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  • Pete-FIN
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Stronger motor makes higher sensitivity?
Hello! My first post here:)
(I asked these questions on a headphoneforum, but didnt get much help, so hopefully you guys can help me.)




I have a few questions related to speaker voice coil and magnet.

I have been told that speaker sensitivity is mostly determined by how "strong motor" the voice coil and magnet together are. Some other aspects also affect speaker sensitivity (like weight of the moving mass), but the biggest factor to sensitivity is the strength of the motor. At Least, this is what I have been told by hifi enthusiasts, I don't have education on this subject, so please, feel free to correct the previous statement if needed.

Here are my questions:

*Can someone please edcate me on the differences of voice coils and magnets (meaby by comparing different kind voicecoils and different kind magnets)?
*What are the very basics when calculating voice coil and magnet related properties (focusing on those calculations that help me understand the strength of the motor and sensitivity of the speaker)?
*Is there a "gain and lose thing" when thinking the strength of the motor (for example, would making stronger motor possibly effects negatively to some other measurable aspect)?

Right now, all I know about voice coils is the basic working principle, and, the more rounds around the voice coil the bigger the resistance for an amplifier.

In your answers, I would be very happy if you could go into very detailed answers about speakers individual parts and how they interact with each other. Outer dimensions, shape, mass, width of gap for coil, material composition, and magnetic properties are some of the factors I'm assuming play a role in making "a powerful motor", and I would be very happy to know more about this complicated subject.

If you have in your browser's bookmarks some good and educational web links related to the topic, please share those too.

if you choose to participate in the debate or answer my questions, I would really appreciate it.




PS. I found some interesting web pages related to this.

https://www.prosoundweb.com/channels/av/use_the_force-_inside_moving_coil_loudspeaker_motors1/
Here is a good article about speaker voice coils. The idea of trade-offs, related to different speaker motor designs, is explained quite well.

http://techtalk.parts-express.com/f...s-regarding-magnetic-field-pole-piece-gap-etc
Here is some interesting discussion about focusing magnetic field in the voice coil gap. Quote: "...based on this principle of focusing the magnetic energy into this one small area, with the lines of flux perpendicular to the direction of the cone movement. This tightly focused magnetic field with many lines of flux give the speaker coil something to push against."

I am still wondering, how to design a woofer that gives a good result in the sensitivity area of speaker operation. I'm sure the strength of the magnetic field in the gap is essential, but there must also be other areas of the speaker motor design that effect the sensitivity. I can only guess these other areas, so proper knowledge would be highly appreciated.

Feel free to join the conversation if you have something to share related to the topic.

  • DVDdoug
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Re: Stronger motor makes higher sensitivity?
Reply #1
I assume you're not building a woofer (driver) and to the end-user, this is all fairly meaningless...  Manufacturers like to tout their design choices but to us it comes down to performance - Sensitivity/efficiency, frequency response, power handling, size, cost, probably the Thiele-Small parameters, etc.   "There's more than one way to build a bridge" but there is no "best way".

The one thing I'd avoid is foam surround.   I've seen too many rotten/disintegrated foam-surrounds.   There are probably acceptable foam materials/compounds but I'd have be sure before I'd take a chance.  I've seen paper cones deteriorate when used as deck speakers in a car (where the sun hits them) but I've got some paper-cone speakers at home that are probably 40 years old, and they are still OK.

Quote
I am still wondering, how to design a woofer that gives a good result in the sensitivity area of speaker operation. I'm sure the strength of the magnetic field in the gap is essential, but there must also be other areas of the speaker motor design that effect the sensitivity.
One thing I've noticed is that "pro" woofers have higher efficiency and higher resonant frequency (which implies less mass) when compared to "home theater" woofers.

And of course, the cabinet makes a big difference.   A horn gives the best efficiency but a low-frequency horn is very large and generally impractical.

  • silverprout
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Re: Stronger motor makes higher sensitivity?
Reply #2
Hello,

Effciency : n0


Motor force : Bl
Measured in tesla-metres (T·m). Technically this is B×l or B×l sin(θ) (a vector cross product), but the standard geometry of a circular coil in an annular voice coil gap gives sin(θ)=1. B×l is also known as the 'force factor' because the force on the coil imposed by the magnet is B×l multiplied by the current through the coil. The higher the B×l value, the larger the force generated by a given current flowing through the voice coil. B×l has a very strong effect on Qes.

https://en.wikipedia.org/wiki/Thiele/Small_parameters

  • Last Edit: 13 December, 2017, 03:41:33 AM by silverprout

Re: Stronger motor makes higher sensitivity?
Reply #3
All things being equal, more motor force means more efficiency.  BUT...all things ain't equal.

To perhaps oversimplify for clarity, and talking about woofers, we have box size, low frequency extension, and efficiency.  These three are interrelated.   If you want good low frequency response from a small box you have, ipso facto, a low efficiency due to pesky and annoying laws of physics.

If you want good low frequency performance and high efficiency, they you will have a B-I-G box, again due to those pesky old laws of physics.  Pay your money and take your pick.
Ed Seedhouse
VA7SDH

  • silverprout
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Re: Stronger motor makes higher sensitivity?
Reply #4
As you can see the motor force (BL) is making the conversion of the energy of electrical world to the mechanical world.


  • silverprout
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Re: Stronger motor makes higher sensitivity?
Reply #5
Sorry, i've forgotten one word in my sentence and the parameters were not defined.
So, here is the complete schematic for the motor force (BL) understanding IMHO.


  • Last Edit: 15 December, 2017, 03:09:30 AM by silverprout

Re: Stronger motor makes higher sensitivity?
Reply #6
I
Sorry, i've forgotten one word in my sentence and the parameters were not defined.
So, here is the complete schematic for the motor force (BL) understanding IMHO.

This is all rather beside the point.  In practice "motor" force is pretty irrelevant.  Choose the low frequency response you want and the size of the box and when you have done that the driver parameters are pretty well determined.  Blatherings about "driver force" are misleading at best, and at worst irrelevant woo designed to confuse the ignorant.
Ed Seedhouse
VA7SDH

  • silverprout
  • [*][*][*]
Re: Stronger motor makes higher sensitivity?
Reply #7
I
Sorry, i've forgotten one word in my sentence and the parameters were not defined.
So, here is the complete schematic for the motor force (BL) understanding IMHO.

This is all rather beside the point.  In practice "motor" force is pretty irrelevant.  Choose the low frequency response you want and the size of the box and when you have done that the driver parameters are pretty well determined.  Blatherings about "driver force" are misleading at best, and at worst irrelevant woo designed to confuse the ignorant.

This is the simplified explanation of the Scanspeak loudspeaker drivers datasheets  :D
I really like the way they try to explain things.