Why ad-hoc SPL car subwoofer?

I need to understand how car SPL competitions works.

Why the use of classic car-audio SPL subwoofers? (speakers with: supermagnets, huge membranes for high excursion and high power handling)

Those speakers have a very low efficiency, then why?

If it's for their Fs is a non-sense. Normally those speakers have an Fs of 30Hz, but also PA subwoofer have this Fs.
An example (of real-measured data) is the FaitalPRO 15PR400: Fs 30Hz, n0 2.8% and 90dB 1W/1mt on his Fs.

Measurements of the Faital here: FAITAL 15PR400-8 (Woofer 15", 8 Ohm, 800 Wmax)

All the SPL subs have 75dB 1W/1mt (and low) on their Fs, very low efficiency (max n0 0.5%), thus requiring an enormous amount of power.

Even using 20kW of power the maximum SPL (+3dB on each power doubling) we can obtain only 120dB on Fs (starting on 75dB).

Varying the frequency, using 70Hz instead of 30, we got about +15dB, but no more.

Then, if not for the Fs, is the impedance? Using high voltage ad-hoc amplifiers we can obtain same results on 8Ohm high efficiency subwoofers (using only 500W and low).

If those are the calculations, are SPL meters tricked? How 140dB of SPL is common in those competitions? How they can achieve this result?


2006-07-25 6:37 am
SPL vehicles will tune the enclosure much higher than FS IIRC. The drivers typically have a higher FS. Low frequency extension isn't the goal. They typically use proprietary drivers for high excursion and power handling. As well as designed to be easily rebuildable. Distortion isn't an issue.