Rate number system for loudspeaker drivers (1940’s-1970’s)

The driver marking generally looks like: A{C}{E}-XX{X}{X} Q{R}{T}

Section 1 – A{C}{E}, alphabetic, from 1 to 3 characters – indicate the type of speaker driver:

B – bas [bass],

H – bredband [full-range],

M – mini,

O – oval,

PM – permanentmagnet standard [permanent magnet standard],

PMB – permanentmagnet bredband [permanent magnet full-range],

PMK – permanentmagnet Kombifon [permanent magnet Kombifon],

PMO – permanentmagnet oval [permanent magnet oval],

S – standard,

U – ultrasuper [ultra-super].

Section 2 – XX{X}{X}, numerical, from 2 to 4 characters: the first one or two characters indicate the geometric dimensions of the speaker driver in inches; the second one or two characters – unknown.

Section 3 – Q{R}{T}, alphabetic, from 1 to 3 characters (may not be used) – indicate the type of speaker diaphragm (and other):

D – D-membran (dämpade) [D-diaphragm (damped)],

H – H-membran (hårda) [H-diaphragm (hard)],

X – X-membran [X-diaphragm],

Y – Y-membran [Y-diaphragm],

Z – Z-membran [Z-diaphragm],

K – kon [cone] (speaker driver equipped with a special tweeter cone),

D and H membranes

D (damped) and H (hard) diaphragms are mainly intended for so-called open boxes, eg for radio and TV.

The H diaphragm is suitable for low power amplifiers. High efficiency and high Q value provide clear and distinct sound reproduction.

The D diaphragm is damped, has lower distortion and self-resonance. The D-diaphragm requires slightly higher power but instead provides better bass reproduction.

X and Y membranes

are conventionally manufactured, but have special membrane masses and edge constructions. X and Y-diaphragms have very low self-resonances and are intended for closed boxes.

Z membrane

Newly designed special membranes for closed boxes. The edge of the Z-membrane is made of a different material on the membrane body, e.g. of solid rubber or of rubber impregnated or rubber vulcanized fabric.

Result (compared to X and Y-memhran): Further reduced self-resonance, many times increased strength against mechanical stresses. Loudspeaker with Z-diaphragm has larger amplitudes.

or

Section 3 - X{X}, numeric - indicates the impedance. Typical for "transitional" (early) models.

Usually, the impedance is also listed on the driver itself or on the driver label. Typically, it is 4, 8, 16 Ohms.

Mark “Tropik” – Tropiksökert (tropicalized model).

 

For example,

• PM-43 – permanentmagnet, standard (permanent magnet, standard), diameter 4”.
• PMB-8003 Tropik – permanentmagnet, bredband, tropiksökert (permanent magnet, full-range, tropicalized), diameter 8”.
• PM-8003-8 - permanentmagnet, bredband, (permanent magnet, full-range,), diameter 8”, impedance 8 Ohms.
• O-4654 YK – oval, Y-membran, kon (oval, Y-diapragm, additional tweeter cone), 4”x6”; but O-4799 ZK has dimensions 4”x6” too.
• U-8030 X – ultrasuper, X-membran (ultra-super, X-diapragm), diameter 8”.

 

N.B. In different years, loudspeaker drivers may have different parameters and, accordingly, different characteristics (maximum power, geometric parameters, weight, frequency range, etc.)

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