because it is physically so small that it does not couple effectively to the air (the air simply gets out of the way of this small moving object, whereas the air could not get out of the way if the moving cherry pit were instead a moving barn door with a large area).
In fact, the laws of physics dictate that, for a diaphragm of fixed diameter and radius and area (as a conventional subwoofer driver is), the coupling effectiveness, measured by a parameter called radiation resistance, falls as the square of the frequency, so it falls (gets weaker) very steeply, as the bass frequency goes lower and the acoustic wavelength gets longer. In contrast, the TRW fan increases its effective radiation area linearly, as the frequency goes lower, thanks to the fact that it takes multiple bites of air per signal cycle (this radiation area increase has been confirmed by the manufacturer's impedance measurements, which show the air load upon the fan at various frequencies). This linear increase in the TRW fan radiating area offsets half of the natural square law decrease dictated by the laws of physics. This means that the TRW subwoofer retains its radiation resistance, its coupling effectiveness to the air, far better than the fixed radiating area cone of a conventional subwoofer driver. With the TRW, the radiation resistance (and coupling effectiveness) falls merely at a gentle linear rate, rather than the steep square law rate that conventional subwoofer drivers suffer. In short, the TRW retains its ability to actually couple to and drive the air, at progressively lower bass frequencies, far better than conventional subwoofers can.
Incidentally, as a technical aside, note that the radiation resistance and coupling strength would remain constant, and not decline at all, if a driver could increase its effective radius linearly with decreasing frequency, since such a driver's area would then be increasing as the square of frequency (the area of a circle is proportional to its radius squared), which would completely offset the square law decline dictated by the laws of physics for a fixed radius diaphragm. But the TRW fan only increases its area linearly with decreasing frequency, not its radius (its radius increases only as the square root of decreasing frequency), so it still suffers a modest decline in radiation resistance and coupling effectiveness at progressively lower bass frequencies. Still, a modest decline is a heck of a lot better than a steep decline. And thus this superiority in radiation resistance, in effective coupling to your room's air, marks yet another way in which the TRW is a far superior subwoofer than conventional subwoofers can possibly be.
D. Comparisons with Conventional Subwoofers in Bass Quality: Pressure
Electric fans in general, and the TRW fan in particular, are very effective at moving huge volumes of air, even at very low frequencies where conventional subwoofers lose their effectiveness (and indeed lose their claim to even be called true subwoofers), as discussed above. This effectiveness and ease, at moving huge volumes of air, is a key factor in the TRW's achievement of superb bass quality and waveform accuracy -- far superior to, and wholly different from, the inferior bass quality and waveform inaccuracies that conventional subwoofers are inherently constrained to and cursed by, due to their intrinsic nature (in other words, these inferiorities cannot be designed out of conventional subwoofers by better design engineering).
Furthermore, the fact that the TRW's effective radiating area gets huge at low bass frequencies also helps the TRW to achieve superior bass quality. That's because a driver with a huge radiating area can generate large volume airflow without resorting to high pressure. In contrast, conventional subwoofer drivers, whose radiating area does not increase at low bass frequencies, and whose radiating area is very small compared to acoustic wavelengths at low bass frequencies, must resort to creating high pressure, madly pumping their small diaphragms with high velocity and high excursion, in order to try to generate decent sound levels at low bass frequencies. Intuitively you can appreciate that a small piston pump must pump harder, with higher pressure, than a large piston pump, which can be much more relaxed, with lower pressure, to achieve the same total airflow volume.
There's a real physical difference between low pressure bass and high pressure bass, and you can hear (and feel) the difference. You can do a simple experiment to demonstrate this to yourself. Hold your open palm in front of and facing your mouth, about 3 inches away from your mouth. Now, let's simulate low pressure bass first. Relax your stomach diaphragm, open your mouth pretty wide (that's the large radiating area, like the TRW), and let a gentle, long "uhhhh" sound emerge from your stomach diaphragm (almost like letting out a belch). Feel the very gentle breeze on your palm, and listen to the relaxed ease of the "uhhhh" sound. Then, let's simulate high pressure bass. Purse your lips into a tight small circle (that's the small radiating area of a conventional subwoofer), and blow hard through this small opening. Feel how different the high pressure air feels as it hits your palm, from how the low pressure air felt. And listen to how the high pressure forced blow sounds so different from the low pressure relaxed "uhhhh".
Now, virtually all musical instruments generate low pressure bass, often employing large radiating diaphragms (bass viol, grand piano, bass drum) and/or large air volumes (pipe organ). When a conventional subwoofer, with its small driver diaphragm (small relative to the large acoustic wavelengths of low bass frequencies), tries to play this bass, it can only do so in a high velocity, high pressure, small volume mode.
That's the opposite kind of bass from the low velocity, low pressure, large volume bass that most musical instruments actually produce. It actually is physically wrong. And, as you just demonstrated to yourself, you can hear and feel the difference between these two opposite kinds of bass. So the wrong kind of bass produced by conventional subwoofers also audibly sounds wrong and feels wrong. Deep bass from conventional subwoofers sounds just like what it is, a small piston madly flailing away at the air with high pressure.
In contrast, as we've just learned, the TRW intrinsically, automatically, and effortlessly increases its effective diaphragm area and its volume of airflow per signal cycle at low bass frequencies. Since the TRW is automatically blessed with a huge diaphragm at low bass frequencies, and can move huge volumes of air per signal cycle at low bass frequencies, it intrinsically, automatically, and effortlessly emulates the same basic mechanisms for producing bass that musical instruments employ, large diaphragms and large air volumes. And, being blessed with a huge diaphragm and large volume airflow at low bass frequencies, the TRW does not have to resort to forced high pressure, any more than musical instruments themselves do. Since the TRW reproduces low bass with the same basic properties as musical instruments themselves do (large diaphragm, large volume, low pressure), the quality of its bass sounds right and feels right (more sonic details later). The TRW's bass, like that of most musical instruments, has an authoritative, massive, relaxed ease, much like the "uhhhh" that came from your relaxed, large stomach diaphragm through the large opening of your wide open mouth. A large area diaphragm that can move large air volume can afford to be relaxed in its efforts, whereas a small piston diaphragm has to be work hard with a forced quality.
You can simulate this contrast with a simple modification of the above experiment. To simulate the frenetic, forced, high pressure in-out pumping, by a conventional subwoofer's small area diaphragm, try panting hard and fast, in and out, forcing the air at high pressure through the same small mouth opening, with your lips tightly pursed into a small circle, and using your cheek muscles to push the air out. To simulate the relaxed ease and low pressure of the TRW's diaphragm, with its large area at low bass frequencies, gently wafting large volumes of air back and forth, try letting your mouth hang wide open, relax your stomach and mouth muscles, and do deep, relaxed, slow breathing in and out, using your stomach diaphragm muscles, and letting the large volumes of air flow gently out by simply relaxing your stomach diaphragm muscles (you don't need to blow air out at all, since it just naturally comes out when you relax your stomach diaphragm muscle, and indeed the only time your stomach diaphragm muscle even works at all is to expand your air intake when you breathe in).
E. Comparisons with Conventional Subwoofers in Bass Quality: Bass Response
Another key factor determining bass quality and accuracy is the low frequency response of a subwoofer, as seen in both the frequency and time domains.
Electric fans in general, and the TRW fan in particular, also are inherently excellent in their capabilities at very low frequencies, indeed all the way down to zero Hz (DC). In fact, conventional fans are intrinsically pure DC devices, continually blowing a constant amount of air in one direction. It actually takes some design work to change this intrinsically DC device into an AC device, as the TRW does by engineering in the feature of variable pitch blades. Thus, it should come as no surprise that fans in general, and the TRW fan in particular, intrinsically has perfect response, in both the frequency and time domains, at very low bass frequencies, down to and including DC. The fan is thus an ideal technology for making a true subwoofer.
This is in complete contrast and opposition to conventional subwoofer drivers, which inherently run into great difficulties trying to reproduce lower bass frequencies. Conventional cone drivers are intrinsically AC devices, and are great for reproducing middle frequencies, but they suffer worse and worse physical handicaps and outright roadblocks, in many distinct ways, as the frequencies get into the bass region, so that by 40 Hz they have pretty much reached the limits of their effectiveness, and they can cover the single 20-40 Hz octave only with poor quality and with severe difficulty, and for the infinity of octaves below 20 Hz they are virtually useless (whereas the TRW covers this infinite octave span perfectly). So cone driver technology is simply not appropriate for frequencies below 40 Hz, which means it should never have been employed in the first place for making true subwoofers.
Of course, the reason that cone driver technology was stretched into subwoofer bass territory was that it was and is the predominant driver technology available, so it was the most convenient choice. But subwoofer systems made with cone drivers are actually poor excuses for subwoofers, and don't even deserve to be called subwoofers, because of these physical handicaps and outright roadblocks cone drivers face at low frequencies. Because of their intrinsic nature, they inherently cannot possibly produce high quality bass.
You're probably already familiar with most of these physical handicaps and outright roadblocks that cone drivers face at low frequencies, and some have already been mentioned above. Here, we'll show how these physical handicaps and roadblocks adversely affect specific key aspects, of the quality of bass that conventional subwoofers can produce. And then of course we'll show how the TRW is completely free of these physical handicaps and roadblocks, so it can produce far, far better quality bass in these same specific aspects.
E.1. Amplitude Frequency Response
First, let's discuss the several distinct handicaps and roadblocks affecting amplitude frequency response, especially at low bass frequencies (precisely the frequencies which it is a subwoofer's primary job to cover well). The excursion of a cone driver approximately quadruples for every halving of frequency, when playing the same loudness level, so cone drivers soon run out of excursion capability as the bass frequency goes lower, even at modest bass energy levels, which means that a cone driver cannot extend to low bass frequencies at any reasonable energy level, even if it were made to have flat frequency response to yet lower bass frequencies. Because of their poor amplitude frequency response at low bass frequencies, conventional subwoofers cannot produce high quality bass, and their low quality bass will lack the correct impact (that kick you feel in your stomach from live bass).
Then, even before a cone driver runs into the abrupt roadblock of its excursion ceiling, it is handicapped by worsening distortion (hence degraded bass quality) at higher excursions, plus thermal limits at higher loudness levels. And, if a cone driver is constructed to have lower distortion at large excursions, say via an overhanging voice coil, it thereby acquires poorer efficiency, which means that it will run into its own thermal limitations sooner (and power amplifier limitations sooner). These further handicaps can also adversely affect bass quality, perhaps indirectly.
Furthermore, cone drivers also have a resonance frequency at the bass end of their range, and their frequency response declines steeply below this frequency, so this frequency marks a roadblock, the lowest bass frequency that they can play effectively. And, attempts to change this resonance to a lower frequency, say by making the woofer cone heavier, degrade efficiency, again meaning that the driver will run into its own thermal limitations sooner (and power amplifier limitations sooner).
In contrast and opposition, the TRW subwoofer does not face any of these handicaps or roadblocks. The TRW happily and effortlessly plays lower and lower bass frequencies, without any limit, even down to DC, and (as discussed above) its performance in some ways gets even better at lower and lower bass frequencies. Moreover, the TRW can play these arbitrarily low bass frequencies at bass energy (loudness) levels far greater than conventional subwoofers can. So the TRW, with its amplitude frequency response down to DC, plays very high quality bass (in a whole different league from conventional subwoofers), with full and accurate impact and kick, just like you hear from live bass.
E.2. Phase Frequency Response
Second, let's discuss a cone driver's handicaps and roadblocks that affect the phase of its frequency response, especially at low bass frequencies (precisely the frequencies which it is a subwoofer's primary job to cover well). A cone woofer's low frequency resonance is a phenomenon based on high reactances interacting, the equivalents of inductance and capacitance. These reactances store energy, and they drastically shift phase. Drastically shifting the phase in turn drastically alters the audio signal waveform, so the reproduced acoustic waveform is not at all an accurate replica of the input electrical waveform.
To make matters worse, these reactances at the woofer's resonant frequency still shift the phase at much higher frequencies than the resonant frequency. At these higher frequencies the subwoofer is putting out its full energy, and then soon starts to blend with the woofer of the main loudspeaker system (since a subwoofer's spectral coverage spans only a couple of octaves). But, since the subwoofer's waveform is drastically altered by phase shift, its acoustic waveform can't add correctly to the acoustic waveform from the main loudspeaker's woofer, so the summed acoustic result will be wrong, and you'll be getting poor quality, inaccurate bass.
This reactive phase shift error is very bad at the resonance frequency, and further degrades the bass quality that might already be ruined by any amplitude irregularities at resonance. And this reactive phase shift error then continues below the resonant frequency, where the woofer's amplitude response is steeply rolling off.
Conventional subwoofer systems employ various distinct enclosure designs, and these enclosure designs impose even worse phase shift errors. Indeed, the enclosure designs (e.g. vented) that do best at extending the flat amplitude response to the lowest possible frequency, and which are often employed for this very reason, are the worst at worsening errors in the system the phase response. These enclosure designs might do best at extending the flat amplitude response, but then they have the steepest rolloff slope for all bass frequencies below resonance, and steeper slopes always mean worse phase shift errors. Likewise, the shape of the corner of the amplitude response curve, at resonance, plays a role in how bad the phase shift errors are. Somewhat higher Q bass enclosure alignments might produce flatter, more extended amplitude response, and are often employed for this very reason, but they have sharper corners in their amplitude response curve at resonance, so they also produce worse phase shift errors. As you can see, the conventional subwoofer is necessarily compromised, being damned if it does and damned if it doesn't, since it faces a compromising tradeoff: going for flatter, more extended amplitude frequency response necessarily brings worse errors in phase frequency response.
In contrast, the TRW subwoofer simply has no reactance at all, at low bass frequencies. So the TRW inherently has perfect amplitude frequency response, without any resonances, rolloffs, or limits to its very low frequency extension. Likewise, with no reactance, the TRW inherently has no phase shift at low bass frequencies. So the TRW intrinsically puts out virtually perfect waveform fidelity, for adding to your main loudspeaker and creating an accurate summed audio waveform from your system. And the TRW does not face any of those compromises that conventional subwoofers necessarily face, for example, the TRW does not have to trade off bass extension of its flat amplitude response against worsening phase errors. The TRW inherently has infinitely extended amplitude response, down to and including DC, and infinitely extended phase response, down to and including DC, without phase errors.
E.3. Time Domain Response
Third, let's discuss a cone driver's handicaps and roadblocks that affect its time domain response, especially at low bass frequencies (precisely the frequencies which it is a subwoofer's primary job to cover well). It's worth noting that time is a physically real entity of the universe, indeed a dimension of the universe, whereas frequency is merely an abstract concept, a convenient artifice invented by humans. Thus, actual acoustical events, and the signals we use to represent them, actually take place in time domain, as time moves forward and the event or signal moves forward, and they do not take place in the frequency domain (not in the same primary sense, but only in an abstract conceptual derivative sense). Likewise, actual loudspeaker diaphragm and radiation events, in other words actual loudspeaker performance, happen in the time domain, as time moves
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