TAD Horn TD-4001 ET-703 4-Way Active Reference Speaker Monitor System DSP & FIR

Subtract SCM-1 4-Way Active Reference Loudspeaker System

Up for sale: the Subtract SCM-1, a four-way, fully active, high-output reference loudspeaker system designed and built by Subtract Music and JW Sound. Over a year of research and development went into a single engineering brief: mastering-grade resolution at output levels no conventional studio monitor can approach — vanishingly low distortion, controlled directivity, and full dynamic ease at 128 dB peaks.

Equally at home in a critical studio environment, a high-end listening bar, or a serious home listening room. Furniture-grade materials throughout - solid walnut horns and waveguides - so it looks as good as it sounds. Custom-tuned presets provide per-channel EQ, crossover, delay, and limiting, with FIR filtering for flat phase response from 300 Hz up. System is designed so the HF acoustic axis lands at seated ear height on the included stands. Horn and midbass enclosure include interlocking skids for precise assembly positioning, as well as carrying handles (midbass handles also serve as mathematically calculated ports for that enclosure).

A note on lineage: anyone who has stood in the DJ booth at Stereo Montreal will recognize this architecture - a large-format TAD beryllium compression driver on a big wood horn, dual 12" mids, super tweeter, and dedicated subs. This is that recipe, rebuilt without compromise: an Alnico TD-4001 at its heart, fully active crossovers with FIR phase correction, modern high-sensitivity mids, and furniture-grade construction - equivalent or better measured performance than the setup that inspired it, in a build that belongs in a living room as much as a booth.

System Specifications

(2) TAD TD-4001 compression drivers - 101 mm (4") beryllium diaphragm, 2" exit, Alnico motor
(2) TH-4001 walnut horns by Athos Audio, built to exact TAD factory geometry
(2) TAD ET-703 beryllium super tweeters on custom walnut oblate-spheroid waveguides (factory waveguides also included)
(2) JBL 2405H slot loaded super tweeters on custom walnut faceplates (swappable HF units)
(2) Dual-12" bass-reflex midbass enclosures - 4× B&C 12NDL88, 60Hz tuning, 6.75" floor stands
(1) Dual-opposed sealed subwoofer - 2x Acoustic Elegance TD18H+ Apollo 18" woofers
(1) Linea Research 88C03 eight-channel power amplifier — the entire system powered and processed by a single touring-grade unit with full DSP and FIR
L-pad resistors and protective capacitors installed on midrange and high-frequency drivers
(2) 11 AWG NL8 LINK Italy touring-grade speaker cable, 25 ft per side (longer lengths available)

Performance

Frequency response (in-room): 18 Hz - 45 kHz ±3 dB (with ET-703)
Maximum SPL: 122 dB continuous / 128 dB peak at 1 m
Coverage: 90° × 50° nominal

Crossovers (acoustic)

TAD ET-703: 7,000 Hz 24dB Butterworth HPF
TAD TD-4001: 600 Hz 24dB Butterworth HPF, 7,000 Hz 24dB Butterworth LPF
B&C 12NDL88: 60 Hz 24dB Linkwitz-Riley HPF, 600 Hz 24dB Butterworth LPF
Acoustic Elegance TD18H+ 21 Hz 24dB Butterworth HPF, 60 Hz 24dB Linkwitz-Riley LPF

Full measurement documentation ships with the system - driver-level and system-level responses, so you know exactly what you're getting.

Dimensions & Weight

Speaker assembly (incl. stands): 1,041 mm (41") H x 965 mm (38") W x 603 mm (23.75") D
Horn assembly: 622 mm (24.5") W x 394 mm (15.5") H x 603 mm (23.75") D
Midbass assembly: 800 mm (31.5") W x 476 mm (18.75") H x 420 mm (16.5") D
Subwoofer: 560 mm (22") W x 610 mm (24") H (635 mm / 25" incl. feet) x 710 mm (28") D
Stands: 965 mm base (38") / 750 mm top (29.5") W x 171 mm (6.75") H x 375 mm (14.75") D
Weight: horn assembly 85 lb · midbass cabinet 65 lb · subwoofer 160 lb

Included Commissioning

For Los Angeles-area buyers, a custom Smaart tuning session (a $1,500 value) is included to integrate the system into your room, using multi-microphone spatial averaging for accurate system response and phase coherence - performed by an engineer with over 20 years of experience designing and tuning professional sound systems. Outside the LA metro area? Contact us to discuss options.