Horn Design tips for cell phone
Howdy folks. I'm interested in experimenting with 3d printing technology to create fancy horns.
I currently have a Reprap Prusa 3D Printer, with a build area of about 190x190x100mm
The nice thing about the 3d printer is it's ability to handle complex shapes just as easily as very simple shapes. It just handles any 3d model 1 layer at a time, so you can make some pretty wild or intricate designs.
I was thinking a fun thing to try at first, and given my relatively small build area, would be some sort of phone dock with integrated horn/waveguide for amplifying a cell phone speaker. I realize this won't be winning any kind of awards for sound quality, but I'm interested in understanding the concepts, and seeing how much of an effect it can have. And maybe in the future using this knowledge I could scale up the idea for a full range enclosure with a serious driver in it.
So I'm wondering if anyone can provide some tips for how to design a horn profile for maximum efficiency and sound quality. Would I have to know very specific specifications(thiele&small?) of the actual driver used in the phone? I have an HTC EVO which I would be using to test this with. Is there some way I could measure or derive whichever significant parameters I would need for this?
One thing I'm curious about is if there is an optimal total length of the horn, or if you can just keep going larger and larger for more and more effect.
Here is an example of a commercial product produced for the iPhone which is the sort of thing I would be interested in doing:
AirCurve - fits iPhone 3G and original iPhone - Griffin Technology
Hrm, maybe this was the wrong section to put this in.
Design tips... lets see:
First off, don't be intimidated by the "mathematically engineered" design in your linked example. I believe that engineering of interesting speakers - including folded/convoluted horns - can't be distilled down to just mathematics. As for measuring parameters of the phone's speaker driver, that may be of use eventually in refining your design, but why not start with some experimental builds based on the dimensional constraints at hand? Perhaps you could construct some straight (non-convoluted) cardboard/tape mockups to evaluate different horn expansion profiles and mouth areas before consuming a lot of - I imagine - pricey printer ammo. Listening tests at this stage would probably be the most useful indicator of whether the concept has the potential to perform to your expectations.
I'd suggest a throat section that tightly couples to the speaker opening on your phone - try to minimize discontinuities or cavities that would surely lead to troublesome resonances. The (eventually) convoluted section should be of narrow, minimally expanding cross-section with curve radii as large as possible relative to cross-section diameter. Once you get it to the desired direction, then you can do the final expansion to the largest practical mouth opening. Expansion profile seems to elicit a lot of emotional discussion - I guess it can affect things like directivity. Once again, some quick mock-ups should give you some idea of how critical that decision will be, and how to direct your further efforts. A conical expansion is pretty hard to beat for simplicity, and personally, I'd start with that.
Once you've made a start and have some initial impressions (and pictures!) to share, I'm sure more pointed suggestions will follow.
By the way, I'm curious about your CAD software of choice for your printer modeling - care to share?
re: Karlson-coupler - here's approximately the size for you already done 50 years ago :D
PS - I recently got a new phone, one that actually plays MP3s (had an old Nokia brick before), so stay tuned for another cardboard horn.
Thanks for the links and great ideas everyone.
Another option which is popular with other 3d printing people is OpenSCAD. It has it's own scripting language, which is fairly simple and easy to learn, but not nearly as powerful as Python.
Well, I know it was suggested that I make some stuff with cardboard first, but generating 3D models is just too much fun.
I've put together a script for generating a wide variety of horn shapes. It is written in Python, for FreeCAD. It mostly generates the Mesh vertexes independently of the FreeCAD functions, so it could possibly be split out to a standalone script. I'm mainly using FreeCAD for visualization and ability to export to common 3d formats in this case.
The idea is that you can provide mathematical functions for each of:
Some examples just for fun:
Radius functoin: Oblate Spheroid
Path Function: Linear
A bunch of exponential radius horns, linear path, circular cross section
exponentinal "radius", circular path along 3/4 turns, Rectangular cross section
I'm still unsure about the way to define certain horn radius equations though. For example exponential horns. I know the simplest form of exponential equation is y = e^x. But this doesn't give any parameters for starting radius, or flare rate(is that the correct term?). Is there a common form of this function used for making horn profiles? I've implemented a sort of exponential function already, just not sure if I did it "properly".
I've also read about tractrix as another common profile, but I'm having trouble finding any euqation to model the radius for that as well.
Plus any other common shapes that I might be missing. Is there any cheatsheet of common horn equations on these boards or elsewhere online?
The script is still a work in progress, but I will be releasing it as open source in the near future when I feel it is more polished.
OK, I found this paper about exponential horn which explains the equation in the first page and a half. http://www.google.com/url?sa=t&rct=j...Xfpx404rKHCuGQ
Cool, so now I can just specify a start radius, end radius, and length, and it computes the rest.
Still trying to figure out the tractrix, and maybe hyerbolic, or others.
Also , you may read the introduction of Ajhorn manual
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