Calculate Driver Reference Efficiency
With & Without Enclosure

Calculate Driver Reference Efficiency Without Enclosure

This calculator is intended to help you determine the reference efficiency of any loudspeaker.
The efficiency of a system is defined as the ratio between the useful delivered power output divided by the input power, denoted by the Greek letter small eta (η).

It has to be destinguished between the electrical power Pe of the amplifier and the emitted sound power of the speaker Pak.

Acoustic efficiency η (eta) of a loudspeaker is:
Acoustic efficiency formula
Common percentages range from 0.3 to about 1.6

Power Handling of the speaker :   Watt
Fs :   Hz
Vas :   Liter
Qes : 
Reference Efficiency :   %    SPL(dB)
Acoustic Power ( Pak ) :   W     ( Value you needed to calculate Port Airspeed. )

Click here to calculate the Port Airspeed

Calculate Acoustic Efficiency (eta) Of A Loudspeaker With Enclosure

Relationship between

  • Efficiency

  • According R.H. Small is there a connection between efficiency eta [%], lower limit frequency F3 [Hz] and box volume Vb [l]:

    Eta [%] = Kn · 10-5 · F33 [Hz]· Vb [l]

    The factor Kn is made up of three components:

    Kn = Kn(Q) · Kn(C) · Kn(G),

    where Kn is the component (C) takes into account only in sealed enclosures. It is:

    Kn(Q) = Qt / Qe  ( For chassis with low mechanical losses (Qm>> Qe) reached Kn (Q) its theoretical maximum of 1 )

    Kn(C) = Vas / ( Vas + Vb )
    ( In soft clamped chassis that are built into a small housing (vas>> Vb) reached Kn (C) its theoretical maximum of 1 )

    The value of Kn (G) depends on the overall quality of sealed enclosures Qtc of the system and bass reflex enclosures depends on the total losses and the total Q Ql Qts of the chassis in open air.

    The whole thing is of course (like all other TSP) only in the area of piston-diaphragm movement, that is usually only in the lower frequency range.

    Required Information:

    F3 [Hz]  = Desired lower cutoff frequency (-3 dB) of the system
    Qts [ ]  = Overall quality of the chassis
    Ql [ ]  = Overall quality of housing losses
    Qtc [ ]  = Overall quality of the finished speaker
    Vb [l]  = Maximum available cabinet volume

    If the ratio of Qm / Qe of 10:1, 5:1 or 2:1, this value at 0.41, 0.79 and 1.76 dB will be reduced!
    In closed boxes, this value is at a ratio of Vab / Vb ratio of 10:1, 5:1 or 2:1, this value is further reduced to 0.41, 0.79 and 1.76 dB!

    Comparison between bass reflex and closed speakers

    F-3 [Hz] 
    Vb [l]: 

    Eta - Vented :  [dB/W/m]
    Eta - Closed :  [dB/W/m]
    With the above specifications the maximum possible sound pressure level in the lower frequency range from 1 watt input at 1 meter distance for radiation into half space.

    Click here to calculate the Port Airspeed

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