I am entertaining the idea of designing speaker cabinets (inspired by some of the more... unusual... designs I've seen here) using my 3D CAD software to create a mold for fabrication. The obvious advantage would be smoothly-curved pathways with almost no discontinuities.
They would be designed for a driver in the 4" range.
Can't find much directly related to this in Search, and the suggested threads when I enter certain keywords are mostly 10+ years old.
The ProtoMold web site has a selection of resins, with characteristics in a table allowing them to be sorted. Injection Molding Materials Guide
The materials with the best ratings for Warp and Dimensional Accuracy are:
Anyone have any opinions on which of these to try first? The Polycarbonate / ABS Alloy is the highest rated, with 'medium' relative cost. The first two have the lowest relative cost, but also the least strength ('medium-low' range).
Come to think of it, dimensional accuracy and warping wouldn't be that much of a problem if all the complex stuff is in one piece, right? So maybe some 6/6 glass-filled Nylon would be a better choice (poor dimensional accuracy, but medium cost & impact resistance and high strength).
Any advice?
They would be designed for a driver in the 4" range.
Can't find much directly related to this in Search, and the suggested threads when I enter certain keywords are mostly 10+ years old.
The ProtoMold web site has a selection of resins, with characteristics in a table allowing them to be sorted. Injection Molding Materials Guide
The materials with the best ratings for Warp and Dimensional Accuracy are:
- Acrylonitrile Butadiene Styrene (ABS)
- Polystyrene
- Acrylic
- Polycarbonate
- Polycarbonate / ABS Alloy
Anyone have any opinions on which of these to try first? The Polycarbonate / ABS Alloy is the highest rated, with 'medium' relative cost. The first two have the lowest relative cost, but also the least strength ('medium-low' range).
Come to think of it, dimensional accuracy and warping wouldn't be that much of a problem if all the complex stuff is in one piece, right? So maybe some 6/6 glass-filled Nylon would be a better choice (poor dimensional accuracy, but medium cost & impact resistance and high strength).
Any advice?
Have you considered making just the baffle out of 3d printing in order to get the waveguide, rounded eges, etc. to improve acoustic performance (good for a few units at lower cost)? The rest of the cabinet can be made of low cost ply or mdf. Having just the front baffle injection molded or molded out of a casting mold is how many commercial cabinets are made. All injection molding is very expensive in tooling costs and is for mass production where you can plan on a ROI.
How many cabinets are you planning to make? A sizeable mold will set you back a couple of 10k $.
As for the material, good of you to check this out beforehand, since different materials have different shrink factors.
You might also want to add polypropylene (with or additives) to the list. It's fairly cheap, and very sturdy, good damping.
For only a few cabinets, you could also look at vacuum molding. Much cheaper, but also less freedom in design.
As for the material, good of you to check this out beforehand, since different materials have different shrink factors.
You might also want to add polypropylene (with or additives) to the list. It's fairly cheap, and very sturdy, good damping.
For only a few cabinets, you could also look at vacuum molding. Much cheaper, but also less freedom in design.
I'd like this to be a successful experiment that leads to a production run, but it has as much to do with my wanting to rely on my design skills over my fabrication skills (that darn hand-eye coordination thing has never been my strong suit).
If you know what you're doing (draft angles, ejectors, sprues, etc.), you can design your own mold and have it fabbed in a machine shop for far less. Places like Protomold.com have also reduced the price of making molds from your 3D object (it'd be 1000's instead of 100's, but still far less than the traditional $20K range).
Polypropylene is one of the materials in the link I posted; it has low cost and high impact resistance, but low strength and poor flash.
Of course, the advantage with a mold is that I can have speaker cases made in a variety of materials for little additional cost.
My current plan is to use a 4" full-range driver mounted on the front panel, with the rear of the speaker driving a mini-horn that comes out either on the front panel or maybe the left and/or right side panel.
Any advice on the best way to proceed? I've seen some images of the HornResp program (too many unfamiliar terms); I'd need a very good tutorial that doesn't assume I'm already an audio expert.
If you know what you're doing (draft angles, ejectors, sprues, etc.), you can design your own mold and have it fabbed in a machine shop for far less. Places like Protomold.com have also reduced the price of making molds from your 3D object (it'd be 1000's instead of 100's, but still far less than the traditional $20K range).
Polypropylene is one of the materials in the link I posted; it has low cost and high impact resistance, but low strength and poor flash.
Of course, the advantage with a mold is that I can have speaker cases made in a variety of materials for little additional cost.
My current plan is to use a 4" full-range driver mounted on the front panel, with the rear of the speaker driving a mini-horn that comes out either on the front panel or maybe the left and/or right side panel.
Any advice on the best way to proceed? I've seen some images of the HornResp program (too many unfamiliar terms); I'd need a very good tutorial that doesn't assume I'm already an audio expert.
You will need to spend some time with the program and then build some prototypes out of wood or foam core to make sure it works, then design the mold. If you are new, there is much to learn and you should look at existing proven back loaded horn (BLH) designs as a starting point. An injection molded BLH is interesting as I have yet to see a cost effective mass market BLH speaker. Other programs like AJHorn, Akabak, MJK also can be used. Akabak being the most flexible and powerful, IMO. Would not be bad to ask for someone to help you with the acoustic design and you implement the injection molded aspect of it.
Thanks for the advice. I was unaware of most of the options you listed, and your suggestion that I defer to an expert for the design is something I had already considered.
After all, there is "Do It Yourself", but there is also "Get It Done Well In Less Than A Year". 😉
Jeff
After all, there is "Do It Yourself", but there is also "Get It Done Well In Less Than A Year". 😉
Jeff
Hi,
I fail to see how you can build a BLH without multiple
interlocking mouldings, and its commercial merit.
rgds, sreten.
I fail to see how you can build a BLH without multiple
interlocking mouldings, and its commercial merit.
rgds, sreten.
Well, then... maybe I'll surprise some people, because I'm thinking it can be done with two pieces. 😉
Jeff
Jeff
Mini & horn usually don't go together. Devices like you are talking about are more characteristically TLs of one sort or another.
It should also be noted that smoothing the inside of a back loaded horn is more often than not counter productive as it allows high frequency information you don't want out of the mouth to come out the mouth.
The most common & versatile existing horn for 4" drivers is the Frugel-Horn Mk3. Free plans at Frugal-horn.com. Other examples of BLH there as well.
How big were you thinking?
dave
Hhmmm... design concerns have changed in the decades since I was home-brewing cabinets. Back then, any sharp corner (e.g. a discontinuity) was considered a secondary radiator due to diffraction effects, so smooth curves were preferred on exterior as well as interior surfaces.
The plans at Frugal-Horns.com are for speaker cabinets much larger than I intend. I'm thinking the same size range as the Sonos Play:1.
I don't know how much benefit I'd get from a transmission line or horn in a small box, vis-a-vis a closed box or vented design (still have to learn how to do some simulations), but using an injection mold process to build them means they won't be significantly more expensive.
Getting back to the Mk3 you mentioned: interesting design. I'm curious how the triangular volume behind the baffle contributes anything to the sound.
Jeff
The plans at Frugal-Horns.com are for speaker cabinets much larger than I intend. I'm thinking the same size range as the Sonos Play:1.
I don't know how much benefit I'd get from a transmission line or horn in a small box, vis-a-vis a closed box or vented design (still have to learn how to do some simulations), but using an injection mold process to build them means they won't be significantly more expensive.
Getting back to the Mk3 you mentioned: interesting design. I'm curious how the triangular volume behind the baffle contributes anything to the sound.
Jeff
Actually, if you can do a mold for polypropylene (glass filled?) for a 2-way monitor with a 6" woofer that would be very attractive. This might be molded as 2 halves that are then heat welded together. If the inner surface of the "outside" shell had lots of hexagonal "honeycomb" structure to it, about 1" deep, this could be reinforced by the builder or filled with sound adsorption material. The PP itself has great dissipation in the acoustic frequency range, so the cabinet would be pretty dead. The honeycomb wall would not need to be all that thick if the combs were only 1" wide each. You could add dye to the PP material to give it some color and some (needed) opacity.
Make the front accept removable rectangular (flat) baffles that can be secured to some threaded metal inserts and you have something that lots of people would buy for small 2-way projects, including myself.
Make the front accept removable rectangular (flat) baffles that can be secured to some threaded metal inserts and you have something that lots of people would buy for small 2-way projects, including myself.
That description seems a bit more complex than I was considering. For instance, I am not expecting the exterior walls to be 1 or more inches thick (necessary for the honeycomb structure you referenced).
While I am thinking two parts, with the first part providing all the baffles plus the speaker & amplifier mounting holes, the second part would be little more than a lid that is bolted onto the open side that allows the molded first part to be removed from the mold (and also provides access for installing the components).
Jeff
While I am thinking two parts, with the first part providing all the baffles plus the speaker & amplifier mounting holes, the second part would be little more than a lid that is bolted onto the open side that allows the molded first part to be removed from the mold (and also provides access for installing the components).
Jeff
Hmmm, OK. Just to be clear the thickness of the PP is, say, 2mm. The mold has a relief that is 1 inch deep. That's NOT the thickness of the PP itself.
I don't think that you will be able to injection mold anything but a thermoset if the requirement is for a thin shell. The mechanical rigidity will be too poor with other materials. And then you will have a nice little resonance machine. This is why I suggested the honeycomb feature. You can use materials that are mechanically less stiff (not completely rigid) but still have some toughness and let the mechanical support of the honeycomb provide the overall stiffness. The lossy PP material would help to damped panel vibrations that are a source of coloration in most boxed speakers because the box resonates and re-radiates sound. You can definitely hear that - it's the signature sound of a cheap boxy speaker. Believe me, I have built several of these and have now turned to OB speakers to eliminate this issue.
Smooth on the outside is good, as is smooth for a front-loaded horn, diffraction on the inside (and expansions at bends) act as low pass filters keeping the HF out of the horn.
The FH3 is about as small as you can go and still call it a horn, and some would debate that even then.
With the size of the Sonus available you will be doing a sealed or vented box.
The pointy bit? That is part of the horn. This is a tapped horn, the driver is placed part-way down the horn.
dave
I always thought that this was a silly idea. What is "sharp" anyway? It depends on the frequency you are talking about and therefore the wavelength of sound.
People would make cabinets with a 1" radius roundover, which already starts to look pretty dumb, but this would still be "sharp" until you reached a frequency of a few kilohertz, so not doing much for anything except the near-edge-of-hearing regime (e.g. above 3kHz).
What you want to avoid are reflections from "sharp" boundaries that constructively interfere. The most extreme example would be a dome tweeter (almost a point source) centered in a round baffle. If you distribute the pathlengths to the diffraction sources then they will be imperceptible without having to resort to making your enclosure a half sphere or the like. Translation: offset the tweeter from each edge in such a way as to maintain a smooth frequency response. The location of favorable positions can be easily modeled in software, too.
Oops, I mentioned a 2-way. Didn't see that this was the full range forum. Apologies.
But a 2-way cabinet constructed this way would be really nice...
Back then, the audiophiles thought that diffraction caused a time smear of the signal, reducing the clarity and also damaging the stereo imaging. I could never hear it, myself, but I don't have Golden Ears.
Horns can be pretty small, but still effective. An example is this item: iPhone horn
My original plan, until I saw the breadth and depth of speaker designs here. 😉
Jeff
That is not a horn, even if it is horn shaped. It may amplify/filter a small range (a horn is good for 3-4 octaves) but is likely to damp everything else down.
dave
I was thinking that the walls would be in the neighborhood of 10-14 mm thick (and more, at some junctures). The curved inner surfaces are supposed to guide the air pressure where it will do some good instead of flexing, but perhaps some additional structural buffering is needed.
Do you have any links to images of speaker enclosures that use the honeycomb approach?
Jeff
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