The positional relationship between the speaker short-circuit ring aluminum and the voice coil bobbin is a key factor influencing nonlinear distortion. The core logic behind this is that their relative position directly determines the uniformity of the voice coil's magnetic field and the stability of its vibration. Nonlinear distortion essentially occurs when the speaker's output waveform deviates from the sinusoidal input signal. This is primarily caused by uneven magnetic field distribution and unbalanced force on the voice coil. Both factors are closely related to the alignment of the short-circuit ring aluminum and the voice coil bobbin. The short-circuit ring's core function is to suppress eddy currents in the magnetic circuit and stabilize the air gap magnetic field, while the voice coil bobbin supports the voice coil and transmits vibrations. Misalignment between the short-circuit ring aluminum and the voice coil bobbin disrupts the balance between magnetic field and vibration, leading to distortion.
Nonlinear distortion is significantly exacerbated when the short-circuit ring aluminum and the voice coil bobbin are misaligned. Ideally, the two should be perfectly concentric, ensuring that the voice coil remains within the uniform magnetic field regulated by the speaker short-circuit ring aluminum during vibration. If they are misaligned, as the voice coil moves up and down, some of the conductors will approach the edge of the speaker short-circuit ring aluminum, causing a sudden increase in magnetic field strength in that area while the conductors on the other side remain in a region with a weaker magnetic field. This uneven magnetic field causes fluctuations in the force applied to the voice coil, causing the force factor (Bl) to deviate from linearity with displacement, ultimately leading to additional harmonic components in the output sound. This distortion is particularly noticeable under high-amplitude conditions.
Improper axial spacing also directly impacts nonlinear distortion. The axial distance between the speaker short-circuit ring aluminum and the voice coil bobbin must strictly match the design value. Excessive spacing weakens the short-circuit ring's stabilizing effect on the magnetic field around the voice coil, increasing the amplitude of the magnetic field fluctuations with voice coil vibration and exacerbating nonlinear fluctuations in the force factor. Excessive spacing can lead to slight collisions or friction between the voice coil bobbin and the short-circuit ring during high-amplitude vibration. This not only introduces mechanical nonlinear distortion but also disrupts the continuity of the magnetic field, causing sudden changes in the force applied to the voice coil. This, in turn, affects the smoothness of the sound, making it prone to hum or waveform distortion, especially at low frequencies.
Radial offset can also induce nonlinear distortion. If the voice coil bobbin is radially offset from the short-circuit aluminum ring, the angles and speeds at which the wires in different locations cut through the magnetic flux lines will differ as the voice coil vibrates. The wires closer to the short-circuit aluminum ring experience greater force, while those closer to the short-circuit aluminum ring experience less force, causing the overall vibration of the voice coil to appear eccentric. This eccentric vibration is transmitted to the diaphragm, inducing asymmetric vibration, known as split vibration. This causes the vibration phases of different regions of the diaphragm to be inconsistent, resulting in fluctuating frequency response and distortion, especially in the mid- and high-frequency ranges, making the sound harsh and lacking in depth.
Tilt and misalignment between the speaker short-circuit aluminum ring and the voice coil bobbin is an often overlooked cause of distortion. If the two are not perfectly parallel but tilted at a certain angle, the magnetic field will be asymmetrically distributed along the voice coil's trajectory. As the voice coil vibrates up and down, the force applied to it shifts, generating additional lateral forces in addition to the axial vibration driving force. This additional force causes the voice coil bobbin to oscillate slightly, increasing friction between the voice coil and magnetic circuit components. It also causes the diaphragm's vibration trajectory to deviate from the ideal piston motion, resulting in distorted output waveforms. In the mid-frequency range of vocals or instruments, this distortion results in reduced timbre and loss of original nuance.
Changes in positional relationships caused by temperature fluctuations can also indirectly exacerbate nonlinear distortion. During speaker operation, the voice coil generates heat due to the current flowing through it. This heat is transferred to the voice coil bobbin, causing thermal expansion. If the initial positioning of the shorting ring aluminum and the voice coil bobbin is not considered to match the thermal expansion coefficients, the expansion of the bobbin as the temperature rises can cause the relative position of the two to deviate, such as decreasing axial spacing or increasing radial offset. This temperature-induced positional change disrupts the originally balanced magnetic field environment, accentuating the nonlinear characteristics of the force factor. This distortion, especially during prolonged high-power playback, can gradually increase with extended operation.
To minimize the impact of this positional relationship on nonlinear distortion, strict precision control is required during the design and assembly stages. Precision molds ensure the concentricity of the speaker short circuit ring aluminum and the voice coil bobbin. High-precision tooling ensures accurate axial spacing and radial positioning. Materials with matching thermal expansion coefficients are selected to minimize temperature fluctuations. Furthermore, dynamic testing is performed before shipment to adjust the position of the two components. This ensures that the voice coil maintains a uniform magnetic field and stable force throughout the entire frequency range, minimizing nonlinear distortion and restoring the true quality of sound.
