3D printed waveguides

[ani_101]

So now, a larger diameter WG will boost lower frequencies and a deeper WG will boost it more. Both diameter and depth affect directivity proprtionally. So you choose your diameter and depth based on your design goals and your throat diameter based on your tweeter, then your constant radius and throat angle are almost predetermined - a larger radius will begin to approximate a straight line, so you just make the radius as small as you can to span the gap between mouth and throat.



I know if I follow the above rules, I'll get a solid performing waveguide, so I only ever need to figure out the transition area if I want to use a specific tweeter. This is where my personal interest lies. However, if you or anyone else has a different aspect that they'd like to explore, I'm down to help with CAD and prototypes.

Dan[/FONT][/COLOR]

I followed till where we choose a throat diameter (based on the done size and surround and keep it as close to the dome as possible) and the mouth diameter (based on how large you want it and then choose the depth you want (any guidelines for what should be a good depth any good mouth/throat ratios that work?). Once we have the throat diameter, mouth diameter and the depth, we now choose the constant transition diameter to span the gap between throat and mouth over the depth - how do we choose the transition angle to determine how large or small the radius should be?

for example the transition angle of 57 - how was this determined? either the constant radius of 3.5 needs to be assumed which will determine the transition angle or the transition angle needs to be assumed which will determine the transition radius.

[TN Allen]

I don't know how DanP does this, however, I'll explain the method I use. I have the option in the software I use of creating an arc tangent to a line at the end point of the line. This can be done for a simple guide by using two circles in parallel planes separated by the thickness of the guide. A line is also created through the center of the circle that represents the intesection of the guide contour and the baffle surface. This line is trimmed at the circle extending outside the circle. There is an option to create an arc using a point and lone. The arc is created between the line end that intersects the mouth cirle, and a point on the smaller circle, that is, the throat opening, that represents an intersection of the line and the throat circle. This can be done in an orthogonal view even though the throat circle and the line are in different planes.

The resulting arc is used with a line through both circle centers, to produce a rotated surface. This surface is all that is necessary to generating a tool path. The transition cross section is therefore a simple arc, tangent to the baffle surface, and at whatever angle results given the guide thicness, and the throat and guide mouth diameter.

The above method for producing an arc is probably available in most CAD software.

[DanP]

I followed till where we choose a throat diameter (based on the done size and surround and keep it as close to the dome as possible) and the mouth diameter (based on how large you want it and then choose the depth you want (any guidelines for what should be a good depth any good mouth/throat ratios that work?). Once we have the throat diameter, mouth diameter and the depth, we now choose the constant transition diameter to span the gap between throat and mouth over the depth - how do we choose the transition angle to determine how large or small the radius should be?

for example the transition angle of 57 - how was this determined? either the constant radius of 3.5 needs to be assumed which will determine the transition angle or the transition angle needs to be assumed which will determine the transition radius.

I guess I didn't mention the angle at the mouth is assumed to be 180 degrees. This leaves only one radius that can connect the mouth at 180 degrees and the throat at some residual angle.

Now if you wanted an 8" waveguide that was 8" deep, you'd have to move to a variable radius, but I think this becomes outside the range of what is useful in home hi-fi. It's actually kind of lucky that the useful (to us home DIYers) range for these combinations falls into such an easily defined set of parameters.

I have actually purchased the hardware and designed most of a waveguide cutting jig based on TN Allen's post a while back, because what he just posted is true: the easiest and cheapest way to do a round guide with a constant radius profile is to mill it right into the baffle. In order to simplify the mechanism, I will be fixing the radius at 2" + the baffle thickness. So all you'll have to do is choose the throat opening dimension and the depth - the radius and mouth diameter will be automatic. This ratio of baffle thickness to profile radius will always be in a good range to provide useful waveguide loading.

With those assumptions you won't be able make a 8" WG that's 1" deep, nor a 5" WG that's 3" deep, but I don't think those are as useful as 8" dia x 2" deep or 5" dia x 1" deep (numbers may not jive, just examples).

Dan

[TN Allen]

Dan,

If you have any questions regarding the jig, don't hesitate ask. Had I known you intended to make one, I'd have sent you the original, although, the wheel bearings are quite loose, and might not have been all that useful.

[DanP]

Dan,

If you have any questions regarding the jig, don't hesitate ask. Had I known you intended to make one, I'd have sent you the original, although, the wheel bearings are quite loose, and might not have been all that useful.

Thanks TN. I've been thinking about this since your original post about the jig (years ago now?). The one I want to build will be adjustable as described above and accomodate at least a 28" long baffle - longer if the WG is not all the way to one end. Once I build it, I may not ever biild a waveguide-less speaker again. There are just too many benefits.

Dan

[johnnyrichards]

If additional testing is needed and a standard faceplate format is decided on, I will gladly build a baffle and take measurements. If the community starts dropping dozens of design concepts, testing will become tedious so the more mics on the project the faster data will be gathered.

[skatz]

Is there any chance that TN and DanP can illustrate whats being said here with diagrams? That would help greatly with my understanding.

[Josh Ricci]

The common problem with 3D or AM printing WG's would be size limitations in some cases, price if the parts are contracted and surface/layer roughness in the WG. The common, cheap tabletop 3D printers leave a fairly rough, stepped surface finish, when producing angled surfaces in the Z direction and the build area is often limited to 10x6x7" or similar. Larger platform and / or higher resolution machines are available but most hobbyists or smaller shops have only the smaller platforms. I have been running various AM equipment at my day job for 13 years and I've got access to a number of different 3D printers and also SLA machines so I've got a bit of experience in this field.

When it comes to the 3D modeling of the WG and making the STL file to print...That should be no problem for someone with access to Solidworks, Inventor or similar. Wouldn't take much time at all once the specifics of the WG design are settled on and it only needs done once. Slight tweaks are quickly made after the basic part file or assembly is created. I can help here if a design gets settled on.

[DanP]

If additional testing is needed and a standard faceplate format is decided on, I will gladly build a baffle and take measurements. If the community starts dropping dozens of design concepts, testing will become tedious so the more mics on the project the faster data will be gathered.

That's a good idea Johnny. As long as all the testers adhere to an agreed upon test protocol, we could accumulate comparable data much faster.

Josh - I only have access to Magics, which as you may know is designed to modify STL files that have been produced in other software. I can and have created good waveguide CAD files, but the process is tedious with my software and difficult to modify. If you have access to parametric modeling software and can change WG dimensions by typing in a number, that would make things easier, but the primary problem still remains of the specific geometry needed at the tweeter dome, which may or may not provide satisfactory results. I think an iterative testing process will be needed here, where slight tweaks may be all that are needed, but complete redesigns may be necessary at times as well. This is why I think the tweeter adapters are a good angle from which to attack this project. Even though I'll be making the parts for "free", I wouldn't want to make an 8" WG in it's entirety over and over just to test the integration in a 2" diameter local area.

Skatz - What part of the conversation would you like to see visually? I'll see if I can draw something up for you.

Dan

[skatz]

Posts 29, 32, 33

[TN Allen]

The common problem with 3D or AM printing WG's would be size limitations in some cases, price if the parts are contracted and surface/layer roughness in the WG. The common, cheap tabletop 3D printers leave a fairly rough, stepped surface finish, when producing angled surfaces in the Z direction and the build area is often limited to 10x6x7" or similar. Larger platform and / or higher resolution machines are available but most hobbyists or smaller shops have only the smaller platforms. I have been running various AM equipment at my day job for 13 years and I've got access to a number of different 3D printers and also SLA machines so I've got a bit of experience in this field.

When it comes to the 3D modeling of the WG and making the STL file to print...That should be no problem for someone with access to Solidworks, Inventor or similar. Wouldn't take much time at all once the specifics of the WG design are settled on and it only needs done once. Slight tweaks are quickly made after the basic part file or assembly is created. I can help here if a design gets settled on.

If some parameters can be chosen I'll do a quick part file and send a .stl file if you want to test it. If preferred I can send one of the files I already have.

[TN Allen]

Here is a set of adapters I milled for use with a 16" guide. There are 3 pieces of Corian, one is glued to the guide, one is for a Vifa radiator ring, and the other if I recall correctly, for an RS28. This approach works with round guides, but is not as easily done with oval guides, where the round throat quickly changes to oval if the guide depth is not carefully designed and milled. This guide and several others were to be part of a testing idea based upon 2' square baffles. I'll try to post more photos later, or Flickr links.

Regarding testing, I do think that in order to quantify the many advantages of waveguides, a more comprehensive testing method is needed. Figuring out what that may be may be more trouble and work than designing and milling guides. Actually, one reason I do so little testing is that I have not come up with a way to test that seems likely to provide meaningful data. Part of this is the so much of what a guide does to enhance listening, is subjective.

[TN Allen]

A few more photos. The first is the back of another guide with adapters for 3 tweeters. The second another 2' Square test guide, and the 3rd an oval guide that will fit in a 2' Square Baffle that can also accept other similar test guides. All of these guides vary in depth, and are stacked MDF. Which is fairly easy to finish, other than at the throat, because it is so soft. That is where a Corian insert, or a piece of Formica glued to the guide back helps to maintain the throat contour while sanding. The last photo is a small oval guide I printed a few years ago, and, the remaining photo is of several guides waiting to be tested. Were these not so heavy and expensive to ship, I'd send them off for testing.

[ani_101]

waveguide Jig? Allen, i think i have seen this somewhere, but do you have the link or more details on this? Dan are you doing any enhancement to this? I also do not fully understand how you are going to use it with a constant depth and the jig automatically calculating the mouth diameter and throat angle. The throat diameter will be fixed and determined by the dome diameter. The mouth angle is fixed at 180.

[TN Allen]

Here is the link to the YouTube video: https://www.youtube.com/watch?v=S92C3QT8fTg

Also the Forum link: http://techtalk.parts-express.com/fo...und-waveguides