The passenger compartment and listening / measurement compartment shall be one and the same. (Intent: Measurements should be taken inside the passenger compartment.)
3-2
No partitions or other barriers may divide or compartmentalize the passenger compartment. (Intent: The listening environment should approximate that found in a typical vehicle.)
3-3
The windshield and front doors to the vehicle must function as an unobstructed boundary to the passenger compartment. (Intent: The listening environment should approximate that found in a typical vehicle, where the doors and the windshield act as "walls" to the listening environment.)
3-4
The size (air volume) of the passenger compartment may not change during competition. (For example: The subwoofer enclosure cannot move forward, airbags may not be deployed, etc.)
3-5
The cabin of the vehicle may not be "pressurized" or "de-pressurized" with a gas or fluid of any type. In addition, the air inside of the cabin may not be replaced with a gas or fluid of any type.
3-6
Nothing must interfere with the placement of the measurement sensor or the use of the sensor placement jig.
3-7
All reflective surfaces, with the exception of the windshield and dashboard, must be located a minimum of 12 inches (30.48 cm) from the measurement sensor. (Intent: Reflective surfaces shall not interfere with the measurement equipment.) For clarification purposes, the dBDRA considers any surface greater than 3/8" (9.525 mm) in width to be a reflective surface.
3-8
The extent to which modifications to the passenger compartment are allowed is limited by the division a competitor is competing in. (See Section 2 entitled, "Competitor Classification System" earlier in this rulebook for a complete listing of competition divisions and classes.)
Additional Guidelines:
For clarification purposes, the dBDRA uses the term "modification" to describe changes to the vehicle that have been made in order to accommodate the sound system or to improve the competitor's score.
Some examples of passenger compartment modifications include:
Replacing the OEM glass
Replacing the OEM dashboard
Replacing the OEM seats
Reinforcing the door panels
Floor build-ups and roof build-downs
Removing or replacing the OEM center console
A Special Note on Equivalent Replacements:
There are several areas in the rulebook where the term "equivalent replacement" is used. The dBDRA considers an equivalent replacement to be a replacement that closely resembles the OEM product it replaces in both form and function. This includes structural rigidity, cosmetics, and size.
Example:
If a competitor is replacing the door panel on a vehicle, it would be acceptable for the replacement to be made of 1/8-inch (3.175 mm) thick fiber board covered with upholstery material, since the structural rigidity, cosmetics, and size of the replacement panel are similar to those of the original panel. On the other hand, a replacement panel made from 1-inch (2.54 cm) thick MDF would not be permissible because the structural rigidity of the replacement panel is different from that of the original. Please note that in this example it is not the thickness of the replacing material that dictates what is or is not acceptable. Rather, it is the similarity of the structural rigidity that was used as the metric.
A Special Note on the Installation of Speakers other than Woofers:
Speakers that are less than 10 inches in maximum diameter may be installed anywhere in the vehicle, provided their installation does not violate any other existing rule.
It is permissible to strengthen door panels at the location where speakers are installed in the doors.
Door pods are also permissible, as are custom fiberglass "build-outs" or other modifications that are made in order to accommodate speakers in the installation location.
General Restrictions Regarding Sound Damping Materials:
Sound damping materials may be used to reduce vibration when installed in accordance with the manufacturer's recommended installation instructions. In certain dB Drag Racing divisions the maximum amount of damping material that may be used at a given location is limited. (See the Passenger Compartment Restrictions section for each division for specific limitations.) Some examples of these limitations are given below.
Street Division Examples:
A Street Division competitor may use 2 layers of damping material on the inside sheet metal of his roof. However, the competitor may not use 2 layers of damping material on his roof and another 2 layers on the backside of his fiberboard headliner because this would result in a total of 4 layers of damping material in this location.
A Street Division competitor may use 1 layer of damping material on the inside sheet metal of his door and another layer of damping material on the backside of his door panel because 2 layers of damping material are allowed at any given location. On the other hand, the competitor may not use 2 layers of damping material on the inside sheet metal of the door and another 2 layers of damping material on the backside of the door panel because this would result in a total of 4 layers in the door location which is prohibited.
General Restrictions Regarding Seats:
Go-Cart seats, arcade game seats, dune buggy seats, etc. are not considered equivalent OEM seat replacements because they do not closely resemble the OEM seat in structural rigidity, cosmetics, or size.
Seats must bolted in the OEM locations of the vehicle with the exception of the Extreme Division.
A minimum separation of 30 inches (76.2 cm) must be maintained between the front surface of the seat back and the sensor location at all times.
If a seat originally came with a headrest then the headrest must remain attached to the seat during competition.
Street Stock Division Passenger Compartment Restrictions
3-9a
Nothing in the sound system may interfere with the normal use and / or operation of the vehicle in front of the B-Pillar.
3-9b
Seats may be folded for competition, but may not be removed from the vehicle. Competitors who fold their seats must be able to demonstrate that the installation of the sound system does not interfere with the normal operation of the seats that were folded.
Street Division Passenger Compartment Restrictions
3-10a
Modifications to the passenger compartment are prohibited.
Additional Guidelines:
The OEM headliner (or an equivalent replacement) must remain in place. Grille cloth, box carpet, etc. may not be attached directly to the sheet metal of the roof in lieu of the headliner.
The OEM door panels (or an equivalent replacement) must remain in place.
The OEM carpeting (or an equivalent replacement) must remain in place.
Cut-throughs in pickup trucks are not permitted.
Sound damping materials may be used to reduce vibration when installed in accordance with the manufacturer's recommended installation instructions. The maximum total thickness of sound damping material applied at any given location may not exceed 5/32 inch (4mm). The sound damping application may consist of mat-type material, spray-on material, or a combination of the two. A maximum of 2 layers of mat-type material may be used at any given location, even if the total thickness of the sound damping material(s) is less than 5/32 inch (4mm).
Expanding foam may be used sparingly throughout the vehicle to seal small openings or reduce vibration, but may not be used to fill voids or other large cavities (such as the dashboard or doors).
3-10b
Nothing in the sound system may interfere with the normal use and / or operation of the vehicle.
3-10c
Seats may be folded for competition, but may not be removed from the vehicle. Competitors who fold their seats must be able to demonstrate that the installation of the sound system does not interfere with the normal operation of the seats that were folded.
Additional Guidelines:
If a vehicle has more than 2 rows of seating, then the additional rows (3+) may be removed at the competitor's discretion.
3-10d
If the vehicle is an extended-cab or king-cab pickup truck, then the "normal use" restriction for "jump seats" that are located behind the front seat of the pickup is waived.
Additional Guidelines:
This waiver only applies to pickups that have "jump seats" located behind the front seat. The dBDRA defines a "jump seat" as an OEM seat that was designed to be folded up against the side or back of the pickup's passenger compartment.
Jump Seats may not be removed from the pickup, but they may be folded in order to accommodate the sound system.
Street Max Division Passenger Compartment Restrictions
3-11a
Modifications to the passenger compartment from the B-Pillar forward are prohibited.
Additional Guidelines:
The OEM headliner (or an equivalent replacement) must remain in place for those areas in front of the B-Pillar.
The OEM door panels (or an equivalent replacement) must remain in place for those areas in front of the B-Pillar.
The OEM carpeting (or an equivalent replacement) must remain in place for those areas in front of the B-Pillar.
Sound damping materials may be used to reduce vibration when installed in accordance with the manufacturer's recommended installation instructions. The maximum total thickness of sound damping material applied at any given location may not exceed 5/32 inch (4mm). The sound damping application may consist of mat-type material, spray-on material, or a combination of the two. A maximum of 2 layers of mat-type material may be used at any given location, even if the total thickness of the sound damping material(s) is less than 5/32 inch (4mm).
Expanding foam may be used sparingly in front of the B-Pillar to seal small openings or reduce vibration, but may not be used to fill voids or other large cavities (such as the dashboard or doors).
3-11b
The front seats in the vehicle may be folded during competition. The rear seats may be folded OR removed from the vehicle.
Super Street Division Passenger Compartment Restrictions
3-12a
Modifications to the passenger compartment from the B-Pillar forward are prohibited.
Additional Guidelines:
The OEM headliner (or an equivalent replacement) must remain in place for those areas in front of the B-Pillar.
The OEM door panels (or an equivalent replacement) must remain in place for those areas in front of the B-Pillar.
The OEM carpeting (or an equivalent replacement) must remain in place for those areas in front of the B-Pillar.
An unlimited amount of sound damping material(s) may be used throughout the vehicle provided no other applicable rules are violated. For those areas located in front of the B-Pillars, the original OEM "look" of the vehicle must be retained.
An unlimited amount of spray foam may be used throughout the vehicle provided no other applicable rules are violated. For those areas located in front of the B-Pillars, the original OEM "look" of the vehicle must be retained.
Contestants may temporarily use tape to seal their air-conditioning vents, heater vents, sun-roofs, driver-side and passenger-side windows when competing provided no other applicable rules are violated.
3-12b
Competitor's may fold or remove any of the seats in the vehicle.
The following restrictions outline what each competitor MUST do and what each competitor MAY do. All other modifications to the passenger compartment are prohibited.
3-13a
Each vehicle MUST have a dash.
Additional Guidelines:
If the dash is an OEM dash, then no external modifications to the dash may be made. (Filling the dash with expanding foam or another material for structural reinforcement purposes and/or internal bracing is acceptable as long as no other applicable rules are violated.) Vehicles incorporating the OEM dash are exempt from the following guidelines with the exception of the final bullet point which discusses the relationship between the dash and the windshield.
The highest point of the top of the dash may not extend above the horizontal plane defined by the bottom of the windshield.
The lowest point of the top of the dash may not be located any lower than 3 inches (7.62 cm) below the horizontal plane defined by the bottom of the windshield.
The minimum depth of the dash at the center of the vehicle shall be 6 inches (15.24 cm) when measured from the edge of the dash to the windshield. The maximum depth shall be 16 inches (40.64 cm).
The plane of the dash bounded in the front by the firewall, in the back by the trailing edge of the dash, and for a distance of 12 inches to the left and 12 inches to the right (measured horizontally) of the sensor placement location must be completely flat with respect to the ground.
The dash must be completely solid (with no holes or perforations) and must extend front-to-back from the firewall to the trailing edge of the dash, and side-to-side from the windshield pillar on the driver's side to the windshield pillar on the passenger side.
The trailing edge of the dash (the edge of the dash that faces the passenger compartment) must be straight and perpendicular to the centerline of the vehicle when viewed from the top.
The relationship between the dash and the windshield shall be such that the sensor can be placed on the windshield and the proper distances from the sensor to the dash (4 inches or 10.16 cm) and the sensor to the windshield pillar (12 inches or 30.48 cm) can be achieved.
3-13b
Each vehicle MAY have a center console.
Additional Guidelines:
The center console may not exceed the height of the lowest part of the top of the dash.
A minimum "open space" distance of 13 inches (33.02 cm) MUST be provided at ALL points between each side of the center console and each door. (Measured horizontally and perpendicular to the centerline of the vehicle.)
Center consoles must not interfere with the "String Test". Competitors may "notch" their consoles or make the console easily removable to comply with this requirement.
If no center console is present, then the 13 inches (33.02 cm) closest to each door will be treated as the open space area.
3-13c
Competitors MAY construct a roof build-down if desired.
Additional Guidelines:
The build-down may not extend more than 3 inches (7.62 cm) below the top of the door jamb.
For those locations in front of the door (between the door and the windshield) and behind the door (between the door and the baffle board), the roof build-down may not extend more than 3 inches (7.62 cm) below the lowest part of the top of the door jamb. For doors with curved door openings, the reference point shall be defined as the intersection between two imaginary lines as shown in Figure 3-13c.
Figure 3-13c - Intersecting Reference Point for curved door openings.
3-13d
Competitors MAY construct floor build-ups.
3-13e
Competitors MAY construct a removable or flip-down panel(s) to cover the OEM foot wells.
Additional Guidelines:
In the interest of safety, competitors are encouraged not to modify the vehicle's OEM foot pedals (accelerator pedal, brake pedal, clutch, and parking brake).
3-13f
Competitors MUST maintain a minimum 30 inch (76.2 cm) vertical separation between the headliner (roof build-down) and the floor (floor build-up) at ALL locations within the passenger compartment except over the center console and the dash.
Additional Guidelines:
A 30-inch (76.2 cm) rod will be used to determine compliance. The judge will hold the rod vertically and move it around inside of the passenger compartment. If the rod's movement is impeded, then the vehicle fails compliance with this rule.
Bracing located outside of the "open space" area defined in section 3-13b shall not constitute an impediment to this test.
Figure 3-13f1 - In the above example, the top trailing edge of the dash defines the vertical plane that is used to establish the front-to-back Free Space area. (Note how the dash is NOT located completely beneath the OEM windshield location.) Not to Scale.
Figure 3-13f2 - In the above example, the OEM top windshield frame defines the vertical plane that is used to establish the front-to-back Free Space area. (Note how the dash is located completely beneath the OEM windshield location.) Not to Scale.
Figure 3-13f3 - In the above example, the top trailing edge of the dash defines the vertical plane that is used to establish the front-to-back Free Space area. This example also depicts how changes to the roof build-down and floor build-up can be made provided a minimum vertical distance of 30 inches is maintained. Not to Scale.
Figure 3-13f4 - In the above example, the OEM top windshield frame defines the vertical plane that is used to establish the front-to-back Free Space area. This example also depicts how changes to the roof build-down and floor build-up can be made provided a minimum vertical distance of 30 inches is maintained. Not to Scale.
Figure 3-13f5 - In the above example, the OEM top windshield frame defines the vertical plane that is used to establish the front-to-back Free Space area. Note the ramp that is used to transition from the trailing edge of the dash to the floor build-up. The "Rod Test" will be applied within the Free Space area bounded by the dashed lines. Not to Scale.
Figure 3-13f6 - In the above example, the top trailing edge of the dash defines the vertical plane that is used to establish the front-to-back Free Space area. Note the "ramp" that is used to transition from the trailing edge of the dash to the floor build-up. The "Rod Test" will be applied within the Free Space area bounded by the dashed lines. Not to Scale.
3-13g
Competitors MAY build-out their door panels if desired.
Additional Guidelines:
The maximum distance the build-out may extend into the passenger compartment is 6 inches (15.24 cm). (Measured from the sheet metal of the door where the OEM door panel was originally attached.)
Cavities in doors are prohibited. (A cavity is a negative build-out that protrudes into the door's interior space.)
3-13h
Competitors MAY install bracing if desired.
Additional Guidelines and Examples:
The maximum aggregate width for all bracing in front of the B-Pillars is 6 inches (15.24cm). (To determine compliance with this guideline, find the widest point on each of your braces. Next, add these maximum widths together. The total value must be 6 inches (15.24 cm) or less.)
The "open space" area defined in section 3-13b must remain free of bracing.
If the brace "Y's" into 2 or more arms, then the width of the brace shall be considered as either the sum of the widest point on each arm, or the maximum width of the single "leg", whichever is larger.
Example 1: A competitor is using a single 4" x 4" brace from the roof to the floor. The widest dimension of the brace is 4 inches, so the competitor is in compliance.
Example 2: A competitor is using a single 2" x 4" brace from the roof to the floor. The widest dimension of the brace is 4 inches, so the competitor is in compliance.
Example 3: A competitor is using two 2" x 4" braces from the roof to the floor. The widest dimension on both braces is 4 inches. The maximum aggregate width for the competitor's braces is 4 + 4 = 8 inches, which is more than is allowable.
Example 4: A competitor has a 2" x 2" brace from the dash to the ceiling, another 2" x 2" brace from the dash to the floor, and a 3rd 2" x 2" brace from the floor to the ceiling. The maximum aggregate width for the competitor's braces is 2 + 2 + 2 = 6 inches, so the competitor is in compliance.
Example 5: A competitor is using two 3" diameter pipes from the floor to the ceiling. The widest dimension of each pipe is 3 inches. The maximum aggregate width for the competitor's braces is 3 + 3 = 6 inches, so the competitor is in compliance.
3-14a
Extreme OS
Additional Guidelines:
No bandpass interiors
Flat, U, V, W walls are required
The minimum distance between the baffle board and the center console is 12 inches.
Figure 3-14a1 - "Flat Wall" example shown above.
Figure 3-14a2 - "U Wall" example shown above.
Figure 3-14a3 - "V Wall" example shown above.
Figure 3-14a4 - "W Wall" example shown above.
3-14B
Extreme OS
Additional Guidelines:
Drivers must be installed symmetrically with respect to the centerline of the vehicle.
Figure 3-14b1 - The above example shows a single driver that is installed along the centerline of the vehicle.
Figure 3-14b2 - The above example shows two drivers that are installed along the centerline of the vehicle.
Figure 3-14b3 - The above example shows two drivers that are symmetrically installed with respect to the centerline of the vehicle.
Figure 3-14b4 - The above example shows three drivers that are symmetrically installed with respect to the centerline of the vehicle.
Figure 3-14b5 - The above example shows four drivers that are symmetrically installed with respect to the centerline of the vehicle.
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