Apparatus and method for monitoring speaker cone displacement in an audio speaker

An apparatus for measuring speaker cone displacement relative to a fixed position in an audio speaker having a voice coil aligned with the speaker cone along a central axis, the fixed position radially offset from the central axis, the apparatus comprising:

• (a) a variable reluctance sensor device;
• said sensor device including a magnetic coil structure fixed relative to said fixed position;
• and a core structure affixed to said speaker cone coaxial with said magnetic coil structure effecting relative motion between said magnetic coil structure and said core structure through motion of said speaker cone at the fixed position on said cone radially offset from said axis;
• wherein said electromagnetic coil structure operates as at least part of a high pass filter having a corner frequency;
• (b) a signal injecting circuit coupled for injecting a predetermined input signal into said magnetic coil structure;
• said predetermined input signal has a frequency substantially below said corner frequency;
• and
• (c) a signal receiving circuit coupled with said one of said first and second units for receiving a signal resulting from modulation of said input signal due to variation of reluctance of said sensor device caused by displacement of said first unit relative to said second unit, and for generating an indicating signal based upon said resulting signal;
• at least one signal characteristic of said indicating signal being related with said cone displacement.

An apparatus for measuring speaker cone displacement relative to a fixed position in an audio speaker having a voice coil aligned with the speaker cone along a central axis, the fixed position radially offset from the central axis, the apparatus comprising:

• (a) a variable reluctance sensor device;
• said sensor device including a core structure fixed relative to said fixed position;
• and a magnetic coil structure affixed to said speaker cone coaxial with said core structure effecting relative motion between said core structure and said magnetic coil structure through motion of said speaker cone at the fixed position on said cone radially offset from said axis;
• wherein said electromagnetic coil structure operates as at least part of a high pass filter having a corner frequency;
• (b) a signal injecting circuit coupled for injecting a predetermined input signal into said magnetic coil structure;
• said predetermined input signal has a frequency substantially below said corner frequency;
• and
• (c) a signal receiving circuit coupled with said one of said first and second units for receiving a signal resulting from modulation of said input signal due to variation of reluctance of said sensor device caused by displacement of said first unit relative to said second unit, and for generating an indicating signal based upon said resulting signal;
• at least one signal characteristic of said indicating signal being related with said cone displacement.