This limitation also of course applies to any power amplifiers built into the subwoofer, which might not be up to the challenge of the subwoofer they are mated with.
Fifth, since conventional subwoofers are very inefficient, only a small percentage of the power supplied by your power amplifier (or the built-in power amplifier) gets converted into bass acoustic energy. This in turn forces your power amplifier to work very hard, having to put out many watts of bass energy for every acoustic watt of bass loudness actually put out by the subwoofer. Thus, the limits for subwoofer bass loudness, due to your power amplifier reaching its power and/or current limits, are reached much sooner, at a much reduced loudness level, thanks to the inefficiency of conventional subwoofers.
Furthermore, a subwoofer's inefficiency gets worse as its cabinet enclosure gets smaller, as its cone area gets smaller, and as its bass frequency extension goes lower (Hoffman's iron law). Nowadays the trend is to make most subwoofers with small drivers (smaller than 18 inches), and with small enclosures (to ensure domestic visual acceptability), and with an advertised reach down to 20 Hz (to make it saleable as a so-called subwoofer). So, nowadays, all of these three parameters conspire to make subwoofers extremely inefficient, which thereby makes them extremely demanding upon your power amplifier (or the subwoofer's built-in amplifier), and thereby in turn limits more severely the maximum bass loudness this subwoofer can in practice achieve.
The TRW is just the opposite, in all these factors that limit the quantity of bass that conventional subwoofers can create.
First, rather than its radiation resistance declining very steeply at lower frequencies, as with conventional subwoofers, the TRW's radiation resistance instead does not decline steeply at lower frequencies. Indeed, the TRW's effective area actually increases at lower frequencies, as opposed to conventional subwoofer drivers, whose area of course remains constant at lower frequencies. Thus, the TRW couples much better to the air than do conventional subwoofer drivers. So the TRW can create much larger quantities of bass (i.e. much louder bass) than conventional subwoofers can.
Second, rather than having a puny and severely limited excursion capability, as with conventional subwoofers, the TRW instead does not have a puny and severely limited excursion capability. Indeed, the TRW does not have any excursion limit at all, and can easily (without effort, strain, or distortion) approach infinite excursion as the frequency being reproduced goes lower and approaches DC. Thus, the TRW can play bass much, much louder than conventional subwoofers can. And the TRW's ability to play bass loudly does not decline as the bass frequency goes lower, as it intrinsically does with conventional subwoofers. So, contrary to conventional subwoofers, the TRW can play bass that is both low in frequency and loud, and can do so easily and effortlessly, without strain or distortion.
Third, the TRW does not have the same physical factors limiting bass loudness as conventional subwoofer drivers do. Because the TRW does not assign multitasking to one engine as conventional subwoofers do, but instead has two engines, each devoted to a single task, the TRW does not have the same physical limitations.
In particular, the voice coil responsible for modulating the signal in the TRW is not also responsible for performing a second task (as it is in conventional subwoofers), the task of creating the airflow that supplies the energy for bass loudness. In the TRW, a second independent engine (the rotating fan motor) is responsible for this second task, which supplies the energy for bass loudness. This second engine does not at all face the same limiting factors that a voice coil, spider suspension, etc. face. Instead, this second engine in the TRW, responsible for creating the bass loudness, can create much higher energy airflow, hence much louder bass, before reaching its limiting factors, which are wholly different in nature and which cut in at a much higher airflow level, hence a much higher bass loudness level (think of the effectiveness of electric motor fans at creating large airflows, e.g. for wind tunnels).
Thus, the TRW can play bass much, much louder than conventional subwoofers, because it does not face the same limiting physical factors, thanks in large part to the fundamental conceptual contrast vs. conventional subwoofers (discussed above), wherein the TRW has two engines instead of one, each engine optimally dedicated to just one task -- and the engine dedicated to generating bass loudness does not have to also contain parts for modulating the signal, parts (e.g. a voice coil and spider) which have severe loudness limitations. The TRW does have some physical limitations involving other factors, but they do not limit loudness until the TRW achieves much, much louder levels of bass than conventional subwoofers can even dream of approaching.
Fourth, the fact that the TRW, in fundamental conceptual contrast to conventional subwoofers, does not multitask, means that the power amplifier in turn, which drives the signal modulating engine of the TRW, only has to perform signal modulation as its single task. The power amplifier of the TRW does not have to also supply the energy to create the airflow to create bass loudness, as it does have to do with conventional subwoofers. Thus, the TRW is not limited in its bass loudness capability by any power amplifier limitations at all. Also, the issues of conventional subwoofer inefficiency putting a further strain and a further limit on the power amplifier's capabilities, hence a further limit on bass loudness, become non-issues for the TRW. And the issues of power amplifier inefficiency, which also limit a power amplifier's drive capabilities to produce loudness from conventional subwoofers, become non-issues for the TRW, since the power amplifier is not at all involved in the task of producing bass loudness.
In the TRW, bass loudness chiefly comes from the task performed by a distinct engine, an engine which is not powered by any power amplifier. Instead, this distinct engine, the rotating fan's drive motor, gets its energy directly from the powerline. So virtually all the energy available from the powerline is directly at the disposal of the TRW's fan motor, to create bass loudness. And the powerline is a far greater source of energy than any power amplifier, however huge, could hope to be. Note that any power amplifier has to get all its input energy from the same powerline, and every power amplifier has less than 100% efficiency (often far less), so some of the energy available from the powerline cannot make it to the output of the power amplifier (but instead produces heat inside the power amplifier, which in turn limits the maximum energy that any power amplifier of reasonable size and cost can put out).
The maufacturer has measured the TRW-17 subwoofer as putting out a loudness level of 115 dB, at 1 Hz (!!!), with low distortion. No other subwoofer comes even close to this low bass performance.
Fifth, the efficiency of the TRW is also far greater than the efficiency of conventional subwoofers. Thus, for a given powerline capability and a given power amplifier size and cost, the TRW can produce far higher bass loudness than a conventional subwoofer can.
The TRW does employ a power amplifier, but only for the single task of signal modulation. Naturally, there are some limits to this power amplifier, and some inefficiencies with the signal modulation process that this power amplifier must drive. But these issues primarily affect only the signal modulation process, and do not directly affect the loudness (bass quantity) capability, since the latter comes primarily from a different engine, the fan motor powered directly by the powerline. The manufacturer recommends that a 200 watt power amplifier is sufficient for driving (controlling) the signal modulation task, even for the huge loudness levels that the TRW is capable of (in contrast to conventional subwoofers, which require 1000 watt power amplifiers to achieve far less loudness).
As you can see, the many factors, which severely limit the loudness and bass quantity capability in conventional subwoofers, simply do not apply to the TRW. The TRW and conventional subwoofers are opposites in being limited by these factors. With respect to these factors, it is conventional subwoofers which are limited hence wrong for obtaining a reasonable quantity of bass (especially at the low bass frequencies which it is a subwoofer's very job to handle well), and it is the TRW which is right, by not be thusly limited in bass quantity by these factors. It is the primary responsibility of subwoofers to play low bass and to create the large acoustic energy required by low bass, so this means that conventional subwoofers cannot even perform their primary responsibilities, and therefore are scarcely worthy of being called real subwoofers in the first place. So, which is the real subwoofer, and which is the pretender? As we said, the TRW is the only subwoofer.
H. Opposites in Pressure and Volume, hence Bass Quality
As a final example of inherently opposite performance, consider pressure and volume. Conventional subwoofers are high pressure pumps, with a high excursion, small diameter piston madly flailing away as it pumps a small air volume with high pressure. This is exactly the opposite of how most natural bass sounds are actually produced, and is the opposite of how naturally produced bass quality actually sounds to us. The bass from a bass viol (plucked or bowed), from a grand piano's large sounding board, from an organ pipe, from a bass drum, are all produced live by large radiating surfaces or volumes, operating at low pressure. Even a cannon shot or similar sound effect, though perhaps produced by a high pressure event at its source, becomes a relatively low pressure, large wavefront by the time it reaches you in open air (assuming you are located at sufficient distance to hear it without having your hearing damaged).
Incidentally, a bass horn, acting a transformer to convert high pressure from the driver into low pressure at the horn mouth, can reproduce the correct low pressure bass sound of the original live event, but practical bass horns cannot extend below 40 Hz, so they make wonderful woofers but are useless as subwoofers.
Conventional subwoofers, with their small area pistons pushing a high pressure, small volume of air at you in the confines of a small room, simply cannot replicate or correctly reproduce the low pressure sound of the original bass event. Thus, conventional subwoofers intrinsically cannot recreate the correct bass quality, nor high quality bass.
The TRW subwoofer is just the opposite. It intrinsically operates in a low pressure, high volume mode, exactly like the original live bass sounds, and the opposite of conventional subwoofers. Sonically, it is instantly obvious that the bass quality from this low pressure TRW subwoofer sounds natural and has the correct bass quality, from all bass events, be they a bass viol, the large radiating sounding board of a grand piano, the huge volume moved by a bass organ pipe, a bass drum, or even a cannon shot from a film soundtrack. And, in direct comparison, it is instantly obvious that the bass quality from conventional subwoofers sounds all wrong in quality, like a high pressure, low volume pump flailing away in a vain attempt to produce some semblance of bass sound.
Again, the low pressure, high volume TRW is just the opposite of conventional high pressure, low volume subwoofers, and it is the TRW that is right and the conventional subwoofers that are wrong. So, which is the real subwoofer, and which is the pretender? As we said, the TRW is the only subwoofer.
Part II: How the TRW Works
The design concept of the TRW is radically new for a subwoofer, and radically different from conventional subwoofers, indeed so different that doubting Thomases can't see how the TRW could possibly work as an audio subwoofer.
But the basic technologies employed by the TRW are actually old, well established, and well proven.
A. Proven Technologies
The engine that provides the airflow, hence the bass energy, in the TRW is simply a fan, directly powered by an electric motor, which in turn is directly powered by the powerline. Electric fan technology is very old, in fact several decades older than the moving coil loudspeaker driver employed by conventional subwoofers. And the electric fan has been very well established and well proven, for over a century, as a very effective and efficient mover of large quantities of airflow. The electric fan is used almost universally, for small applications like venting your computer case, for medium applications like ventilating or exhausting your domestic room or attic, and for large applications like power station cooling and wind tunnels. If any doubting Thomas thinks that fan technology cannot move enough air to create thunderous bass in a domestic room, let him try to stand upright in a wind tunnel.
The second engine in the TRW, which tracks the audio signal and modulates the airflow in accurate sympathy, is simply variable pitch for the fan blades. This variable pitch blade technology has been employed and proven for nearly a century, for example in airplanes, where the propeller blade pitch is varied to suit varying conditions. Airplane propeller blades even reverse their pitch, thereby providing negative airflow, to very effectively brake the airplane after landing touchdown (even more effectively than the old fashioned technology of wheel brakes can do). If any doubting Thomas thinks that variable pitch blades cannot effectively modulate airflow, to reproduce a positive and negative audio signal waveform, let him try to stop a heavy airplane, after landing touchdown, with old-fashioned wheel brakes alone.
Doubting Thomases will be further reassured by the fact that these two old technologies have already been successfully combined in a loudspeaker (though not a subwoofer), over half a century ago, a loudspeaker that can play extremely loud and put out huge amounts of acoustic energy. The moving vane loudspeaker, used extensively in World War II, used one engine to move air, and a second engine to modulate the airflow via a variable pitch blade, just as the TRW subwoofer does. And this moving vane loudspeaker, using the same basic technologies united together as in the TRW subwoofer, could generate such huge acoustic energy and loudness that it was used to communicate between warships that were located far (perhaps miles) apart! If these same technologies as used in the TRW have long ago been proven to be able to generate this kind of acoustic energy and loudness over the open air space above the ocean, then doubting Thomases can be reassured that the TRW can generate all the acoustic bass energy you could possibly want within the confines of a domestic room space.
The TRW drives its rotating fan directly by an electric motor, working straight off the powerline, at constant rotational velocity. The TRW modulates the fan blade pitch with a voice coil, which is mechanically linked to the variable pitch blades, and which is driven by a conventional power amplifier responding to the bass audio signal input.
As the blade pitch is modulated in response to the bass signal, the blades push more or less air forward, or more or less air backward (for the negative portions of an AC bass signal waveform). Note that the TRW fan can happily and effortlessly thereby reproduce bass signals of arbitrarily low frequency (as discussed above, this is the complete opposite of conventional subwoofers, which get into progressively worse trouble, in many ways, as the bass frequency to be reproduced goes lower). The TRW can even happily, effortlessly, and accurately reproduce DC (zero Hz), by simply holding the blade pitch fixed while the fan continues to rotate.
B. Comparisons with Conventional Subwoofers in Air Volume
The diameter of the fan in the TRW is about 19 inches. So it's instructive to compare its performance, in moving air and thereby creating acoustic bass energy, with a conventional subwoofer driver of 18 inches diameter. An 18 inch diameter cone driver also happens to be the maximum size employed by conventional subwoofers, even huge (and hugely expensive) monsters, so this comparison pits the TRW performance against the very best that conventional subwoofer technology can offer.
In the following comparison, we will deliberately oversimplify. The idea is to convey, as clearly as possible, the key operative principles at work here. This means omitting details which would add more confusion than information.
B.1. Batch of Air, per Excursion vs. per Revolution
Assume that the 18 inch cone woofer makes a 1 inch excursion, and that the TRW's fan blades are likewise set at a 1 inch pitch. Assume that the circular area of the cone piston of the 18 inch driver (discounting its surround area) is equivalent to the circular area within the 19 inch diameter of the TRW's fan (discounting its hub area).
Consider first the cone of the 18 inch woofer. With one excursion, it grabs a batch of air, and pushes it forward. How much air does it grab in this batch? The volume of air it moves is basically the area of the cone times the 1 inch excursion. Consider next one of the fan blades of the TRW's fan. With one revolution of the fan, this blade cuts into and grabs a batch of air, and pushes it forward. How much air does it grab in this batch? The volume of air it moves is basically the area swept by the fan blade in one revolution times the 1 inch bite from the blade pitch. As you can see, the cone of the large 18 inch woofer is closely equivalent to one fan blade of the TRW's 19 inch fan, both moving basically the same volume of air.
Note that this equivalent volume of air is moved by the cone woofer in each of its excursions, and is moved by one of the TRW's fan blades in each of its revolutions. But that's comparing apples to oranges (excursions to revolutions). So, before we can make the comparison complete, we first have to find a way to convert between excursions of the woofer (e.g. the number of excursions per second the woofer makes) and revolutions of the TRW fan (e.g. the number of revolutions per second it makes). After doing this conversion, then we can compare apples to apples, for example
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