Thanks so much for the kind words and feedback, guys. Here are the T/S parameters and impedance response from the weekend. Thoughts appreciated - I feel like I should be happy, but I have a limited understanding of how to insightfully interpret the results. Need to find a good, cheap PC program for measuring the frequency response... I'll share that soon as well. Cheers.
Piston Diameter: 8.543 inches (217mm)
SPL: 94.36 dB 1W/1m
R(e): 9.216
F(s): 19.51
Q(ts): 0.2242
Q(es): 0.2389
Q(ms): 3.656
L(e): 0.4473
M(md): 17.5 grams
M(ms): 22.5 grams
V(as): 20.05 cubic feet (567.8 liters)
I don't often see Qts so low along with such high Vas. Of course I really don't deal with super soft suspension woofers at all.
How does this model? What does changing the field do to parameters. Will it do what you want in a practical size box?
Hi Hentai,
I admire your technical skills and I think you are one of the few builders of field coil driver who ALSO be willing to talk about technical details and simulations (as opposed to "you have to hear yourself to believe")
Other than the great flexibility of fine tuning the sound(Qes, BL, etc), do you think those claims that field coil drivers "greatly reduces distortion" because of "less flux modulation, more stiff field" to be true, or has a technical background supporting the claims?
My gut feeling is that if the field coil current are regulated perfectly(little to no variation/modulation with music signal playing), it might has some advantages, but that still can't stop the irons near the gap being modulated?
I admire your technical skills and I think you are one of the few builders of field coil driver who ALSO be willing to talk about technical details and simulations (as opposed to "you have to hear yourself to believe")
Other than the great flexibility of fine tuning the sound(Qes, BL, etc), do you think those claims that field coil drivers "greatly reduces distortion" because of "less flux modulation, more stiff field" to be true, or has a technical background supporting the claims?
My gut feeling is that if the field coil current are regulated perfectly(little to no variation/modulation with music signal playing), it might has some advantages, but that still can't stop the irons near the gap being modulated?
A good estimation I saw was this one:
Midrange distortion
But then I think it’s geometry dependent.
Also bl(I) seems more important and I was hoping saturated magnet will flatten bl(I), but seems Lowther still has high distortion
Lowther EX3
Midrange distortion
But then I think it’s geometry dependent.
Also bl(I) seems more important and I was hoping saturated magnet will flatten bl(I), but seems Lowther still has high distortion
Lowther EX3
Well, I suppose I've really done it.... I quit my well-paying job as a software engineer a few months ago to devote a couple of years of my life to my creative fascination with this project. I couldn't be happy mass producing a driver or loudspeaker, but I certainly could be producing compelling artworks built around a great driver of my own making. So, that's my plan at present. I aim for either wild success, or as beautiful a failure as I can manage... that seems reasonable.
Lots of posts soon to come - the cabinets are well under way and this driver measures very well.
Lots of posts soon to come - the cabinets are well under way and this driver measures very well.
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Driver, V2
Where to start?
Well, after discovering that a guy with an art degree and obsessive personality traits could (with the tailwind of the vast internet at his back and excellent individuals such as yourselves) both design and build a great sounding driver, I decided that instead of finishing the prototype off with a cabinet I wanted to redesign for something a bit more serious, and mindful of things I didn't like about the first version.
Many weeks were spent in Fusion 360... with the guidance of my spiritual adviser, Leonard the Cat.
There were key things to address in the new design. First, the prototype ran pretty hot - technically safe, but too hot to feel comfortable selling it to anyone in a cabinet. I wanted a motor with lower resistance, at least 1.5T of flux in the gap, +/-3mm Xmax or better, and that could be perform well with a 12V power supply and remain comparatively cool. That ended up as this, shown in FEMM:
Fantastic. Next, while a wooden frame sounds fun and interesting, it definitely isn't as stiff and dependable as a metal frame, and contributes nothing to wicking heat away from the motor. I wanted to design an aluminum frame this time that acts like a heatsink, attached the length of the motor along with a little thermal paste and with a lot of surface area exposed to the air. Eventually, the motors came back from the mill and the frame aluminum and brass elements from waterjet cutting:
Hentai, I'm glad you asked about chrome on the motors. A more learned man would have gladly paid the $250 or so for the mill to include plating, but instead all of the metal you see in the new driver is hand sanded and hand polished, by me, to a mirror finish. I won't be doing that nonsense again, should I earn the right to order the next batch of steel... it'll come to my doorstep already plated and polished. Kidding aside, I'm getting a cortisone shot in my wrist tomorrow to fix the wear caused by the collective effort over the past several months...
The spider... keantoken, you were right about silk not being a good choice. Over time and a lot of use, the silk slowly got... very, very tired. Yeah, it started to simply sag - and as we speak the voice coils in the prototype are sitting way too low in the gap. I loved the softness of the suspension in the first version however, and the wide footprint. 3D printing was the best compromise... I decided to make the spider in two parts - a hard, lightweight carbon fiber collar and an industrial strength, flexible TPU attaching the collar to the frame arms. It weighs about a gram:
Next, the cones and surrounds. In the first version I made the mold forms myself from plaster, but having added a 3D printer to my tool set I just printed, sanded and sealed perfectly symmetrical mold forms for the whizzers, and two-part molds for the main cones and surrounds for easy removal of the main cone (the pictured mold comes apart at the surround ring):
I eventually found a higher quality hosho paper to work with as well, and now the main cone, whizzer and voice coil former are all hosho washi. I absolutely love the natural, detailed sound they produce. Here's some of that, a voice coil and wet cones drying on the molds:
I'm still using the same wonderfully light and thin lambskin leather for the surrounds - I can't imagine ever wanting to try something else.
Okay, it's late here and I'll wrap this up as a first installment. Tomorrow, I hope to share and discuss the measurements from the driver, and talk about the cabinet design. Everything I've done so far spells a very low Qts... all else about the T/S params is ideal for me, but I don't really want that - I want a nice, easy to build bass reflex design, and a loudspeaker that will play +/- 3dB to 40Hz. I am led to believe that I can achieve that, and the Xmax and low mass I want with the addition of a simple series resistor to increase Qes... and in testing that does appear to be the case. More tomorrow.
Where to start?
Well, after discovering that a guy with an art degree and obsessive personality traits could (with the tailwind of the vast internet at his back and excellent individuals such as yourselves) both design and build a great sounding driver, I decided that instead of finishing the prototype off with a cabinet I wanted to redesign for something a bit more serious, and mindful of things I didn't like about the first version.
Many weeks were spent in Fusion 360... with the guidance of my spiritual adviser, Leonard the Cat.
There were key things to address in the new design. First, the prototype ran pretty hot - technically safe, but too hot to feel comfortable selling it to anyone in a cabinet. I wanted a motor with lower resistance, at least 1.5T of flux in the gap, +/-3mm Xmax or better, and that could be perform well with a 12V power supply and remain comparatively cool. That ended up as this, shown in FEMM:
Fantastic. Next, while a wooden frame sounds fun and interesting, it definitely isn't as stiff and dependable as a metal frame, and contributes nothing to wicking heat away from the motor. I wanted to design an aluminum frame this time that acts like a heatsink, attached the length of the motor along with a little thermal paste and with a lot of surface area exposed to the air. Eventually, the motors came back from the mill and the frame aluminum and brass elements from waterjet cutting:
Hentai, I'm glad you asked about chrome on the motors. A more learned man would have gladly paid the $250 or so for the mill to include plating, but instead all of the metal you see in the new driver is hand sanded and hand polished, by me, to a mirror finish. I won't be doing that nonsense again, should I earn the right to order the next batch of steel... it'll come to my doorstep already plated and polished. Kidding aside, I'm getting a cortisone shot in my wrist tomorrow to fix the wear caused by the collective effort over the past several months...
The spider... keantoken, you were right about silk not being a good choice. Over time and a lot of use, the silk slowly got... very, very tired. Yeah, it started to simply sag - and as we speak the voice coils in the prototype are sitting way too low in the gap. I loved the softness of the suspension in the first version however, and the wide footprint. 3D printing was the best compromise... I decided to make the spider in two parts - a hard, lightweight carbon fiber collar and an industrial strength, flexible TPU attaching the collar to the frame arms. It weighs about a gram:
Next, the cones and surrounds. In the first version I made the mold forms myself from plaster, but having added a 3D printer to my tool set I just printed, sanded and sealed perfectly symmetrical mold forms for the whizzers, and two-part molds for the main cones and surrounds for easy removal of the main cone (the pictured mold comes apart at the surround ring):
I eventually found a higher quality hosho paper to work with as well, and now the main cone, whizzer and voice coil former are all hosho washi. I absolutely love the natural, detailed sound they produce. Here's some of that, a voice coil and wet cones drying on the molds:
I'm still using the same wonderfully light and thin lambskin leather for the surrounds - I can't imagine ever wanting to try something else.
Okay, it's late here and I'll wrap this up as a first installment. Tomorrow, I hope to share and discuss the measurements from the driver, and talk about the cabinet design. Everything I've done so far spells a very low Qts... all else about the T/S params is ideal for me, but I don't really want that - I want a nice, easy to build bass reflex design, and a loudspeaker that will play +/- 3dB to 40Hz. I am led to believe that I can achieve that, and the Xmax and low mass I want with the addition of a simple series resistor to increase Qes... and in testing that does appear to be the case. More tomorrow.
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Thank you so much, guys! I’m working up another long post and additional pics, along with t/s params and more details, questions - we’re flying all day, but I’ll see if I can’t get it up here before we lose WiFi on the flight... Hopefully you’ll all like the cabinets as well, they’re a pretty bold design that exposes the driver to view - glass, santos mahogany, brass, aluminum and black granite...