Sound insulation and vibration damping

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Introduction

The sound/noise insulation and vibration deadening properties of almost any vehicle (except high-end luxury vehicles) can be improved through the installation of various sound insulating and vibration deadening/damping materials.

Jimnys are no exception there. They are relatively cheap vehicles, and therefore all of them have relatively poor sound insulation applied from the factory.

Factory sound insulation

In Jimny 3

The factory sound insulation which is (relatively sparsely) applied to the interior of most Jimnys 3 consists of the following:

1. Bitumen compound, glued on about 70% of the floor area;
2. Small pieces of bitumen-based mats, glued on the side door outer panels and on the side panels below rear side windows;
3. Cotton scrap material (about 15 mm thick), glued on about 80% of the underside the floor carpet;
   • This material is called by various names, like "felt", "jute", "dew" ....
4. Large rubber pad (with 5 mm thick cotton scrap underlay), just placed against the "firewall";
   • A "firewall" (in this context) is the metal wall / panel between front passengers' legs and the engine;

There is no sound insulation at all on any of the interior plastic trims (side door trim, rear door trim, rear side trim below rear side windows), nor below the roof.

In Jimny 4

Info needed ...

Installation

The general principles of choosing and installing sound insulation and vibration deadening/damping materials in a Jimny are all the same as in most other vehicles.

Also don't forget to factor in the work of dismantling the interior trim and assembling it back together.

Start educating yourself on this generic world Wikipedia article.

The good news regarding Jimnys in this process are:

1. Their interior is relatively easy to dismantle;
2. They are quite small vehicles, so they need relatively small amounts of material and relatively small amount work to apply them;

Best practices on vehicle sound proofing

Introduction

The following notes and advice represent an "abridged" knowledge and experience, which are the result of reading, watching, listening to and talking to various sources and schools of thought regarding acoustic treatments, sound proofing in general, and automotive sound proofing in particular.

Important notes on proper applications

There are numerous wrong ways to do vehicle sound proofing, and only a few correct ways.

There is a high risk to end up doing it by one of the wrong ways, especially because there is a LOT of misleading information and mis-recommendations regarding these topics on the Internet.

That is mainly for two reasons:

1. Ignorance by laymen who represent themselves as experts;
   • Many of them preach their advice and principles based on faulty experiments and thus faulty conclusions, or a mix of correct and faulty principles;
   • There is also a lot of "hearsay knowledge" which has become "common knowledge" just due to the widespread of misinformation;
2. Greedy interests by sound proofing material manufacturers and professional installers;
   • Most of them aim to sell maximum quantity and/or the most expensive materials, without the regard if such quantity is justified regarding its effectiveness, or if the type of material is actually optimal for the application.

The risk of misapplication can lead to:

1. Using excessive amounts of (usually) expensive materials with no additional gain;
   • This can also result in an excessive increase in vehicle's weight;
   • This has a lasting negative impact on vehicle's performance and its fuel economy.
2. Not achieving the desired effect, thus wasting material and effort;
3. Both of the above;

Main principles of vehicle sound proofing

General points

When approaching any sound proofing project, the first step is to determine the following:

1. Types of sounds against which an insulation is desired;
2. Sources / directions of such sounds;
3. Environment factors and risks (moisture, heat, fire, toxicity, appearance, etc.);
4. Special circumstances (accessibility to the area of application, ease of future removal in case of some repairs, etc.);

Generally, these are the types of sounds encountered in a moving vehicle:

1. Various metal and plastic panel vibrations;
   • These are usually caused by engine and transmission operation, irregular road surface, and operation of audio speakers.
2. Operating noise of an internal combustion engine;
   • Diesel engines are particularly "strong" performers in this regard;
3. Exhaust system noise;
4. Transmission operation noise;
   • This means noise caused by the rotation of various gears;
5. Rolling tyre noise;
6. Air friction noise;
   • Noise of air moving underneath the vehicle, around the vehicle and over the vehicle;
7. Rain drops hitting the vehicle (roof, hood, windows, etc.);
8. Various environmental noises and sounds;
   • Examples: other vehicles passing by, people laughing on the street, animals barking, howling, roaring and squeaking on the field, angry drivers honking, a volcano erupting nearby, mines and rockets exploding in the vicinity, etc.

All these sounds can roughly be classified in three main types:

1. Low frequency (bangs, drums, hums, etc.);
2. Medium frequency (roars, shouts, hurls, howls, etc.);
3. High frequency (pitches, screams, squeaks, etc.);

No single material can block all types of sounds, nor is applicable to every surface and in every mounting position.

Therefore, applying at least two types of materials (a two layer insulation) is a minimum requirement for having any hopes of achieving a comprehensive sound insulation in a vehicle. Applying three types of materials (in three layers) provides an even better solution.

Those three types of materials /layers are:

1. A "viscoelastic" material - CLD (Constrained Layer Damper);
2. A sound absorbing material - usually a CCF (closed cell foam);
3. A sound blocking material - usually a MLV (Mass Loaded Vinyl);

Layer 1 - CLD

Notes on CLD materials:

• A viscoelastic material is the first layer, and it is usually the most expensive of the three types of materials.
• The main trick is in the viscoelastic adjective.
  • Such materials combine the properties of both viscous and elastic materials in one - they resist movement (viscous), and they return back to original shape after the deforming force has perished (elastic).
    • This means that such materials absorb relatively strong mechanical stress (vibration is a mechanical stress) relatively well, and they turn its mechanical energy into low level heat.
• Therefore, the main purpose of a CLD material is to dampen vibrations of a base panel to which it is applied (stuck onto).
  • CLD materials have relatively poor insulation properties of airborne sounds (wind howls, engine roars, people shouting, etc.).
• Vehicle manufacturers have traditionally (ever since the dawn of automobiles) used bitumen as the CLD layer with varying amounts of application inside a vehicle (depending on the price / class of vehicle).
• A much better (and much more expensive) material for this purpose is butyl, which has gained prevalence over bitumen in the 21st century.
• For CLD applications, butyl (in its raw form) is produced with a layer of thin aluminium foil.
  • Such CLD products are usually called "alubutyl".

Bitumen and butyl CLD sheets look and feel very similar, and therefore a layman can not discern any practical differences between the two materials. Therefore, many people see no reason to pay a premium price for alubutyl CLDs, when they can get classic bitumen CLDs for less than a third of the price.

Main differences between alubutyl and bitumen are:

1. Temperature dependency characteristics.
   • Bitumen is quite brittle when cold, and quite soft and squishy when warm.
   • Mechanical properties of butyl are much less temperature dependent than those of bitumen.
   • Therefore, bitumen has a risk of delaminating (partially separating or even falling off from a surface) when it gets really warm.
     • • This is especially the risk with dark-colored vehicles on hot sunny days.
       • If the bitumen partially delaminates from a metal panel, there is a high risk of moisture getting trapped in between, rusting the metal panel.
2. Installation process.
   • Bitumen (and the intended underlying surface) have to be heated up significantly with a torch or a hot air gun during installation.
     • Reason: it is the only way to make the bitumen soft and tacky enough so that there is a hope of adhering it properly to the surface.
   • Raw butyl is naturally quite "tacky" and has strong self-adhesive properties.
     • Therefore, butyl does not require any additional adhesives and does not require heating up with a hot air gun when applying (as long as the environment temperature during application is over approx. 12-15 degrees Celsius).
     • This difference also makes the installation of alubutyl CLDs much easier and faster than bitumen CLDs, especially in awkward and hard to reach areas (example: inside doors).
3. Material's vibration damping performance varies significantly based on its hardness.
   • Therefore, bitumen loses a significant amount of its intended performance (because it becomes too stiff or too soft) whenever the ambient temperature is outside of its "normal" range (15-25 C).
   • Butyl, having a more consistent hardness through a wide temperature range, is a more uniform performer.
4. Risk of corrosion promotion.
   • If a CLD material partially delaminates from the underlying metal panel, moisture can get trapped in between, thus promoting unseen corrosion.
   • Bitumen carries a certain risk of delaminating in the future even if applied properly (see more above).
   • Butyl sticks so well to a surface (when applied properly) that there is practically no chance of moisture ever coming in between it and the underlying surface.
5. Odor emission and toxicity.
   • Bitumen, being a type of tar, usually stinks on tar whenever it gets quite warm.
     • Apart from being unpleasant, tar smells are usually not really healthy.
   • Butyl never emits any kind of odor.
6. Ease of removal.
   • Butyl is much easier to remove in the future than bitumen (in case that some repairs on the bodywork are needed).
     • Only bare hands and a lot of pulling are required (plus some minor cleanup of some of the remains by bare hands).
   • It is very hard to remove bitumen on an ambient temperature (unless chiseling it off is an acceptable method).
   • There two typical methods of removing bitumen:
     1. Hot method: Heating it up significantly with a hot air gun or a torch so it becomes super soft. Then scraping it off.
        • This is quite messy - almost like removing a hazelnut spread.
     2. Cold method: Cooling it to extreme levels (around -70 degrees Celsius) by covering it with dry ice (frozen CO2) so it becomes super brittle. Then simply shattering it with a hammer.
        • This is reported as an easiest method, but has the logistical complexity of handling the dry ice.
7. Vibration damping performance.
   • The viscoelastic performance of high quality alubutyl CLDs is usually at least twice as good as the performance of typical bitumen CLDs, even in bitumen's optimal temperature range.
   • This means that usually at least a double amount of bitumen CLD material has to be used to achieve the same vibration damping effect as a high quality alubutyl CLD.
   • This defeats bitumen CLD's cost saving advantage.
     • This is especially valid when considering the additional work of applying a double layer and the weight which the double amount of bitumen CLD material adds, permanently affecting vehicle's performance and fuel economy.

Additional notes on CLDs:

1. Beware that some CLD manufacturers do not specify the material used, and that some of them used a mix of butyl and bitumen.
   • Use CLDs only made by brand name manufacturers which clearly state to be 100% butyl (with aluminium foil) and which have good reviews.
2. The two main performance parameters of alubutyl CLDs are MLF (mechanical loss factor - vibration damping "strength") and its temperature dependency, which should be observed in correlation.
   • • Therefore, when comparing two different CLDs, an ideal method would be to have the "MLF to temperature dependency" graphs for both of them.
     • If such graphs are not available, but only single MLF values, then it makes sense to compare those individual MLF values only if both are stated for the exact same temperature.
     • For example, it is invalid to compare MLF of alubutyl product A to MLF of alubutyl product B if MLV A is stated for 25 degrees C and MLF B is stated for 15 degrees C.
3. When choosing an alubutyl CLD, prefer those which have some sort of physical embossment pattern on their aluminium layer (usually repeated honeycomb or rectangles).
   • This pattern serves as an indicator during the installation.
     • When alubutyl is pressed in using a pressure roller tool during the installation, the embossed ribs in the aluminium foil largely disappear if pressed in properly.
     • This indicates that that area of the CLD has been pressed in properly for permanent and complete surface adhesion.
4. Look for the specification of aluminium foil's thickness.
   • Preferred thickness is around 100 ym, while thickness of around 60 ym usually represents a cheap / budget solution.
5. Beware that there are some specialized alubutyl CLDs with relatively thin butyl layer and relatively very thick aluminium foil (around 0,3 mm or even more).
   • These CLDs are not optimal for vibration damping of solid panels - they are instead meant to seal large technological holes /cavities in the bodywork and to structurally strengthen the metal panels around the hole.
     • Typical application example is when there is a high performance speaker in a door.
       • The inner door cavity serves as a "box / enclosure" for the speaker, and sealing its technological opening and strengthening the surrounds improves the acoustic performance of the speaker.

Layer 2 - sound absorbers

To be written ...

Layer 3 - MLV

To be written ...

Recommended additional works

While you are having the rear interior of the car dismantled in order to install sound insulation, you might use the opportunity to perform some additional modifications along the way:

• Installation of a pair of rear speakers;
• Rust protection of the body cavities through the application of wax for example;
  • Note: Do not apply anything on the panels on which you intend to apply sound deadening materials!
  • After applying sound deadening materials and letting them cure for a while, you might apply small amounts of wax on any remaining exposed naked parts of the body panels;
• Rear cabin lamp installation and wiring;
• Installation of wires for rear parking sensors, tow bar, rear reversing camera, concealed GPS tracking unit, 12 V DC charging outlet in the trunk, whatnot, etc.

Examples of Jimnys with applied sound insulation

Most of these examples have been stumbled upon on the Internet. No evaluation of the quality or purposefulness of the work in them has been performed!

• Example 1 on a Jimny 3 from Russia;

References

Until this article gets properly written, gather some more knowledge at the following forum topics:

• Bonnet insulation;
• Sound deadening;
• Vaxxi's sound proofed Jimny;

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Page last edited on 21/05/2019 by user Bosanek