-2;
L7 = 3.0e-2;
L8 = 3.9e-2;
L9 = 2.5e-2;
L10 = 30.5e-2;
L11 = 4.0e-2;
L12 = 5.2e-2;
L13 = 3.7e-2;
L14 = 4.0e-2;
L15 = 5.4e-2;
L16 = 4.0e-2;
L17 = 17.0e-2;
L18 = 3.0e-2;
L19 = 4.7e-2;
L20 = 4.0e-2;
L21 = 4.2e-2;
L22 = 4.8e-2;
L23 = 3.4e-2;
L24 = 13.9e-2;
L25 = 20.9e-2;
}


Driver Def='Driver''Driver'
Node=1=0=100=3


Waveguide 'Horn segment 1'
Node=3=2
WTh=41.4cm HTh={S1}
WMo=41.4cm HMo={S2}
Len={L1}

Waveguide 'Horn segment 2'
Node=3=4
WTh=41.4cm HTh={S2}
WMo=41.4cm HMo={S3}
Len={L2}

Waveguide 'Horn segment 3'
Node=4=5
WTh=41.4cm HTh={S3}
WMo=41.4cm HMo={S4}
Len={L3}

Waveguide 'Horn segment 4'
Node=5=6
WTh=41.4cm HTh={S4}
WMo=41.4cm HMo={S5}
Len={L4}

Waveguide 'Horn segment 5'
Node=7=6
WTh=41.4cm HTh={S6}
WMo=41.4cm HMo={S5}
Len={L5}

Duct 'Duct segment 6'
Node=7=8
WD=41.4cm HD={S6} Len={L6}

Waveguide 'Horn segment 7'
Node=8=9
WTh=41.4cm HTh={S7}
WMo=41.4cm HMo={S8}
Len={L7}

Waveguide 'Horn segment 8'
Node=9=10
WTh=41.4cm HTh={S8}
WMo=41.4cm HMo={S9}
Len={L8}

Waveguide 'Horn segment 9'
Node=11=10
WTh=41.4cm HTh={S10}
WMo=41.4cm HMo={S9}
Len={L9}

Duct 'Duct segment 10'
Node=11=12
WD=41.4cm HD={S10} Len={L10}

Waveguide 'Horn segment 11'
Node=12=13
WTh=41.4cm HTh={S11}
WMo=41.4cm HMo={S12}
Len={L11}

Waveguide 'Horn segment 12'
Node=13=14
WTh=41.4cm HTh={S12}
WMo=41.4cm HMo={S13}
Len={L12}

Waveguide 'Horn segment 13'
Node=15=14
WTh=41.4cm HTh={S14}
WMo=41.4cm HMo={S13}
Len={L13}

Waveguide 'Horn segment 14'
Node=15=16
WTh=41.4cm HTh={S14}
WMo=41.4cm HMo={S15}
Len={L14}

Waveguide 'Horn segment 15'
Node=17=16
WTh=41.4cm HTh={S16}
WMo=41.4cm HMo={S15}
Len={L15}

Waveguide 'Horn segment 16'
Node=18=17
WTh=41.4cm HTh={S17}
WMo=41.4cm HMo={S16}
Len={L16}

Duct 'Duct segment 17'
Node=18=19
WD=41.4cm HD={S17} Len={L17}

Waveguide 'Horn segment 18'
Node=19=20
WTh=41.4cm HTh={S18}
WMo=41.4cm HMo={S19}
Len={L18}

Waveguide 'Horn segment 19'
Node=21=20
WTh=41.4cm HTh={S20}
WMo=41.4cm HMo={S19}
Len={L19}

Waveguide 'Horn segment 20'
Node=21=22
WTh=41.4cm HTh={S21}
WMo=41.4cm HMo={S20}
Len={L20}

Waveguide 'Horn segment 21'
Node=22=23
WTh=41.4cm HTh={S21}
WMo=41.4cm HMo={S22}
Len={L21}

Waveguide 'Horn segment 22'
Node=23=24
WTh=41.4cm HTh={S22}
WMo=41.4cm HMo={S23}
Len={L22}

Waveguide 'Horn segment 23'
Node=25=24
WTh=41.4cm HTh={S24}
WMo=41.4cm HMo={S23}
Len={L23}

Waveguide 'Horn segment 24'
Node=25=26
WTh=41.4cm HTh={S24}
WMo=41.4cm HMo={S25}
Len={L24}

Waveguide 'Horn segment 25'
Node=26=27
WTh=41.4cm HTh={S25}
WMo=41.4cm HMo={S26}
Len={L25}

Duct 'Du1' Node=100=26
WD=41.4cm HD=30cm Len=1.7cm

Radiator 'Horn mouth' Def='Horn segment 25'
Node=27

 

[soho54]

The above was with a 229.6cm path length.

 

[soho54]

I will need the temp where you were at the time you took the measurement, and altitude as well to see what a difference it will make.

 

[Brian Steele]

Brian Steele,

I have a preliminary AkAbak model set up. The first thing I noticed is that the HR model posted here is a bit different than the base numbers from the Excel sheet from there. I'll look into it more later.

This is just a starter model with the extra mass and resistance of the bends not included, the path length has just been approximated. The next step would be to remove the corner sections and replace them with Acoumass/resistance components to take the edges off the peaks and displacement.

Here is a pic of the AkAbak model on the left, and the original HR sim on the right.

Good stuff. The Akabak impedance plot is a closer match to what I've actually measured. The resonance frequency is almost an exact match.

As I mentioned in my previous message, the spreadsheet has a bug wrt calculation of the horn length.

 

[Brian Steele]

I will need the temp where you were at the time you took the measurement, and altitude as well to see what a difference it will make.

Temp=29C
Altitude=~75 ft above sea level

 

[soho54]

OK, for 29c at 22.86m above sea level I get a speed of sound of 348.444m/s, with an air density of 1.165009649kg/m3.


Here is the default AkAbak sim on the left, and the adjusted constants on the RIGHT.

 

[BP1Fanatic]

Vol (1) is calculated using S1, S4 and L, and it's not dependent on any of the measurements of the box, so it's somewhat misleading at this point.

My fault Brian! I knew about the Vol (1) calculations. I should have stated {Vol (2) = Vol (1)}.

Is the centerline version available for download?

 

[Brian Steele]

My fault Brian! I knew about the Vol (1) calculations. I should have stated {Vol (2) = Vol (1)}.

Is the centerline version available for download?

Version 1.2.0 attached.

1. Plot options added for driver (top-mount and bottom-mount), centerline, advanced centerline, minimum length, maximum length.

2. Goal-seeking for effective length is now included (default is advanced center line, but the other options are also provided). This unfortunately complicates the operation of the spreadsheet a bit - I'm going to check to see if it can be simplified.

3. I've cleaned up the format of the spreadsheet a bit.

 

[Brian Steele]

Forgive my manners - I forgot to thank "Soho54" for the "advanced-centerline" idea to determine the effective length of the horn. After reviewing each of the different methods yet again, that method seems to produce the closest match to the results that I obtained with POC #2.

I forgot to mention that I also fixed two minor bugs with the calculations for the panel dimensions. One bug made the driver's baffle slightly too long, and the other made the internal panel on the other side of the mouth slightly too long as well. These are corrected in v1.2.0

 

[soho54]

Hey thank you, for taking the time to putting this spreadsheet together.

I'm glad you caught the two odd panel lengths. They were the reason I asked for you to verify my model was what you built.

 

[soho54]

I also finished up the Hornresp model.

As this fold is a "digitized" fold of a single flare rate horn it has several straight sections that will give HR a minor hiccup. Mainly the middle impedance spike will hit a couple hertz higher, and the resonate frequency will be a little bit higher. There is also the case of the drivers mounting sections, but it's effects are minor in the scheme of things.

I also noticed once you get done it will be easy to get the data to put into HR or AkAbak. Very nice sheet.

I don't know why I had that voltage in there?

 

[Brian Steele]

I also finished up the Hornresp model.

As this fold is a "digitized" fold of a single flare rate horn it has several straight sections that will give HR a minor hiccup. Mainly the middle impedance spike will hit a couple hertz higher, and the resonate frequency will be a little bit higher. There is also the case of the drivers mounting sections, but it's effects are minor in the scheme of things.

I also noticed once you get done it will be easy to get the data to put into HR or AkAbak. Very nice sheet.

I don't know why I had that voltage in there?

Eek - how did you end up with 198.72 cm^2 for S1? My target for S1 was 270 cm^2

 

[Kravchenko_Audio]

Hey thank you, for taking the time to putting this spreadsheet together.

I am remise in adding my thanks as well. I can only vaguely understand how work went into this Brian. If you keep tweeking it it will be a very powerfull piece of code. THank you very much for your work!

I'm still playing with it.

Mark

 

[Brian Steele]

Hey thank you, for taking the time to putting this spreadsheet together.

I'm glad you caught the two odd panel lengths. They were the reason I asked for you to verify my model was what you built.

I didn't think the panel length errors would cause to much issues. Panel F was about 1~2mm too long and Panel I was about 5mm too long. There are some approximations involved with Panel F's position, so it's best to lay out the rest of the horn, then use Panel F to join Panel G to Panel A.

I've attached v1.3.0 of the spreadsheet - this version allows the user to highlight specific panels in the graph. I've indicated in the plot which panels were incorrectly sized.