How Speakers are Built
The first electronic loudspeaker designs were introduced in the 1920"s, and while there have been many improvements in component materials over the decades, not much has changed in the basic functionality of a loudspeaker: a permanent magnet interacts with an electromagnet (voice coil) to move a cone back and forth to produce sound waves. Founded in 1966, Eminence has been a leading supplier of loudspeakers for professional audio, musical instrument, car audio and home hi-fi applications to many of the world"s most recognized brands. While our own components and manufacturing processes have evolved, the way we assemble speakers today doesn't differ that much from when we started. Here"s how we do it.
At the heart of every loudspeaker is the electromagnet, more commonly known as the voice coil, which uses an electric current to produce its magnetic field. The first step in making a voice coil is the winding process. A Kapton, Nomex, paper, or fiberglass former material is wrapped around a steel mandrel, which is used to keep it round during this process. These former materials are chosen for their thermal power handling and sonic contributions. Next, copper or copper-clad aluminum wire is wound to specific lengths according to the design. The coil is then baked to cure the adhesive used for coating the wire. An assurance bead of glue is added at the top and bottom of the winding. As an added quality assurance measure, we double-bake our coils at this point. For added strength we often add beryllium or copper strips to the coil. Then a paper collar is wrapped around the coil to protect the wire that goes from the winding to the tensile leads. These leads are then spliced onto each end of the winding. We then check the DC resistance and overall quality of each coil. Fun fact: Eminence makes 95% of our voice coils in-house.
When the voice coil receives an electric current and produces a magnetic field, it is repelled by the permanent magnet fixed to the loudspeaker basket. These magnets come in various sizes and materials, but interestingly enough, they aren"t magnets at all until the loudspeaker assembly reaches the end of our production line. Eminence uses ferrite, lightweight neodymium, and alnico (a combination of aluminum, nickel, and cobalt) magnets. Fun fact: Eminence uses over 360,000 magnets each year.
There are a few metal parts used in the construction of a loudspeaker: the basket, top plate, back plate, and core. At Eminence we use a variety of loudspeaker basket types and sizes. Our cast-aluminum chassis range from 5" to 18" in diameter, and our stamped steel models range from 6.5" to 15". We also have a variety of powdered metal and steel cores, in both vented and solid construction, and range in size from 1" to over 4". The top and back plates are stamped from rolls of steel in our Press Shop. The top plate is either welded or staked to the basket, and the back plate will have a round core welded or staked to the center of it. These two plates will eventually sandwich the permanent magnet. Once our metal parts are assembled, they are then sent through our in-house e-coat paint process. A uniform coating of cationic epoxy paint is applied over the entire surface of the metal parts to a controlled thickness of less than 0.001". Fun fact: Eminence purchases over 1,160 tons of American made steel each year, the majority of it from Steel Technologies right across the street from our factory.
The soft parts of a loudspeaker are the cone, dust cap, spider, and surround. Our cones come in many different sizes and the bodies are typically made of paper. The surrounds can be made of paper, cloth, Santoprene, rubber, or foam. The spider and the surround make up the mechanical suspension, which brings the cone back to its original resting position. Fun fact: Eminence purchases over 310,000 cones each year from suppliers in the USA, UK, and Malaysia
The first step of the final assembly process is to attach a terminal board to the painted basket/top plate assembly using either glue or rivets. Next a rear gasket is applied to the basket to create a seal with the enclosure if the speaker is to be front-mounted. Next, the magnet and painted back plate/core assembly is glued to the top plate using a centering gauge to ensure a uniform magnetic gap, the narrow space between the permanent magnet and the metal core where the voice coil sits. A bead of glue is applied to the flange of the basket to attach the cone surround. A vacuum is then used to remove any debris from the magnetic gap. A Mylar gauge is then inserted into the voice coil to help the technician set the exact coil height for the given loudspeaker design. A bead of glue is then added around the coil to adhere it to the spider.
The next step is to apply a bead of glue to the bottom of the spider, and then place it over the voice coil and attach it to the basket. At this point the voice coil is glued to the spider, which is glued to the basket. The cone is then inserted into the basket, and is pressed into the bead of glue that was applied earlier. Another bead of glue is then applied to attach the cone to the voice coil. The lead wires from the coil are fed through the two small holes that were pre-drilled through the cone and then through the terminals. The Mylar gauge is then removed from the voice coil and the exposed lead wires are covered, or dressed" with a rubber cement for added strength.
An edge treatment is used to seal porous cloth surrounds, as well as for sonic and performance enhancements. A final bead of glue is applied to the cone to attach the dust cap, which is used to keep dust and debris from getting inside the magnetic gap. Once the dust cap is in place, the speaker is then sent through our C-core magnetizer, using a field strength of 20 tesla meters to create the magnet. A front gasket is then added to the basket to create a seal with the enclosure if the speaker is to be rear mounted. The tensile leads are crimped to the terminals and the excess wire is trimmed. A small bead of glue is applied to each terminal to fix the lead wires in place.
The speaker is fully assembled at this point. A conveyer belt slowly moves the speakers through an oven to cure the glue, and then a technician at the end of the line sweeps the speaker with an audio signal. This is to ensure the final product is working properly and has no visible or audible defects.
Fun fact: 100% of the speakers manufactured in the Eminence factory are listened to by a person.
Cosmetic enhancements are applied last, including a back plate label and a rubber magnet boot to provide a clean and professional look. If the product is going to an OEM customer, it is typically assembled on a pallet, shrink wrapped and staged in our shipping department. Otherwise, the speaker is sent to our packing line to be boxed and stored in our warehouse for distribution to virtually any destination in the world.
Fun fact: In addition to pro sound, car audio, and musical instrument applications, Eminence products can be found in sports arenas, aircraft carriers, Carnegie Hall, and even the Smithsonian Museum as part of a sound art exhibit.