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post #31 of 66 Old 06-28-2010, 01:57 PM - Thread Starter
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System 'Simple Horn'


Def_Driver 'Dayton RSS390HF-4'
Sd=829.60cm2
Bl=14.67Tm
Cms=2.87E-04m/N
Rms=9.94Ns/m
fs=17.9999Hz
Le=1.00mH
Re=3.30ohm



Driver Def='Dayton RSS390HF-4''Driver'
Node=1=0=2=3

Enclosure 'E1'
Node=2
Vb=11.89L
Sb=831cm2

Duct 'Throat Chamber'
Node=3=4
SD=829.6cm2
Len=8.02mm

Horn 'Horn Segment'
Node=4
STh=85cm2
SMo=2.943m2
Len=4.015m
T=0.98
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post #32 of 66 Old 07-18-2010, 09:45 PM
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This has been a HUGE help, just wondering if you did and advanced modeling thread somewhere or if its still in the works. I'm trying to figure out how to model impedance equalizers and other things

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post #33 of 66 Old 07-18-2010, 09:57 PM - Thread Starter
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There are two partial medium level lessons in the works, but no time table to completion right now.

If you can better explain exactly what you are trying to sim I'll help with them specifically, if I can.

I am assuming you are talking passive EQ work here.
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post #34 of 66 Old 07-18-2010, 11:39 PM
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If there were a way to get this into the sim I'd be very interested to see how it effects it


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post #35 of 66 Old 07-19-2010, 12:19 AM - Thread Starter
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No problem. Here is a reference picture, and I'll post the scrip tomorrow. I have got to go to bed now.
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post #36 of 66 Old 07-19-2010, 07:52 AM - Thread Starter
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Ok, what you have to do is take your network map, and assign node numbers to all the connection points, like I have done one post above.

In AkAbak you do not want to put in wire runs (you can but why?) so you remove the un-needed points, and you get this.


Now it is just a matter of going Net>Electric up top and filling in the various Caps, Coils, and Resisters.

Here you go.
System 'Imp. Comp. Passive EQ Example'

Def_Driver 'Dayton RSS390HF-4'
SD=829.6cm2
fs=18Hz
Cms=0.287e-3m/N
Rms=9.94Ns/m
Bl=14.67Tm
Re=3.3ohm
Le=1mH



Driver 'D1' Def='Dayton RSS390HF-4'
Node=1=0=100=101

Resistor 'Req'
Node=1=2
R=5.1ohm

Coil 'Lm'
Node=2=3
L=6.957H
Rs=0.294ohm

Capacitor 'Ce'
Node=2=0
C=61.51uF

Capacitor 'Cm'
Node=3=0
C=2.972mF


Enclosure 'E1'
Node=100
Vb=315L
Lb=1m

Radiator 'Rad1' Def='D1'
Node=101


I was assuming Rm/Lm was a Coil and it's DRC. If not, you would do it like this:

Resistor 'Req'
Node=1=2
R=5.1ohm

Resistor 'Rm'
Node=2=3
R=0.294ohm

Coil 'Lm'
Node=3=4
L=6.957H
Rs=0.2ohm |Just guessing a DRC here. You can leave it out, but you will want to add it back in during finale rendering/component choice.

Capacitor 'Ce'
Node=2=0
C=61.51uF

Capacitor 'Cm'
Node=4=0
C=2.972mF
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post #37 of 66 Old 07-19-2010, 11:18 PM
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Awesome thanks for the help. its all about the nodes I guess. I follow the chain but I'm still a little fuzzy about the renaming of the driver nodes [Node=1=0=100=101] I know you wrote they flow from left to right so 1=(+) 0=(-) so which would 100 and 101 be? does it go [Node=(+)=(-)=(-)=(+)] or [Node=(+)=(-)=(+)=(-)]

I cut it back to the basics [Req, Ce] on the imp.eq the thing would cost to much to put together, guessing that's why they aren't used in most designs

the basic imp.eq brings the peak @ 52Hz from 64ohms down to 51ohms and it doesn't cost that much

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post #38 of 66 Old 07-19-2010, 11:41 PM - Thread Starter
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The first two are electrical (voice coil connections)

The second pair are the physical nodes (diaphragm/cone)

1=0=Cone Rear(100)=Cone Front(101)

The enclosure attaches to the Cones Rear(100)

The radiator gets attached to the Cone Front(101)
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post #39 of 66 Old 07-20-2010, 08:30 AM - Thread Starter
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I have to stop posting so late.

Node=(+)=(-)=(Driver rear)=(Driver front)
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post #40 of 66 Old 07-20-2010, 10:07 AM - Thread Starter
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OK, I have fixed a couple of minor text errors, and added some pictures to the beginning sections.

If anyone was having problems with anything please run back over that section again.

I have also change the images a few times today, so if you were here earlier today you may want to refresh your browser.
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post #41 of 66 Old 08-21-2010, 04:16 PM
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How would I go about modeling bracing in a TH? My best guess would be to to something similar to your explanation of a dual port box. But how to make them end up in the same area when numbering them differently? Am I trying to over complicate things maybe hahaha. I've successfully made a few great sounding small TH enclosures but it's time to step it up and I know bracing is a must!

Thanks!

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post #42 of 66 Old 08-24-2010, 08:21 PM - Thread Starter
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It depends on the bracing, but you can do what you say by using the same node points.

Lets say you want to add a dividing brace at your 10 duct1 11 spot, just go...

10 duct1a 11
10 duct1b 11

Now you have two parallel ducts in the same spot.
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post #43 of 66 Old 08-28-2010, 10:08 AM
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Thanks soho54, that makes sense. I came up with another question. Tom Danley made a comment in a post about the added mass of folding

Quote:


Also, at low frequencies how one parses the extra mass that each bend represents can cause the measured result to be different as in this case, I did not account for enough bend mass and the result was acoustically a little longer than my model and reality has more viscous loss than I estimated.

Is there a way to model this effect in Akabak?

Also might be cool to add a section for lining/stuffing sections using the "visc=#" (#=1-50) from what I've read. I'm still playing with it and no where no a pro

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post #44 of 66 Old 08-28-2010, 12:24 PM - Thread Starter
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What TD seems to be talking about is a different (more advanced) way to model a horn. What you do is model the straight sections as waveguides/ducts only, and the bends are modeled as base forces of mass/resistance/compliance, and not waveguide/duct elements.

AkAbak can do it, but getting it right is not easy. My experimental equations for the AcouMass and AcouResistance for one bend are longer than most of the full simple scripts I have posted in this thread.

If you look up those two elements (might as well check out AcouCompliance as well) in the AkAbak manual it will give you the idea, and base equations. Then you have to figure out how to apply it to bends with changing area, different degree corners, and frequencies. Just so you know the simple 90deg corner mass equation will not work right here, so don't waste your time there.

It is much simpler to just physically account for the path length, and model that way.

Something along the lines of this will give you good results with a horn with multiple bends.

You use each triangle section though the bend as a waveguide element. This will adjust the mass/resistance properties though the bends on it's own, and get it pretty darn close. If you do it correctly the FR and impedance peaks and dips will line up the the true measured ones. The Q of the peaks and dips will be a little different, and will generally be a little less in magnitude as the frequency rises, but you can get a very accurate model without you having to become a PhD level math whiz.

EDIT:I should add that this only works at sub frequencies. If you need bandwidth much above 150Hz you will want to learn the hard way. The dimensions through the bends must be less than 1/4WL of the frequencies in question.

Stuffing is also a pain as there are no defined reference points there. No area, rayls/ms or fiber density inputs. The visc numbers are imaginary, so you just have to guess. You could manually input your own code to account for it, but it will not be easy. Here is a link to some math to give you an idea of how to handle it.
http://auralization.blogspot.com/?zx=549be658a4a7f370
Scroll down to the Friday, June 09, 2006 JO Derivation Scan post.
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post #45 of 66 Old 08-28-2010, 06:26 PM
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Awesome! Thank You for the link. Looks like I've got more reading to do I love this stuff

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post #46 of 66 Old 08-28-2010, 08:53 PM - Thread Starter
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A word on that link,
Just use it to get an idea of how you can try and implement your own method. It has a nice table or two, and is a pretty good swing at it. There has been some questioning of the validity of some of the equations there. This is the site of the guy questioning it, and there is some very good stuff here as well.
http://teodorom.altervista.org/blog/

Here are a couple of papers on fillings in sealed enclosures, and a few other things. First up is an old one by Leach, then a newer one that will prove interesting on several levels.
http://users.ece.gatech.edu/mleach/papers/Filling.pdf
http://grputland.com/files/thes.pdf

Here is a very interesting paper on horns from Leach as well. Make sure to read the letter to the editor section too.
http://users.ece.gatech.edu/mleach/p.../HornPaper.pdf

Here are a couple more that are about horns.
http://www.audioxpress.com/magsdirx/...olbrek2884.pdf
http://www.audioxpress.com/magsdirx/...olbrek2885.pdf
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post #47 of 66 Old 09-20-2010, 04:56 AM
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Great work there soho! It's a good resource for the diy community and great to see diyers helping each other out. I haven't had a chance to read through it all and give it a go, but learning this thing is on the to do list!
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post #48 of 66 Old 05-08-2011, 06:55 PM
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I've been side-tracked the last several months with work but I've got a new question I hope you can help me with. Akabak has a helmholtz calculator but how do I get it to run in the script? I'm working on reducing unwanted peaks in my TH designs

Thanks

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post #49 of 66 Old 08-13-2011, 09:55 AM - Thread Starter
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Quote:
Originally Posted by eye_fling_poo View Post

I've been side-tracked the last several months with work but I've got a new question I hope you can help me with. Akabak has a helmholtz calculator but how do I get it to run in the script? I'm working on reducing unwanted peaks in my TH designs

Thanks

Sorry, I missed this question. I don't quite understand what you want to do with it here.
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post #50 of 66 Old 08-13-2011, 01:52 PM
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Wondering if there is a way to sim something similar to the way DSL used Helmholtz resonators in the DTS-20 to tame the unwanted peaks


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post #51 of 66 Old 08-15-2011, 11:01 AM - Thread Starter
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It is very easy to add in the "resonators" in AkAbak.

All you need to do is add a duct near the front tap or throat, and ground the other end to "0" to cap it off.

The length of the duct is determined by the frequency you are trying to null, and the diameter you play with to get the "Q" right.

I'm on lunch break right now, and can't for the life of me remember the equation for determining the length. It is really simple, and I am 80% sure I remember, but... you can find it on my Eazy Horn Spreadsheet at the bottom with the extra stuff.
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post #52 of 66 Old 12-29-2011, 08:09 PM
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I'm trying to get the graph of a vented box to match from HR to Akabak.

Here's what I'm seeing:

HR exported Script shows the enclosure being modeled as a Duct, whose area*length is equal to the enclosure volume. This produces a frequency response graph pretty much identical to the actual HR plot. But when creating a nearly identical script from scratch and specifying the enclosure from Net->Acoustic menu, even though it has the proper volume, and length, generates a different frequency response plot.

here is a pic of akabak "generic" script vs HR vs akabak w/ HR exported script




soho54, if you would be so kind as to tell me what in the world is going on, I can resume being sane, as this tiny little thing is driving me nuts.


oops, here are the scripts

Generic script where enclosure is modeled as an enclosure from the Net->Acoustic Menu:


HR-type script (edited the original to simplify it) where the enclosure is modeled as a duct:



Does this mean that HR simulates the enclosure as a duct? one predicts a huge null in the response and the other predicts a huge spike, right after 100 Hz. Which one will reflect reality?
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post #53 of 66 Old 12-30-2011, 08:21 AM - Thread Starter
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Quote:
Originally Posted by OscarJr View Post

one predicts a huge null in the response and the other predicts a huge spike, right after 100 Hz. Which one will reflect reality?

They are both right and wrong for the same reasons.

The differences you are seeing are mainly do to the path length difference between the open end of the port and the measuring/listening point in the two sims in relation to the driver.


In the image below the HR (double duct) sim is up top, and the simple AkAback model is below.




I say they are both right because they are correctly simulating two slightly different set ups. They are both a little wrong, because in real life the open end of the port will probably not be in either simed location.

This can be changed simply in one dimension with HR using the "Path" slider in the Wizard, or entered into the Combined Response option when Calculated.

You can also alter the Radiators positions in 3D space in AkAbak, but it is a little more involved.


Hope this helps.
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post #54 of 66 Old 12-30-2011, 09:53 AM - Thread Starter
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I forgot to add that you also need to remember that the peaks and valleys are exaggerated in the simulations.

Things are more blurred in real life. The difference between the two would be pretty insignificant in the real world.
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post #55 of 66 Old 12-31-2011, 09:51 PM
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I see now. I think. According to HR, zero path length difference implies the port output is radiated from the same "spot" as the speaker, which is not possible, but works because its a close enough representation of a front-facing port, correct?
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post #56 of 66 Old 01-02-2012, 06:44 AM - Thread Starter
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Not quite.

My examples above show you what AkAbak makes of the HR export script and the "generic" script.

The difference in the way the enclosure and port are positioned effects there path length to the simulated listening point. This is what causes the two different frequency responses for what seems like the same exact enclosures on the surface.


The HR export uses this double duct setup because it is actually the way the HR program simulates things. A "0 Path" does not mean the driver and port are coming from the same location. It means that you are going the leave things as the HR default.

If you want to move the port closer to the LP/MP you us a negative value, and further away then the default is positive.

It's like time aligning the driver and port to the positions the physical build will have.
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post #57 of 66 Old 01-02-2012, 04:44 PM
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Quote:
Originally Posted by soho54 View Post

If you want to move the port closer to the LP/MP you us a negative value, and further away then the default is positive.

It's like time aligning the driver and port to the positions the physical build will have.

This is the main part that I'm just not sure of: in HR, if path length is indeed specified as zero, then the distance from the driver radiator to the LP is the same as the distance from the duct radiator to the LP, correct? (if correct, then that means that the duct radiator is on the same baffle/plane as the driver, correct?

if so how can your diagram (which is essentially the same as the HR schematic) be correct, where the duct radiator is (length of rear chamber+duct length) cm away from the driver radiator?
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post #58 of 66 Old 01-03-2012, 06:10 AM - Thread Starter
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Quote:
Originally Posted by OscarJr View Post

This is the main part that I'm just not sure of: in HR, if path length is indeed specified as zero, then the distance from the driver radiator to the LP is the same as the distance from the duct radiator to the LP, correct?

No, this is incorrect. If you check the HR help file "0" means the distance between the driver and port is equal to Lrc plus Lpt or chamber plus port length.

Hornresp models the enclosure as seen in the schematic view. If you want to alter the driver to port distance you the change the Path which is in cm. A negative number moves the port in the direction on the driver. A positive number pushes it further away in time.
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post #59 of 66 Old 01-03-2012, 09:09 PM
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Ah I see. MUCH clearer now.

One last question. Is it possible to make the script that specifies an Enclosure (not double duct) to mirror the double duct plot?
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post #60 of 66 Old 08-17-2012, 05:09 AM
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Hi

just wondering if you could explain how radiation cones work specifically with regard to conical horns. a few things are puzzling me:

with a conical horn the manual says that because the radiation cone will have a constant convexity the sides of the horn are the same as the radiation cone. if I make the radiation cone smaller but keeps the same wall angle so it still follows the horn walls but only covers part way down from the throat this significantly improves the HF response without affecting the LF response. But if I make the whole horn smaller it does not improve the HF response. what is going on here?

If I have a horn that is made of two conical sections so that the flare angle is greater nearer the mouth how should I specify the radiation cone? I'm thinking I should specify it as the same shape as the section nearer the throat but does Akabak know to locate it in the first waveguide near the throat or will it put a small radiation cone in the middle of the wider section near the mouth? Does this matter? Or I can make it the shape of a cone that fits the section near the mouth but extrapolate the walls back into the horn to where their apex would be to get the radius? In this case does it make a difference if I use a horn section or waveguide+radiator?

I know it is possible to get decent HF response from a 1" driver on a conical horn because I have seen measurements of it. the only way I can get a decent sim from a 60 degree 40cm long conical is to specify the radiation cone as about 5cm long and 5cm high. as it is playing wavelengths down to about 1.5kHz which is roughly 22cm this doesn't seem right. the longer frequencies must experience the whole of the horn as a radiation cone - so shouldn't the size of the radiation cone be frequency dependent???

I'm a bit frustrated the manual doesn't have more examples of such a complicated subject - can you shed any light on this?

cheers
Phil
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