![]() ![]() The Matlab/Octave scripts used for finding the design parameters can be downloaded here. The LTspice simulations for all examples can be downloaded here. The voltage representing the transfer function is scaled so as to be constant with variations of the source amplitude ampl and amplifier gain value gain.Äownloadable LTspice Simulations and Matlab/Octave Scripts These represent the peak displacement of the cone in millimeters, the SPL at distance dist, and the transfer function G( s) (or H( s) if it is an assisted alignment) respectively. On the right side of Figure 3, three test voltages are provided, denoted by displacement_mm, SPL and transfer_function. Given a correct computation of the element values, a direct, one-to-one relationship is established between the synthesis and analysis, allowing for verification of both the design equations and the software code for solving them. It can be seen in Figure 3 that reflecting all electrical and mechanical elements to the acoustical side of the circuit will result in an acoustical analogous circuit of identical form to Figure 1. This simplifies the equivalent circuit and the computations of the element values from the driver Thiele-Small parameters. The effective mechanical mass M MS is really the sum of the mechanical mass M MD of the driver diaphragm assembly itself, plus the acoustic mass loads on the front and back of the driver reflected through the transformer to the mechanical section. To ensure that G( s) has the form of a high-pass filter function, the voice coil inductance is neglected. All parameters are in MKS units unless they explicitly have a units suffix as in e.g. The parameter dist is the distance in meters, used to compute the dB SPL. The box volume in cubic feet, box tuning frequency in Hz and box Q are entered as VBcuft, fBox and QL respectively. param statements under "Measured driver parameters". The Thiele-Small parameters of the driver are entered as. When such a filter is used, its transfer function is entered as a Laplace expression for the scale factor of a voltage-controlled voltage source. For assisted alignments, a filter (not shown) is placed between V1 and E2. Voltage source V1 represents the preamp output voltage, while voltage-controlled voltage source E2 represents a power amplifier with THX-compliant gain. The circuit keeps the electrical, mechanical and acoustical portions separate to allow for easy probing of different types of physical quantities without resorting to transformations between the electrical, mechanical and acoustical domains. Simulation Schematic of a Typical Unassisted Vented Box Alignment The schematic of a typical simulation is shown below in Figure 3.įigure 3. In contrast, the simulations provided here are structured so that the transfer function of the loudspeaker plus box is identical to G( s) given in Small and here in (1), with transfer function coefficients given by (14) - (17). Leach's approach includes the effects of more complex phenomena than those usually considered, including mutual coupling between the port and driver, as well as a more complex model of radiation impedance than the acoustic mass loading that's typically used. The simulation technique is a variant of the approach used by Leach, except that it uses the free LTspice simulator, originally from Linear Technology. Schematic and Description of Typical Simulation In some cases, alignments with little or no practical usage will arise. All the possible alignment classes are evaluated for each n value of the assisted alignments: one fifth-order, three sixth-order, three seventh-order and six eighth-order. A collection of assisted alignments of order n from 5 through 8 will be designed, analyzed and compared to the unassisted alignments with add-on high-pass filters to determine if there is any advantage to incorporating the filters into the design process itself. First, an unassisted system will be examined without any external filter, then with four different add-on high-pass filters. Simulations of frequency response and displacement will be performed. These simulations will all use the Dayton RSS390HF-4 driver, which is well suited to large vented-box subwoofers having a -3dB frequency in the neighborhood of 20 Hz. In order to verify the theoretical results, debug the related design software and evaluate potential designs, a collection of SPICE simulations of various systems will be performed in this section and the results presented. Simulating Designs Using SPICE General Approach
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