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TWO-WAY HERTZ PRO. Hertz: it’s a technical unit for cycles per second, but it’s also an Italian car audio equipment marque, established 20 years ago this year, and sharing a stable under Elettromedia with Audison. Here we’re looking at a pair of component speakers from the Hertz Mille range, the Pro MPK 165.3 two-way speaker system — which is about midway up in the Mille range. Below this is a two-way coaxial unit, above is a three-way system (and above that Hertz’s Mille ‘Legend’ offerings). The MPK 165.3 comes in a pack with two tweeters, two bass/midrange drivers, two crossover networks, along with grilles and hardware. The hardware includes both flush and raised mounts for the tweeters.

TALKING PARAMETERS We’ll look at all these bits individually in a moment, but first I’d like to note some welcome figures provided in the booklet that comes with the speakers. (They are also available in a tech sheet available from the Hertz website.) These are the ‘Electro-Acoustic



Parameters’ of the drivers. These are not the standard specifications, such as frequency response and power handling. These are things like the effective diameter of the drivers (usually measured from the mid-point of the roll surround), the free air resonant frequency, and even more obscure parameters going by such names as Qes and Vas and Re. This are the specifications that allow system designers to tune enclosures to provide the best performance for the speakers (sometimes they’re called the Thiele/Small parameters). That these are provided up front speaks well of Hertz. Whether they’ll be useful is less certain. After all, the opportunities to provide well-designed enclosures in a car are limited, other perhaps than for subwoofers. The bass/midrange units (model number MP 165.3) are nominally 165mm models (effective diameter 132mm, if it matters). They feature a 25mm voice coil of pure copper that’s wound on a Polyamide former. This, says Hertz, provides both high power handling and “very low intermodulation distortion of vocals”

(I’m not quite sure how). The cone is called an ‘Exponential V-cone’, made of pressed pulp with cotton fibres, and rather than the usual rounded dust cap over its centre, in the middle it tends to recede slightly more sharply into a hollow point. Hertz says that this and its overall shape is geometrically optimised for midfrequency linearity and dispersion”. There are assorted other features for this driver which Hertz says provide for “improved efficiency”, and “low distortion at high power levels”. Its electrical resistance is 3.1 ohms. Actual impedance is a frequency-based curve that depends on a number of things, including enclosure design. Nominally the package as a whole is the usual four ohms.

HIGH FREQUENCY SUPPORT The MP 25.3 tweeters have a 29mm diameter — both effective and nominal — and adopt a soft dome using something called Tetolon fibres. (If you do an internet search for Tetolon, you’ll mostly find links to Hertz and Audison

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