Amplifier

Since 1980, Harmonic Design has developed loudspeaker, signal processor and power amplifier as one system. Amplifiers, DSP and control software are created in-house — expertise built up over decades: hd established the use of system controllers as early as 1988, analogue at the time; in the early 1990s the MLSSA measurement system took computer-aided loudspeaker development to a new level, followed in 1994 by the first in-house digital signal processor. The current system amplifier range — hd QT series, hd QT-ETH series and hd SpaceAMP series — is designed as a universal platform: a single device concept drives the entire loudspeaker range, from compact installation systems to line arrays in touring use. The factory presets are laid out consistently across platforms: a loudspeaker behaves identically on every amplifier in these series, regardless of series or power class. Systems can therefore be expanded, reconfigured or moved to a different amplifier platform without having to redo the tuning.

The three series cover different application profiles. The hd SpaceAMP series is the installation amplifier: four channels in a 9.5″ single rack unit, with Dante and Gigabit Ethernet — designed for fixed installation, where mounting space, continuous operation and network integration matter. The hd QT-ETH series is the flagship: up to 4 × 3,000 W, sampling rate of up to 192 kHz, 32-bit converters, Dante/AES67 and AES3, plus full remote control over Ethernet — for demanding touring as well as large fixed installations. The hd QT series is the basic version for touring and installation: the same four-channel Class-D platform with FIR and IIR filters and multi-stage limiter architecture, configured via USB and the display on the unit.

Loudspeaker and amplifier are developed together; driver parameters, protection limits and filter curves pass directly into the factory presets. The basis for this is our in-house EAR — Electro Acoustic Research: a Class 1 anechoic chamber of some 1,000 m³ with maximum sound absorption, complemented by EMC pre-compliance measuring stations. A measurement robot creates an exact acoustic 3D model of every loudspeaker and makes all parameters quantitatively measurable. The result is higher usable sound pressure, additional headroom and linear behaviour ex works — not only in frequency response, but equally in impulse accuracy, tonal depth and low distortion. The factory presets cover a wide range of applications and are supplied ready for operation.

The hd QT-ETH series operates at sampling rates of up to 192 kHz with high-resolution 32-bit converters. This reduces latency, stabilises phase response into the upper octaves and allows FIR filters to act precisely within the acoustically relevant range; complemented by IIR filters, delays of up to one second and a multi-stage limiter architecture of peak and RMS limiters. Group delay correction is an integral part of the signal processing, and every speaker file is optimised with FIR filters for maximum linearity. What matters in practice is not brief peak output but the power available throughout operation. The switch-mode power supplies are designed for this sustained output: the hd QT12-ETH delivers 4 × 3,000 W into 4 Ω and likewise 4 × 3,000 W into 2 Ω, without collapsing as load impedance decreases.

The system is controlled with hd LevelZ 2, our own remote control and simulation software for Windows and macOS: real-time editing of all parameters over the network, central management of multiple devices and groups, and an integrated hd loudspeaker database. At the device, a 4″ touchscreen and a rotary encoder are available; new loudspeaker models and presets are delivered through regular updates. For questions on configuration and system design, a personal contact is available — development, manufacturing and support are located at the same site in Neckarwestheim.