The Transducers' Voice Coil

[smowry]

@KSTR

If we look at the equation for transducer efficiency we see the same thing. We don't really care about the length of conductor; we care about the volume of conductor.

Where is a constant.

Then substituting Beta for (B^2)(l^2)/Re = (B^2)Volume of conductor/resistivity N^2/W. The efficiency dependence on length disappears. The true dependence is on volume and we clearly see the 1/Mms^2, Sd^2, and Beta dependencies.

A theoretical rectangular wire example when a manufacturer has an 8 ohm and a 4 ohm version of the same transducer and voice coil and magnetic assembly dimension are the the same, then length and cross-section of conductor are different accordingly (the condition that you describe but relative to position), 1.0 W @ 1.0 m sensitivity will be approximately the same but 2.83 V @ 1.0 m will exhibit a 3 dB delta. Note that the 4 ohm version will have a greater packing factor and the 4 ohm version will be slightly more efficient because the volume of conductor will be slightly higher with less insulation, remembering that the amplifier sees the entire coil.

UPDATED AND CORRECTED!

 

[KSTR]

If we look at the equation for transducer efficiency we see the same thing. We don't really care about the length of conductor; we care about the volume of conductor.

The easiest way to explain that to other people is with dual VC drivers, coils wired in series vs. parallel.
The efficiency does not change, nor does motor force etc, only the impedance level is changed and thus voltage-based sensitivity.
L^2/Re stays constant when going from parallel to series, L has doubled but Re quadrupled.

 

[smowry]

@KSTR

Yes, Beta stays the same for series vs. parallel but BL and Re vary, while the volume of conductor remains the same.

Outstanding post!

 

[mwmkravchenko]

The easiest way to explain that to other people is with dual VC drivers, coils wired in series vs. parallel.
The efficiency does not change, nor does motor force etc, only the impedance level is changed and thus voltage-based sensitivity.
L^2/Re stays constant when going from parallel to series, L has doubled but Y

The easiest way to explain that to other people is with dual VC drivers, coils wired in series vs. parallel.
The efficiency does not change, nor does motor force etc, only the impedance level is changed and thus voltage-based sensitivity.
L^2/Re stays constant when going from parallel to series, L has doubled but Re quadrupled.

Yup. The tapered wire diameter idea could provide more turns in the same gap width and be a very complicated way to flatten the motor force. It's less complicated to go to underhung motor. Also less distortion over a few fronts.

 

[mwmkravchenko]

Napkin sketch but the concept is there. With a 50% existing gauge or less wire draw you can keep more turns in place without the overall losses in a wide gap. The caveat is a higher Re. Thus not a greater motor force. Everything I have ever seen or done to flatten a B X L curve will cost you something. Don Keele did a great summary of the available motor topologies that was done by a giant at JBL. Performance wise and underhung is king. But it is also the most costly to make if you want an ever playing field of efficiency and performance.

 

[smowry]

@KSTR

So the dual voice coil example shows that Beta stays the same for series vs. parallel but Bl and Re vary, while the volume of conductor remains the same.

Now what about inductance, Le with unit mH? Well Le goes as Re and varies for series vs. parallel. However, the transducer's frequency response remains unchanged, why?

The answer is that we don't really care about Le in the case of dual voice coils. What we care about is the "break frequency" of the 1st order low pass transducer characteristic that goes as Re/Le.


So for series vs. parallel, the break frequency remains unchanged!

 

[smowry]

Yup. The tapered wire diameter idea could provide more turns in the same gap width and be a very complicated way to flatten the motor force. It's less complicated to go to underhung motor. Also less distortion over a few fronts.

Some transducer engineers consider the square root of Beta to evaluate the motor. The unit of Beta^0.5 is N/(W^0.5) or force/square root of power. So the tapered wire method only works if the volume of the conductor in the gap is increased relative to position, volume(x), which implies an increase in the wind diameter. If we don't care about the length of the conductor, length of the conductor l = N(pi)diameter, then with respect to Beta, the true motor figure of merit or the square root of Beta, we don't care about N, the number of turns.

 

[smowry]

My Masters project was a ribbon transducer that I constructed in the EE and Materials labs at URI. I vapor deposited aluminum onto a Mylar strip and suspended that diaphragm between two long ferrite magnets with two horseshoe shaped steels strips to implement a magnetic circuit. I had ZERO turns and it sounded good. Dr. Jackson gave me an A. However, the primary issue was low impedance. Volume of Al vs. impedance created a design paradox.

The more turns a coil has, the higher the inductance. The more volume in the gap, the higher the force/square root of power in. Re = (resistivity)length of conductor/cross-section with unit ohm.

 

[smowry]

When I joined the transducer research group at Bose, TRES, nobody would dare to utter the term Bl. It was always Beta. Using Bl would surely lead to ridicule or worse, transfer to manufacturing. If Dr. Bose ever heard one of his transducer engineers use Bl in a technical discussion, that would have been hugely problematic. Bl alone is a meaningless parameter.

 

[smowry]

Then why is Bl(x) the large signal parameter and not Beta(x)? Folks cannot handle the truth of how nonlinear their motors are! Klippel could have used Beta and then motors from various transducers could be compared regardless of impedance. Bl(x) does show linearity but Bl(0) = Bl is still a meaningless parameter. Beta(x) shows both linearity and motor efficiency and motors can be compared regardless of impedance! Does Dr. Klippel know this? Yes, I told him.

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

 

[mwmkravchenko]

When I joined the transducer research group at Bose, TRES, nobody would dare to utter the term Bl. It was always Beta. Using Bl would surely lead to ridicule or worse, transfer to manufacturing. If Dr. Bose ever heard one of his transducer engineers use Bl in a technical discussion, that would have been hugely problematic. Bl alone is a meaningless parameter.

It's a good thing I don't work at Bose then.

A semantics game is not exactly useful.

For what it's worth I agree with your statements about Beta, and BL. We both know what each other is describing. If you need to have it in Beta, OK. I have no idea where B x L started. I have the Philips technical journal all the way back to the 30's, and it's interesting to read how many of the loudspeaker parameters they used and described would be current even now. As you have mentioned a few times Steve. Parts of this business are well entrenched. With little to no innovation. That's something to be expected when there are companies that are pumping out nearly a million drivers a day.

As for the tapered wire idea. It is interesting. But not without costs. And the complexities to wind such a coil are manifold. The cost of the R&D to pull it off would be equal to do many drivers in a underhung motor style that solves most of the issues in the first place.

Always interesting playing transducer ping pong with you Steve.

 

[smowry]

Working at Bose was an outstanding experience. I learned huge and I equate my 3.5 years in TRES to a PhD in transducers. There were no professors that I could have studied under after receiving my masters that would have prepared me to do transducer R&D at the level that Bose did. Not to mention, Bose paid me. I worked with real Transducer R&D Engineers and Scientists. Was it a demanding environment? Absolutely!

Bl(x) is a "Key" nonlinear Klippel parameter. Bl is a "Key" Thiele/Small parameter. And no, I did not give Dr. Thiele nor Dr. Small the Beta run down. Note that Dr. Small was one of nicest people I have ever met. He liked underhung motor topology.

Neville Thiele: Audio Engineering Pioneer | PDF | Loudspeaker | Electronics

Neville Thiele is an Australian audio engineer known for pioneering work in loudspeaker design and simulation. He developed the Thiele-Small parameters in 1961 to characterize drivers, which became widely adopted and are still used today. Throughout his career he held several engineering roles...

www.scribd.com

Voice Coil Interviews Dr. Richard H. Small

Interview with Dr. Richard H. Small, by Steve Mowry, originally published in Voice Coil in 2006.

audioxpress.com

Unfortunately, unless someone can show me otherwise, I claim the tapered wire concept is heresy! If I have not made that clear by now, something is wrong. Remember, the concept is not related to people, rather it is related to transducers.

 

[Audionaut]

The most advanced magnet wire that never was is Rectangular Anodized Aluminum Clad Copper (ACC). The primary reason is the lack of demand from the loudspeaker industry.

I think Magnat already used it in its all-ribbon speakers and the top-of-the-line Transpulsar model in the late 1970s and early 1980s.

 

[Audionaut]

Magnat was a highly innovative loudspeaker company.
The name still exists, but it is no longer the same company, as is unfortunately the case with many audio companies.

They also launched the plasma tweeter around 1980.
.

 

[smowry]

@Audionaut

Thank you for sharing.

I vaguely remember Magnat. In the 70's, I was in my 20's. I did not become a Transducer Engineer until I was 43.

Yes they did use anodized Aluminum ribbon wire. I can see that. However, so did Bose and TAD. I cannot read German language but I do not believe that Magnat used Rectangular Anodized Aluminum Clad Copper (ACC), rather they used Rectangular Anodized Aluminum wire. ACC is essentially copper ribbon wire with a thin layer of aluminum deposited over the copper. The aluminum clad layer can then be anodized to form insulation rather than an enamel insulation.

Now if you can translate the part of their info sheet(s) that indicates Rectangular Anodized Aluminum Clad Copper (ACC) wire voice coil, please translate into English and post it. I am extremely interested in this topic. If not perhaps @KSTR or @Salt can do the translation.

 

[Audionaut]

How do you rate the dual gap MMAG motor design of the Epique series from Dayton Audio?

Dayton Audio - E150HE-44 5-1/2" DVC MMAG Extended Range Subwoofer 4 Ohms per Coil

E150HE-44 5-1/2" DVC MMAG Extended Range Subwoofer 4 Ohms per Coil

www.daytonaudio.com

Test Bench: The E150HE-44 5.5” Full-Range Subwoofer from the Dayton Audio Epique Line

This Test Bench explication focuses on the Dayton Audio Epique MMAG E150HE-44 "full-range subwoofer," in itself an interesting concept. Like its larger E180HE-44 brother in the Epique line, the E150HE-44 is based on the patented Multiple Magnet Air Gap (MMAG) technology invented by Enrique...

audioxpress.com

 

[Audionaut]

Now if you can translate the part of their info sheet(s) that indicates Rectangular Anodized Aluminum Clad Copper (ACC) wire voice coil, please translate into English and post it.

You selected a graphic in Dutch. However, both the Dutch and German brochures only stated that it was aluminum flat wire and did not specify the exact alloy or composition.

 

[smowry]

You selected a graphic in Dutch. However, both the Dutch and German brochures only stated that it was aluminum flat wire and did not specify the exact alloy or composition.

Thanks. Rectangular Anodized Aluminum Clad Copper (ACC) wire is not an alloy. It's Al or Cu. The flat Al wire is high performance but Beta = (B^2) wire volume/resistivity.

The resistivity of copper is significantly lower that aluminum and thus Beta will be greater with ACC wire. Some voice coil manufacturers like ATON use rectangular copper wire but copper cannot be anodized and retangular must use some type of enamel insulation.

 

[smowry]

How do you rate the dual gap MMAG motor design of the Epique series from Dayton Audio?
View attachment 503826

Dayton Audio - E150HE-44 5-1/2" DVC MMAG Extended Range Subwoofer 4 Ohms per Coil

E150HE-44 5-1/2" DVC MMAG Extended Range Subwoofer 4 Ohms per Coil

www.daytonaudio.com

Test Bench: The E150HE-44 5.5” Full-Range Subwoofer from the Dayton Audio Epique Line

This Test Bench explication focuses on the Dayton Audio Epique MMAG E150HE-44 "full-range subwoofer," in itself an interesting concept. Like its larger E180HE-44 brother in the Epique line, the E150HE-44 is based on the patented Multiple Magnet Air Gap (MMAG) technology invented by Enrique...

audioxpress.com

It looks good; however, I will not recommend any Dayton products. I have issues with Parts Express. Perhaps Mark @mwmkravchenk can help you with that. I can recommend the equivalent Purifi product but the cost is 4 to 5 times greater! One comment, I can make about Dayton is do not expect the parameters to be what they advertise. If you make a purchase, you should acquire the parameters yourself or have someone reliable do it for you.

 

[Audionaut]

I will not recommend any Dayton products

No, I don't want to buy anything, I'm just interested in the motor design.
I only buy speakers from the PA corner > BMS, RCF, B&C, 18sound, Sica, Beyma and FaitalPRO.