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Speaking of Speakers

My first engineering design role out of NYU Engineering in 1972 was at Empire Scientific designing ‘loud speakers’ for audio. I had a large anechoic chamber at my disposal and worked with speaker companies like Rola Jenson, JBL, Bose (Excellent Bass in small speaker designs such as a ‘bookshelf’ speaker), Cerwin Vega (For really ‘Booming” Bass!) and CTS to give me Bass, Mid-Range, and Tweeter variety speakers. Most of these companies were based in the Mid-West United States.

I would specify the type of magnets to use such as Alnico or Ceramic magnets, and the size (usually 12” or 15” for the woofers) and strength of the cone material. After getting the speaker design done, I would create the wooden cabinet (It was a quality piece of furniture) we had our own wood shop craftsmen, decide if it would be ‘ported’ or ‘sealed’ for the Bass sound needed, and then design the crossover circuitry for the Bass, Mid-Range, and Tweeter speakers—I used passive designs in those days with Resistors, Capacitors, and Inductors.

I spoke to Mike Van Den Broek, Sr. Applications Engineer, PUI Audio, Inc., and he told me why so many speaker companies were based in the US Mid-West. He said that in Kentucky, there is a loud speaker manufacturer named Eminence and the guy who started that, Bob Gault, had previously worked for Magnavox and he left there and started his own company making 18” sub-woofers in the 60s; his first customer was Ampeg. In the 80s, when there was a sub-woofer craze, Eminence was kicking out everyone’s speakers.

A conventional speaker like those I designed in the 60s, and are pretty much the same basic construction today, is made up of:

  • The cone , usually made of paper, plastic or metal, is attached on the wide end to the suspension.
  • The suspension , or surround , is a rim of flexible material that allows the cone to move, and is attached to the driver's metal frame, called the basket .
  • The narrow end of the cone is connected to the voice coil .
  • The coil is attached to the basket by the spider , a ring of flexible material. The spider holds the coil in position, but allows it to move freely back and forth. There can be one or two spiders.

Van Den Broek told me that PUI Audio does most of their design here, but manufacturing is done outside the US. They do optimization there at their facility in Dayton, Ohio. The primary difference between the speakers I designed and the micro- and mini-speakers that PUI Audio makes is that the diaphragm is connected directly to the voice coil as opposed to an Aluminum or cardboard 'former' to which the voice coil was connected (See this Audio xpress article here). The surround of the speaker acts as both the surrounding and the spider.

There are fewer parts doing more of the job.

The following is an assembly diagram of the different micro speaker parts from PUI Audio's design, order of assembly, and picture of the magnetic motor:

      (Images courtesy of PUI Audio)

      (Images courtesy of PUI Audio)

      (Images courtesy of PUI Audio)

      (Images courtesy of PUI Audio)

      (Images courtesy of PUI Audio)

      (Images courtesy of PUI Audio)

      (Images courtesy of PUI Audio)

      (Images courtesy of PUI Audio)

      A 3D cutaway of PUI Audio's ASE02506MS-LW90-DSM-R (the pre-characterized speaker Maxim includes with the MAX98390EVM DSM Smart Amplifier solution) This is a DSM-Ready micro speaker that comes pre-packaged in a compact enclosure with 90mm lead wires for east system integration. (Images courtesy of PUI Audio)

      A 3D cutaway of PUI Audio’s ASE02506MS-LW90-DSM-R (the pre-characterized speaker Maxim includes with the MAX98390EVM DSM Smart Amplifier solution) This is a DSM-Ready micro speaker that comes pre-packaged in a compact enclosure with 90mm lead wires for east system integration. (Images courtesy of PUI Audio)

Micro speakers are also a little different than many other dynamic loudspeakers in that the magnetic motor resides on the inside of the voice coil, with the magnetic back plate transferring the south pole to the outside of the speaker, for this particular speaker.

PUI Audio micro speakers use one, three, or five magnets placed within the motor structure depending on the sensitivity requirement of an application. In many cases, a five-magnet system is used for the highest sensitivity, but recently they have been able to achieve great performance using a single N50-grade magnet. There is a great deal more magnetic product so that the voice coil is completely saturated with flux.

The voice coils for their micro speakers are heat treated as they are wound for great power handling performance. PUI Audio’s factory precision automated equipment also allows them to wind voice coils to a specific DC resistance specified by customers, allowing them to optimize the speakers with the amplifier they choose for extended battery life and/or peak Sound Pressure Level (SPL).

All of PUI Audio’s Mobile Series micro speakers (and smaller receivers used for headphone applications) feature a special diaphragm material and are assembled using special glues to achieve an IP67 rating to prevent dust and water ingress.

      Click here for larger image 
(Images courtesy of PUI Audio)

      (Images courtesy of PUI Audio)

Van Den Broek said that Maxim Integrated is “super into audio” unlike some semiconductor companies that just dabble in audio, Maxim has the same passion for audio that PUI Audio does. Maxim’s Dynamic Speaker Management (DSM) Smart Amplifier technology, coupled with PUI Audio’s speaker designs has just an amazing sound unlike any other small speaker.

See also this EDN article Dynamic Speaker Management (DSM): Micro Speakers on Steroids

1 comment on “Speaking of Speakers

  1. Andy_I
    June 19, 2019

    I was very interested in audio around the time you were designing speakers, but I had to contend with the electronics, and left the speakers to the experts.  Speakers were a mystery to me – although I do recall “disassembling” a few loudspeakers as a child.  I look forward to reading your references.

    I assembled my first stereo system around a pair of Acoustic Research bass-reflex boxes.  The radio studios where I worked had Advents everywhere, plus a pair of ported JBLs with a comfortably forward sound in one of the studios, and large (3' by 3' by 3') Altecs for really loud sound at remote locations.

    Not that it matters, but Kentucky was my home for a while when growing up.  (Nothing to do with speakers.)  My dad's company sent him there to help open a factory.  I think Kentucky was chosen because land and labor were available.

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