Manufacturer specs:
Configuration: Active 15" bassreflex subwoofer, front-fire system
Frequency response: 18 - 150 Hz
Level and crossover-frequency adjustable
Phase adjustable 0°-180°
High-level input
2 low-level inputs
2 low-level outputs
Standby circuit
Switchable mains voltage 115/230V
Front-fire construction
Aerodynamically optimized port with screwed aluminium flanges
High-power long-throw woofer with hardened paper cone and huge carbon dustcap
Aluminium die-cast basket
Real-time limiter
Active SPL equalization
High quality real-wood veneer / silver varnish
Dimensions: 482x630x520 mm
Weight 46 Kg


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This was definitely one of the best looking subs that day. Really gorgeous finish and details. Although I was a bit worried how badly those small ports would "whistle" during testing (four approx. 1.5" diameter ports equal with a single 3" port). The Heco uses a 300 W (RMS) D class amp which stayed really cool during extreme testing. The crossover can't be bypassed, so you can't use this with speakers needing a crossover higher than ~100 Hz. The lowest setting is only around 60 Hz. Frequency response could extend a little bit deeper, now the -6 dB point was at 26.5 Hz. Maximum output started to look really good until the 110 dB started to compress heavily at the lower frequencies; I'm pretty sure a larger port would have helped there. In mid/upper bass range the max output goes well over 105 dB. THD stays reasonably low at lower levels, but shoots the skies below ~35 Hz at higher levels; luckily it's mainly 2nd order. Group delay should not be audible at any frequency. Spectral decay is pretty typical for a vented subwoofer, with some ringing around the tuning. Spectral contamination stays slightly lower than average at 90 dB and 95 dB levels. One could squeeze a little bit more performance out of a 15" ported sub than the Heco shows.

+ Pretty good extension
+ High mid and upper bass maximum output capability
+ Low overall distortion up to 100 dB output level
+ Build quality and looks

- Deep bass output/port compression at higher levels
- Somewhat high deep bass distortion at high output levels
- Some ringing around the tuning frequency

http://www.hometheatershack.com/forums/subwoofer-tests-archived/985-heco-celan-sub-38-a.html