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In the early seventies, A.N.Thiele and Richard H. Small devised a set of formulas to predict how a driver would perform in any given box. Thiele was the senior engineer of design and development for the Australian Broadcasting Commission and was responsible at the time for the Federal Engineering Laboratory, as well as for analyzing the design of equipment and systems for sound and vision broadcasting. Small was, at the time, a Commonwealth Post-graduate Research Student in the School of Electrical Engineering at the University of Sydney.

Thiele and Small devoted considerable effort to show how the following parameters define the relationship between a speaker and a particular enclosure. However, they can be invaluable in making choices because they tell you far more about the transducer's real performance.

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.

Enter the Thiele-Small parameters and calculate the Flat Response ( Step 1 )
V_b, F_b, F₃ and EBP are calculated and the Frequency Response is plotted
EBP - The efficiency bandwidth product, a rough indicator measure is calculated.
A common rule of thumb indicates that for EBP > 100, a driver is perhaps best used in a reflex enclosure,
while EBP < 50 indicates a clsed enclosure. For 50 < EBP < 100, either enclosure may be used effectively.
Now you can repeat these calculations with a New V_b for the housing ( Step2 )
Both frequency curves ( Flat and Custom ) are displayed for comparison

EBP < 50 - use only for a sealed box
EBP 50 - 100 - can be used in either
EBP > 100 - vented box only
EBP > 130 - can be used for horn loudspeakers

Qtc = 0.5 : Perfect transients, but low efficiency (over damped).
Qtc = 0.707 : This is the number most people try to reach for, as it gives good transients
and flat response with minimum cutoff.
0.7 < Qtc < 1.2 : Better efficiency, somewhat degraded transients, steeper roll off.
Qtc > 1.2 : High efficiency, bad transients, bad frequency response (under damped).

Calculate V_b , f₃ , f_b and EBP

V_as - Volume of air equal to the speaker's spring characteristics
Q_ts - Total Q of driver
Q_es - Electrical Q factor
F_s - Free air resonance of speaker
EBP = Efficiency Bandwidth Product

V_b - The airspace volume of the box. The volume of the driver and any building material needs to be added to this value.
F₃ - lower -3db frequency
F_b = Box frequency

Thiele-Small Parameters :

Flat Calculation :

Custom Calculation :

V_as [liters] :

V_b [liters] :

* New V_b [liters]

Q_ts :

F₃ [Hz] :

Q_es :

F_b [Hz] :

F_s [Hz] :

Q_tc :

EBP :

Peak :

Step 1:

Step 2:

Q_tc

Frequency Response

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