How We Simulate TPCD (And How You Can Too)

The engineering freedom of a Thin-Ply Carbon Diaphragm (TPCD®) is vast. By tailoring thickness and stiffness at any given point across the diaphragm stiffness can be maximized, mass minimized and resonances controlled. A simulation-driven approach lets us evaluate the endless possibilities before the production of physical prototypes.

Why we simulate

We have three main purposes for simulations:

• To efficiently engineer geometries and diaphragm constructions including tailored thickness and stiffness in all points in the diaphragm.

• To show the potential performance and behavior of TPCD diaphragms for specific drivers and applications. 

• To push the boundaries of the TPCD technology by testing (sometimes radical) concepts and solutions in a virtual environment.

What we simulate

As stiffness or thickness of a diaphragm is changed in any position, the modal behavior will change. Since a TPCD diaphragm with a specific geometry can be made in thousands of different thickness and stiffness configurations, each with its own modal behavior, the most efficient way to optimize the diaphragm construction is through simulation. 

Figure 1: TPCD with different modal behaviors because of different constructions and/or at different frequencies

As opposed to aluminium or plastic diaphragms that are isotropic (the same material properties in all directions), a TPCD cone or dome is orthotropic, meaning the material properties vary in relation to the carbon fiber directions. We use this to our advantage by engineering the diaphragm for tailored modal behavior. Consequently, to fully capture these possibilities we model in 3D.

In radial direction, a basic configuration is to tailor a thickness profile, making the diaphragm stiff or rigid where that is needed, and thin with minimum mass in areas where that is most beneficial.

In circumferential direction the configuration can be to vary the stiffness-to-density as well as bending stiffness in different locations to tailor the modal behavior. Concretely, in a cone, this may involve creating different areas with different speeds of sound so that the vibrations from the voice coil at the cone neck arrive at different times at the cone edge to avoid symmetric and severe break up modes.

A typical use of TPCD engineering involves optimizing the diaphragm construction to remove problematic modes. In over-ear headphones, a typical mode is a bending mode around the voice coil causing cancellation between the dome part (inside of the voice coil) and the cone part (outside the voice coil). This cancellation leads to loss of SPL at the frequencies where this mode appears. By simulating the headphone diaphragm, we can detect this mode and simulate the effect of a reinforced voice coil area in preventing the mode from occurring. Needless to say, this makes the development process more efficient and enables us to maximize performance.

Figure 2: Headphone diaphragm comparison at 12.2 kHz: uniform thickness (left) and reinforced voice coil area (right).

One important aspect when working with composite materials is that the elements in the mesh should be properly oriented (since the material properties depend on the direction). In isotropic materials no attention needs to be paid to the element coordinate system. But in orthotropic materials the properties will be applied along the axis of the element coordinate systems. It is therefore important that they are properly oriented from the start and follow the curvature of the diaphragm (as shown in the pictures below).  

 
Figure 3: Mesh elements aligned with the curvature of the diaphragm

Do you want to simulate TPCD?

Our philosophy is to make it easy for you to simulate, explore and experiment with the performance and potential of TPCD in your drivers, loudspeakers or headphones. Therefore, we can provide you with information, data and material properties to enable you to explore the possibilities with TPCD diaphragms in your own environment. We can provide you with the full orthotropic property package or a simplified isotropic equivalent should you wish to use an axisymmetric set up as a starting point.

Reach out to us by filling in the form below to get access to our simulation data and information kit.  To help you in the process we are happy to connect you with our simulation engineers.