The Blog is back, after a long pause! Today we’re writing about one of the new developments here at Tymphany: the FLT shallow compact woofer products, which use the newly developed Plica™ suspension technology.
The Market Need
In late 2010, Tymphany embarked upon an effort to develop small compact woofers in the 3” to 4” size range. It was something we saw as essential, given the changes we have seen in the audio marketplace these past few years. Soundbars have become a prevalent solution for adding audio quality to televisions, as television manufacturers have concentrated their technology offerings on video quality, and thinner, lighter televisions.
Of course, thinner televisions offer design challenges for the development of soundbar products. Producing good, deep bass requires woofers that can displace a lot of air. Traditionally, this has been accomplished with deepened woofer, resulting in soundbar products which would be much thicker than the televisions…a jarring visual experience, to say the least. As an example, Tymphany’s own TG9FD10-08 would result in a minimum soundbar depth of perhaps 45 mm; the panels on some of the high end LED televisions today, such as the Samsung 40″ LED 6420 Series (2011), are as thin as 30 mm, excluding wall mounting brackets which might add another 5 mm in thickness.
The challenge we set for ourselves, was to develop a set of compact woofers which would be no taller than 35 mm. This would allow for the design of systems which would have the same thickness as the televisions, giving these systems a competitive edge in performance plus looks perspective.
The Technical Challenge
How to make a compact woofer that works well when it is that shallow?
Let’s start with an understanding of the normal design approaches, taken before. A couple of examples exist from our own catalog. The 3” PLS-P830987, has a compact neodymium motor and performs down to 100 Hz, and has a top-to-bottom height of roughly 51 mm. The 3.5” TC9FD18-08 is powered by a wide but shallow ferrite motor, and performs down to 123 Hz, and its height is roughly 41 mm. For many years, the TC9 has been a popular solution for shallow bass coupled with full-range performance, but in this situation it is just too tall.
Let’s list off the factors which drive a typical transducer’s height, to provide more insight:
• Effective cone height: Most cones are not flat, and the height of the shape, from where they are attached to the basket (by way of the surround), to where they attach the voice coil, adds to the height of the transducer. Cones have their typical conical shape to take advantage of the “geometric stiffness” that such a shape provides.
• Spider clearance: The spider typically attaches to the voice coil, under the cone, and clearance between cone and spider is required to account for the spider thickness, and to account for the glue used to attach the voice coil and spider together. The cone and spider must also be kept apart, to prevent the two parts hitting during cone/spider/coil motion.
• Excursion clearance: To make sound, the transducer must move air. The more air it can move, the louder the transducer can play at low frequencies. Therefore, the design of the transducer must account for the planned amount of movement. Clearance must be planned for between the spider and the motor parts, and also between the bottom of the voice coil and the motor.
• Motor geometry: In the motor, there are a few key dimensions which require height in the transducer. The top plate thickness is one such dimension. The Xmax, which is the amount that the voice coil windings are taller than the top plate, to control motor linearity, is another such dimension. The back plate thickness is the third such dimension.
These dimensions are all illustrated in the figure below.
The Technical Approach
In reviewing the factors driving the design of the typical transducer, the engineering team decided to take an approach which broke with convention. Here’s how:
• Flat cones. Instead of using conically shaped cones, for stiffness, the engineers took a look at flat cones, with materials and thicknesses selected to preserve the stiffness of the cone over the desired operating bandwidth.
• Compact neodymium motor. This frees up as much space in the transducer as possible, by keeping the motor small and close to the voice coil.
• No spider. This eliminates the need for clearance between the cone and spider. It makes the defining dimension for excursion change from spider to motor, to cone to motor.
It is worth remembering why the spider is in the transducer in the first place. The spider and surround act together to control the cone and coil motion, limiting rocking mode behaviour and ensuring that the coil motion is along the transducer’s axis, so that the coil does not hit the motor. Removing the spider requires a different solution, to prevent this issue.
Given these changes away from the traditional woofer approach, the transducer interior would look similar to the figure below.
In this figure, you can see the space available for the second suspension element, which would be replacing the spider.
If you are interested in learning more, please subscribe to our rss feed below. Next week, we will describe in more detail our design solution to small compact woofers.