Let’s say that you are building a car audio system intended to produce as much bass as possible. In that case, you are going to need subwoofers capable of handling vast amounts of power. You’ll also need amplifiers capable of pushing those subwoofers to their limits. It’s not uncommon to see cars and trucks with more than 5,000 watts of power being sent to a single subwoofer. In these systems, it’s common to see a pair of amplifiers in what’s called a strapped configuration driving a single speaker. This article explains how the concept of strapping works to deliver massive amounts of voltage and current to your subs.
Strappable Car Audio Amplifiers
First and foremost, you’ll need to make sure that the subwoofer amplifiers you have chosen are capable of being strapped. Making this assumption without checking the owner’s manual can result in a lot of frustration. If you try to strap two amplifiers that aren’t designed for this application, you will damage one or both of them.
Second, don’t assume that a subwoofer amp model is strappable because it has a master/slave switch or an audio signal input and output separate from the standard RCA input connections. Those inputs and outputs may exist to make it easy to daisy-chain multiple amplifiers together, so only a single sensitivity control, crossover adjustment, infrasonic filter and remote bass boost setting works for several amplifiers.
Strapping a subwoofer amplifier involves using two identical amplifiers. The amps must have some sort of master/slave switch, and depending on their design, might also have a polarity or phase control switch. For our example, we’ll assume we are using a single voice coil high-performance subwoofer, just to keep things clear. In reality, as long as the load impedance doesn’t exceed the rated limits of the amplifier, you can wire up as many subwoofers as you want.
Wiring Two Amplifiers to One Subwoofer
Image Caption: A pair of Rockford Fosgate Power T2500-1bdcp amplifiers wired to a single T3S2-19 19-inch Superwoofer. Individually, these amplifiers can produce at least 2,500 watts of continuous power into a 1 ohm load.
The drawing above shows the positive and negative speaker wiring, along with the required jumper wire that runs between the two amplifiers for this pair of Rockford Fosgate amplifiers. Your installer must obtain the correct strapping information from the amplifier manufacturer for the models you have chosen. Unfortunately, that information is not universal or transferable.
Aside from the right speaker wiring, these particular amplifiers have to be connected using a bd-Sync cable and a set of RCA cables. The top amplifier is set to master mode. This amplifier will be responsible for gain adjustment, low-pass crossover filtering, infrasonic filter selection and the remote Punch EQ control function. When set to slave mode, the second amp takes the audio signal from the output of the preamp stage of the first amp and feeds it to the output stage of the second amplifier. This configuration bypasses all the adjustments on the second amplifier.
For this configuration to work, the polarity of the second amplifier has to be inverted relative to the first. On the Rockford Fosgate amplifiers, this is achieved by setting the phase switch to 180 degrees. With this setting engaged, if the audio signal from the positive terminal of the first amplifier is increasing in voltage, the same terminal on the second amplifier will be going more negative. The result is twice as much voltage being applied to the subwoofer as would be available with a single amp, up to the current delivery capacity of the amp design. In the case of these two amplifiers, that would be 5,000 watts of power into this 2 ohm load.
Load Impedance Matters
Just as when your installer bridges a stereo amplifier to a subwoofer, the minimum load impedance decreases compared to when speakers are connected to a single channel. For the Rockford Fosgate amps, the minimum load impedance is 1 ohm when each amp is run independently. However, when two amplifiers are strapped to a single subwoofer, the minimum load impedance is 2 ohms.
The minimum load impedance is cut by half because the power production attempts to quadruple. Allow us to explain.
If a single T2500-1bdcp can produce 2,500 watts of power into a 1 ohm load, the maximum current it can supply to the sub would be 50 amps, and the voltage would be 50 volts. Strapping the amplifier now presents the subwoofer with up to 100 volts across the terminals. If we apply 100 volts to a 1 ohm subwoofer, the power would be 10,000 watts, and the load would draw 100 amps of current. While impressively powerful, these amplifiers can’t supply that much current, so we need to double the impedance to cut the load current in half. Delivering 100 volts across a 2 ohm load results in 50 amps of current flowing through the subwoofer.
Things to Think about When Strapping Amplifiers
By the way, you will want your installer to run at least eight AWG power cables from the amps to the subwoofer. By way of an example, the voltage drop across 12 feet (6 feet for the positive lead and 6 feet for the negative) of eight-AWG copper wire that is passing 50 amps of current is 0.404 volts. So it wouldn’t be crazy to make two runs, or upgrade to six or four-AWG cable if it’s available to reduce that drop and deliver more power to your subwoofers.
Not to sound all preachy, but a potential of 100 volts is a very high voltage. The electrical outlet in the walls of our homes operates at 120 volts. We know it’s not safe to play with those circuits. Make sure your installer has secured all the electrical connections to your subwoofers properly. You don’t want a wire coming loose or shorting. You also don’t want anyone to be able to touch those terminals when music is playing. Quite simply, the results could be lethal.
If you plan on competing in a car audio competition where maximum output matters, then look into car audio amplifiers that are strappable. This configuration delivers more voltage to your subwoofers and will increase the efficiency of your system compared to using low-impedance subwoofers. A specialist mobile enhancement retailer near you can help you choose amplifiers that will deliver thousands of watts to your subs. Drop in today to find out what’s available.
