This SPL format is very easy going.
The rules are as accomodating as possible so that it allows people to get LOUDER with their chosen installs or categories.

SPL Testing Types & Categories:
Propper Droppers is totally different to any other SPL format.

All the SPL measurements are taken from the inside of the car with the SPL sensor positioned on the drivers or passengers headrests.
The SPL Sensor is always facing towards the front windscreen.
This way you get a good idea of the SPL levels that your ears are subjected too as well.

A series of tests are carried out to see how well the system performs at playing certain low bass frequencies as loud as possible.

The test consists of:  Playing 5x Test Tones.
1: How loud your system can possibly play - Peak SPL.
2: Playing the following set tones. 40Hz - 33Hz   -25Hz - 20Hz. This shows you how well your system performs at playing low bass.
3: After the test has been carried out. All the scores are added together and then divided by 5. This works out your average score.
It`s the average score that determines the systems position on the pd SPL Leagues.

These are the main pd categories.

BOOT BOOMERS: Currently Split into 5x Groups:
BB1 - Boot Boomers 1: Any Sized Subwoofers up to 1x 8" / 1x 10"
2: BB2 - Boot Boomers 2: 2x 8" / 2x 10" / 1x 12"
3: BB4 - Boot Boomers 4: 4x 8" / 4x 10" / 2x 12" / 1x15"
4: BB6 - Boot Boomers 6: 6x 8" / 6x 10" / 4x 12" / 2x 15" / 1x 18"
BBX - Boot Boomers Extreme - Anything that exceeds BB6 or the standard BB height limit of 2" above top of rear seats.

Boot Boomers Limits:
1: The system has to be within the boot area of the car as in, it has to be in the boot area behind the rear seats.
2: Boot Boomers height limit is limited to 2" above the top most level of the rear seats. This does not include the headrests.

Any part of the box or bass system which exceeds this limit will be put into BOOT BOOMERS EXTREME.

This includes:
A: Any part of the subwoofers including the surround.
B: Ports
C: Scooped canopys
D: Bass Amplifiers

Other amps or speakers are allowed past this level, as long as they are not part of the equipment used to reproduce bass frequencies. 

BOOT BOOMERS EXTREME: This category is for any boot system that does not fall into the rules above.
It allows for any type of boot system as long as it is behind the rear most seats.

A: Full walled boots are allowed - boxes that go right up to the roof are allowed, anything really.

NO-WALL:  Wot?!!  No back seats?

No-Walled systems that are a lot larger than normal and usually take up both the rear seat areas and boot areas of the vehicle.

NO WALL Limits:

1: The box or subwoofer enclosure itself must not be higher than the center point of the side windows. Any system that has a subwoofer enclosure that is above this level will be put into WALLED category.

1a:The systems amps and subs when mounted mags out, can extend beyond the height limit in this category.

2: Any type of internal build, battery trays and vehicle modification are allowed in this class except external power supplies.

3: You are NOT ALLOWED to build a baffle @ the B-Pillars to seal off the area above the box as this has the effect of walling off the front cabin area.

4: Pick up trucks with Blow Throughs, although having their systems within the NO-Wall height limit will also be regarded as a walled system because the cabin area is completely walled off.

WALLED: Typically the loudest type of vehicle sound systems around.
1:The rear off the car is normally filled with a huge wall of subwoofers which fill up the whole vehicle starting from just behind the front seats, filling the space from top to bottom of the vehicle and also extending into the boot area.

2: Any type of internal build, battery trays and vehicle modification are allowed in this class except external power supplies.

SPL Leagues:
Your position in the SPL leagues is worked out as follows:
Peak = 152.7dB @ 33Hz
40Hz = 150.4dB
33Hz = 152.7dB
25Hz = 151.6dB
20Hz = 150.7dB

All these scores are added together & then divided by "five" - Five being the number of different scores that have been achieved.
By doing this we get the TOTAL AVERAGE score achieved during the SPL testing session. Which in this case would be 151.6dB

The SPL Measuring Equipment:
pd uses an industry standard SPL sensor as used by the worlds most popular SPL organisations.
Known as the Term Lab Sensor - It is currently the most accurate & reliable way of testing for SPL.

SPL Readings:  Must be taken using a TermLab sensor. The Sensor must also be placed in the same position for each car.

SPL Sensor  Positions etc:
We are attempting to get an SPL reading which is as reasonably accurate as possible, as if you were listening to it.
To that end we take the SPL readings from roughly where your head would be when sitting in the vehicle.

1: The Sensor is attached to a HEAD REST, which represents the person in a seated position.
This headrest position has a fixed distance of 1100mm from the front of the headrest to the bottom most part of the front windscreen either to the left or right of the dashboard depending on which side the SPL sensor has been positioned.

1a: The sensor must always be facing forwards towards the front windscreen and fitted in either the passenger or drivers Head Rest at the set distance of 1100mm.

1b: Once the SPL Passenger or Drivers sensor position has been chosen it has to stay in that position for the whole SPL test.

1c:The only time the SPL sensor position can be changed is when the whole testing procedure has been completed and the participant wants it to be moved to the opposite position and another test carried out to see if any of their previous scores have increased.

This is allowed due to the design of some systems (Mainly walled systems) where the Port is to one side of the vehicle making certain frequencies louder at the driver and passenger positions.

2:On no account should the seats be pushed all the way forwards or the seat backs be positioned in such a way to increase SPL.

1:  Hearing Protection is provided & is advised to be worn during the SPL testing process.
2:  Disclaimer for damage against equipment & personal injury due to exposure of high SPL levels should be signed before any test is to be carried out.
3:  Engines can be left running / idling - The accelerator is allowed to be pressed if the participant feels that this may help to increase his / her score, whilst playing a test tone.

  All SPL categories can have as much bass amps that will fit into the available space of the category that their system falls into.
4a: Batteries can be positioned anywhere throughout the vehicle - Amplifiers that are not used for powering subwoofers can also be positioned anywhere throughout the vehicle.

  All categories can have as much sound deadening / strengthening mods as the owner wishes.
5a: The use of Baffles to cover certain windows is allowed. Please read the Baffle section to see the restrictions.

No restrictions on any type of playback equipment - Cd Players , DVD Players, I-POD, USB, SD, Hard Drives etc can all be used.

  There are normally no restrictions on the amount of time it takes to carry out an SPL test.
7a:However if the tests are being carried out in an open day / event where prizes or trophies are being given out or there are many people waiting to be tested (Over 15), then there is an advised 30sec time limit for each frequency attempt.

The testing is normally carried out by using an officially available test CD or a digital form of test CD.
8a: However if the participant feels that their system can play certain frequencies louder by actually playing music instead of the test tones that are provided on a Test CD etc then they are free to try using that method.

The use of external battery supplies and power sources which are outside the vehicle are currently prohibited.
9a: Battery trays are allowed however they must be positioned within the inside of the vehicle - The only exception is Rule 9b.
9b: Build downs to stored batteries from below the floor pan are allowed provided the tray has been constructed in a safe manner and also completely seals the batteries from the outside of the vehicle - rendering the battery tray as part of the internal structure of the vehicle.

More than one person can be inside the vehicle whilst testing.
11: The SPL sensor can be placed on either the passenger or drivers head rests.
11a: The SPL sensor, once positioned on passengers or drivers head rest must remain in that position throughout the SPL testing process.
11b: You cannot swap the positions mid testing but you can re-test with the sensor on a different side afterwards
Any higher scores can be taken as the participants systems score.
This benefits system that are built for other SPL formats as the port is usually to one side of the vehicle.


1: Any combination of doors, windows or sunroofs, even the boot, can be opened or closed to try & and achieve a higher SPL score.
2:  Doors, windows, sunroofs, roofs and body panels etc can be pushed against to try & achieve a higher score.

This is where two subs are mounted in such a way as to provide extra motor strength but still using the same cone area as a normal subwoofer.
Clam shell method is the most popular method of mounting in this way.
Any system which participates using this type of set up will have each clamshelled pair of subwoofers classed as one Subwoofer because you are still using the equivalent cone area of one subwoofer per ISO pair. 


1: The standard SPL test does not allow for any kind of port or box alterations in which to increase specific frequencies.

The idea of this test is to see just how well your current set up performs at playing low bass.

If a port blocker is used then the scores achieved during the SPL test with that set up will be used if it happens to be louder average than the previous system.

SPL Testing @ Ultra Low Frequencies                  Testing your car audio system  at its Peak SPL and at four set frequencies of  40Hz   33Hz   25Hz   20Hz  ////////////   The pd SPL format started booming in the U.K. in 2008.  Created by Marcos H Barnes A.K.A. Mega Heavy Bass. A former SPL competitor.//////////  dB readings are taken from the vehicles Head Rest    The doors and windows are allowed to be opened.   Like to know more?       ...Then please feel free to browse this site.       Thank You For Your Interest.           Copyright 2011 by "Marcos H Barnes"
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