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Woofer in bass reflex enclosure

Woofer in bass reflex enclosure. Contents. Description of the analysis Model summary Geometry Overview Enclosure Driver Force balance on cone Electromagnetic model Results Model extensions Ideas. Description of the analysis.

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Woofer in bass reflex enclosure

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  1. Woofer in bass reflex enclosure

  2. Contents • Description of the analysis • Model summary • Geometry • Overview • Enclosure • Driver • Force balance on cone • Electromagnetic model • Results • Model extensions • Ideas

  3. Description of the analysis The behavior of a loudspeaker depends on the driver, the enclosure, and the listening environment The purpose of this analysis is to measure the sensitivity of a woofer mounted in a bass reflex enclosure and placed in a room The sensitivity is defined as the sound pressure level measured at a listening position 1 m away from the woofer, given a nominal driving voltage with an RMS value of 2.83 V. A frequency range of 10 – 1500 Hz is investigated

  4. Model summary The woofer is mounted in a bass reflex enclosure and placed in the corner of an open room All structures are assumed to be rigid The cone vibrates with a prescribed acceleration in piston mode By sampling the pressure load on the cone and using separately modeled electrical characteristics, the motion of the cone can be normalized to the nominal driving voltage Finally, the acoustic pressure at the listening position is evaluated

  5. Geometry overview • The dimensions of the enclosure are w * b * h = 22 * 17 * 30 cm • The room extends from the corner to infinity in all three coordinate directions. In the model, this is described by a perfectly matched layer (PML) outside the here shown geometry • The geometry was set up using COMSOL’s built-in CAD tool

  6. Geometry, Enclosure Cross-sectional top to bottom view of the enclosure and the room Side view showing the driver and the vent

  7. Geometry, Driver Cone Basket Pole piece, top plate, magnet Voice coil

  8. Force balance on cone • The mechanical properties Rs and Cs of the suspension and the electrical properties BL and Zb are known • The integrated pressure force on the cone, Fa, is measured • A scalar equation adapts the velocity of the cone so that it corresponds to the nominal driving voltage V0

  9. Electromagnetic model • Force factor BL from magnetostatic analysis • Blocked coil impedance Zb as a function of the frequency from AC analysis • This model is included in the Acoustics Module model library

  10. Results • Sound pressure level as iso-surfaces, at 1500 Hz

  11. Results, 105 Hz SPL outside the speaker Cross-sectional view • Near the Helmholtz resonance of the enclosure, much of the sound exits through the vent

  12. Results, 324 Hz SPL outside the speaker Cross-sectional view • Resonances form between the enclosure and the corner of the room

  13. Results, 1500 Hz SPL outside the speaker Cross-sectional view • At high frequencies, the details of the geometry become more important as complicated resonance patterns appear

  14. Results, Sensitivity

  15. Sensitivity, cont. Compared with the baffled driver, the SPL mostly increases with the enclosure and the room The vent pushes the sensitivity around 100 Hz

  16. Model Extensions, ideas Change the size and the shape of the enclosure Line the enclosure with some damping material Include some more detail: dust cap, spider, ... Vary the listening location and the layout of the room Let some or all mechanical parts be non-rigid

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