Sound insulation and vibration damping

The content of any article might be expanded / improved in the future - revisit it sometimes.
Seen a mistake? Know something that isn't written? Edit and change this article yourself!
Some images in the article (if present) can be enlarged by clicking on them.

This article is just an embryo. It is an idea for someone to "pick up" onto and to expand the article further.

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 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" (the 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, so educate yourself about them elsewhere. 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 and listening 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 proper 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;
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, which has a lasting negative impact on vehicle's performance and 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. Internal combustion engine noise;
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. Environmental noise;
   • Examples: other vehicles passing by, people laughing on the street, animals barking, howling, roaring and squeaking on the field, a volcano erupting nearby, mines and rockets exploding in the vicinity, etc.

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

1. Low frequency (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 position.

Therefore, applying least two types of materials (in two layers) are 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 - 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.
• The main trick is in the viscoelastic adjective.
  • Such materials combined the properties of both viscous and elastic materials in one - they resist movement, and they return back to original shape once deformed.
    • 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 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 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.
• In CLD applications, butyl (in its raw form) is paired with a layer of thin aluminium foil, and that is 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:

• Mechanical properties of butyl are much less temperature dependent than those of bitumen.
  • Bitumen is quite brittle when cold, and quite soft and squishy when warm, while butyl is much less susceptible to temperature variations;
    • Therefore, bitumen has a risk of delaminating (partially separating or even falling of from a surface) when it gets really warm.
      • This is especially the risk with dark-colored vehicles on hot sunny days.
      • If the bitumen delaminates from a metal panel, there is a high risk of moisture getting trapped in between, rusting the metal panel.
• Bitumen (and the intended underlying surface) have to be heated up significantly with a torch or a hot air gun during installation, as it is the only way to make the bitumen soft and tacky enough so that it can adhere to the surface.
• Material's vibration damping performance varies significantly based on its hardness.
  • Therefore, bitumen loses a significant amount of its intended performance whenever the ambient temperature is outside of "normal" range (15-25 C).
• Raw butyl is naturally 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 10 degrees Celsius).
    • This makes the installation of alubutyl CLDs much easier and faster than bitumen CLDs, especially in awkward and hard to reach areas (example: inside doors).
  • Butyl sticks so well to a surface when applied properly that there is no chance of moisture ever coming in between it and the underlying surface.
• Bitumen, being a type of tar, usually stinks on tar when it's quite warm.
  • Apart from being unpleasant, tar smells are usually not really healthy.
  • Butyl never emits any kind of odor.
• Butyl is much easier to remove in the future than bitumen (in case that some repairs on the bodywork are needed).
• Finally, the viscoelastic performance of high quality alubityl CLDs is usually at least twice as good as the performance of typical bitumen CLDs, even in their 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, especially when considering the additional weight which the double amount of CLD material adds, permanently affecting vehicle's fuel economy.

Additional notes on CLDs:

• 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.
• 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, the embossed ribs largely disappear if pressed in properly, thus indicating that that area of the CLD has been pressed in properly for permanent and complete surface adhesion.
• Look for the specification of aluminium foil's thickness.
  • Preferred thickness is 100 ym, while thickness of around 60 ym represents a cheap / budget solution.
• Beware that there are some specialized alubutyl CLDs with 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 meant for sealing large holes for speaker enclosures.
    • Perfect application example is sealing large technological holes in side doors, if there are high performance speakers in the doors.

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;

---

Page last edited on 14/05/2019 by user Bosanek