Accoppiamento Mutuo
Mutual Coupling
J. Audio Eng. Soc., Vol. 52, No. 4, 2004 April
J. Eargle, Honorary Member, and (1) JBL
Professional, Northridge, California, U. S. A.
(2) JME Consulting Corporation, Los Angeles,
California, U. S. A.
M. Gander, AES Fellow and JBL Professional, Northridge, California, U. S. A.
|
Questo lo
lascio in inglese per il sig. Calabrese (altrimenti dice che ho tradotto
“male”) L’originale
è in rete. |
In the LF range over which their response is
essentially omnidirectional (ka = 0.2 or lower), a doubling of closely
spaced driving units will result in an increase in acoustical output of 3 dB
for a fixed input power reference level [39, 48, 52, 53]. The progression in
efficiency increase is shown in Fig. 9 for one, two, and four LF transducers,
respectively.
Thus, by Equation 1 [Rendimento= [ρ0(Bl)2
SD2 /RE]/(2pc
Mms2) ], the efficiency will have doubled. For the case where the two drivers
are wired in series, the analysis goes as follows: The new driver has twice the
cone area, twice the moving mass, four times the (Bl)2 product, and twice the value of RE. Again,
by Equation 1, there will be a doubling of efficiency.
Mutual coupling often appears to give something for
nothing, but there are clear limits to its effectiveness.
With each doubling of cone area, the ka = 0.2
upper response frequency corner moves downward approximately by a factor of
0.7, since this is the reciprocal of the value by which the effective cone
radius has increased. As the process of adding drivers is continued, in the
limit it can be shown that the efficiency of an ensemble of direct radiators
cannot exceed a value of 25% [38]. Because of these constraints, the
approximation of power doubling for each twotimes increase in drivers is
accurate only at very low frequencies and only if the efficiency values are low
to begin with.
Fig. 9. Illustration of mutual
coupling of LF drivers.
Trattoda:
HISTORICAL PERSPECTIVES AND TECHNOLOGY OVERVIEW OF LOUDSPEAKERS
FOR SOUND REINFORCEMENT*
*Revised and expanded from a presentation at the
Institute of Acoustics 12th Annual Weekend Conference, Windermere,
England, October 25-27, 1996.
J. Eargle, Honorary Member, and (1) JBL
Professional, Northridge, California, U. S. A.
(2) JME Consulting Corporation, Los Angeles,
California, U. S. A.
M. Gander, AES Fellow and JBL Professional, Northridge, California, U. S. A.
Revised and expanded from a presentation at the
Institute of Acoustics 12th Annual Weekend Conference, Windermere,
England, October 25-27, 1996.
J. Audio Eng. Soc., Vol. 52, No. 4, 2004 April
[38] Keele, D. B. (Don), “Maximum Efficiency of Direct Radiator
Loudspeakers, 91st AES Convention, New York, October 1991; preprint 3193.
[39] Klapman, “Interaction Impedance of a System of Circular Pistons,” J. Acoustical Society of America, vol.
11, pp. 289-295 (January 1940).
[48] Strahm, C., “Complete Analysis of Single and Multiple Loudspeaker
Enclosures,” presented at the 81st AES Convention, Los Angeles, 12-16 November
1986; preprint 2419.
[52] Wolff, I., and Malter, L., “Sound Radiation from a System of
Circular Diaphragms,” Physical
Review, vol. 33, pp. 1061-1065 (June 1929).
[53] Zacharia, K. and Mallela, S., “Efficiency of Multiple-Driver
Speaker Systems,” presented at the IREE (Australia) Convention, 1975.