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Reviewer: Srajan Ebaen
Financial Interests: click here
Source: 27" iMac with 3.4GHz quad-core Intel Core i7, 16GB 1.333MHz RAM, 2TB hard disc, 256GB SSD drive, ADM Radeon HD 6970M with 2GB of GDDR5 memory, PureMusic 1.87 in hybrid memory play with pre-allocated RAM and AIFF files up to 24/192; Audirvana 1.3.1, April Music Eximus DP1, Esoteric/APL Hifi UX1/NWO-M, Audiophilleo 2
Preamp/Integrated: ModWright LS-100 with Synergy Hifi tubes, Esoteric C-03, Bent Audio Tap-X
Amplifier: First Watt SIT2, FirstWatt J2, ModWright KWA 100SE
Speakers: Audiomanufacture Boenicke B10, Aries Cerat Gladius
Cables: Complete loom of Zu Audio Event, Entreq USB cables
Stands: 2 x ASI HeartSong 3-tier, 2 x ASI HeartSong amp stand
Powerline conditioning: 1 x GigaWatt PF2, 1 x Furutech RTP-6
Sundry accessories: Extensive use of Acoustic System Resonators, noise filters and phase inverters
Room size: 5m x 11.5m W x D, 2.6m ceiling with exposed wooden cross beams every 60cm, plaster over brick walls, suspended wood floor with Tatami-type throw rugs. The listening space opens into the second storey via a staircase and the kitchen/dining room are behind the main listening chair. The latter is thus positioned in the middle of this open floor plan without the usual nearby back wall.
Review Component Retail: $1.295/ea.

Clayton Shaw of Spatial Computer: "Our Black Hole is an active acoustic pressure reduction device. It was designed to improve sound quality in domestic environments as the only known means of dealing with room-induced anomalies in a compact form factor. An active acoustic pressure absorber was first mentioned by HF Olsen in his 1957 book Acoustical Engineering, a reference text still in common use today. In 1990 Nelson Pass was awarded the active low-frequency acoustic resonance absorber US patent 4899387 in which he outlined a clever embodiment of the concept along with application and performance criteria. He released a production design as the Phantom Acoustics Shadow. Robert Harley reviewed it for Stereophile and found it highly effective. The Shadow was only produced for a few years. We have taken up the mantle with the Black Hole. Our focus was to simplify and improve where possible and reduce size and price. We view this approach as an integral part of a total room solution that may also include passive treatment and equalization to optimize the listening experience. The Black Hole is even more useful when a given installation makes passive bass traps impractical. Its compact 15" cubed dimensions allow most listeners to integrate it into their room plan. The Black Hole employs a heavy-duty 12" driver and a 350-watt power amp to provide enough output to civilize a typical listening room of 15' x 25' or smaller. Larger rooms may require two units. The main requirement is that the unit be located against a wall boundary where acoustic pressure builds up. Along a wall or in a corner behind the listening seat is recommended but some experimentation tends to be required for the best results in the listening position. A/B comparisons are easy since the device can be turned on/off during the listening session."

Still puzzled about the what, why and how come? Think noise-cancelling headphones, then apply the same basic principle—cancellation of sound via its anti phase at equal amplitude—to a subwoofer. Add a microphone with mic pre and analog processing. Place this IQ-enhanced sub in a pressure zone behind your seat, ideally a corner which creates the worst-case reading for the mic and thus the highest degree of compensation. At minimum it will be against a wall.


Presto, active cancellation of undesirable bass. Two or more large abutting surfaces (wall/floor, wall//ceiling/wall) create pockets of high bass energy. Such pressure zones cause resonance. That's bass mud. Not only don't LF impulses stop on time, reflected upper harmonics get damped and attenuated. And while we listen to music, location-specific mud subliminally but constantly telegraphs a room's boundaries to our ear/brain. So we'd really like to turn this <300Hz resonance behind us way down. Or off completely. Ideally.


Not only does this address these effects, it subjectively enlarges a room as though the rear wall had moved back or vanished. That's because without such pressure zones our ear/brain doesn't register the same boundaries. We believe ourselves to be in a larger space of less confinement. During music listening we predominantly 'hear' our rooms by their bass problems.

These two graphs are before/after readings of how one Black Hole in a particular installation reduced reverberation time between 30 and 60 cycles by 50%. That's significant. As momentary freeze frames of dynamic conditions, these graphs don't tell the whole story of course. Also the effectiveness of this device will be influenced by placement.

Implicit in this concept is inaction if you play music without low bass or over speakers of such restricted bandwidth that the problem the Black Hole addresses isn't caused in the first place. Equally implicit is that how far a counter sub's output keeps up with the output of the main speakers will determine how linear the degree of 'mud raking' remains at higher volumes. Large spaces and/or high playback levels might necessitate more devices. The smaller the space the more dramatic the improvements should be.


click on each graph to enlarge it
Clayton's matte-black subwoofer with 12-inch polymer/cellulose woofer, dual grill-less 12-inch passive radiators and 350-watt class D plate amp is a stock TruAudio CSUB-12 designed in Utah and made in China. It's a well-built installation grade and very robust unit without costly sex appeal. What exactly turns it into a Black Hole to remove the dark-blue section in the before/after cumulative spectral decay plots and so improve the nasty 40Hz ridge? Couldn't the same be achieved if the TruAudio—or any other subwoofer—were simply set to 180° phase and connected line or speaker-level to the main system? This begs a counter question. Just how would you determine the exact phase rotation at the actual sub location to create the perfectly inverse setting? The value at that location is not likely to be 0° or 180°. It thus won't be addressed by basic subwoofer controls.