Calculate the effect of additional mass on the Thiele-Small Parameters

The calculation is based on the relative growth of Massa-moving mass (mms) of the driver.
The Equivalent Volume ( Vas )and the Transducer constant ( BI ), however, remain unchanged. The efficiency decreases due to the extra mass by 20 * log (M).

Since the resonance frequency drops and increases by the same factor, there is an overall reduction in the quotient fs / Qts, which is relevant for the lower limit frequency that can be achieved, by the factor M.

By doubling the moving mass, which causes the resonance frequency to drop by root(2) and the value to increase by the same factor, a halving of the achievable lower cut-off frequency is to be expected in the first step, while the required housing is doubled.

However, this only applies if the overall quality remains in the optimal range for the selected housing type due to the increase in mass. If Qts gets too high, these formulas are less and less correct. That is why bass drivers with a powerful drive, i.e. lower Qts, are ideal.

Efficiency Bandwidth Product (EBP) is a number which shows the trade-off between efficiency and bandwidth of a driver. It is useful in determining if a driver is suited for a sealed or vented box and is also used to determine suitability for horn loading.

A suitable driver should have:
  • Low Fs
  • Low Qts
  • High Mms
Please do not exaggerate the additional mass, there are physics limits!

TSP Woofer :

Calculated new Parameters :

Fs: Hz  new fs: Hz
Qms:   new Qms:
Qes:   new Qes:
Qts:   new Qts:
Mms:   new Mms:  grams
SPL: db (1 W/1 m)  new SPL: dB (1 W/1 m)
Added mass: grams  new EBP =  
EBP =  
SPL loss = dB (1 W/1 m)
Mass-Factor = %

 Example ( SEAS Prestige CA26RE4X 10" Paper Cone Woofer )

Original TSP + 50 grams + 100 grams + 150 grams  
Re 6.1 6.1 6.1 6.1 ohms
Le 3.08 3.08 3.08 3.08 mH
Fs 25 16.5 13.2 11.3 Hz
Qms 3.99 6.05 7.57 8.83 -
Qes 0.30 0.45 0.57 0.66 -
Qts 0.28 0.42 0.53 0.62 -
Mms 38.5 88.5 138.5 188.5 grams
SPL 91 83.8 79.9 77.2 dB

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