A Symmetrical Transducer Topology

[mwmkravchenko]

Both were pushed a fair distance to give you an idea of the force required. Hope it helps.

As I mentioned before I don't take a lot of effort to do these calculations as our real world iterations tend to make a proper salad out of them.

I'll be away this weekend at a retreat in the Wilds of Canada but I'll bring my torture top with me. If you need another simulation let me know. I managed to get an invite to Doug Schneider's Canadian Audio Cognoscenti retreat. As I've joked for the past 35 years, I've fooled them so far

 

[smowry]

Hi @mwmkravchenko,

Thank you, but what did you use for material properties?

Modulus:

Density:

Poisson's Ratio:

 

[mwmkravchenko]

Hi @mwmkravchenko,

Thank you, but what did you use for material properties?

Modulus:

Density:

Poisson's Ratio:

I was away this past weekend Steve. We made up a table back in 2017 of the different spider materials. I'll see if I can find the information that you need. Obviously I have it, It's in the program in order to make the calculations! But the question is where do I have it!

 

[mwmkravchenko]

Hi @mwmkravchenko,

Thank you, but what did you use for material properties?

Modulus:

Density:

Poisson's Ratio:

See what happens when it has been 8 years since we launched this thing! I forget where I put what. So the genius idea was to have a materials table. It's normally buried far right.

 

[smowry]

@mwmkravchenko

Kindly let me confirm the isotropic linear elastic material properties.

Type 10 (Pro Surround)
Young's Modulus: 50 KSI
Poisson's Ratio: 0.35

This appears to be a cotton/polyester blend. In 2006 I used 25,000 PSI for Modulus and 0.3 Poisson's Ratio for cotton/poly. Back then I would understate modulus so as not to mask any geometric instabilities. So this seems to check out okay.

https://pearl-hifi.com/06_Lit_Archive/14_Books_Tech_Papers/Mowry_Steve/Another_Spider_Article.pdf

Type 4 (Spider)
Young's Modulus: 500 KSI
Poisson's Ratio: 0.35

The Modulus seems overstated. 500 KSI is typical of a high performance diaphragm material like high performance polymer and seems too stiff for suspension components.

Mechanical Properties-Modulus of Elasticity equal 500 ksi polymer product list

List of polymers which Mechanical Properties-Modulus of Elasticity equal 500 ksi

www.lookpolymers.com

FINEsuspension has default spider material properties for typical fabric of 100 KSI and for Conex of 150 KSI and 0.33 Poisson's Ratio for both.

Anyway, I will use your material properties for the surround simulation so that we can compare results.

Type 10 (Pro Surround)
Young's Modulus: 50 KSI
Poisson's Ratio: 0.35

However, for spider simulations, I will use the FINEsuspension default material properties and most likely 100 KSI for modulus.

 

[mwmkravchenko]

@mwmkravchenko

Kindly let me confirm the isotropic linear elastic material properties.

Type 10 (Pro Surround)
Young's Modulus: 25 KSI
Poisson's Ratio: 0.35

This appears to be a cotton/polyester blend. In 2006 I used 25,000 PSI for Modulus and 0.3 Poisson's Ratio for cotton/poly. So this seems to check out okay.

https://pearl-hifi.com/06_Lit_Archive/14_Books_Tech_Papers/Mowry_Steve/Another_Spider_Article.pdf

Type 4 (Spider)
Young's Modulus: 500 KSI
Poisson's Ratio: 0.35

The Modulus seems overstated. 500 KSI is typical of a high performance diaphragm material like carbon fiber and seems way too stiff for suspension components.

https://www.lookpolymers.com/findproperty.php?pid=2&sx_id=114&value=500

FINEsuspension has default spider material properties for typical fabric of 100 KSI and for Conex of 150 KSI and 0.33 Poisson's Ratio for both.

Anyway, I will use your material properties for the surround simulation so that we can compare results.

Type 10 (Pro Surround)
Young's Modulus: 25 KSI
Poisson's Ratio: 0.35

However, for spider simulations, I will use the FINEsuspension default material properties and most likely the Conex properties.

I think that we can both enter in what ever material properties that we wish Steve. I use this mostly for making sure that I have the excursion that I need. I use Hakken for spiders and they know what they are doing much better than I do. I do not mind leaving the design of these things to the guys that do it all day every day. If I have dual mirrored or whatever then we get a little more involved. What ever we input as to the material properties has a lot less to do with the end result. We don't know the phenolic setting properties, the heat at press, or the compression of the linen or what ever fabric we choose. I learned a long time ago to turn off the OCD on some things. I chase flux, generally to good results. Motor shapes and cooling ideas. Other than that I work with those who I trust.

 

[Y~BNA]

I have not designed a transducer in 10 years. I am retired in Phuket, Thailand. However, the work of Dr. Jack and his staff at KEF on their VECO feedback control revived my interest in transducer design. I realized that some of the alternative transducer topologies that I had independently investigated could have applications with control systems. I feel like there is some unfinished business; however, not to the extent that I would unretire and accept clients and/or commercial transducer development projects. Having said that, I am fascinated by the ASR forum phenomenon and the job that Amar et al. has done to bring together the AV community. Then my objective of this thread is to simulate and design a coaxial transducer array concept real time, posting simulation results for comments and discussion. In that way the ASR community becomes quasi-consultants to a, hopefully interesting and fun, transducer design exercise. Typically, transducer design is a secret agenda. Don't tell anyone what we are doing and therefore don't exchange ideas. Whereas, I agree with Dr. Jack, nothing is really new in transducers. Most transducers produced today still use the Rice-Kellogg topology with cantilever voice coils that were first used in 1924!

Here's a bit of history of the evolution of this concept dating back to 2005.

1. https://pearl-hifi.com/06_Lit_Archive/14_Books_Tech_Papers/Mowry_Steve/Steallus_Motor_Design.pdf

2. https://pearl-hifi.com/06_Lit_Archi.../Mowry_Steve/Air_Core_Tweeter_Magnet_Assy.pdf

3. https://pearl-hifi.com/06_Lit_Archive/14_Books_Tech_Papers/Mowry_Steve/DRAGONS.pdf

I plan to use Loudsoft's FINE software. I have contacted Peter and Dorit and I am waiting for their reply. I have invited them to visit this thread. Peter is perhaps the most experienced transducer engineer ever with the highest number of projects of all time.

View attachment 469711

Kindly find a transducer concept sketch below. None of the parts have been designed or documented except the tweeter. The parts in the sketch are essentially place holders. The concept has evolved quite a bit recently. Note the simplicity of the assembly.

View attachment 469707

The primary magnetic gap has linear permeability. The center coin is 304 Stainless, which has about the same electrical conductivity as that of the magnets and like the magnets has relative permeability ~1.0. The primary light alloy basket is the motor assembly's heat sink. A unique feature is that the high permeability secondary magnetic gaps contain passive sensor coils. With regards to the lumped parameter transducer model below, and knowing that if a AC Voltage is supplied to voice coil which is in a DC magnetic gap, then a velocity is created in the moving assembly but this implies that if we apply a velocity to a passive coil in a magnetic gap, then a voltage, is generated.

View attachment 469713
So now the transducer has additional terminals connected to the sensor coils. This concept requires a feedback controller and a current source amplifier for the low frequency transducer to reach its highest performance potential. The AMT tweeter has flat impedance and it is not know if a current source amp would improve performance. The coaxial array should be active with DSP so that the tweeter and midwoofer can be time aligned.

Typically, the first comment that I receive from colleagues is that it is isobaric. Well I don't see that, and it is misleading. The way I see the diaphragm topology is as a sandwich composite, a really thick and poor sandwich but no less a sandwich. There are faces and a core. The core happens to be air which is a fluid. The moving assembly is effectively one diaphragm with a front and a back side with air in between.

There are subtopics within this thread related to the concept development and implementation.

1. DSP
2. Feedback Control
3. Current Source
4. Almost Air Core Transducer
5. Spider-less or are the surrounds the spiders?
6. Full complementary symmetrical topology
7. Coaxial AMT

So please let the discussion begin. All serious comments, questions, and/or concerns are welcome and encouraged.

This seems interesting from an OB Dipole POV. Since i'm personally interested in the (presently unattainable) ideal of 100%