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The Tannoy Monitor HPD series was released in 1974 and produced untilaround 1980. Distinguishing physical features of this model are:

• a plastic magnet cover, in a natural buff-colour (not painted)
• a cast chassis basket that is finished in gold, with either 4 or 8 fixing holes depending on age
• a low-frequency driver surround that is a roll-surround made from plastic-foam (the so-called "Tannoplas" surround.)
• a low-frequency driver cone with eight ribbed-girders fixed to the rear face of the cone (to minimise cone-break-up)

This model is often confused with the Monitor Gold because the chassisis painted gold. However, the Monitor Gold did not have the plastic-foamroll-surround of the HPD-series (except on some very late-model MonitorGolds), nor the "girdacoustic" low frequency cone.

The Monitor HPD was available in three models:

• Monitor Gold 10-inch
• Monitor Gold 12-inch
• Monitor Gold 15-inch

See also cabinet designs forthese drive-units

The HPD-series was the last model in the classic series first launchedin 1947. All models from the Monitor Black through the Silvers, Reds, Goldsand lastly the HPD's uised the same basic design with minor refinementsto LF cone surrounds, dustcovers, rear-loading of the HF diaphragm. Perhaps the most significant performance changes were achieved throughthe use of more sophisticated crossovers on the later models like the MonitorGold's and Monitor HPD's. Desirable features of the HPD series are: Ticonal-G magnet (a trade-name for Alnico) Very low-resonance LF cone (around 20Hz, versus closer to 30Hz for all previous designs). A down-side is that the high-compliance close-cell roll-surround on the LF unit disintegrates after about 15 years, requiring replacement). High power rating of 85 Watts integrated programme material A more transparent dust-cover than the Monitor Red and Monitor Gold, giving better treble clarity Well controlled LF cone with the so-called "girdacoustic" ribbed strengthening on the rear face (as shown at left).