Now, the TRW is a great subwoofer, as we have seen, and more. But how on earth could the TRW, or any subwoofer, operating only at low bass frequencies, be of such broad sonic benefit, and at midrange and treble frequencies, when merely added to a system?
       The midrange and treble frequencies (as well as the upper bass) came from the main loudspeaker system, driven by their own dedicated power amplifiers. But these components could not be the direct agent, of the distortions we heard and the many adverse sonic consequences therefrom.
       Firstly, these components are the very best of their kind available, and are known for their enormous dynamic capability with low distortion, so they could not directly be the source of strain and distortions we heard, at what were merely moderate listening levels (the power amplifiers were Krell monoblocks).
       Secondly, regardless of the capabilities of these main system components, the bald fact was that they were still playing exactly the same signal at the same level when the TRW was merely switched in or out of being added to the system, so their internal behavior could not possibly have changed, to in any way be directly responsible for the many and dramatic sonic changes we heard. And, again, we all heard these same changes, we repeatedly heard them, we heard the same changes on many kinds of music, and these same changes remained consistent in character for all kinds of music.
       We next checked out the electronics chain, in case some subtle second order effect was causing these sonic changes. But this double check failed to reveal any possible spurious explanation.
       For example, the TRW was switched in and out by merely rotating its input volume control, and there is a buffer stage before this volume control, isolating this volume control from previous electronics in the chain. Thus, there could not be a subtle change in loading (say nonlinear loading) upon the previous electronics in the chain that could conceivably affect the signal.
       Furthermore, the system's electronic crossover has separately buffered outputs for its output feeding the TRW and its output feeding the main signal to the main loudspeakers, so there is no way that any change in one leg's loading could affect the signal going out the other leg.



E.2. Plausible Explanation of TRW Magic

       So that leaves us with only one possible explanation. As Sherlock Holmes wisely said, whenever you have eliminated all other possibilities, then whatever hypothesis remains, however implausible, must be correct. Actually, it's not so implausible, since we have already noted several examples of the same phenomenon with the TRW in the above discussions.
       In the above sonic comparisons, there were two concrete examples, the cannon shot and the plucked bass viol, where the TRW, when added to the system, effectively overwhelmed and offset the spurious ringing of the misbehaving subwoofers. Then, in our earlier discussion of the physical handicaps plaguing conventional subwoofers, we discussed how their region 3 ringing could cause FM distortion of all music, at all frequencies, as detected by the ear. Now, all we have to do is put these two concepts together. Presto! We have a plausible explanation of this seemingly strange phenomenon, whereby merely adding the TRW makes the whole system sound, at all frequencies, cleaner, clearer, and more natural, just as we in fact kept hearing.
       Recall that virtually all music keeps changing, and is therefore composed of transients, especially singular transients that do not identically repeat themselves. All transients actually contain spectral energy to extremely low frequencies, approaching DC. Therefore all musical transients stimulate the region 3 spurious ringing of conventional subwoofers, which is triggered whenever there is spectral energy at the subwoofer's resonance frequency or at any lower frequency. This region 3 conventional subwoofer spurious ringing, stimulated by all musical transients at all frequencies, creates Doppler or FM sidebands in the room air, around every musical sound, even those musical sounds at midrange and treble frequencies. The human ear's inherent nonlinearity then acts as a detector of these sidebands, turning them into full fledged FM distortion. It so happens that FM distortion has all (and exactly) the various adverse sonic properties and consequences we reported hearing above, when the TRW was not included in the system.
       Presto! A plausible explanation of the various distortions and consequent other sonic degradations we heard from the system without the TRW.
       We have come to accept these distortions as part of the hi-fi experience. But, when the TRW is added to this system, and we suddenly, in direct comparison, hear the system without these distortions, then those distortions become obvious, and become unacceptable. When we hear how the system is so much cleaner, clearer, faster, more articulate, and more musically natural with the TRW, then the system without the TRW suddenly is revealed as having been artificial hi-fi, instead of real music.
       And what exactly is the magic by which the TRW achieves this change?
       Simple. The TRW is simply doing the same thing that we already saw it doing above with the cannon shots and the plucked bass viol. The TRW's added contribution, that is so very accurate at low bass frequencies, reproduces correctly, in the time domain, the low bass content of each and every musical transient. Because that low bass content extends down to DC for most musical transients, the low bass content of the signal, and the accurately tracking TRW, stay positive for a long time (relative to the time frame of the midrange or treble musical transient).
       So the TRW stays positive, even while the conventional subwoofers are ringing and alternating between positive and negative air pressure, thus creating those FM distortion sidebands. And, because the TRW can put out such a huge amount of low bass energy, far greater than conventional subwoofers, the TRW's positive pushing, nearly DC contribution overwhelms and offsets the misbehaving conventional subwoofers' ringing AC contribution. Additionally, the TRW's nearly DC contribution, staying positive, biases the positive and negative swinging output from the ringing conventional subwoofers, so that the net total acoustic pressure in the room never swings negative. Thus, the TRW effectively overwhelms the distortion sidebands created by the misbehaving ringing of the conventional subwoofers.
       Presto! We now have a plausible explanation for all the things we heard, for the totally unexpected sonic magic that the TRW can wreak upon the total system sound, at all frequencies.

F. The TRW without Other Subwoofers

       In our sonic listening testing, we next repeated all the musical selections, but this time with a different test setup. The TRW was the only subwoofer employed, and there were not any of the conventional subwoofers in the system. We simply listened first to only the main loudspeakers, which had excellent response down to 40 Hz, and then repeated the musical selection with the TRW switched in. We had several reasons and goals for this alternative protocol.
       In the previous setup above, the base system was already a full perfectionist dream system, complete with three massive state-of-the-art conventional subwoofer systems. And it was important for us to sonically discover what the TRW might be able to achieve even beyond the best conventional subwoofers, when added to this system. But the vast majority of us will not already have three giant subwoofers in our system and be adding the TRW as a fourth. Most of us will want (or can afford) only one subwoofer, added to our main loudspeakers, which will have good response down to at least 40 Hz and perhaps to 30 Hz, but not much below. So it behooved us to also evaluate the sonics of the TRW when added only to main loudspeakers, as the only system subwoofer.
       Furthermore, we had nagging doubts that some of the TRW's tightening of bass transient response, noted above, might have been due to spectral overlap with the three conventional subwoofers, combined with a fluke of temporal misalignment, whereby the TRW's bass contribution was out of phase with, and thus partially cancelled, the boomy output of the conventional subwoofers. By eliminating the other subwoofers entirely from the picture, and by also eliminating any spectral overlap with the woofer of the main loudspeaker system, we could better assess the sonic qualities of the TRW's bass contribution on its own.
       Additionally, even though the measured response of the TRW-17 does extend up to 40 Hz, there are good reasons (discussed below) to limit its high frequencies at about 25 Hz. So, on behalf of all of you who would want the TRW as your only subwoofer, and would want to combine the TRW with full range loudspeakers that, to cite the worst case scenario, might go down only to 40 Hz, we wanted to find out what the TRW would sound like, as the sole subwoofer, when we deliberately simulated this worst case scenario, by purposely leaving a 15 Hz gap in the system response, between the 25 Hz upper limit the TRW was set to and the 40 Hz lower limit that the main loudspeakers were set to. Since we also wanted to sonically test the sound of the TRW without possible contamination from any spectral overlap, we could kill two birds with one stone, by deliberately listening with this 15 Hz gap.
       The results of this second sonic testing phase are easy to summarize. First, all of the TRW's sonic virtues and benefits cited above were still very evident, and still sonically amazing.
       There was of course less ringing boom for the TRW to overcome, since the conventional subwoofers had been deleted. But some ringing boom was still evident from the woofer of the main loudspeaker system, and the TRW was still very effective at acoustically quenching this, to give us that same tight, impactive, well defined bass from the whole system that it had before. Note that here, because there was virtually no spectral overlap, it became clear that the TRW's sonic benefits, not only in being tight itself but also in reducing the lingering boom from the main loudspeaker's woofer, must have been due to the DC pedestal and positive acoustic biasing mechanism discussed above, and not due merely to happenstance phase misalignment and cancellation.
       The sonic magic that the TRW wrought before, in making the whole system sound cleaner and clearer and more musically natural, even at midrange and treble frequencies, was still very obvious in this new system setup. If our plausible hypothesis above is correct, this means that the conventional woofers of the main loudspeaker system also create significant FM distortion, acoustically in the room, with their spurious ringing (these FM distortion sidebands would be slightly farther out, since the main loudspeaker woofer rings at a higher frequency or pitch than the conventional subwoofers did).
       Our most important new finding, from this new system setup, was that the TRW-17 integrates superbly with main loudspeakers, as the only subwoofer in the whole system. Spectral coverage sounded seamless and natural, even with the 15 Hz gap that we had deliberately left in the system response. It is a well established fact that the brain automatically, subconsciously fills in these kinds of spectral gaps, especially on familiar types of sounds (music or voices or sound effects). The brain does this exceptionally well, literally synthesizing the missing information to fill in the gap, when there is accurate information both below and above this spectral gap, as there is here (especially with the TRW's superb waveform accuracy). Thus, there is good scientific reason for the superbly seamless integration we heard between the TRW and the main loudspeaker, even with the 15 Hz gap.
       Our experimental finding here, backed by good scientific basis,  means that you can confidently use the TRW as your only subwoofer, even if your main loudspeakers do not extend any lower than 40 Hz.

Part V: Practical Considerations

A. Enclosure Box

       Hoffman's iron law dictates that the very best, most capable conventional subwoofers come in huge enclosure boxes, which make a huge imposition into your listening room (examples are the Wilson XS and Avant Garde subwoofers). The TRW extends far, far lower in bass than any conventional subwoofer, and can move far more air and play much louder. So it would be reasonable to assume that the TRW comes in an even bigger box enclosure, which makes an even bigger intrusion into your listening room.
       But it doesn't. In fact, the TRW doesn't come in any box enclosure at all. Moreover, the TRW does not intrude into your listening room at all.
       How can this be? Has the TRW, along with its radical technology that's the opposite of conventional subwoofers, also managed to reverse the laws of physics and acoustics? No. You just have to think big. Really big.
       As discussed above, the TRW's bass performance is in a whole different class than even the best conventional subwoofers, and indeed is unique. The TRW is unique in the quantity of bass generated, both in terms of low frequency extension and also in terms of energy loudness. The TRW is also unique in the quality of bass generated, both in terms of accurate transient (time domain) response and also in terms of accurate low pressure bass sound. One of the keys to all this TRW performance is the fact that the TRW can move huge volumes of air. But, in order for the TRW to be able to move huge volumes of air, its fan must have unfettered access to huge volumes of air. That's why the TRW, for optimum performance, requires a huge box enclosure, much larger than even the largest enclosures employed by conventional subwoofers. The laws of physics and acoustics dictate that it needs a huge volume of air to work with, which means a really huge enclosure. Also, the TRW extends extremely low in bass frequency, which corresponds to extremely long wavelengths, which means that any enclosure should have very large dimensions.
       How then could one come up with a large enough enclosure box for the TRW? Simple. Think outside the box (sorry). How does the TRW manage to come into your house, without bringing along a huge box enclosure that intrudes into your house space? Rather than bringing an enclosure box into the house, instead the TRW simply uses the house itself as an enclosure, a really big enclosure.
       Fortunately, most of our houses have handy just such a huge volume, that is substantially unused. The TRW fan is installed in your house's attic, basement, or garage, whichever is conveniently close to your listening room. The TRW employs that whole attic, basement, or garage space as its enclosure box, faced by the back side of the fan driver (just as an enclosure box is faced by the back side of a conventional subwoofer's cone driver). And, from that location near your listening room, the front side of the TRW fan driver is ducted into your listening room via a vent in the wall or ceiling. Thus, the TRW subwoofer does not intrusively take up even one cubic inch of listening room space. And its workings are hidden away in an unused space within your house's shell.
       The TRW uses this house enclosure box as an infinite baffle closed box. Ideally, the volume of this infinite baffle closed box should be as large as possible. In fact, the TRW works wonderfully if its fan is installed in an outside wall of your house, such that the back side of its fan actually faces the infinite volume of the great outdoors as its "enclosure box". One installation tried this, and the sound was great inside the house. The only problem was that, even with the TRW subwoofer's huge acoustic output at very low frequencies being quickly dissipated in the great outdoors, neighbors several blocks away began complaining that their dishes, apparently possessed by the devil, were on occasion mysteriously dancing about on the shelf. Of course, if you live on an isolated farm, you can go for this simple approach. For most of us, the most practical installation of the TRW will be in an attic, basement, or garage, any of which should have sufficient volume to be a good enclosure box.
       What happens if your house does not have an optimally large attic, basement, or garage that is conveniently close to your listening room? What happens if you have to employ a smaller house space as a back enclosure? With conventional subwoofers, if you use an enclosure box that is too small for the given subwoofer driver, the system resonance frequency goes up, and so the subwoofer system does not extend as low in bass frequency.
       Interestingly, this engineering rule does not apply to the TRW. Because the TRW employs a fundamentally opposite technology than conventional subwoofers, the TRW does not have reactances at low bass frequencies, and is inherently a DC device rather than an AC device. Thus, the TRW will still have full response down to DC, and will retain its superb bass quality, even if your house geometry forces you to install it with a backside enclosure volume that is smaller than recommended.
       The only TRW performance aspects you would sacrifice, by employing a smaller than recommended volume for the backside enclosure, would be efficiency and maximum possible loudness level. And the TRW has plenty of extra margin in both these performance aspects, so you can afford to sacrifice somewhat in these parameters, if need be.

B. Listening Room Contribution

       Since we're now looking at really big volumes, it behooves us to also examine the volume of the enclosure box on the front side of the TRW fan, which is of course your listening room. Here, on the front side of the TRW fan, an infinite volume with infinite dimensions is not ideal. Instead, ordinary listening room volumes, with ordinary room dimensions, actually work to help the TRW's bass response.
       You see, when bass frequencies go lower their acoustic wavelength in air gets longer, and, when the wavelengths get long enough to approach the dimensions of the listening room, the boundary

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