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Monday, January 21, 2019
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  Relationship between

  • efficiency
  • lower limit frequency
  • volume of housing

  • 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

    Calculate efficiency (ETA)

    F3 [Hz] : Qts : Ql : Qtc : Vb [l] :
    Eta [dB/W/m] (Vented) : Eta [dB/W/m] (Closed) :
    Eta [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

    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!