Saturday, 24 August 2013

Beyma Coax 15XA38Nd Option - Closed Box

This is my design option for a closed box design for the coaxial 15XA38Nd speaker. I have purchased this for over two years, I have not yet had the chance to open them since my departure from home. As I am relocating back home, I have decided that this is the first speaker that I should be building.
Cabinet Plan.
The following is the bill of materials. I have elected to use two layers of 12mm plywood as means of construction and only allowed for dampening around the inside faces of the cabinet. By using two layers of ply with a suitably, softer (i.e., less stiff) glue, I hope to reduce the panel resonance.

Bill of Materials
The results in a box with an approximate volume of 115 litres not included any of the dampening. I have run the simulation in Basta for this design and the following are the simulation results. The crossover is the same one as the standard Beyma crossover that can be bought separate from the speakers. The design is a relatively simple 2nd order crossover with a zobel network on the 15" low frequency driver. The approximate crossover point is 1.8 kHz. The components for the crossover that I have chosen is Jantzen Superior Z-cap, Jantzen Wax coil inductors and Jantzen Superes range.

The low frequency driver has a inductance of 1.5 mH and capacitance of 15 uF. The high frequency driver has an inductance of 1.5 mH and capacitance of 2.2 uF. The LF zobel is 8r2 and 8.2 uF.
Base Scenario.
Base Scenario with Linkwitz Transform.
Base Scenario with Linkwitz Transform and Room Gain. With this scenario, the source voltage is 6V.

So far, the predicted performance is pretty good. So the process now is to order the crossover components. The next step is to order the plywood cut to size followed by the damping materials. With the LT bass boost, the Xmax of the driver limits the power output to 4.5 W, which produces about 6 V and a cone excursion of 4mm. The estimated SPL at 1m would be around 103 dB.

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