The Great Hybrid Hype is real
A lot of hype about hybrid technologies has floated around in recent years, most notably from the automobile world. With cars being a main focal point in American society, these technologies have become synonymous with energy, monetary and environmental savings. In automobile hybrids, most of these savings result from advanced electronic hardware.
Interestingly, at least one of those electronic technologies has made its way into car audio. Rockford Fosgate has developed a new concept in amplifier design, which they unveiled at the 2006 Consumer Electronics Show in the form of the attention-getting T15kW. The gist of this amplifier is to store ungodly amounts of energy, enabling it to produce 15,000 watts at greater than 100 percent efficiency. In other words-achieving the impossible. With our curiosity piqued, we went directly to the source, the Rockford Fosgate engineer responsible for the T15kW, Anthony D'Amore, for a little insight on this seemingly impossible achievement.
Some have reviewed the specifications of the T15kW with hybrid technology (HT) without understanding what the technology is. This causes them to refer to Ohm's Law (circa 1827) and immediately say this amplifier is either impossible or trying to break Ohm's Law. Ohm's Law has been correct for 179 years and I'm sure it will remain correct for many years to come. This technology in no way breaks Ohm's Law.
The real law that we need to talk about is the first law of thermodynamics, or Conservation of Energy. This states that energy cannot be created nor destroyed; additionally, you can only get the same amount of energy out of a system as the amount of energy that was put in. This is true for every amplifier, including the T15kW.
Here's a quick review of what "efficiency" means, as I will refer to it later. (Efficiency = Power Out f· Power In.)
Let us take a typical Class A/B amplifier for example. Say it puts out 200 watts RMS and it takes in 300 watts to do this.
Efficiency = 200 f· 300 = 0.67 or 67%.
How do we know how much power it took in? This is where Ohm's Law is helpful. We knew it took in 23.8 amps to do this at 12.6 volts.
23.8A x 12.6V = 300W
Conservation of Energy does not say "Power In Equals Power Out." It says "Energy In Equals Energy Out." What's the difference? "Power" alone tells us nothing about length of time; "Energy" does (Energy = Power x Time). When you get your electric bill in the mail they don't charge you for how much "Power" you used, they charge you for how much "Energy" you used, hence the unit "Kilowatt x Hours." A kilowatt-hour is a lot of energy and I doubt we will ever see the unit used in mobile audio. When referring to the T15kW, though, we could use the unit kilowatt-second, meaning 1 kilowatt for 1 second. However, there is already a unit of measure for energy that is commonly used in the audio world: the joule. A joule is to energy like the gallon is to water. It is a quantity of energy and is defined as 1 watt-second or 1 watt for 1 second. OK, I know that is a bunch of info, but it's necessary to really understand the topic.
I suppose we should talk about storing energy now, as in a capacitor. The formula for how much energy a capacitor can store is: (1/2 x C x V2). Which reads 1/2 times the capacitance (in farads) times the voltage squared. As an example, let's find out how much energy is stored in a 1-farad capacitor that is connected to the +12V system.
(1/2 x 1 farad x 12 x 12) = 72 joules or 72 watt-seconds
If you are still with me, now we have the basis to discuss the operation of the T15kW and its hybrid technology.
You cannot put out more power than you take in, or can you? The answer is YES YOU CAN, for periods of time. The HT system in the T15kW stores a huge amount of energy, well into six figures of joules. It is capable of this by using the latest technology in capacitors designed for use in hybrid vehicles and large wind-turbine electricity generators. The operation of the system is somewhat analogous to the operation of a hybrid vehicle. During some conditions, a hybrid car runs on just electric power; other conditions, on just gasoline power; and under "full throttle" conditions, on both systems. The T15kW has two systems in a way. It has the high-voltage system, which is stored in the amplifier, and it has the 12-volt system from the vehicle. When the T15kW's output power is low, it uses power from the high-voltage system to run the amplifier and very little energy from the 12-volt system trickles in. When output power is relatively high, it uses the high-voltage system along with some energy from the 12-volt system to keep the high-voltage system charged. When it is at "full throttle," it uses both systems to their capacity to supply the output devices with the maximum amount of energy possible.
So how can this work and why doesn't it just "run out" of energy? The key is that music is very dynamic, meaning it has loud times, like a kick drum, and relatively quiet times, like ... well, like anything that is not loud. During loud times, the system releases energy for instantaneous efficiency of well over 300 percent. During quiet times, it absorbs energy; the instantaneous efficiency at this point could be as low as 0 percent. HT is an energy management system. The "average" efficiency is still similar to other amplifiers. But, you must read the last two paragraphs to understand the big picture. The system in this amplifier was designed so that it could play typical music continuously at 15 kilowatt levels. After all, this is an audio amplifier we are talking about and audio amplifiers were intended to play music. With the HT system inside, the T15kW plays music like no other amplifier before it.
The question has been asked, "What about a sine wave, like for an SPL competitor?" The T15kW has plenty of energy to get through a three-second sine wave burst. However a five-minute "death match" competition is not the T15kW's forte. Who wants to torture their investment like that anyhow?
So why would I design such a system? First of all, this amplifier will make your ears smile when you hear it. Or you'll be smiling from ear to ear. So we're talking sound quality. Secondly it has the ability to deliver incredible amounts of dynamic power. But maybe more importantly, when getting into the multi-kilowatt range, the power delivery from the 12-volt system becomes more and more inefficient. The HT system in the T15kW solves this though current-averaging to help with efficiency. Let's talk about why current-averaging is useful.