Why don't they use more than 12v in high power car audio?

Question

In every single high-powered car audio system I've seen, in person and on the internet, the amplifier has been run off of the main 12 volt power system.

Such systems feature multiple parallel runs of heavy-gauge (Commonly 2 AWG or lower) wire between the battery and amplifiers and several alternators in parallel to supply the required current, which is in the hundreds-of-amps range. For a 5KW system, the maximum current would be around 400 amps.

Additionally, modern class D subwoofer amplifiers often have easily 2/3 of the internal space dedicated to converting the ultra-high-current 12 volt input up to a higher voltage, typically 70-100 volts, to drive the subwoofers.

Instead of using the 12v and boosting it, an alternative approach would be to have the alternators wired in series or using higher turn count windings to generate a higher voltage (70-100 volts as above) and run the output stage directly off of that. It would be a much simpler setup, as you could omit the voltage booster section of the amplifier and would only need the output stage and signal processing.

Why isn't the latter setup used in high-power car audio systems?

[Edit] For clarification, I am not concerned with "normal" (~1kw or less) car audio setups. I'm asking about competition builds where they are using extremely high amounts of power and are so weighted down with equipment that their primary purpose is to make noise and set SPL records, not be everyday commuting vehicles.

Answer 1

Bass drops and batteries.

There is only one way to handle an instantaneous power spike that exceeds the capacity of the alternator, and that is to draw it from the battery.

If you were to rebuild your secondary alternator to produce 100 volts (completely possible), and then purchase and install gear that used that for power, if you do not subsequently attach a battery bank that is rated for that same voltage (or boosted to pretend to have that voltage), then you only have the output from that one alternator. Period. Exceeding its capacity will break it.

In the current method, you have access to the output of both alternators and the battery that already had to be there for the car to start, and you didn't have to buy a second battery or the booster to make it play nice with a 100 volt system. Doing what you propose halves your available power and requires at least one additional battery or battery bank.

Answer 2

It depends on what class of car design you look at. There are many with higher power than the 12V bridge amplifiers.

I think your premises are false therefore the conclusion is also. If you are the rare person that needs 6kW 100V generator for an audio system, add a 2nd alternator.

Here is one such IC for that market.

The PMP11769 reference design is a complete solution for a 700W automotive external amp. The boost converter provides 36.0V @ 10.0A continuous / 20.0A peak from an input voltage of 9-16V. It contains two premium Class-D audio amplifiers, which provide 2x 175W @ 4-Ω load (left & right channel) and 1x 350W @ 2-Ω (subwoofer).The design is well suited for car audio external amp applications due to its thin profile and high power output.

• Interleaved Synchronous Boost + Audio Amplifier
• Output 36.0V @ 10.0A (continuous) / 20.0A (peak)
• Free-Running switching frequency of 250 kHz CCM
• one TPA3251D2 in stereo mode (175W 4Ω )
• one TPA3251D2 in mono mode subwoofer (350W 2Ω)
• -12.0V @ 50mA) with LM2841X-Q, +3.3V @ 50mA) with TPS7A6633-Q
• ~> 95% efficient 3~10A
• 0.6% V overshoot 10A to 20A