Hi folks. I'm normally a regular in the car audio section here, but for the past few months I have been toying with an idea and I am looking for some insight on research material and just how overall plausible this is.
I am considering attempting to build a 18" subwoofer based on the old Cerwin Vega Stroker line. I'm sure some of you are familiar, but they were a car audio sub released in the late '90's. I have heard that many of them made it into home audio builds, so hopefully you are familiar.
I found that the soft parts for these drivers are still available aftermarket. This got me thinking-- how hard would it be to build one of these from the ground up. It seems there are quite a few bare frames available for reasonable prices, but the magnet/motor assembly is going to be the tougher part of the equation. My understanding is that ferrite/ceramic magnet stacks are glued up and then magnetized. I am guessing that this is beyond the reach of even a modest home shop.
I am thinking that it might be possible to build a custom neodymium motor in a well equipped shop. I have a fairly good size home machine shop and also a well equipped fab/welding shop. I can easily machine pole plates and am thinking that I should be able to do a neodymium motor with multiple magnets spaced around the circumference. There are commercial drivers like this, but it seems to be rare in subwoofer offerings.
I do realize that it is likely to cost as much or more than a commercial driver would cost. That is not the point. I like to build things, I like audio, and I would like to learn about the process of constructing the actual driver.
I'm looking for the following:
Thanks!
Jason
I am considering attempting to build a 18" subwoofer based on the old Cerwin Vega Stroker line. I'm sure some of you are familiar, but they were a car audio sub released in the late '90's. I have heard that many of them made it into home audio builds, so hopefully you are familiar.
I found that the soft parts for these drivers are still available aftermarket. This got me thinking-- how hard would it be to build one of these from the ground up. It seems there are quite a few bare frames available for reasonable prices, but the magnet/motor assembly is going to be the tougher part of the equation. My understanding is that ferrite/ceramic magnet stacks are glued up and then magnetized. I am guessing that this is beyond the reach of even a modest home shop.
I am thinking that it might be possible to build a custom neodymium motor in a well equipped shop. I have a fairly good size home machine shop and also a well equipped fab/welding shop. I can easily machine pole plates and am thinking that I should be able to do a neodymium motor with multiple magnets spaced around the circumference. There are commercial drivers like this, but it seems to be rare in subwoofer offerings.
I do realize that it is likely to cost as much or more than a commercial driver would cost. That is not the point. I like to build things, I like audio, and I would like to learn about the process of constructing the actual driver.
I'm looking for the following:
- Is this within the grasp of a well equipped home shop?
- Am I crazy for attempting this?
- Are there any books or other resources that I could study; google searches tend to return a lot about cabinet building and very little about building a driver
- If I do build it, is there a reasonable method for testing driver parameters?
Thanks!
Jason
While it is feasible it isn't easy and won't result in good performance if you don't know what you are doing.
Mach 5 Audio makes their own drivers - he machine the motors, charges the magnets and winds the voice coils. But they still use all the other parts bought from different manufacturers - the cone, the surround, the spider, the coil former, the magnets, the baskets, the gaskets (if used).
If all you want to do is build a motor you certainly can but I would highly advise researching into good motor design first. If you want it to have a lot of usable excursion the lossy inductance is going to be a big factor and you should probably copy or figure out how to design an advanced motor like the new Rockford T3.
You really should look at the Rockford T3 page - T3 19-inch Subwoofer | Rockford Fosgate®
This isn't called a superwoofer for nothing, the tech in this thing is way advanced compared to what other vendors are selling. It's not new tech, in fact it's pretty old and all patents on the motor design have expired, including the JBL patent that the Rockford is based on (and I'm pretty sure JBL borrowed the idea from a previous patent) but it's good design.
Also note that you have to get all the other parts just right too - the coil, the surround, the spider(s) or you will have a driver that doesn't perform well.
You can also look into STEALUS motor design, I'm not familiar with it but Mach 5 Audio seems convinced it's the next logical step forward.
And don't forget the evolution of drivers is continuing with moving magnet drivers, nothing new either but commercially available now from powersoft. The commercial ones have huge 40 inch cones.
For super serious subs it's starting to look like moving magnet designs are the way forward, although I really haven't even looked at the tech because I can't make one and can't afford the prices of what's available commercially.
This is a HUGE topic, it's not really as simple as machining a motor and adding a few neo magnets, you really have to know what you are doing. And if you do know what you are doing you can know the outcome before you even start.
All this stuff can be simulated with FEMM or BEMM or whatever, I'm not exactly sure what they use. But that's a deep rabbit hole too, I think you have to script your inputs for the simulator and that's way over my head at this point, I've never even looked at this type of simulator before.
Good luck, you're going to need it. And a lot of it.
But on the other hand, if all you want to do is make something for display purposes just so you can say you did it, that's easy enough.
Also all driver parts are available cheap from China, just look around Alibaba website, it's kind of like the Chinese ebay for manufacturers I guess.
Mach 5 Audio makes their own drivers - he machine the motors, charges the magnets and winds the voice coils. But they still use all the other parts bought from different manufacturers - the cone, the surround, the spider, the coil former, the magnets, the baskets, the gaskets (if used).
If all you want to do is build a motor you certainly can but I would highly advise researching into good motor design first. If you want it to have a lot of usable excursion the lossy inductance is going to be a big factor and you should probably copy or figure out how to design an advanced motor like the new Rockford T3.
You really should look at the Rockford T3 page - T3 19-inch Subwoofer | Rockford Fosgate®
This isn't called a superwoofer for nothing, the tech in this thing is way advanced compared to what other vendors are selling. It's not new tech, in fact it's pretty old and all patents on the motor design have expired, including the JBL patent that the Rockford is based on (and I'm pretty sure JBL borrowed the idea from a previous patent) but it's good design.
Also note that you have to get all the other parts just right too - the coil, the surround, the spider(s) or you will have a driver that doesn't perform well.
You can also look into STEALUS motor design, I'm not familiar with it but Mach 5 Audio seems convinced it's the next logical step forward.
And don't forget the evolution of drivers is continuing with moving magnet drivers, nothing new either but commercially available now from powersoft. The commercial ones have huge 40 inch cones.
For super serious subs it's starting to look like moving magnet designs are the way forward, although I really haven't even looked at the tech because I can't make one and can't afford the prices of what's available commercially.
This is a HUGE topic, it's not really as simple as machining a motor and adding a few neo magnets, you really have to know what you are doing. And if you do know what you are doing you can know the outcome before you even start.
All this stuff can be simulated with FEMM or BEMM or whatever, I'm not exactly sure what they use. But that's a deep rabbit hole too, I think you have to script your inputs for the simulator and that's way over my head at this point, I've never even looked at this type of simulator before.
Good luck, you're going to need it. And a lot of it.
But on the other hand, if all you want to do is make something for display purposes just so you can say you did it, that's easy enough.
Also all driver parts are available cheap from China, just look around Alibaba website, it's kind of like the Chinese ebay for manufacturers I guess.
Also be aware that playing around with big charged magnets is extremely dangerous. You could smash your fingers right off, big neo magnets are POWERFUL.
Thank you for the input! The redrockaccoustics link has some excellent info.
I did not really think that this was going to be this complex until I read through some of the whitepaper available @ the link above. I still want to do it, but I need to give it more thought and would still love to hear more input on the subject. I don't want it to end up as just a display piece, I would rather it actually worked. After all, if I wanted to just hang it on the wall I could just machine nice looking cylindrical spacers and skip purchasing magnets all together...
It is somewhat hard to fully convey my motivation. I have no desire to invent or pioneer any new ground in driver design, nor do I want to go into any sort of production, this will me one, or possibly 2 if it all works out well and just for me. Mostly I have a love for these particular speakers, and I think it would be an awesome project IF I could pull it off successfully.
I see there is some modeling software available, even for motor design as seen in the link above. I'm sure it is great for someone who will be doing this commercially, but for a one off hobbyist run-- it is a little bit more than I expect I need.
Does it need to be this complex though? I guess I am wondering is, if all I want is similar performance to the stock version with its ferrite motor-- then don't I only need a motor with the same or similar gap strength? Does it matter how you achieve this? If the gap strength is actually higher, is that a bad thing?
I appreciate the call to be realistic, and maybe this will go nowhere, but my thinking is that if I want to learn about this, I have to start somewhere. Why start with a 6 inch driver or something when I know that something I have a passion for is more likely to keep me motivated?
Thank you for the warning about magnets. I am aware of the dangers-- you can easily get into limb crushing territory with these. It's actually something I am more than a little concerned about going forward and one of the few reasons I haven't already just started designing something. I haven't worked out how you get 6-8 big neos aligned, equally spaced and then lowered onto what amounts to a steel plate with a big steel pin in the middle. I'm thinking that I would cut some aluminum fixture plates on my CNC mill and possible turn an aluminum tube for the center pole piece. Getting it onto the steel without missing fingers or teeth is still something I haven't thought of a possible solution for.
Thank you again for all the input.
Jason
I did not really think that this was going to be this complex until I read through some of the whitepaper available @ the link above. I still want to do it, but I need to give it more thought and would still love to hear more input on the subject. I don't want it to end up as just a display piece, I would rather it actually worked. After all, if I wanted to just hang it on the wall I could just machine nice looking cylindrical spacers and skip purchasing magnets all together...
It is somewhat hard to fully convey my motivation. I have no desire to invent or pioneer any new ground in driver design, nor do I want to go into any sort of production, this will me one, or possibly 2 if it all works out well and just for me. Mostly I have a love for these particular speakers, and I think it would be an awesome project IF I could pull it off successfully.
I see there is some modeling software available, even for motor design as seen in the link above. I'm sure it is great for someone who will be doing this commercially, but for a one off hobbyist run-- it is a little bit more than I expect I need.
Does it need to be this complex though? I guess I am wondering is, if all I want is similar performance to the stock version with its ferrite motor-- then don't I only need a motor with the same or similar gap strength? Does it matter how you achieve this? If the gap strength is actually higher, is that a bad thing?
I appreciate the call to be realistic, and maybe this will go nowhere, but my thinking is that if I want to learn about this, I have to start somewhere. Why start with a 6 inch driver or something when I know that something I have a passion for is more likely to keep me motivated?
Thank you for the warning about magnets. I am aware of the dangers-- you can easily get into limb crushing territory with these. It's actually something I am more than a little concerned about going forward and one of the few reasons I haven't already just started designing something. I haven't worked out how you get 6-8 big neos aligned, equally spaced and then lowered onto what amounts to a steel plate with a big steel pin in the middle. I'm thinking that I would cut some aluminum fixture plates on my CNC mill and possible turn an aluminum tube for the center pole piece. Getting it onto the steel without missing fingers or teeth is still something I haven't thought of a possible solution for.
Thank you again for all the input.
Jason
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If you just want reasonable performance that's easy enough to do. Just copy an existing design.
Not sure why you would only strive for reasonable though, if you are going to go to this amount of effort. It's not that hard to copy the Rockford design but you will need a custom basket, and I have an idea for that too. It will look funny and actually use two baskets back to back but would be functional.
There's a few designs with neo studs around the outside, but the Rockford page I linked to makes a believable case for using a single central slug though.
If you don't want more than 6 - 12 mm usable excursion though, things will be pretty simple. You won't have to worry about lossy inductance issues and you can just copy something that already exists.
Also be aware that there are baskets and soft parts available for cheap up to 32 inches. Why go small? Make s showpiece. With a 32 inch driver you don't really need a ton of usable excursion to make a lot of noise.
Not sure why you would only strive for reasonable though, if you are going to go to this amount of effort. It's not that hard to copy the Rockford design but you will need a custom basket, and I have an idea for that too. It will look funny and actually use two baskets back to back but would be functional.
There's a few designs with neo studs around the outside, but the Rockford page I linked to makes a believable case for using a single central slug though.
If you don't want more than 6 - 12 mm usable excursion though, things will be pretty simple. You won't have to worry about lossy inductance issues and you can just copy something that already exists.
Also be aware that there are baskets and soft parts available for cheap up to 32 inches. Why go small? Make s showpiece. With a 32 inch driver you don't really need a ton of usable excursion to make a lot of noise.
Also maybe contact Mach 5 Audio. He's done this and he knows what works. He might not have a lot of time to chat but he could definitely tell you how to build a motor that will work and might sell you all the parts you will need including a wound voice coil, basket up to 32 inches in size, cone, surround, spider, magnets and whatever else you need like glue and a dustcap. This stuff is cheap but if you don't know Chinese you'll likely have to order all these parts separately and end up paying too much for shipping if you go the actual manufacturer route on Alibaba.
Also be aware that when you glue it all up everything needs to be precise or you could end up with an offset coil (either vertically or horizontally) that could rub or fail and/or rob you of usable excursion. You might want to buy extra parts to practice. You WILL need shims to put it together, you can probably make them or maybe Mach 5 will sell you those too.
I'm not sure he's going to sell you anything or even talk to you but it doesn't hurt to try.
There's also other small build house vendors that assemble drivers, Pierce Audio and Fi and Sundown but I'm not sure if any of these guys would be willing to help you.
Also be aware that when you glue it all up everything needs to be precise or you could end up with an offset coil (either vertically or horizontally) that could rub or fail and/or rob you of usable excursion. You might want to buy extra parts to practice. You WILL need shims to put it together, you can probably make them or maybe Mach 5 will sell you those too.
I'm not sure he's going to sell you anything or even talk to you but it doesn't hurt to try.
There's also other small build house vendors that assemble drivers, Pierce Audio and Fi and Sundown but I'm not sure if any of these guys would be willing to help you.
Just a guy,
First off, let me apologize. I just reread my post, and I did not intend to imply that the red rock acoustics link was the only one of value-- I am at work at the moment, and had not yet had a chance to look over the link you provided. I will study it soon, I have already bookmarked it 🙂
I'm not striving just for reasonable. IMO the original CV Strokers are very good to excellent drivers. From a comparison standpoint to even modern car audio drivers, they are far more efficient and still have better power handling than many of the newer high power/competition drivers. Even their more modern namesakes, while capable of handling tremendous power, are much lower efficiency. IIRC their 18 was rated at something like 96dB @ 1W 1M. I realize this might not be ground breaking from a home audio standpoint, but for mobile audio this is head and shoulders above a lot of the crowd.
The original Stroker was not a high excursion beast, Xmax was like +/-.7(ish) inches, puts it something like +/- 18mm. I love the way my little Strokers sound (have several 12" models, and owned both 15's and 18's when I was young and dumber), and second, but not really most important, I love the way they look as well.
Why the size? If it works, I may build a pair, and actually use them. If I use them, it will most likely be in a automotive installation and that will limit my size constraints a bit. That said, I would love to build something like a 32" sub, that would be wild. If I find that building an 18 is a fun and rewarding project, then maybe I will move onto something like that-- I also have other design ideas I would love to experiment with after I gain some knowledge. I am sure they have been done, or attempted. I'm getting off on a tangent, but I have wondered it is is feasible to build a driver with a fixed electromagnet instead of permanent magnets. Also, the moving magnet and fixed VC sound extremely interesting as well. Experimenting with rotary servo type drivers (I'm not sure exactly what the proper name would be, but I talking rotary vane with basically a rotary DC motor as the motor), or even rotary blade drivers with variable pitch blades.
Thank you again for taking the time to discuss with me 🙂
Jason
First off, let me apologize. I just reread my post, and I did not intend to imply that the red rock acoustics link was the only one of value-- I am at work at the moment, and had not yet had a chance to look over the link you provided. I will study it soon, I have already bookmarked it 🙂
I'm not striving just for reasonable. IMO the original CV Strokers are very good to excellent drivers. From a comparison standpoint to even modern car audio drivers, they are far more efficient and still have better power handling than many of the newer high power/competition drivers. Even their more modern namesakes, while capable of handling tremendous power, are much lower efficiency. IIRC their 18 was rated at something like 96dB @ 1W 1M. I realize this might not be ground breaking from a home audio standpoint, but for mobile audio this is head and shoulders above a lot of the crowd.
The original Stroker was not a high excursion beast, Xmax was like +/-.7(ish) inches, puts it something like +/- 18mm. I love the way my little Strokers sound (have several 12" models, and owned both 15's and 18's when I was young and dumber), and second, but not really most important, I love the way they look as well.
Why the size? If it works, I may build a pair, and actually use them. If I use them, it will most likely be in a automotive installation and that will limit my size constraints a bit. That said, I would love to build something like a 32" sub, that would be wild. If I find that building an 18 is a fun and rewarding project, then maybe I will move onto something like that-- I also have other design ideas I would love to experiment with after I gain some knowledge. I am sure they have been done, or attempted. I'm getting off on a tangent, but I have wondered it is is feasible to build a driver with a fixed electromagnet instead of permanent magnets. Also, the moving magnet and fixed VC sound extremely interesting as well. Experimenting with rotary servo type drivers (I'm not sure exactly what the proper name would be, but I talking rotary vane with basically a rotary DC motor as the motor), or even rotary blade drivers with variable pitch blades.
Thank you again for taking the time to discuss with me 🙂
Jason
Absolutely, that sounds like a good resource to persue. I have 4 12" Stroker mechanical assemblies that I recently purchased. I have every intention of reconing these myself. I expect this will be my "baby step" to learn about assembly.
Thank you again,
Jason
No need to apologize, I'm just making sure you follow up.
The Strokers are not even moderately special by today's standards, any reasonably priced modern pro driver will match or beat them (probably badly).
As for sensitivity, what manufacturers list is the mid band sensitivity. Subs are not used in the mid band, they are used in the sub band. Simulate the Stroker compared to something modern like a B&C 18tbw100 and see what you get. The B&C is cheaper and will likely beat the pants off the Stroker. There are car audio drivers that will righteously whup it too.
The rotary concept is a commercial reality, has been for years now. It's called the Thigpen rotary sub. It's nothing special, you can absolutely DESTROY that thing with a few amps and carefully chosen drivers in an IB. Plus it costs $15000 - $20000 per unit (US) so you can buy a LOT of gear for that price and get several times more output across the entire usable frequency range. Also the rotary subs are only good at very low frequencies, their claim to fame is strong output at 3 hz (but not as strong as a good IB system), and they max out at about 30 hz. Plus you have to build a long, winding tunnel full of stuffing so they aren't too loud.
Note that this video was posted 11 years ago. Also note that these things are VERY dangerous, in the video the guy is scared it's going to rip itself apart. VERY dangerous especially if you have pets or kids running around.
https://www.youtube.com/watch?v=E7Bkrypxzs4
Also, the stupid fan sub is ALWAYS on, making noise and drawing power and possibly killing children even when it's not making useful sound. And it's a 1/3 hp motor powering that thing (IIRC) so it draws a fair amount of power even at idle.
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I knew I had seen that fan thing somewhere before! Yes, I see how that could definitely be dangerous. It's probably only possible for Home or commercial installation. That said, I would think that you could make it relatively safe, but it is also likely something that I would just like to do to see and experience it, not to run full time in a HT setup.
Attached is a random internet picture of what I had in mind when I described a servo type rotary vane driver. I don't know if there are any other commercially available drivers of this sort, but I know they are long since abandoned by Phoenix Gold. It is another infrasonic driver, I have always thought it would be neat to attempt a build of one of these, but larger than 12". These drivers sadly suffered from their permanent magnets spalling and fracturing and that has made a lot of them that are out in the wild freeze up and likely get landfilled even though they can sometimes be repaired.
Thanks,
Jason
Attached is a random internet picture of what I had in mind when I described a servo type rotary vane driver. I don't know if there are any other commercially available drivers of this sort, but I know they are long since abandoned by Phoenix Gold. It is another infrasonic driver, I have always thought it would be neat to attempt a build of one of these, but larger than 12". These drivers sadly suffered from their permanent magnets spalling and fracturing and that has made a lot of them that are out in the wild freeze up and likely get landfilled even though they can sometimes be repaired.
Thanks,
Jason
Attachments
That was designed by Tom Danley I believe but was totally messed up in the production phase - cost cutting and stuff.
I gave a rotary sub a whack myself but didn't finish it - https://sites.google.com/site/amateuraudio/projects-1/the-rotary-sub
Now that I know more I never should have even tried (except for the learning experience) because you can do far better with regular drivers.
There's also plenty of videos of diy rotary subs on youtube.
I gave a rotary sub a whack myself but didn't finish it - https://sites.google.com/site/amateuraudio/projects-1/the-rotary-sub
Now that I know more I never should have even tried (except for the learning experience) because you can do far better with regular drivers.
There's also plenty of videos of diy rotary subs on youtube.
Very cool! I bookmarked that as well. You pretty much did exactly what I was thinking, right down to the swashplate mechanism. Seeing as that was the weak point in your design, I may still have a go at it in the future. I can machine most of those parts myself, so may have a bit of advantage due to that.
For some reason I actually have to go do some work today, so I am probably out of here for now. Thank you for your time.
Sincerely,
Jason
For some reason I actually have to go do some work today, so I am probably out of here for now. Thank you for your time.
Sincerely,
Jason
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