SQ Contesting
Back in the days when we concentrated on SQ (Sound Quality) alone, the best battery for a system was the car’s stock battery. This is due to the fact that large, “upgraded” batteries tend to consume more alternator energy than their smaller counterparts. Adding a second battery just for the sound system always increases the load on the alternator, and that means more alternator ripple noise. It’s also true that rear seat- and trunk-installed batteries cause more alternator ripple to flow over the car, which means more noise points for SQ judges to deduct. Leaving the stock battery in the vehicle means more high-voltage alternator energy, with less alternator ripple, for the SQ system. This is the way to go for SQ systems.

The car’s battery only has to be large enough to reliably start the car on a cold day. That’s it! I can recall a car at the Georgia Master’s Invitational contest one year with four large golf cart batteries in the trunk of his SQ vehicle. Not only was the suspension “upgraded” to that of a cement truck, but a High Output Alternator (HOA) was also added just to handle the increased load presented by the golf cart batteries. I mentioned this fact to the car’s owner and also mentioned that if he removed the golf cart batteries he could also remove the HOA. Guess what he said?

“I like those golf cart batteries because I can listen to my system for 12 hours with the engine off and there is no alternator whine.”

Yeah, no alternator whine with the engine off, but the alternator whine in this car sounded like a racing fire engine when driving down the street. The point here is that SQ contesting does not include a category for listening to a system for long periods of time with the engine off. A single stock battery and normal alternator would be just fine for SQ judging. When we start awarding points for how long a system can be played with the engine off, then Mr. Golf Cart Battery will certainly be a contender.

SPL Contesting
With SPL contesting, the loudest system wins. Until someone figures out how to increase the efficiency of power amplifiers and speakers, high SPL systems will need high-energy power supplies. Let’s say that the maximum belt-driven alternator power is 3.5 kilowatts. This works out to around 240 amps at 14.5 volts. Even using the most efficient amps and best motor-to-cone speaker ratios, it would certainly be difficult to win an SPL contest with just one 240-amp alternator connected to the stock battery. How many huge alternators would it take?

Designing a system with enough alternator energy to win an SPL contest is a tough assignment. The solution is to add lots of huge batteries — just like our friend with the golf cart batteries. Sure, it’s possible that the HOAs merely top-off the batteries, but the SPL system will continue to be powered for 30 seconds or more by the energy stored in the batteries. Yes, the battery voltage is certainly lower than the alternator’s output. However, the bottom line here is that, for SPL contesting, the current requirement is so great that the systems end up running on battery energy. Tons of storage batteries and huge charging systems are needed to win SPL contests today.

SPL and SQ Contesting
The alternator ripple in a serious SPL vehicle is difficult to hear due to the absence of mids and tweeters. Problems arise when contestants decide to enter both SPL and SQ contests with the same vehicle. The SPL system requires multiple batteries and HOAs, but a stock battery and normal alternator would best supply the SQ system. So what’s the answer?

Daily Drivers and Contesting
Before we answer that question, let’s consider the possibility that the contesting vehicle could also be a daily driver. For this system, the answer is that the battery only has to be large enough to reliably start the car on a cold morning. The alternator has to be large enough to reliably charge the battery and power all the car’s electrical accessories. Our ultimate answer must weigh the importance of each of the three goals.

With a modest SQ system or daily driver, the stock alternator and battery are adequate. When SPL contesting is the goal, then it’s time to increase the battery capacity and/or the alternator’s output. The problem is that everything that is done to improve the SPL system will be detrimental to the SQ and daily driver systems. Likewise, using the battery and/or alternator of an SQ or daily driver system to power an SPL vehicle is not going to produce an optimal contesting situation. Priorities have to be set and then the systems can be designed accordingly. One thing is for certain: It’s going to be difficult to find a vehicle that wins in both SQ and SPL — and is a daily driver!

Battery Ratings
It’s a fact that battery performance is the poorest when the temperature is low. For this reason, battery manufacturers measure the current capacity in amps under extremely low temperatures. This measurement is known as the Cold Cranking Amps or the CCA rating of the battery. Interstate Batteries defines their CCA Crank Test as: “The temperature of the battery electrolyte is brought to 0 degrees F in the center cell. The current drawn from the battery for 30 seconds while maintaining a voltage at the terminal posts of 7.2 volts (1.2 volts per cell) is the CCA rating of the battery.”

Although we use this same definition at our Autosound 2000 Test Labs, we seldom test for CCA. We have a special test program for our battery tests and usually let the battery only drop down to 10.5 volts at STP (Standard Temperature and Pressure). The differences between battery ratings can be huge. Another battery test is the Reserve Capacity test. Here the battery is loaded (i.e., 25 amps) and the time for the battery’s voltage to drop to 10.5 volts (1.75 volts per cell) is measured in minutes.