Designing your own motor

[*Ace* 10+ year member]

Cheapest FEA software you will get for loudspeaker design :
http://www.dyneanalytics.com/

Very good bang for buck on it.

Thank you very much!! Would you be able to make any additional comments or tips about motor design? If not I understand because I'm sure that might be considered "trade secrets".

Thanks for you help so far //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

 

[SPLaudio 5,000+ posts]

your best bet is to get online and read about how a motor works as much as you can.

a tc9 is a very basic but good motor design that has been used for sq-spl depending on the soft parts used. tc was a build house many yrs ago that did very well why there is sooo many motors out there. most all the tc motors have been copied and different features added. most motors use 1010 steel which is cheap and very magnetic and good motors use y35 for slugs..

 

[*Ace* 10+ year member]

Have been doing a bunch of reading and got my quote for the MoTIV software. Does anyone know any good software for simulating soft parts. On one of his website, Dan Wiggins says he uses Calculix and IMPACT. Does anyone have any experience with these two programs (SPLaudio, sundownz)?

Edit: Also sundownz, do you know when DYNE analytics will have their VIBRAT and Coil Designer programs ready? Thanks

 

[*Ace* 10+ year member]

Ok this question is more for Jacob and other manufacturers. I know you guys are busy but it would definitely be appreciated. If anyone else knows the answer, please chime in.

So from what I understand after doing some more reading (and correct me if I'm wrong), the T/S parameters of a subwoofer really aren't as important as people make them out to be in a sense. What I mean is that the T/S parameters will only tell you what kind of enclosure you will need to build for a given frequency response, nothing else. They won't tell you that sub "A" is better than sub "B" without knowing what you are trying to achieve. So when designing a subwoofer the first thing you would need to decide is what kind of application you want your sub to play well in, or what "niche" you want to fill (it doesn't make sense to me to start designing something without knowing what you are trying to achieve with your product).

So let's say you want to design a subwoofer that is suited for small ported enclosures only, with good low bass extension and with a flat as possible frequency response. Obviously I'm willing to sacrifice efficiency in this example. Do you guys first grab some enclosure software (or any software that models out frequency response for a given alignment), throw in some random T/S parameters and change them around until you find the correct values that give you the enclosure size and frequency response you want, or at least as close as possible to it? I just don't think it would be very cost effective to randomly put parts together, measure the T/S specs and pray that they match the design goals.

If so, I would imagine you then start using FEA software to mess with different materials and quantities of them to find what combinations give you the T/S values that you need correct? The final step being that you know what combination of materials will give you the specs you want, so you then begin searching for suppliers that can provide those materials at your specifications?

 

[Beatin' 10+ year member]

I was thinking about building my own subwoofer as well.

My idea revolved around taking a dual 15" sealed box, cutting out the front panel, and putting in a massive rectangular woofer. The motor would be mounted within the box and the box would act as both the enclosure and basket.

 

[Electrodynamic 10+ year member]

So from what I understand after doing some more reading (and correct me if I'm wrong), the T/S parameters of a subwoofer really aren't as important as people make them out to be in a sense. What I mean is that the T/S parameters will only tell you what kind of enclosure you will need to build for a given frequency response, nothing else. They won't tell you that sub "A" is better than sub "B" without knowing what you are trying to achieve. So when designing a subwoofer the first thing you would need to decide is what kind of application you want your sub to play well in, or what "niche" you want to fill (it doesn't make sense to me to start designing something without knowing what you are trying to achieve with your product).

Yes. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif That is exactly where to start. You have to have a goal in mind to begin with.

So let's say you want to design a subwoofer that is suited for small ported enclosures only, with good low bass extension and with a flat as possible frequency response. Obviously I'm willing to sacrifice efficiency in this example. Do you guys first grab some enclosure software (or any software that models out frequency response for a given alignment), throw in some random T/S parameters and change them around until you find the correct values that give you the enclosure size and frequency response you want, or at least as close as possible to it? I just don't think it would be very cost effective to randomly put parts together, measure the T/S specs and pray that they match the design goals.

You actually modify the motor and compliance to achieve the desired result. Moving mass stays the same as what you specify it as (you input non-coil moving mass as your coil has a specific mass). You then change the motor to affect the performance of the subwoofer as a whole and, of course, as part of the system.

If so, I would imagine you then start using FEA software to mess with different materials and quantities of them to find what combinations give you the T/S values that you need correct? The final step being that you know what combination of materials will give you the specs you want, so you then begin searching for suppliers that can provide those materials at your specifications?

With motors, yes. With soft parts, no. Not only do the materials have different effects on performance but so does the shape and size of the materials. If you wanted to get into designing your own spider(s) and surround(s) and you have the funds to support the cost of the software go ahead and do it. However, there are people out there (Red Rock Acoustics has a spider design service) that can do whatever you want for a nominal charge.

 

[SPLaudio 5,000+ posts]

^ Nick has no clue ;p

 

[*Ace* 10+ year member]

You actually modify the motor and compliance to achieve the desired result. Moving mass stays the same as what you specify it as (you input non-coil moving mass as your coil has a specific mass). You then change the motor to affect the performance of the subwoofer as a whole and, of course, as part of the system.

This part I'm a little confused about, and maybe it's because I didn't word my question very well so let me try again. I know you have to modify the motor and compliance to get the parameters you want, but my question is, how do you know what parameters you want in the first place? We'll go with my previous example again. I want to design a 12" subwoofer that is suited for ported enclosures only, has good low end extension, and doesn't require as large an enclosure as some other drivers of the same size. Well how do I know what is required for a subwoofer to fit those specifications? The T/S parameters of a subwoofer would tell us if it's capable of doing the above, correct? And if so, well, what are those T/S specs? Is the Qts .56 or .29? Is the Fs 39Hz or 23Hz? Is the Cms .23 or .78? I'm guessing the only way to know is to take some enclosure software and enter your own custom parameters and model them out. First start by making the Qts .33, the Fs 28Hz, the Vas 10l, etc. and then model that up in your software and see if the frequency response graph is showing the results you are aiming for and if it calls for the same enclosure size that you want to use. If it doesn't, change the parameters again until you find something that does model up to what your goal is. I understand you still have to do real world testing to make sure you like the sound etc, but this would be an efficient way of pointing out the right direction correct? Does this method sound correct or no? If not, what is the correct method?

I'm not sure if you use MoTIV or not, but I read the thread Dan Wiggins and Kevin Haskins made on the walk through of designing a 5.25" midwoofer motor. In a nutshell Dan asked Kevin for the typical box Kevin would like to use for the mid woofer, and what kind of frequency response he would like. Kevin then modeled up some T/S specs on some software (looked like enclosure modeling software) and then gave those T/S specs to Dan, and the enclosure size he wanted to use. That thread is why I figured I needed to know what T/S specs I wanted before I even attempt to design anything. I just want to know, how do I find out what specs I need for my goal.

With motors, yes. With soft parts, no. Not only do the materials have different effects on performance but so does the shape and size of the materials. If you wanted to get into designing your own spider(s) and surround(s) and you have the funds to support the cost of the software go ahead and do it. However, there are people out there (Red Rock Acoustics has a spider design service) that can do whatever you want for a nominal charge.

Yes I have visited the Red Rock Acoustics site and saw that they have many different FEA tools for designing speakers. I haven't gotten a quote on any of their software though.

So most manufactorers don't use FEA for the soft parts? When you started out, did you just slap some random soft parts on, measure the T/S specs, and order new ones based on the results you got until it was perfect? That sounds like a lot of money and time when you could just enter the specs of known materials for soft parts, model them up in FEA and have the FEA software results show you what the final Cms, Qms, etc. would be without actually having to buy any soft parts at all. But then again, as I have come to find out, FEA software is EXPENSIVE, and maybe it would be cheaper to buy random soft parts and take measurements until it's perfected.

And thanks again for answering my questions //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif It is VERY much appreciated //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif

 

[sundownz Pro Seller]

FEA is a great starting point and a great tool to start the development brand new parts (especially their non-linear behavior, naturally); but nothing beats having your hands on it to dial it in.

At a certain point after handling 1000s of different parts you can also "just know" what will work for many applications... many of us that have been in it for a while can push on a cone and get a close guess of the CMS of a driver. Nick and I were talking the other day and we can guess Qts and Fs of a sub pretty quickly simply looking at BL^2/RE and knowing what we typically use for cones and spider stiffness on a given power level driver -- becomes pretty natural.

Taking a good look at a spider we can also tell roughly if it has the throw we need or not; same goes for a surround (we have formulas on hand to calculate both manually as well).

In any ideal world you would simulate everything in FEA before getting a prototype; but in reality that is pretty uncommon in smaller companies as many FEA packages can run $20-30k (DYNE MoTIV is the first really affordable / good and intuitive program for motors). You must also know that you don't always get the spec exact when you produce a part as well -- often having to tweak material to hit the FEA targets as all that data still goes through human beings and often a language barrier -- so hands-on tweaking is still VERY critical. There is also the invaluable Klippel testing that you can get from a real prototype to confirm any simulations / expectations.

Also; if you designed by WinISD type graphs you'd see people make high VAS / Low Fs drivers for SPL *laughs* WinISD tends to show a MASSIVE peak in the 40s-50s with one of those in a small ported box. So there is also a degree of knowing what happens in reality vs. modelling when it comes to T/S goals. But to answer your question here at the end; we do have an idea of what T/S we want in mind before going into a project but often times with experience it doesn't take much tweaking to get there as you'll already have a good idea of what needs to be done. Typically as designers we also talk more in terms of CMS, MMS, and BL (BL^2/RE) rather than extrapolated spec like Qts, Qes, VAS, etc.

 

[ciaonzo 5,000+ posts]

FEA is a great starting point and a great tool to start the development brand new parts (especially their non-linear behavior, naturally); but nothing beats having your hands on it to dial it in.
At a certain point after handling 1000s of different parts you can also "just know" what will work for many applications... many of us that have been in it for a while can push on a cone and get a close guess of the CMS of a driver. Nick and I were talking the other day and we can guess Qts and Fs of a sub pretty quickly simply looking at BL^2/RE and knowing what we typically use for cones and spider stiffness on a given power level driver -- becomes pretty natural.

Taking a good look at a spider we can also tell roughly if it has the throw we need or not; same goes for a surround (we have formulas on hand to calculate both manually as well).

In any ideal world you would simulate everything in FEA before getting a prototype; but in reality that is pretty uncommon in smaller companies as many FEA packages can run $20-30k (DYNE MoTIV is the first really affordable / good and intuitive program for motors). You must also know that you don't always get the spec exact when you produce a part as well -- often having to tweak material to hit the FEA targets as all that data still goes through human beings and often a language barrier -- so hands-on tweaking is still VERY critical. There is also the invaluable Klippel testing that you can get from a real prototype to confirm any simulations / expectations.

Also; if you designed by WinISD type graphs you'd see people make high VAS / Low Fs drivers for SPL *laughs* WinISD tends to show a MASSIVE peak in the 40s-50s with one of those in a small ported box. So there is also a degree of knowing what happens in reality vs. modelling when it comes to T/S goals. But to answer your question here at the end; we do have an idea of what T/S we want in mind before going into a project but often times with experience it doesn't take much tweaking to get there as you'll already have a good idea of what needs to be done. Typically as designers we also talk more in terms of CMS, MMS, and BL (BL^2/RE) rather than extrapolated spec like Qts, Qes, VAS, etc.

Nailed it. Mass, compliance, and force.
Speaking of building drivers, have you received my last couple emails?

 

[*Ace* 10+ year member]

Typically as designers we also talk more in terms of CMS, MMS, and BL (BL^2/RE) rather than extrapolated spec like Qts, Qes, VAS, etc

Nailed it. Mass, compliance, and force.

Ok this makes sense to me I think. Let me know if the following is right. I know enclosure specs also play a part, but I mean in general.

1) Mass + Compliance will give me my Fs value. A speaker with a lower Fs usually will have better low end extension with everything else being equal. So if I want good low end extension in my subwoofer, I will be messing with it's compliance and mass right?

2) The compliance of a sub will also tell me two things. One is how large of an enclosure I need. The more compliant the driver is, the larger the enclosure needed. Second, the more compliant the driver is, the better low end extension it'll have.

3) Finally, BL and MMS are going to tell me what the sensitivity of the driver will be right? Increase MMS and decrease BL and efficiency drops. Increase BL and decrease MMS and efficiency increases.

So BL^2/Re, MMS, and CMS are the three parameters I will be messing with/worried about the most to achieve my driver goals? Let me know if I misunderstood or got any of the above wrong.

Thanks guys //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif