Question
Speaker cones seem to be made out of a lot of different materials. Hasn’t some particular material emerged as the best to be used or is it just the manufacturers want to have something unique to their own speakers?

– Tim, L
Orlando, Fla

Answer:
One of those debates which had been raging for decades is about metal vs. paper or various exotic diaphragms. Each has its merits and every manufacturer has their preferences. Let’s discuss the basic function of the loudspeaker and how the diaphragm (and we are only discussing cones here) is supposed to function and what is actually happening in the “real world”.

The material used to create a “perfect” speaker cone would need to be as stiff as steel, light as a feather, and able to start and stop on a dime. Unfortunately, the perfect driver does not exist in the real world, so speaker designers select materials that allow them to get as close the ideal as possible.

The best thing about plastic (polypropylene) cones is that they perform pretty well and their manufacturing uniformity is very high and inexpensive to produce. These cones have a major advantage in that they are highly damped and lossy. This means they can have a controlled break-up, which results in a smoother high frequency roll-off. Some people argue that plastic cones tend to not sound as snappy or lively as stiff paper cone counterparts. This can be attributed to an almost capacitive storage effect inherent in soft cone type drivers. However, if well engineered, a good, well damped plastic diaphragms can excel at midrange frequencies and at a fraction of the cost of producing a quality paper cone driver.

Paper formulations have all the good points spoken about above, but the paper cone can actually absorb moisture from the air, changing its mass and damping characteristics. Cost, manufacturing complexity-uniformity issues, performance considerations, etc. make diaphragm materials selection a very difficult aspect of loudspeaker design. Paper cones, made in part from felt and wool have a combination of stiffness, low mass and loss inherent in the material that often make the best sounding cones. Sometimes rubber can be added to the paper to increase its durability. Tweeters have to vibrate at very high speeds (20kHz range) and are often made from metals such as aluminum, titanium or silk. They must be very stiff while remaining light weight. Mids and woofers are often made with paper (with additives), Kevlar, ceramics or exotic items such as wood. All of these different materials are selected by the designer to achieve that elusive goal: the “ideal” speaker. Frankly, these variables allow the comsumer a variety of choices and keep us all from buying the same style boring box speakers. Viva la difference!

 

  • Gene DellaSala

    Hi Jim, a fellow Audioholics reader noticed you lifted a passage from one of my articles to put in your article. I would ask that you either give me credit for it or please rewrite the section in question.

    Please see below:

    I was reading articles comparing speaker cone material
    when I discovered the exact text in two different articles “written”
    by two different articles.

    Jim Milton’s second paragraph in his answer found here:
    http://hometheaterhifi.com/q-a/speaker-cone-material-best-performance/

    echos Gene DellaSala’s words here:
    http://www.audioholics.com/loudspeaker-design/loudspeaker-drivers/diaphragm-material

    The ideal loudspeaker diaphragm would never flex and would exhibit
    perfect pistonic motion. It would be infinitely rigid, well damped
    (stops on a dime), and the speed of sound through the material would be
    unlimited. The mass would ideally be zero and the break up mode
    frequency would be infinity.

  • Gene DellaSala

    Thank you. I asked the author to please credit us or rewrite the passage in question.

  • tannoy615

    Lol that is so funny , glad to See your only joking

  • Terroantula

    Surely Spider Silk is perfect?