HEDD Audio Type 05 A-Core

HEDD’s new A‑Core range sees the company return to making all‑analogue monitors — and the results are impressive.

Back in 2017 I reviewed HEDD Audio’s debut offering, the Type 07 studio monitors (SOS March 2017). Although they could be fitted with a range of digital interface cards that allowed for direct AES3 and various audio‑over‑IP connections, they were otherwise pure analogue monitors.

By the end of 2020, the Type series had evolved into their current Mk2 guises, with pretty comprehensive onboard DSP (including a zero‑phase Lineariser filter), analogue and digital inputs, and the choice of sealed‑box or reflex‑port operating modes. My colleague Phil Ward wrote a magisterial review of the Type 07 Mk2 in SOS October 2021, and summarised it as “a seriously high‑performance nearfield monitor”.

Now, in 2025, HEDD Audio have gone back to their roots by releasing entirely analogue reworkings of those Mk2 speakers. These new monitors are called the Type 05 A‑Core and the Type 07 A‑Core, and pair the Mk2’s cabinets, AMT (Air Motion Transformer) tweeters, custom honeycomb woofers and twin 100W analogue ICEpower Class‑D amplifiers with newly designed analogue filter boards.

For this review, HEDD Audio sent over not only a pair of the brand‑new Type 05 A‑Core monitors, but also a pair of the current Type 05 Mk2s, which remain in production. Since the only differences between the A‑Core and the Mk2 versions are the former’s analogue filter boards and the latter’s DSP boards, this made for an interesting comparison that we’ll come to later on.

Meet The Maker

Berlin‑based Heinz ElectroDynamic Design (HEDD) have a 50‑plus‑year back story that is pretty unique in our industry. Physicist Klaus Heinz, the son of Physics Nobel Prize laureate Ernst Ruska, first became interested in loudspeakers while at university. After graduating, he opened a high‑end hi‑fi shop in Berlin, which in turn led to an encounter with a loudspeaker by US company Electrostatic Sound (ESS). That loudspeaker, the AMT1, was the first to utilise the original, rather bulky, dipole AMT (Air Motion Transformer) tweeter, which had been invented in the 1960s by the late German‑born American physicist and inventor Oskar Heil (1908‑1994). The sound quality of that original AMT (which is still available from ESS as the I‑Large) made such an impression on Heinz that, in 1985, he travelled to the US to study under Heil. There, he refined Heil’s AMT design to reduce its overall dimensions to those of a conventional high‑performance tweeter and improve its reliability. In 1999, Heinz founded ADAM Audio, a company whose reputation and success were built on the back of his ART (Accelerating Ribbon Technology) and X‑ART tweeter refinements of Heil’s AMT. At the time, that style of ribbon tweeter was unique in the studio monitor market.

Heinz stepped down from ADAM in 2014 and, together with his son, musicologist Dr Frederik Knop, founded HEDD Audio in 2015 in order to continue his development of the AMT concept. HEDD Audio now produce three HEDDphones (yes, they went there), six studio monitors, two subwoofers and the giant, and reassuringly expensive, Tower Mains monitors.

AMT Overview

All HEDD products — including the HEDDphones — feature Heinz’s latest refinements of the AMT design. In simple terms, an AMT tweeter is an electromagnetic transducer that uses a pleated diaphragm to push and pull air in and out of the folds. The resulting airflow moves approximately four times faster than the surface of the tweeter itself. This speed delivers an accurate performance accompanied by low distortion, which results in a smooth and detailed high‑frequency performance across a bandwidth that can extend from under 2kHz up to 40kHz.

The HEDD AMT’s diaphragm is made of Kapton polyimide film (think space blanket without the silvering), with an aluminium circuit pattern etched on it. In a fully assembled AMT, the diaphragm (hand‑folded at HEDD’s Berlin factory) sits inside the strong magnetic field generated by a neodymium magnet. When an alternating current is passed...