Real SPL


Real SPL is a peak hold (burp) division of ISPLL. Real SPL is metered on the windshield with all doors closed. The competitor must run 3 different “burps.” Each burp must be separated by at least 10Hz (i.e. 36, 46, and 56). All 3 scores will be averaged to indicate the Real SPL score. This allows for a more musical and realistic assessment of the competitor’s system. The classes are divided based on a combination of the 1 ohm rating of the amplifier(s) used and the total cone area of the subwoofer(s) used.

Class Matrix

Orange - Cone Area Restricted


1. Competitors are allowed to use any source of sound (i.e. music, tones, etc.). They may also use CD, MP3, iPod, USB, or any other source device.

2. The maximum frequency to be used is 70Hz. There is no minimum frequency.

3. There must be a minimum of 10 cycles between each burp (i.e. if the first burp is 58Hz, the next burp must be 48Hz or lower, then the final burp must be 38Hz or lower-assuming the second burp was 48Hz).

4. Metering will take place on the passenger side windshield (legal position). All doors, windows, hatches, trunks, etc. must be closed during the runs.

5. Seats may be removed.

6. Cone area restrictions: T1 – <253” | T2 – <354” | NW1 – <354” | NW2 – <708” | W1 - <708” | All other classes unlimited

7. Maximum charging voltage for classes T1-3, NW1-3, and W1-3 is 15.5V and classes T4, NW4, and W4 is 19.5V.

8. There are no battery limits in any class. ISPLL believes that this unnecessarily restricts the ability of competitors to use their system fully outside of competitions (i.e. demo and daily usage).

9. Engine RPM should not go above 2500RPM consistently during metering.

10. Competitors are allowed to change/alter ports (you may not change the box/subwoofers/amplifiers-excl. settings) between runs. They have 3 minutes to perform all alterations and then the judge will start the next run.

11. Competitors must wear hearing protection during metering if their vehicle exceeds 150dB.

12. All vehicles must be daily drivable (drive at least 50 miles on one tank of gas and drive the posted speed limit).

13. The NR class will ignore rules 2, 7, and 12. This is the No Rules class and shall only follow the general guidelines of a 4 wheeled form of transportation.