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Soundproofing Solution for 4WD Coaches

Soundproofing Products Used

In the engine compartment:

soundproof foam with fireproof acoustic facing
Megasorber FG50GR
50mm thick acoustic foam with a grey fireproof acoustic facing

On the floor:

Self-Adhesive Vibration Isolation and Damping Sheet
Megasorber DIS8
2mm thirck self-adhesive vibration isolation and damping sheet

Onto the body panels:

Self-Adhesive Constrained-Layer Vibration Damping Sheet
Megasorber D14
2mm thick self-adhesive constrained layer vibration damping sheet

Megasorber's Next Generation Acoustic Foam

Please note: Since this project was completed, we have introduced our next generation acoustic foam:

Megasorber FM
Acoustic Foam Sound Absorbing Panel, lightweight, fireproof for engineering applications
Fire-safe, light-weight, UV and hydrolysis resistant, excellent thermal insulation, long service life, optional fluid-repellent facing

The Vehicle Noise Problem

The 4WD coaches used for outback exploration tourist trips had an extremely annoying whining noise which caused discomfort and headaches for the passengers, especially during long trips. On one occasion, the passengers refused to get back on the bus, demanding the company send a quieter bus. The whole fleet was taken out of service.

The bus builder and the chassis companies spent the next 12 to 18 months trying to fix the noise issue. Various sound insulation materials and soundproofing methods were trialed to reduce the whining noise.

After spending thousands of dollars and adding about a half tonne of extra weight to the coach, the whining noise persisted. The devastated owner then contacted Megasorber whose engineers took on the challenge.

4WD Touring Coach with Noise Problem
The 4WD coach with a high level whining noise causing discomfort to passengers. On one occasion passengers refused to get back on and demanded a less noisy bus.

Summary of the Megasorber Soundproofing Package and Noise Measurement Results

The Megasorber team developed a cost-effective system using its patented soundproofing materials and state of the art sound absorption techniques.

Soundproofing for the Floor

After removing all the old insulation materials, Megasorber DIS8 was installed on the floor. DIS8 is a unique vibration isolation and damping product developed by Megasorber. The DIS8 system provides exceptional noise reduction for the low frequency structure-borne noise as well as increase the sound transmission loss. And yet, it is only 2mm thick and it is relatively simple and easy to install.

Soundproofing in the Engine Compartment

Megasorber FG50WR-GRA was installed above the transfer case or diff hub. FG50WR-GRA is a light weight acoustic panel with a water repellent, fireproof and sound absorbing Soundmesh G8 facing (Patented). The water repellent facing makes it very easy to clean off any mud or dust.

Whist the Soundmesh G8 facing is extremely tough and durable, the Megasorber engineer added an extra expanded metal mesh in front of the product to provide double protection against rocks and stones.

Soundproofing for the Body Panels

Megasorber D14 was applied onto the body panels. It is a light weight product and designed to reduce "drumming" noise effectively.

Hear how Megasorber effectively reduced the whining noise in the touring bus:

 

Noise testing was conducted at cruising speeds of 80 km per hour (80km/h) and 100km per hour (100km/h) before (as received) and after installing the Megasorber soundproofing package. The test results are shown in the graphs below. In summary, the Megasorber Soundproofing package:

See our Understanding Noise Levels page to better understand decibel and frequency levels.

At a cruising speed of 80km/h, it is evident that:

 

Soundproofing for Buses and Coaches
L-R: The old insulation materials installed under the floor board (as received); the old insulation materials after removal; and Megasorber FG50 installed under the floor board with expanded metal mesh in front of the product to provide double protection against rocks and stones

Noise Level before and after the installation of
Megasorber Soundproofing Package
Cruising speed: 80km per hour

Graph showing noise reduction in bus travelling at 80km per hour

At cruising speed of 100km/h, it is evident that:

Noise Level before and after the installation of
Megasorber Soundproofing Package
Cruising speed: 100km per hour

Graph showing noise reduction in bus travelling at 100km per hour

Details of Soundproofing Installation and Noise Measurement Results

The Megasorber soundproofing package was installed in two separate stages. Noise testing was conducted before the first stage and after each stage.

The noise tests were conducted under the following conditions:

Stage 1: Installation of Megasorber DIS8

DIS8 is a unique vibration isolation and damping product which provides exceptional noise reduction for low frequency structure-borne noise as well as increase the sound transmission loss. It is only 2mm thick and it is relatively simple and easy to install.

The DIS8 was applied onto the substrate first. Then a top layer of 3mm thick steel plate was adhered on the top of the DIS8. Areas treated with the DIS8:

A Schematic Drawing of Installation of Megasorber DIS8 Floor Soundproofing System

Floor Soundproofing System for Bus

 

Noise Measurement Before Soundproofing
The Noise Measurement Before Installation of the Megasorber DIS8 Floor Soundproofing System

 

Noise Measurement After Soundproofing
The Noise Measurement After Installation of the Megasorber DIS8 Floor Soundproofing System

 

Test Results Before and After the Installation of DIS8

Acceleration:

  1. The primary whining noise was located at 800Hz, with a noise level at 87 dB(A).
  2. The second harmonic of this whining noise was 1,600Hz, with a noise level at 80 dB(A).
  3. The application of DIS8 reduced the primary whining noise by 6 dB(A) and the secondary whining noise by 10 dB(A).
  4. The application of DIS8 reduced the overall noise by 7 dB(A) from 88 dB(A) to 81 dB(A).

Comparison of Noise Level before and after installing Megasorber DIS8
Acceleration from 65km/hr to 100km/hr

noise level test results before and after soundproofing

Deceleration:

  1. The primary whining noise was located at 630Hz, with a noise level at 83 dB(A).
  2. The second harmonic of this whining noise was 1,250Hz, with a noise level at 86 dB(A).
  3. The application of DIS8 reduced the primary whining noise by 21 dB(A) and the secondary whining noise by 6 dB(A).
  4. The application of DIS8 reduced the overall noise by 8 dB(A) from 88 db(A) to 80 dB(A).

Comparison of Noise Level before and after installing Megasorber DIS8
Deceleration from 100km/hr to 65km/hr

noise level test results before and after soundproofing

Stage 2: Installation of Megasorber D14 and Megasorber FG50

Underside of the floor: First the cavity was filled with one layer of Megasorber FG50, a light-weight acoustic soundproofing panel with a water repellent, fireproof and sound absorbing Soundmesh G8 facing. Then the chassis metal beam was covered with a second layer of FG50. Expanded metal mesh was used on the FG50 to protect and prolong the life of the soundproofing.

A Schematic Drawing of Installation of Megasorber FG50 Under the Floor Board

Under Floor Board Soundproofing

 

Above the transfer case: 3mm steel plate was added across the chassis just above the transfer case. The underside of the steel plate was lined with Megasorber FG50. The system proved to be simple and easy to implement, even though there are even better options.

A Schematic Drawing of Installation of Megasorber FG50 Above the Transfer Case

Soundproofing for Coach Transfer Case

 

Installation of steel plate above transfer case
The Installation of Steel Plate Above the Transfer Case

 

Installation of soundproofing above transfer case
The Installation of Megasorber FG50 with Expanded Metal Mesh Above the Transfer Case

 

Step case: Megasorber D14, a 2mm thick self-adhesive vibration damping sheet, was applied onto the metal plate. Then Megasorber FG50WR was installed with 3mm thick steel plate placed on top. All edges were sealed.

Soundproofing Treatment of the Step Area

Soundproofing of Stairs

 

Metal panels: Megasorber D14 vibration damping sheets were applied onto the metal plate near the transfer case as well as on the back wall panels.

Vibration Damping Sheets Applied to Coach Wall Panels

 

Test Results After the Installation of Megasorber FG50 and D14

Acceleration:

  1. The primary whining noise was reduced by a further 7 dB(A), from originally 87 to 81 to 74 db(A).
  2. The second harmonic of the whining noise was reduced by a further 13 dB(A).
  3. The overall noise level was reduced by another 6 dB(A), ie. from 81dB(A) to 75 dB(A).

Comparison of Noise Level before and after installing Megasorber Soundproofing Package
Acceleration from 65km/hr to 100km/hr

noise level test results before and after soundproofing

Deceleration:

  1. The primary whining noise somehow increased by 5 dB(A) but still reduced overall from originally 83 to 62 to 67 dB(A).
  2. The second harmonic of the whining noise was reduced by a further 7 dB(A).
  3. The overall noise level was reduced by another 6 dB(A), ie. from 88 to 80dB(A) to 74 dB(A)).

Comparison of Noise Level before and after installing Megasorber Soundproofing Package
Deceleration from 100km/hr to 65km/hr

noise level test results before and after soundproofing

Soundproofing Project Results

Note that we envisage even more noise reduction after the installation of all the seating. We estimated this will be another 2 to 3 dB(A) of noise reduction.

Feedback from Vehicle Owner

"The test went extremely well and everyone was very impressed with the results. We had our owner Geoff and also Rob McG and Rob T on board, together with the operations staff from Broome and everyone agreed that the vehicle is now extremely quiet in general and the problem frequencies, while still present, are no longer a concern. The vehicle is now ready to go into service."

Contact Megasorber Today for a Customised Solution to Your Noise Problem