Improving the Interior Sound Quality Through Sound Deadening!

    In this tech article, I detail several ways to improve the sound quality of the interior, as well as reducing the overall intrusion of road noise into the cabin. This section will be broken up into various areas of the body. Where appropriate, I will reference existing Ford parts that can be salvaged from other Ford vehicles either from a junkyard or through the dealer. The desire to improve sound quality can be two-fold; to reduce cabin noise, and to improve sound acoustics from the car's audio system. In either case, sound deadening can lead to a more luxurious and solid feeling vehicle.

(Gratuitous picture of my interior. Why wouldn't you want this to be quiet?)

Click the links to go to a specific area:
 - Hood & Engine - Mechanical Noise Isolation, Engine Harmonics
 - Floor Pan / Firewall - Sound Insulation (Deadener / Dynamat)
 - Doors (F/R) - Sound Insulation & Coating
 - Roof - Sound Insulation (Deadener / Spray)
 - Trunk & Firewall - Sound Insulation (Deadener / Dynamat)
 - Windows / Door Glass - PPG "Safe & Sound"
 - Intake & Exhaust - Mufflers, Airboxes Piping, Dampeners

- Hood & Engine - Mechanical Noise Isolation, Engine Harmonics

Although most of the items listed in this tech article help to reduce outside noise, much of noise intrusion in the cabin comes from the engine. To properly explain this, sound produced from the engine can be grouped into two categories, there is the mechanical sound that's given off by the moving parts / accessories (video), and then there is the cabin sound produced by the engine harmonics (video).

Few people if anyone are genuinely interested in the first kind of sound, that is... the sound generated through the moving parts. This includes the ticking of the injectors, the sound of the pulleys / water-pump / alternator / radiator fan, etc. This sound typically can intrude into the cabin through the firewall, often through worn or missing electrical conduit grommets. P71s typically are missing one or more of these as a result of police equipment being removed prior to sale of the vehicle. This should be checked first as anything else done on the vehicle to reduce sound would be pointless until this is fixed.

Another way to reduce engine noise is through hood insulation. All models of Grand Marquis, and all P73 and P74 equipped vehicles will already be equipped with this hood insulation (picture on right). On the other hand, the P71 Police Interceptor will be missing this insulation (picture on the left). This sound insulation greatly reduces the undesireable engine mechanical noise, and is a simple plug-and-play from the donor vehicle to the receiving vehicle. The insulation panel is held in place by 12 tree-clips.


Another item that Lincoln installed on the earlier 1st generation "whale" Town Car (98-02) was the use of plastic resonance tubes in the radiator core support. These black plastic tubes (shown below) served a dual-purpose. Known as Core Protection Shields, they provided a plastic shield between the opening to prevent water from constantly draining into the cure support hardware. In addition, these plastic shields were also installed to help cancel out any sound resonance that was caused by the radiator fan assembly which if not properly isolated by the radiator mount, would transfer back into the frame and then into the cabin. These can be easily removed by the donor vehicle and pushed into place on the receiving vehicle under the core support shroud. The part number for these shields is: F8VZ-8K223-AA.


Mechanical noise can also be eliminated through the use of an engine beauty cover (see below). Most P71s will likely have their engine beauty cover removed completely, while the beauty cover found on the LX and Grand Marquis models vary in size and shape by year. Generally, the most sought after is the one from the 2003 model year due to it's size, but that's often subjective. You can further reduce this sound by attaching foam padding to the underside of the beauty cover.

The second kind of noise discussed earlier are the engine harmonics, this is the sound that's produced through the combustion operation of the engine. Most people prefer the sound of the engine roaring through the cabin, even if muffled; however, should you prefer to reduce this sound as much as possible, there are a number of ways to help eliminate engine harmonics under the hood. Ford sells a number of different intake tubes, some more aggressively restrict sound than others. This is done through the use of sound baffles and sound attenuation chambers. Pretty much anything found on a P71 will have absolutely no sound attenuation properties whatsoever, while the more luxurious (perceived or otherwise) and newer the vehicle, the more sound chambers are added to the intake tube. Two examples of intake tubes are shown below. The 2003-2004 Crown Victoria and Grand Marquis are shown on the left, while the 05-11 Crown Victoria and Grand Marquis are shown on the right. The one on the right will provide better performance while reducing engine harmonics..


- Floor Pan / Firewall - Sound Insulation (Deadener / Dynamat)

One of the most cost-effective ways to quiet an interior, is through the use of additional insulation and sound deadener to the floor pans. Most Crown Victorias from the years of 1995-2011, come with some factory sound insulating matting. This is typically installed in the center areas of the foot-wells in both the front and rear of the vehicle's cabin. This sound deadener however only provides the absolute minimal sound deadening and can be significantly improved upon. As shown in the first two images below, Dynamat was installed throughout the floor pans of my 2002 Crown Victoria. Many stereo installers will tell you to install enormous sheets of the most expensive stuff you can buy. While this certainly will reduce road noise, it adds significant weight and does very little over and above what I have done. The trick in proper adhesive mat placement is to make sure that all thin or openly flat areas of the sheet metal are properly covered. Sometimes a small square is all that is needed to prevent sound resonance, vibration, or noise intrusion. If you don't want to spend the money on Dynamat, you can always go with adhesive tar paper, spray-on rubberized undercoating, or both for the maximum effect.

In addition to adhesive paper or rubberized spray to the floor pans, there are other components that your car may or may not have been equipped with. All P73 and P74 Crown Victorias and all models of Grand Marquis left the factory with rubber-backed foam padding that is hung on the rear-seat firewall (see image below). This foam panel is custom fitted to the floor pan of the vehicle. The panels are compatible between 1995-2011 Grand Marquis and 98-2011 Crown Victorias, and aero Crown Victorias from 1995-1997. The earlier the model, the thicker the rubber typically is. The earliest years used jute padding while the later years (98+) used a foam backing. You won't get much benefit by adding a second one on top of an already existing one, but if your car is missing this, or wasn't equipped with it to begin with (P71), adding it will help significantly. Without this, the vehicle will experience a substantial amount of noise intrusion from the trunk, particularly through driveshaft and differential whine.

Adding sound insulation and dynamat can be done in a weekend, but requires substantial dissasembly of the interior to do properly. I recommend performing this job while working on another task such as stereo wiring or seat replacement. It is not something you want to do more than is necessary. I also recommend giving the carpet a good thorough cleaning while it is out of the car.

- Doors (F/R) - Sound Insulation & Coating

One of the most commonly overlooked areas for sound intrusion, are the doors. Through the many openings in the door panels, both inside and outside, there is direct noise intrusion. This intrusion comes in from the road through the drain vents in the door, gaps in the window channels, etc. Most vehicle doors including those on the Crown Victoria, include a vapor barrier that separates the interior space and the hollow steel door. If this vapor barrier is compromised it can add a significant amount of road noise into the cabin. Besides the vapor barrier, not much else in terms of sound deadening typically exists in the doors. Unfortunately, the Crown Victoria and Grand Marquis have gone through a long-period of decontenting through the life of the platform. Generally speaking, the earlier the vehicle, the more sound-deadening that came standard. The doors are no exception to this. Examining the difference between a 1995-96 door panel to even a 2002 door panel reveals vast differences in sound deadening content and material. The jute padding in the 95-96 Crown Victoria is backed with a thick rubber/plastic layer. Although the difference may seem minimal, this small change further resists sound infiltration from the door frame. I scoured a junkyard in order to find clean interior door panel padding with the plastic layer, and I simply glued this layer onto the already existing layer of jute padding in my 2002 door panels. The older padding layer is not only a little bit thicker, but even covers more area under the doors. The before and after difference in sound quality was noticeable with only this change.

DOOR PANEL DIFFERENCES BETWEEN 95/96 and 97-02 (Click Images for Descriptions):

In addition to upgrading the inside-facing areas of the door panel, it is also crucial to take care of the inside of the door. The inner-facing side of the outer door panel is a relatively flat section of sheet metal that is very prone to noise resonance. Although most Crown Victorias and Grand Marquis should have some form of sound deadening there, this is typically nothing more than a 12"x4" piece of sticky asphalt paper. After years of exposure to ambient weather, this asphalt sheet can begin to peel away and crumble. To significantly squelch any resonance from the doors, a product called "rubberized undercoating" can be sprayed on this panel, and this was the approach I took on my 2002 Crown Victoria LX. I first peeled off any part of the factory sound matting inside the door that was either peeling or not completely attached. I then cleaned the entirety of the door panel surface (inside) with alcohol and a rag. I made sure it was completely clean, and then liberally taped off every portion of the inside of the door that I didn't want exposed or covered by the rubberized undercoating. The areas that should be protected include the drain vents in the bottom of the door, lock mechanism, window channels, etc. I proceeded to spray until the panel was covered with about 2-3 layers of rubberized undercoating. The only down-side to using rubberized undercoating is that it stinks horribly. The smell will persist for at least a month until it has had time to completely cure. The particular product that I used for this was Duplicolor's Undercoating (shown below).

- Roof - Sound Insulation (Deadener / Spray)

Another area of the car that typically gets little attention is the roof panel. The inside of the Crown Victoria's roof has absolutely no sound deadening from the factory. The only means of sound reduction is through the headliner. In the aftermarket, the biggest fix for this was simply to install a landau or carriage roof as shown here on this Presidential Edition. Using rubberized undercoating on the underside of the roof panel will give nearly the same effect as having a carriage or landau top on the car, without the look that some often find to be questionable. This will eliminate a substantial amount of sound that comes from other noise pollution both inside and outside such as highway traffic with large trucks, semis, airplanes, rain, and wind. Another positive aspect of sound insulation in the roof is improved heating and cooling and improved resistance to temperature fluctuations in the car. Many enthusiasts may also choose to put Dynamat on the inside of the roof such as in this custom hot-rod. While this certainly works, Dynamat can lose its adhesive qualities over time and the sheets can literally detach. For this reason, I recommend rubberized undercoating as the preferred method.

In additional to sound-deadening material, another approach is the addition of a Police Interceptor / P71 roof reinforcement panel. This panel came from the factory on nearly all Police Interceptors from 1998-2011 and can be easily mounted in a non-Police Crown Victoria or Grand Marquis. Some of the 2003+ CV/GMQs came with a plastic support panel which can be easily modified to work with this support panel. The original part number for the roof "REINFORCEMENT" panel is 1W7Z-5450244-BA. The panel comes with thick fibrous asphalt matting which presses firmly against the inner-roof panel. Although originally meant to help properly support emergency lights mounted to the roof, this helps brace the roof in an impact and also significantly limits vibrations from permeating throughout the roof panel. For more information on the roof panel, please visit my Ford Police / P71 Factory Roof Reinforcement Panel page.

- Trunk & Firewall - Sound Insulation (Deadener / Dynamat)

One of the more common areas to reduce vehicle cabin noise is in the trunk through additional sound insulation to the trunk walls and firewall. It is important to understand however that most of the noise generated through the trunk is as a direct result of mechanical noise produced by the vehicle. The trunk is regularly exposed to suspension noise, differential whine, and exhaust resonance. The trunk essentially acts like an enormous sound box, both amplifying and echoing the noise into the cabin. Adding Dynamat under the trunk carpet can greatly improve the elimination of sound resonance. Likewise, spraying rubberized undercoating on the inside of the quarter panels (as shown below) can also substantially improve sound quality just as we explained for the roof panel. Be sure to properly clean the panel with alcohol and metal prep to ensure proper adhesion of the rubberized undercoating.

- PPG "Safe & Sound" Door Glass

In 2004, Ford began to offer a new glass option which was listed on the order sheet as "Laminated Security Side Glass" for an up-charge of $295. This new option was available for both the Crown Victoria and Grand Marquis and included new window glass with embeded laminant. The laminant slightly increases the thickness of the glass, but provides a number of benefits which include:

- Blocks 95% of UV Rays
- 10x Impact Resistance
- Reduces Outside Road Noise

Click here to see an example window sticker from a Grand Marquis with this option.

The glass can be identified on the vehicle by locating the "Safe and Sound" print on the glass accompanied by the PPG logo. This is inscribed into the glass directly above the door handles. All moveable windows in the vehicle will have this, while the 1/4 windows will not. I have not yet installed these in my own car, so I can't even begin to give advice on how to do it; however, here is a promotional video from PPG that outlines the benefits of these laminant windows.

- Intake & Exhaust - Mufflers, Airboxes Piping, Dampeners

Exhaust is another often overlooked area for improving interior sound quality. Most automotive enthusiasts want a nice quiet interior, with a deep throaty exhaust. Because the exhaust note is ultimately generated not only from the muffler you choose, but from the air-box as well, achieving the desired result is more of a science than merely cobbling together a bunch of random parts. Resonance can begin with the design of the air box and intake tube. An air box and tube with multiple baffles will often eliminate resonance, while an open element air filter and large smooth plastic intake tube will create significant resonance, regardless of the exhaust components.

Stock Airbox

Marauder Airbox

Open Element

Ultimately, I recommend the Mercury Marauder or the 2008+ P71 air box, and a 2004 P71 intake tube for the best compromise between improved performance, exhaust sound, and cabin sound quality. This allows some low-level resonance, but only on hard-acceleration. Note: when using a 2004 P71 intake tube on a 1998-2002 model year vehicle, it is recommended that you install a low-profile oil cap to improve clearance of the oil filler.

The second half of this equation deals directly with the exhaust itself, though there are multiple facets to this as well. Generally speaking, the smoother the exhaust piping, the less non-desirable exhaust "noise" will be replicated. This is important to consider when looking for an aftermarket exhaust system. Cheap mechanically-bent pipes will often give an exhaust sound that is less desirable, while a professional mandrel-bent exhaust will give a more desirable sound (in addition to improved exhaust flow).

Muffler selection is also important in determining a desired result. The three main muffler styles are turbo, chambered, and straight-through. Each style has its own set of benefits and drawbacks. Note, the factory mufflers are a variation of the turbo muffler.

- TURBO mufflers typically use a set of perforated tubes, which often guide the exhaust gasses through the muffler in an S-shaped pattern. Although this design is more restrictive than other styles, the S-design allows the gasses to travel through more tubing for better noise reduction. Ideal for street applications, some turbo-style mufflers also incorporate a sound deadening material, which is packed around the tubes for increased muffling.

- CHAMBERED mufflers are ideal for street machines and are designed to reduce exhaust noise while providing a throaty performance sound. They use a series of inner chambers that are configured at specific lengths to reflect sound waves against each other. As the sound waves bounce into one another, they cancel each other out, causing a reduction in exhaust noise. The exact exhaust tone and noise reduction of chambered mufflers depends on the size and number of the chambers. Some manufacturers also use sound-deadening baffles or inserts within the chambers to further reduce or alter exhaust sound.

- STRAIGHT-THROUGH mufflers, or glass-packs, are designed to allow maximum flow—and horsepower. These mufflers feature a straight, perforated pipe wrapped in sound absorbing material such as fiberglass packing. This setup allows exhaust gas to flow through the pipe with very little restriction but provides almost no sound reduction than chambered mufflers. If you are reading this article, you're probably not considering straight-through mufflers.

Turbo Muffler

Chambered Muffler

Straight-Through Muffler

In addition to the proper selection of mufflers and piping, some models of the Crown Victoria and Grand Marquis were sold with resonator pipes. These resonator chambers were mounted under the trunk, just before the exhaust outlet at the bumper. Despite the name, these pipes actually reduced exhaust resonance. They were essentially small versions of the Cherry-Bomb-style mufflers placed inline between the muffler and the exhaust outlet. As best as I could identify, these resonators came stock on the LS and LSE Grand Marquis and the LX Crown Victoria when ordered with dual exhaust. These resonators were never installed on the P71 Police Interceptor.

Without Resonators

With Resonators

Finally, Ford also included "exhaust dampeners" in some models of the Crown Victoria and Grand Marquis. For the most part, the higher-end vehicles were often equipped with both front and rear exhaust dampeners, while the P71 and less expensive models were not. A fully-equipped, dual exhaust vehicle would include a total of four exhaust dampeners. This would include two (one on each side) placed in-line where the exhaust header pipes mounted to the H-pipe. Another set of exhaust dampeners were then mounted to the exhaust clamp where the muffler exited to the tailpipe. Here is where it gets tricky, not all high-end dual exhaust vehicles came equipped with both front AND back exhaust dampeners. Most dual exhaust Crown Victoria LX and Grand Marquis LS vehicles came equipped with only the front (header pipe to H-pipe) dampeners; however, the Crown Victoria LX HPP and Grand Marquis LSE typically included all four.

It gets less straight-forward with single-exhaust vehicles. Although vehicles sold with a single exhaust have only one outlet, the vehicle is essentially a dual exhaust up until after the catalytic converter header pipes. At this point, instead of an H-pipe as found on the dual exhaust vehicle, the car would be equipped with a Y-pipe. From the header-pipe to the Y-pipe the LX, GS, and LS models may have come with one or two exhaust dampeners. There was no rhyme or reason and it was entirely dependent upon what the assembly line employee decided at the moment. They are side-specific so you would want to pull the pair from a vehicle equipped with both.

So what is an exhaust dampener? The exhaust dampener essentially is a fully enclosed steel can that is mounted to an arm attached directly to the exhaust piping. This hollow can would typically help eliminate the exhaust resonance by capturing and diffusing the harmonics within the can itself, rather than the exhaust tubing. These do a surprisingly good job and I highly recommend installing these where not otherwise equipped.

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