1-1     Competitors may use any music format they choose to achieve their highest Sound Pressure Level ( SPL ). This includes test tones, sine sweeps, MP3’s, commercially available CD’s and burned CD’s. Competitors in the Basic and Advanced divisions may choose to “burp” their system for a few seconds or play all out for the full 30 seconds.

1-2     The music format must be played through an audio device such as CD players, CD Changers, MP3 players, flash drives or hard drives.

1-3     There is an 80 Hz limit in all peak SPL classes.

1-4     The competitor may have their vehicle running during their run as long as the following requirements are met:

• The emergency brake must be set
• The wheels are chocked or blocked
• A maximum engine idle speed is not to exceed 2000 RPM.

1-5    Only the person operating the sound system is allowed to remain in the vehicle. Those sitting in the vehicle must sit on the drivers side as long as proper hearing protection is used. Competitors sitting in the vehicle may not sit in such a way as to manipulate their SPL score. This is up to the discretion of the head judge.

1-6    Competitors may choose to open their doors, windows and other openings of the vehicle during the metering process, however doors and other openings are not to be slammed during this time.

1-7    Once the SPL metering process begins, competitors will have 30 seconds to achieve their highest SPL. Any adjustments can be made to the sound system before, during and/or after that time. Additional runs may be allowed if time permits.

2-1     No obstructions or modifications can effect the placement of the sensor and/or manipulate the SPL reading. This includes any items ( seats or other obstacles ) within 12” of any part of the sensor.

2-2     Standard sensor position will be at the “legal” position 12” from the passenger A pillar and 4” off of the dash measured horizontally and vertically.

2-3     All windows and openings need to function normally. No obstructions can prevent the openings from functioning normally. They must be able to open and shut and also roll up and down. Silicone used on windows ( to prevent leaks ) need to prove that the modification doesn’t effect the SPL score. Sun roofs in walled vehicles do not need to function.

2-4     The vehicle must have front seats. If seats came with headrests and/or armrests then those items must remain in place. Seats may not be modified.

2-5     Front seats may be folded and adjusted for competition but may not be removed from the vehicle.

2-6     Rear seat backs in trunk vehicles may be folded. Solid non/folding trunk vehicles may unbolt / latch their rear seat back. The removed seat back must remain in the vehicle on top of the bottom seat as if folded. Modifications allowing the rear seat to partially stay open must be made in the cargo area.

2-7     Second row seating in vans and SUVs must remain in the OEM location. They can be folded but not removed. Third row seating may be folded or removed from vehicle.

2-8     If the vehicle is an extended-cab or king-cab pickup truck with side mount seats, you do not need to be able to fold the side seats as normal operation.

2-9     All interior panels/carpet, including those in the trunk, hatch or cargo area must remain in OEM position unless custom trim panels are used. Custom panels must be covered or painted.

Notice - The spare tire cover, spare tire and tools may be removed.

2-10   Interior modifications are limited by the class the competitor competes in.

Notice - Examples of interior modifications (but not limited too):

• Replacing/Modifying the OEM windshield/side windows
• Replacing/Modifying the OEM dash and components
• Replacing/Modifying the OEM seats
• Replacing/Modifying the OEM door panels
• Replacing/Modifying the OEM headliner
• Replacing/Modifying the OEM floor
• Replacing/Modifying the OEM carpeting
• Replacing/Modifying any OEM interior panels

          Notice - Seat Limitations

• Seats not allowed: Go-Cart seats, arcade game seats, dune buggy seats, etc. They are not considered OEM equivalent.
• Aftermarket seats or those from another vehicle are allowed provided they serve both form, size and function of the original OEM seat. Seats must remain in the forward facing position.
• Seats must be fully bolted and secured.
• OEM seats must remain in their original place.
• Replacement seats must be bolted in the rear most OEM bolt hole location.
• Custom seat brackets will be are at the sole discretion of the head judge.
• Modifying seats in order to fold or slide forward past their original OEM specification is prohibited.

2-11     Door panels must not be glued or siliconed on. In other words, they can not be sealed to the door and must be easily removable if required.

2-12     Custom interior panels are allowed as long as the modification to the panel is to accommodate accessories, sound or video system; as long as they are designed/built from the original OEM panel.

2-13     Custom fiberglass dashes must resemble the original dash in size, form and function. Structural reinforcement is allowed only to those areas where aftermarket accessories, sound or video system are installed.

2-14     Custom center consoles are allowed as long as they are not designed to manipulate the interior of the vehicle to increase the competitors score. This will be at the discretion of the head judge.

3-1     Each vehicle must be capable of being registered, licensed/tagged to drive on a Hwy.

3-2     The vehicle must be capable to drive into the judging lanes. In other words, the vehicle must be able to propel itself using the engine and OEM or equivalent drive train.

Notice - If the vehicle breaks down either at the show or on the way to the show or if foul weather does not permit the driving or unloading of a vehicle, then the vehicle may enter the judging lanes by any means possible. This is at the sole discretion of the head judge.

3-4     Modifications to the body of the vehicle are not allowed if the modification will increase the vehicle’s interior volume. This includes, but not limited to, cutting of the floor, wheel wells and other areas that will change the interior volume of the vehicle. Airbag suspension modifications are allowed.

3-5     The judge must be able to see inside of the vehicle during the metering process to observe the metering equipment. This includes side windows and/or front window.

3-6     People are allowed to hold or sit on the vehicle while being metered provided no other rules are broken. The competitor takes responsibility for all parties involved.

3-7     OEM or equivalent door and hatch seals must be in place. They may not be added to or modified, unless specified by a particular division.

3-8     Standard door and window openings may not be sealed, taped or siliconed shut during the run. 

3-9     Competitor may switch vehicles at any point during the season. No borrowing, renting or switching vehicles for finals.

3-10   National competitors may not share a vehicle at the same event. However, they may create a “team name “ and run under that name. Only 1 vehicle may be assigned to a particular competitor and/or team per show.

Example: Competitor A may not share their vehicle and/or system with Competitor B at the same event. Also, Competitor A may not allow Team C to use their vehicle as a "team vehicle".

4-1     The audio equipment must be designed for use in a 12-Volt automotive environment.

4-2     The audio equipment must be available for purchase through legitimate auto sound businesses.

4-3     Use of wireless remote controls, IR repeaters, Bass Knobs and/or podiums is allowed in all classes.

4-4     The subwoofers must be powered by the audio amplifiers in the vehicle.

4-5     The maximum voltage of the vehicle’s electrical system can not be higher than 15.5 volts in any national class during the 30 second run. In most cases measurement will be taken at or near the amplifier. In some situations due to install or other unforeseen issues, measurement can be taken elsewhere.

Notice - Battery Limitations

• Aftermarket automotive batteries are allowed.
• Only batteries designed for automotive use such as AGM, Flooded, maintenance free & Lithium will be allowed in the Basic Divisions. Stationary batteries or non-automotive batteries such as Telecoms, UPS or batteries designed for other purposes such as wheel chairs or other commercial equipment are not permitted in the Basic Divisions.
• Batteries must be 12 volt only.
• Hybrid 3 post 12/16 volt batteries are not permitted.
• 14volt, 6volt or 2volt combinations are not permitted
• Custom home-made batteries are not allowed.
• Aftermarket battery trays and/or brackets may be installed.
• Additional batteries may be mounted in a cargo area and/or under the hood. No battery boxes underneath the vehicle permitted.
• Vehicles with batteries installed in an unsafe manner, according to the head judge, will not be permitted to compete.

4-6     The use of aftermarket alternators and external voltage regulators is allowed provided no other rules are violated. There is no limit on the number of alternators used as long as they’re all ran off the same motor, belt or chain.

4-7     External generators, battery chargers and other charging devices ( excluding alternators ) may not be used in the judging lanes or while the vehicle is being metered.

4-8    Passive radiators are allowed provided they are commercially available. They are not considered woofers and will not be counted. Custom or homemade passive radiators are not permitted.

5-1     Nothing in the sound system may interfere with the normal daily use and/or operation of the vehicle. This includes equipment on the floor or seat. See specific divisions for details.

5-2     Amplifiers may be mounted under front or rear seats as long as the installation doesn't interfere with normal operation or seating position.

5-3     No aftermarket sub amps and/or batteries may be mounted in the center console or center console area.

5-4    Subwoofer enclosures are required to be located behind the edge of the driver’s door to the edge of the passenger door referred to as B-Pillar and/or doorjamb. This is referred to as the “B” pillar rule or test.

Notice - The following test will/can be performed - “B” pillar test: A string is passed through both doors and ran up and down the doorjamb. Nothing in the audio system may interfere with this test. OEM moldings attached to the enclosure are not counted.

Notice - Non-Wall Pickup Trucks :

• Single cab pickup trucks (not an extended-cabs or king-cabs) with the subwoofer enclosure behind the front seats, the subwoofer enclosure can not be in front of the "B" pillar by more than 4" at any point.
• All other pickups ( extended-cabs, king-cabs, etc. ) the “B” pillar test is required.
• In the Basic Division all equipment must reside within the cab of the vehicle. Only batteries are allowed to be mounted in the bed of the vehicle.
• In the Basic Division full size trucks with forward facing rear seats, the enclosure shall be under or behind the rear seat. Rear seat must be in its OEM location.
• In the Advanced No Wall Division, pickups are allowed to remove or modify any part of their back seats to incorporate the sound system.

Notice - Wall Pickup Trucks :

• In the Advanced Divisions all equipment can be in the bed of the truck provided a commercially available bed cover or camper shell is used.

5-6     The cargo area in vans and SUVs will be behind the second row seating. If the vehicle does not have second row seating in place, then that vehicle can not compete in the basic division unless otherwise noted.

5-7     The audio system can not interfere with the normal operation and seating position of the vehicle. If the vehicle is an extended-cab or king-cab pickup truck with side mount seats, you do not need to be able to fold the side seats as normal operation. The side mount seats must remain in place.

5-8     In two seat vehicles such as CRX, EXP, RX7 or Corvette, all equipment ( excluding source unit and battery under hood ) must be behind the B-pillar and can't be setting behind the front seats on the floor. Equipment location is subject per division.

5-9   A speaker wall is any subwoofer enclosure that is taller than the top of the rear seat back (not including head rests) or taller than the bottom of the rear side or rear glass, which ever is lower.

Notice - Box Height

• Anything that is attached to or sitting on the subwoofer enclosure including, but not limited to, speakers, amplifiers, processors etc., is considered to be a part of the subwoofer enclosure and will count towards the “wall” test.
• Any aftermarket audio components installed to increase the competitors SPL score, that is installed in non OEM locations will be counted towards the wall test. Components installed for Mids/Highs purposes will be permitted upon judges discretion.
• If the vehicle is a two seat vehicle such as CRX, EXP, RX7 or Corvette (excluding pick up trucks), then the maximum height of the enclosure shall be 16” measured at its tallest point from the bottom of the floor. Floor build-ups in relation to box height will be at the sole discretion of the head judge.
• Vehicles such as standard cab pick, extended cab and king cab pickups the maximum box height will be at the bottom of the rear window.

5-10     Trunk vehicles may port through the rear deck utilizing existing openings only. Modifying or cutting the rear deck or OEM package tray cover is prohibited. The only allowed modification is the removal of the back of the rear seat in none folding vehicles and/or rear speakers.

5-11     Competitors may use their spare tire well to install additional equipment. This includes but is not limited to: amps, batteries, wiring, CD changers, speakers and enclosures. This area must also be available for inspection.

5-12     There is no limit on sound dampening. All sound dampening must be installed in such a manner that the OEM door panel/panels headliner must attach normally using the factory OEM tabs/screws. Rear deck lid or other places in the cargo area where there is not a OEM cover may be used. Sound dampening must be used in accordance to the manufacture's recommendation. No sound dampening shall be visible or placed on top of interior panels. Products such as Dynamat, Road Kill, Accumat are considered approved materials.

5-13     The use of duct tape or other adhesive tapes is not permitted within view of the passenger compartment or cargo area to hold panels in place, to seal gaps between panels or to cover vents

5-14     The use of, but not limited to, glue, silicone and/or additional screws is not permitted to attach OEM panels in place.

5-15     Expanding foam may only be used in limited amounts in front of the B-pillar. Expanding foam may not be used to fill any large voids such as under dashes or doors.

5-16     All batteries and capacitors are encouraged to be mounted and securely fastened for safety.

5-17     Competitors may not share same common equipment unless one competitor is out of the competition.

5-18     All subwoofer speaker wires must be capable of being inspected from the sub amp to the enclosure.

5-19     Competitors are required to have all (+) positive speaker wires going to the enclosure(s) ran in such a way that they can all be clamped at one time.

5-20     Competitors are strongly encouraged to have their installations neat in appearance. Bare wood or unfinished materials are discouraged. Recommended finish materials are: paint, carpet, Formica, Plexi, stainless steel, aluminum, vinyl. Competitors taking the time to do so will be rewarded by having photos of their vehicles posted on the official website www.midwestspl.com and other forms of media used by Midwestspl.

6-1     Competitors are classified by the components of their sound system and modifications to the vehicle.

6-2     All the subwoofers mounted behind the “B” pillar in the competitor’s vehicle will be counted to determine what class they can compete in. Subwoofers mounted in an OEM center console will not be counted. Subwoofers 10” or larger mounted in front of the “B” pillar may be asked to be disconnected or inoperable during the run.

6-3     In some classes a power rating along with the sizes of subwoofers is used. The higher of the two ratings will determine a competitor’s class.

Example: Competitor “A” has 2-10” speakers and 1000 watts. The entry level class allows for 2-10’s and 500 watts therefore the competitor would be moved up into the class that allows for 1,000 watts. However, competitors may choose to turn down their 1,000 watt amp to produce 500 watts of power during their run and remain in the entry level class.

Example: Competitor “B” has 500 watts and 4-12’s; this competitor would be in the third division because of the number and size of subwoofers.

6-4     Each competitor may compete in 1 class per division ( IE: Basic, Advanced, Xtreme, Kaos  & Mayhem ) at a regular season event as long as their particular audio system installation, vehicle regulation meets each class’s requirements.

Basic Division

Classes:

• Basic 1 – Up to 1-15, 2-12’s, 3-10’s or 4-8’s, up to 500 watts ( max clamped )
• Basic 2 – Up to 1-15, 2-12’s, 3-10’s or 4-8’s, up to 1,000 watts ( max clamped )
• Basic 3 – Up to 1-18, 2-15’s, 4-12’s or 6-10’s, up to 2,000 watts ( max clamped )
• Basic 4 – Unlimited Speakers, up to 4,000 watts ( max clamped )
• Basic Trunk - Unlimited Speakers, up to 2,000 watts ( max clamped )

7-1     CRX's are not allowed in the Basic 1-3 Divisions

7-2     Structural modifications to the passenger or cargo compartment are not permitted.

7-3     Custom installations and/or custom panels are permitted provided no other rules are violated. See rule 4-12

7-4     All windows and openings need to function normally.

7-5     Subwoofers and enclosures must be in the “cargo” area.

7-6     Subwoofers and enclosures may not sit on top of a folded rear or 2nd row seat.

7-7     Seats and seat backs must be fully functional when the enclosure is in its competition position. If the vehicle is an extended-cab or king-cab pickup truck with side mount seats, you do not need to be able to fold the side seats as normal operation.

7-8     Enclosures may be "built" into the trunk of the vehicle. However, the construction may not be permanent and must easily be able to return the vehicle to its original/OEM condition. Competitors may be asked to provide proof that the installation meets these guidelines.

7-9     Speaker walls are not permitted. See Rule 7-10

7-10   Any audio equipment used to produce SPL must be below the window line referred to as the wall test.

7-11   Two seat vehicles such as CRX, EXP, RX7 or Corvette, may have equipment, excluding the subwoofer(s) and enclosure, up to the B-pillar. The enclosure and anything attached to it must be 15” behind the B-pillar.

Exception: If the two seat vehicle has less than 24" of maximum B-pillar to back depth in the cargo area, then that vehicle may use all of the cargo area for the subwoofer enclosure and equipment installation provided no other rules are broken.

7-12   Commercial vehicles, those with no rear 2nd or 3rd row seating and/or have floor cuts such as handicap van or an ambulances are not allowed.