Harrison Labs® calls its unique and efficient line of amplifiers Audio Engines™. HLABS's capacitors are sometimes called stiffening caps. A cap is necessary to provide short term power burst (less than 1 second) that the audio battery delays during chemical reaction delay. The Bat™ is a compact low ESR (equivalent series resistance) audio battery that is necessary to supply your amplifier(s) with long term (up to 1 hour) that the alternator cannot supply. Remember that the alternator takes time to recharge the battery(s). Competition Audio Engine™ amplifiers can be used to drive DVC (dual voice coil) woofers for maximum power. Some competitors use either 14 volt or 16 volt (2- 8volt in series) batteries to force the amplifiers to produce higher power. To charge these batteries, FluxCap™ (charger versions) must be used to boost your alternator voltage. HLABS new 300 AMP FLUX CAP  can be used with 12 volt audio batteries to boost the voltage to your amplifier(s) to as high as 16 volts (14.7 volts is standard.) The FMOD™ crossover comes in pairs and has a fixed crossover frequency. The FMOD CABLE™ has a choice of 2 frequencies depending on direction of connection. The PFMOD™ is a 2 channel low pass, high pass, or 2-way adjustable crossover. Attenuators reduce audio signal to match a very high level (line driver output) to a lower level amplifier input. Engine noise, hiss, alternator whine can be reduced or eliminated by using noise gates and ground loop isolators. The X-CONNECT™ is available as a ground loop isolator/line level adaptor to speaker level or as an adjustable attenuator. If you are designing or building a woofer box or enclosure, take a look at our Speaker Box Design Sliderules. Do you need a digital voltmeter or ammeter or temperature meter  that you can add to your system? HLABS has the VM-1 universal meter that you can build into your system.