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Old 23rd March 2011, 09:13 PM   #3641
GM is online now GM  United States
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Ah! I misunderstood. Sorry, haven't messed with AkAbak yet since I've not had a need to.

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Old 23rd March 2011, 09:59 PM   #3642
sdad is offline sdad  United States
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GM:

Absolutely no problem at all. I see how given the tools available, a quick build to an excellent product is normal. Most of us will opt for using these tools as it is by far the most expedient. For some undetermined reason I've never been one to take this practical approach. Nope, I've got to beat on things until my brain throbs uncontrollably.

I do not have the resources to come up with the suggested drivers I keep reading about. Best I can do is work with the cast offs I find while dumpster diving in Ebay. As a result, I find my satisfaction in the theoretical, rather than the substantive. What I have discovered is that reasonable driver, coupled with a good design, makes for an enjoyable result. It's that elusive good design that I'm in pursuit of. To get to that good design, I need to know how to best use the tools.
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Old 23rd March 2011, 10:22 PM   #3643
AllenB is offline AllenB  Australia
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I think people put far too much on what driver they use, ie: its reputation. I understand you want certain specs for your tapped horn, that's obviously not what I'm talking about though. I'm currently getting some great sound out of some embarrassingly cheap drivers as subs.
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Old 23rd March 2011, 10:53 PM   #3644
soho54 is offline soho54  United States
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Quote:
Originally Posted by sdad View Post
Here's a quick sketch of what I am trying to model . the 2 spkrs front load into a common cavity (what I called the horn) The rear of each spkr is kept separate from each other, as I want to investigate the effects of different resonant lengths being summed inside that common cavity.

I hope this makes sense.
OK, this is how I would start.

I have marked the nodes on the picture to make it a bit easier to understand. The thicker lines outline the individual segments, and the thin line is the distance to use. The green segments are ducts, red are waveguides, and the purple two are ducts or waveguides depending on whether there is any expansion to them in the dimensions not shown. The gray line is the radiator.

This "simple" model will not take the drivers physical displacement in the horn path into consideration. As that is a harder nut to crack.

Hope this helps.
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File Type: jpg example.jpg (29.9 KB, 345 views)
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Old 23rd March 2011, 11:23 PM   #3645
soho54 is offline soho54  United States
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Looking back at it, you may have meant for the opening/exit/output from the common area to be forward/towards the viewer.

If that is the case just move the radiator from node 152 to 151.
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Old 23rd March 2011, 11:59 PM   #3646
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Try this example:

Tapped Horn For Car

(I think there are some errors in the script provided, though.)

The essential point is to understand that AkAbak allows you to split and merge ducts and waveguides. Remember to match the areas - if you are joining two 100 cm2 mouths to a single throat, the throat has to be 200 cm2.

Here's a basic 4 segment tapped horn schematic using Hornresp-like areas (S1 to S5) and segment lengths(L12 to L45). Exporting a design from Hornresp should produce a similar schematic.

Code:
|            -------Driver1-------
|           |                     |
|S1<--L12-->S2<--L23-->S3<--L34-->S4<--L45-->S5-- Radiator
With example AkAbak node numbers added:

Code:
|            -------Driver1-------
|           |                     |
|S1<--L12-->S2<--L23-->S3<--L34-->S4<--L45-->S5
|11         12         13         14         15-- Radiator
|------------------------------------------------
Define all the horn segments with the "waveguide" element.
(A "Horn" element in AkAbak is a "Waveguide" with a "Radiator" added to its mouth.)

Now add a second horn in parallel:

Code:
|            -------Driver1-------
|           |                     |
|S1<--L12-->S2<--L23-->S3<--L34-->S4<--L45-->S5
|11         12         13         14         15-- Radiator1
|------------------------------------------------
|21         22         23         24         24-- Radiator2
|S1<--L12-->S2<--L23-->S3<--L34-->S4<--L45-->S5
|           |                     |
|            -------Driver2-------

This should generate the same SPL curve, but 6 dB higher in output.

Finally, merge the 2 horns:

Code:
|            -------Driver1-------
|           |                     |
|S1<--L12-->S2<--L23-->S3         |
|11         12         13         |
|----------------------S3<--L34-->S4<--L45-->S5
|21         22         13         14         15-- Radiator
|S1<--L12-->S2<--L23-->S3         |
|           |                     |
|            -------Driver2-------
Remember to make S3 (for the L34 segment), S4 and S5 equal to twice the original areas.
The SPL curve should match that for the previous version.
This script simulates the drawing you provided earlier of the two horns oppposite each other with a shared mouth area.

You can now make the lengths of the 2 segments in the "second" horn different from the corresponding sections in the "first" horn.
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Old 24th March 2011, 12:09 AM   #3647
sdad is offline sdad  United States
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soho54,
Thanks, I think I've got it based on how you defined the nodes. What I think is going on is, as a snippet:

.
.
.
.
Waveguide 'W3' Node=10=150 .........
Waveguide 'W4' Node=100=150........
Duct 'D5' Node=150=151.......

And, yes, I am radiating from the front, not down.

I guess what I was missing is setting up node 150 for WG3 and WG4 may have an area of 1000 each but D5's node 150's area could be at 2000 (example only). The ducts I used originally were intended to keep the areas constant, that was the only use. For whatever reason I assumed the areas needed to be constant

I tried this out in AkAbak with success.

Knowing this is going to go a long ways in my modeling. Thanks!!!!!!!!!

I have yet to look, so I should be quiet until I do, but while here I can't help but ask about modeling microphonics. I'd like to introduce a set of drivers with a different bandpass into the same chamber as the 2 original drivers

BTW, what did you use to mark up the pdf?
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Old 24th March 2011, 12:14 AM   #3648
sdad is offline sdad  United States
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Don Hills, Thanks for the post. Must have come in as I was writing response to soho54.
You directly stated what occurred to me while looking at soho54's markup : the areas of multiple outputs can be summed into a single input. That is HUGE.

Now I will go back and read balance of your post.

Finished reading.
Yup, I got it. Makes sense. I can mash things together any 'ol way I wanna knowing this fact.


The technique of doing the 180 (or whatever angle) is to create a series of waveguides apparently. Is there a rule of thumb for how fine to divide?

Last edited by sdad; 24th March 2011 at 12:22 AM.
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Old 24th March 2011, 01:28 AM   #3649
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You don't have to fold / divide when you're simulating in Hornresp or AkAbak. Design it as a straight horn, then fold where required when you build it. Folds in a tapped horn have no significant effect on the response within the intended (bass) passband. They only affect the response at high frequencies.

I've tried it both ways in AkAbak - a simple straight horn with 3 segments, then a 15 to 20 segment model of the actual horn as folded and built. I carefully modeled the bends in a simliar manner to soho54's picture to allow for the changes in area as the bend is traversed. There was no significant difference in the results in the passband. Remember that a tapped horn only works properly over a 2 to 2.5 octave range at best. (40 to 100 Hz, for example.)
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Old 24th March 2011, 01:56 AM   #3650
sdad is offline sdad  United States
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Thanks Don,

The very little I've played with I see less than 2 octaves of useable passband. That's ok, as I am looking very seriously at narrow passbands. I want to emphasize distortion minimization so small xmas with narrow passbands seemed to be called for. The Big concern is the interaction between passband drivers. I want a common radiator for as many drivers as possible, Helmholtz convinced me of that. However, what affect will 4 thumping 12"er's going to have on my 4" er's. I have a LOT to look at.
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