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ALMA International 2007 China Symposium. “Simulation of T/S Parameter Production Tolerances”. By Patrick Turnmire Redrock Acoustics. Thiele / Small parameters (T/S), Frequency Response and Power Handling, are the primary evaluation standards for loudspeaker performance. .

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ALMA International2007 China Symposium

“Simulation of T/S Parameter Production Tolerances”

By Patrick TurnmireRedrock Acoustics


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Thiele / Small parameters (T/S), Frequency Response and Power Handling, are the primary evaluation standards for loudspeaker performance.

“Simulation of T/S Parameter Production Tolerances”

For production testing, both frequency response and power handling have clear standards and a good engineering basis for those standards.

Thiele / Small parameter standards, however are typically assigned arbitrarily with no consideration of their relationship to the parts’ tolerance specifications that actually cause the parameter variance

- or to the real performance variations!

( System F3, Tuning, SPL )


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A typical Tolerance Specification for T/S parameters might look like this:

“Simulation of T/S Parameter Production Tolerances”

  • How these relate to the Parts Specifications is not considered!

  • ( How do parameters change when part values change? )

  • How these relate to the Performance of the speaker is not considered!

  • ( What parameters are important for the performance? )


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What we need to do is: look like this:

  • Identify which parameters are important for performance.

“Simulation of T/S Parameter Production Tolerances”

  • Identify how part changes affect parameters

  • (especially the important ones)

  • Set parameter tolerances that are based on reasonableparts tolerances.


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Which parameters are important for performance? look like this:

Performance is typically defined by:

System F3

Tuning ( Qtc for sealed and infinite baffle, Fb for vented )

Sensitivity

“Simulation of T/S Parameter Production Tolerances”

These are not defined by single parameters, rather by ratios of parameters:

Fo / Qts ratio

BL2 / Re ratio

Good control over these ratios, means good control over the performance of the system.


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How do part changes affect parameters? look like this:

Speaker parts specifications are typically a combination of dimensions with tolerance values, and part-specific specifications such as DCR (coils), deflection (spiders) Fo (cones), etc.

“Simulation of T/S Parameter Production Tolerances”

Changes in parts values typically change more than one parameter.

For example:

Coil DCR affects every parameter

Cone Fo affects Fo, Qts Qes, Vas

Motor Dimensions affect Qe, Qts, BL, SPL


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In fact all of the speaker parts tolerances interact to produce a wide range of variance in the speaker parameters

To accurately calculate parameter variations based on the tolerances of individual parts you need to create a complex matrix of all of the important variables and their tolerances.

“Simulation of T/S Parameter Production Tolerances”

Then calculate how these variables affect every parameter through the full range of their tolerances.

Easy Right?

Fortunately….


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“Simulation of T/S Parameter Production Tolerances” produce a wide range of variance in the speaker parameters


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Input values produce a wide range of variance in the speaker parameters

“Simulation of T/S Parameter Production Tolerances”


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Tolerance Calculations produce a wide range of variance in the speaker parameters

“Simulation of T/S Parameter Production Tolerances”


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Coil DCR Change of +/- 5 % produce a wide range of variance in the speaker parameters

“Simulation of T/S Parameter Production Tolerances”


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Cone F produce a wide range of variance in the speaker parameterso +/- 10% & Spider Deflection +/- 15%

“Simulation of T/S Parameter Production Tolerances”


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Typical Magnet Part Tolerances produce a wide range of variance in the speaker parameters

“Simulation of T/S Parameter Production Tolerances”


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Complete set of Typical Tolerances produce a wide range of variance in the speaker parameters

“Simulation of T/S Parameter Production Tolerances”


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Complete set of Typical Tolerances – Better Coil produce a wide range of variance in the speaker parameters

“Simulation of T/S Parameter Production Tolerances”


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Summary using Tolerance Worksheet: produce a wide range of variance in the speaker parameters

Using Qts, Qes and Vas for QC parameters can be misleading and cause unnecessary failures.

“Simulation of T/S Parameter Production Tolerances”

Coil Re has a large affect on important parameters and improving tolerance can greatly improve total speaker tolerances.

Large Changes in Cone Fo and Spider Deflection have little affect on important parameters.


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Performance – Based T/S Tolerance Model based on Part Tolerances

“Simulation of T/S Parameter Production Tolerances”

These values can easily be achieved with reasonable part tolerances

( Coil tolerances have to be improved from the +/- 5% DCR standard )


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Questions, Comments? Tolerances

“Simulation of T/S Parameter Production Tolerances”


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