This review page is supported in part by the sponsors whose ad banners are displayed below
The additional hardware which turns the bundled TruAudio (or any other sub for that matter) into a Black Hole are five items. First is the microphone, a Dayton Audio EMM-6 true omni 6mm electret condenser measurement unit with 200Ω impedance and 10mV input sensitivity. Then comes a Whirlwind inline attenuator to knock down that high sensitivity by 20dB. Joined together the attenuator + mic plug into Clayton's small mic pre with rotary mini pot and phantom power switch. (The recommended setting is for the mini pot to be fully counterclockwise. That's not mute but a pass-thru with a small amount of gain that won't overload the sub's input stage. The subwoofer's volume control should be as high as possible without causing microphone feedback).
The mic pre is designed and built in Utah and custom-configured for Clayton. It plugs into the wall via a small two-prong wall wart and live power is activated with a switch and confirmed with a green LED. The final item is a 1-foot 6.3mm-to-RCA cable. This feeds the output from the mic pre to the left/white stereo input of the subwoofer. The mic pre velcros to the subwoofer next to the plate amp to be in close proximity to the active woofer. The analogue circuitry inside Clayton's box accounts for the small physical offset between microphone and bass driver.
In my setup the most suitable Black Hole event horizon was really 1 meter behind the listening seat against the side wall of the narrower passage which connects living room to kitchen. I was aware that the actual room corner behind my writing desk would create a stronger (seis)mic reading but I didn't have the required physical space for the subwoofer there. I did have a single 5-meter length of XLR however. This invited offboarding the microphone in the corner clipped to a stand (the provided 1-foot leash is good only for the intended Velcro placement right against the sub). The stand put the microphone at the same distance with the left speaker as the subwoofer was to both speakers. But for the right speaker the mic's time-domain capture was way off. Maximum cancellation depends on precise and not approximate or partial counter phase. Back to the Velcro and TruAudio unit it was.
During an experiment I connected the mic pre to an Amphion Impact 400 and placed the microphone on a stand in the corner with a 5-m XLR
Clayton Shaw: "If you study the Pass patent you'll see two core points where we diverge. His solution had the microphone in the center of the woofer and he located his device on the front wall. After a few years of remotely measuring and installing our Spatial speaker/room correction software suite for customers all over the world, I noted how nearly all of them suffered 10dB to 15dB response aberrations below 300Hz. For higher anti-phase subwoofer output to compensate for this, I needed more gain before feedback than I could achieve with Nelson's embedded microphone location. I had to physically decouple the microphone from the driver enclosure.
Mic pre mounted with Velcro, mic inserted, one passive radiator facing the viewer, active driver firing sideways into the room
"After many experiments exploiting all possible in-room locations I've concluded that we achieve far superior results when the Black Hole is placed behind the listener. In front we observed lobing interference with the main speakers. I started this project with a very complex DSP-based approach. Over time and very pragmatically I've since arrived at a simpler all analogue solution that is rather more effective. For traditional passive absorbers to be effective below 100Hz and offer any significant attenuation requires considerable size and mass. Our active approach gets away with a very robust 12-inch woofer in a compact box. That's because we have active gain. It's not just cone surface doing the job. Excursion and air displacement are very significant factors in our favor.
Black Hole turned sideways to show the rear panel with mounted mic preamp and short signal cable
"I thus shopped for the smallest possible subwoofer that had the requisite bandwidth and undistorted output capabilities I needed. I wanted a solid not furniture-finished box that would spend money on the essentials only.
With the mic pre's gain set to minimum as recommended, you should be able to run this subwoofer's volume control very high. This creates maximal cancellation and is sufficient for the average US-style living room of 12' x 20' or 15' x 25'. For larger spaces I recommend two or more units. With your friend's massive JL Audio Gotham subwoofer, he might enjoy fantastic results substituting the TruAudio unit with his high-output luxury beast. It'll be important though to mount the microphone at about the same distance to the driver as with our unit or the built-in time delay will be wrong."
"I currently have about 75 of these in the field. Only one has come back when the customer couldn't hear a difference. Everyone else seems very happy. Many of them are beginning to take measurements. This begins our task of formally documenting the results. We've already found frequency-domain graphs to not reflect the totality of what's going on. The time-domain improvements are as important if not more so. Here reverberation plots are quite illustrative. Even so we're still struggling with how to best capture the true scope of improvement in a graphic fashion that's both factual and intuitive to the layman. To most the concept is new despite the Pass precursor. As such we have some communicating and educating to do. That's not my forté. Hopefully owner endorsements and more before/after measurements will tell their own story to convince the naysayers to give it a try. Or else go with a forest of tube traps. Either way the problem needs addressing. Once you've heard music without it, you won't go back."
