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Stronger motor makes higher sensitivity?

Discussion in 'Sound Science' started by Pete-FIN, Oct 10, 2017.
  1. Pete-FIN
    I have a few sound science 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 sound science 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.

    Meaby my questions are somehow related to headphones, but I'm mostly looking information related to speakers. If you have headphone specific info of voice coils and magnets, feel free to share that too.

    And 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.
  2. 71 dB
    You are practically asking us to give you a course on dynamic loudspeakers…

    Sensitivity is a combination of many things. Bl (force factor), damping, mass, cone
  3. ev13wt
    If the motor is too powerful for the membrane, the membrane will "buckle" i.e. not react linear. If you cannot disipate the heat, coils will "melt". Then you have all the crap about full wave, half wave, closed boxes, semi open boxes, ears, hrtf ... damping, impedance, load, practicality of membrane materials, resonances and impedance coupling.

    This is a great big subject. Lets start compiling resources. I wish to learn more about this as well.

    Lets start here: https://en.wikipedia.org/wiki/Helmholtz_resonance
  4. Pete-FIN
    Thanks for joining the conversation :)

    All info related to speaker sensitivity is very welcome, but I would like to focus on the electromagnetic motor of speaker unit. The three questions I asked in the first post, are all voice coil and magnet related questions, and that is the specific area of speaker science that I would really like to know more.

    I do know Helmholtz resonance and Helmholtz resonators. I have contemplated building a hole or slot resonator to my listening room. For people who dont know what Helmholtz resonator panel looks like, heres few pics that came up with google,
    Hole resonator:
    Slot resonator:
  5. ev13wt
    Nice! Very interesting approach with the resonators.

    Simply put: a stronger motor does not make a better anything.

    Buy this book, or find an E-Version of it:

    Mendel Kleiner

    Edit: at work will post excerpt later
    Last edited: Oct 10, 2017
  6. castleofargh Contributor
    maybe I shouldn't say that, but for the sake of information, head-fi is probably not the best place to ask about speakers. headphone needs and concerns aren't the same as speakers', and the specs are here to confirm it. speakers are something complicated enough not to mix in some half knowledge about headphones IMO.

    I read a few stuff from Floyd Toole, but it ends up being mostly about acoustic and fidelity. I don't remember reading anything about how to hand pick a magnet and roll a coil with a wire and some crazy glue ^_^. anyway I don't know where you're starting or what you really wish to know(everything is too much).
    lowest starting point I can think of https://en.wikipedia.org/wiki/Solenoid#Pneumatic_solenoid_valve to at least get the all number of turns and current in the wire thingy. but of course this completely disregards the diaphragm and its mechanical properties, as well as the volume of air it will be trying to move or how the casing will limit that. all of which end up being relevant when measuring both impedance and sensitivity of the final speaker(if it's a single driver type). and somehow all that still feels like only the tip of the iceberg.
    I can't imagine a way to dumb it down into something practical where you go "I want that, what do I do?" without some fancy 3D model software or a great deal of experience in making speakers.
  7. Pete-FIN
    A bump to my own thread :)

    The science of voice coils still interests me and I found some interesting web pages related to this.

    Here is a good article about speaker voice coils. The idea of trade-offs, related to different speaker motor designs, is explained quite well.

    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.
  8. Muinarc
    I think driver design is a sadly ignored topic around here.

    I always try to point people to this video to show how huge the changes a driver can make (and thus different headphones) vs. changes between DACs or amps. Here you have 15 drivers of the same diameter with very similar design characteristics (full-range guitar cabinet drivers which should all have high sensitivity) yet they can sound so different just in this recording, I'm sure the differences are even more stark in person.

    On this topic @Pete-FIN, you might look into PA (public address) speakers and their designs, they all tend to aim for very high sensitivity measurements so that they can be efficient with as little amplification as possible.

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