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Suspension part




  • Spider
  • Surround




  • Woofer
  • Other Transducers


Spider and surrounds are critical parts of the mechanical system determining the total stiffness of the suspension and centering the rest position of the voice coil in the gap. The shape of the stiffness nonlinearity causes nonlinear distortion and limits the maximal peak displacement. The asymmetrical shape of the curve may rectify the ac signal causing a dc component in the voice coil displacement which moves the coil away from the rest position. Visco-elastic properties of the suspension material may cause a memory effect of the suspension, such as creeping of the displacement, loss of stiffness for low frequencies and after high peak displacement. 
Therefore, the static, quasi-static and point-by-point (incremental) methods provide data which cannot describe the dynamic behavior of the suspension at audio frequencies. Reliable data require a dynamic operation above 10 Hz in vertical orientation while the inner and outer rim of the suspension part is clamped in a similar way as used in the final application. The properties of the suspension part highly depend on temperature, humidity and vary over time.

Challenges in the Design

  • High peak displacement for small size
  • Symmetrical shape of the stiffness characteristic versus positive and negative excursion
  • Desired soft limiting to protect the voice coil former
  • Stiffness K(x=0) at rest position is constant over time (ageing)
  • Stiffness K(x=0) at rest position is independent from peak displacement xpeak
  • Suspension characteristics are independent on climate conditions

Most Important Characteristics

  • Stiffness K(x=0) at rest position
  • Shape of the stiffness characteristic K(x)
  • Force-deflection curve F(x)

Critical Issues



  • Asymmetrical shape of the K(x) characteristic generates dc displacement which moves the coil away from optimal rest position and generates Bl intermodulation distortion
  • Stiffness K(x=0) at rest position decreases over time and may cause motor instability




Audio Engineering Society
AES2 Recommended practice Specification of Loudspeaker Components Used in Professional Audio and Sound Reinforcement
AES-ALMA Standard test method for audio engineering – Measurement of the lowest resonance frequency of loudspeaker cones

International Electrotechnical Commission
IEC 60268-5 Sound System Equipment, Part 5: Loudspeakers
IEC 62458 Sound System Equipment – Electroacoustic Transducers - Measurement of Large Signal Parameters 
IEC 62459 Sound System Equipment – Electroacoustic Transducers - Measurement of Suspension Parts

Other Related Information



Most relevant Measurements 

Modules of R&D SYSTEM

Modules of QC SYSTEM

Stiffness K(x) versus displacement x

Suspension Part Measurement (SPM)

Compliance C(x) versus displacement x

Suspension Part Measurement (SPM)

Force-deflection curve

Suspension Part Measurement (SPM)

Effective stiffness Keff (small signal parameter)

Suspension Part Measurement (SPM)

Linear Suspension Test (LST)

Maximal peak displacement XC limited by suspension nonlinearity (C(x) decreases to 75 %)

Suspension Part Measurement (SPM)