HOW MODERN SUBWOOFERS CAME TO BE - MORE OR LESS
TOBY Customers often comment, “Subwoofer systems used to be so large. Now they are smaller, they play lower and sound better, too. How?”
Main Reason: Built-in high power amps. Self powered subs have become de rigor in home theater set-ups since the mid-nineties. Conveniently, when all the bass is sent to a single powered subwoofer, it becomes possible to use 5 or more small speakers for the surround, without over-filling the room.
There would be no compact subwoofer systems without self power. Subwoofer amps offer easy equalization to extend low bass, even when the enclosure is “too small.” With steep low pass filters—usually adjustable- all higher frequency sounds—like voice--are removed cleanly. High power digital amps are small, light-weight, and low cost. Hundreds, even thousands of watts are possible.
Second Reason: Long throw subwoofer drivers. First, some acoustic background…
Listeners often comment, “That subwoofer moves some air!” Any sound we hear is made by moving air. This is easy for tweeters. At 4000 Hz, a tweeter diaphragm makes tiny excursions, but lots of them. At matching loudness, [SPL] a sealed woofer moves exactly the same amount of air per unit time as the tweeter. But at 40 Hz, the woofer has to do it with larger excursions since it is moving more slowly (fewer strokes per unit time).
For every halving of the frequency a woofer must move 4 times as far to keep the SPL the same. For example to reach 20 Hz at the same SPL as 40 Hz with the same size woofer, the cone must move at half the speed, but 4 times as far! Hence the necessity for long throw drivers.
A decade or two ago we had large “woofers” that worked in three-way systems, playing from up to 400 Hz to as high as1500 Hz. There were few, if any, woofers that were optimized to be used only below 100 Hz, not even eighteen inch models. A quarter inch peak to peak excursion was typical to keep efficiency high.
Modern compact powered subs often use small diameter woofers, perhaps a ten, instead of a twelve, but what is lost in smaller diameter cones must be made up in longer excursion. In modern small sealed or vented enclosures the cones must do all the work, traveling long distances in-and-out. Small enclosures and high power amps call for a new breed of driver. A long throw subwoofer.
In modern subwoofers every part is different from the “old woofers.” It starts with longer voice coils for longer travel. The “old” coils might be ½ inch long. The new coils start at an inch long and go up. That cuts down on efficiency. Larger magnets are used to make up the efficiency. Back plates are deeper so the longer voice coils will not hit bottom.
Longer travel means deeper baskets to avoid bottoming of the cone. These baskets have a larger plateau for a larger diameter [accordion] suspension, again, to allow longer excursions.
Larger surrounds allow a longer excursion. These are usually half-rolls of foam or rubber attached to the edges of the cones. As they grow larger across, they must also grow and thickness and stiffness to withstand the high internal pressures generated inside small subwoofer enclosures. To minimize cone breakup, the cone body is made more rigid and more massive. High mass lowers the resonance which is good. It also lowers the efficiency, but that is easily compensated for by powerful digital amps.
We know that as frequencies go lower, the cone must travel farther, but it still must maintain low distortion. When a woofer doesn’t have to produce usable mid range frequencies, the accuracy below 100 Hz can be optimized. The new drivers lower distortion by better venting of the air beneath the dust cap and the suspension. This also improves power handling. Magnet circuits have been improved.
Note: In the bass range, large acoustic loaded enclosures like horns, bandpasses and reflexes are able to help move air by acoustic leverage in certain bands. That means that the woofer cones [pistons] can travel shorter distances, but they still “move the air” through the loaded horns or ports.
How does TOBY Corp implement these concepts in our CUBE 14 powered subwoofer? The enclosure IS small, less than a cubic foot internally.
First, it DOES have a high power digital amp--300 Watts RMS into 4 Ohms. It is so EFFICIENT that it does not need a heat sink.
Second, it DOES have two LONG THROW ten inch TOBY HIGH MASS subwoofers which have carbon doped cones and rubber half roll surrounds. They are capable of a one inch excursion.
Although the system resonance is 54 Hz, the driving power of the amp is EQUALIZED to extend the response an octave lower—3 dB down at 26 Hz. The low pass slope is 24 dB/8ve and adjustable over the commonly needed crossover range of 60hz to 100hz