Wide Dynamic Range Compression Benefits Health And Social Care Essay

Adults with a moderate sensorineural hearing loss have a need for soft sounds to be amplified to help with clarity of speech without going over a level which the person finds too loud. Moderate sensorineural hearing loss is caused by damage to outer hair cells, which can lead to a reduced dynamic range and ultimately, recruitment. The dynamic range is the range between the threshold of hearing and the uncomfortable loudness levels (ULL). Venema (1998) refers to this as the floor (threshold) being raised and the ceiling (ULL) remaining the same. When the ULL’s are unchanged, as thresholds worsen, an irregular increase in loudness is perceived typically referred to as recruitment. In order to distinguish between different types of hearing aids and find the most suitable for this type of hearing loss we have to look to see if the hearing aids can encompass the person’s dynamic range without going over their uncomfortable loudness levels. It has been suggested that output limiting compression (CL) and wide dynamic range compression (WDRC) hearing aids are more beneficial for this type of hearing loss compared to linear hearing aids with peak clipping. Ultimately, for a moderate sensorineural hearing loss it is believed that WDRC is the most beneficial type of amplification at this time.

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The outer hair cells in the organ of Corti have been referred to as the amplifiers of the cochlea (Brownell, et al., 1985). In the absence of outer hair cell function, a moderate sensorineural hearing loss of around 40-50 dB is present (Ryan and Dallos, 1975). The most prevalent type of hearing loss in adults is presbyacusis or age-related hearing loss (Valente, et. al. 2008). Presbyacusis begins as a bilateral, symmetrical, high frequency sensorineural hearing loss affecting the outer hair cells in the basal end of the cochlea. People with this type of hearing loss tend to complain about background noises such as speech babble in a noisy pub. This can account for, what is commonly referred to as the upward spread of masking, which is caused by lower frequencies masking higher frequencies (Valente et. al., 2008). This results in softer, higher frequency sounds from speech such as consonants being masked by lower frequency speech sounds such as vowels. Presbyacusis causes a subtle decrease in hearing over time (Valente et. al., 2008) and as a result, patients do not usually attend clinics until their families notice that the television is too loud or the patient themselves realize that they cannot hear as well in noisy situations as they used to.
Hearing aids can include different types of compression circuits, which can benefit different types of hearing loss. Let’s first look at input and output compression circuits. They differ to each other depending on where the volume control is located in the circuit. Output compression circuits have the volume control before the compression takes place. This type of compression affects the compression kneepoint and the gain but not the maximum power output. It is also the type of circuit used with CL amplification strategy and is associated with high compression ratios and kneepoints. Input compression has the volume control located after the compression circuit; therefore the sound is compressed before the volume control affects the sound. This means that the kneepoint is unaffected while the gain and maximum power output are. This type of compression circuit is what tends to be used with wide dynamic range compression (WDRC) strategy and is associated with low compression ratios and kneepoints (Venema, 1998; Dillon, 2001).
The first type of compression is output limiting compression amplification. The input is linear until it reaches a high kneepoint and then it compresses the sound with a high compression ratio (Venema, 1998; Valente, et. al., 2008). This type of compression is very similar to peak clipping (PC), which is found in linear hearing aids, however it is more pleasant for the listener than PC because there is less distortion. People with normal hearing or mild to moderate hearing loss will notice that the quality of speech is more distorted with limiting when compared to people with severe to profound hearing loss who will not notice this effect as much (Dillon, 2000). In a study of 12 adults with mild to moderate sensorineural hearing loss, sound quality and clarity were improved with output limiting compression when compared to peak clipping (Hawkins and Naidoo, 1993). It is generally accepted that linear hearing aids with peak clipping no longer have a place in audiology clinics and hearing aid companies have stopped manufacturing them.
Wide dynamic range compression (WDRC) is a compression strategy that aims to amplify soft sounds by a lot, medium sounds by a moderate amount and loud sounds by a small amount (Souza and Turner, 1998). WDRC tends to give more gain to soft sounds and has fairly short attack and release times (Marriage, et al., 2005). WDRC is a nonlinear compression strategy, which tries to mimic the non-linearity of the cochlea and attempts to account for loudness recruitment with sensorineural hearing loss (Moore, et al., 1992). The threshold kneepoint is usually low at around 50 dB in order to amplify quiet sounds, compressions ratios are usually lower than 4:1 and attack and release times are short so that consonant sounds are not masked by vowel sounds (Valente, et. al., 2008). WDRC is a relatively new compression strategy that is used commonly in modern digital technology hearing aids.
There are mixed views as to whether WDRC is of more benefit than linear amplification. It has been noted in some literature that measurable benefits of WDRC include improved hearing for soft speech sounds (Souza and Turner, 1998), speech in quiet, speech in noise, more comfortable listening situations for loud speech (Moore, et. al., 1992; Davies-Venn, 2009) and improved acclimatisation (Yund et. al., 2006). In contrast it has also been reviewed that WDRC may improve audibility but not necessarily intelligibility when compared to linear amplification (Marriage, et. al., 2005; Souza and Turner, 1998). WDRC may be of more benefit for people with mild to moderate sensorineural hearing loss compared to people with severe to profound sensorineural hearing loss. This may be due to the suggestion that as hearing gets worse i.e. in severe to profound sensorineural hearing loss that temporal cues are relied on more heavily to understand speech. Since fast WDRC can change temporal cues it may be that this population of hearing aid wearers benefits more from compression limiting (Jenstad and Souza, 2005; Davies-Venn et. al. 2009).
In 1992, Brian Moore, et. al. tested twenty subjects with moderate sensorineural hearing loss, measuring speech discrimination ability in quiet and speech reception thresholds (SRTs) in noise. The subjects were fitted with two types of hearing aids: Linear amplifiers and two-band WDRC compressors. They were tested with their new hearing aids and also in an unaided condition and with their own original hearing aids. With the compression hearing aids the subjects had good speech discrimination scores at all intensity levels in the quiet and the other three conditions showed decreasing speech intelligibility as the intensity level got quieter. The WDRC aids proved to help subjects achieve lower SRTs in noise compared to the other conditions. Patients with reduced dynamic ranges also benefited from the compression hearing aids more than the linear aids in that they found the loud sounds more comfortable. When surveyed the subjects also preferred the sound of the WDRC hearing aids (Moore, et al., 1992).
Another benefit of WDRC over liner amplification is improved acclimatisation. Acclimatisation is the time it takes for the brain to get accustomed to sound from a particular type of amplification and to have increased speech recognition. Yund et. al. (2006) did an acclimatisation study with 39 subjects with mild to moderate sloping sensorineural hearing loss, who had never worn hearing aids. They showed that subjects who wore the WDRC hearing aids experienced acclimatisation, whereas the patients who wore linear hearing aids did not show any increased speech discrimination scores. They believed this was because the WDRC hearing aid was able to process the normal hearing dynamic range into the dynamic range of subjects with mild to moderate sensorineural hearing loss. After a period of wearing linear amplification, subjects were then fitted with WDRC hearing aids. These subjects still struggled with acclimatisation after a period with their WDRC hearing aids and needed extra help in the form of auditory training to get rid of the effects of the linear amplification on the brain. Overall, it was concluded that hearing aids with more sophisticated technology may be the best aids for acclimatisation (Yund, et. al., 2006).
One study compared the benefits of linear and nonlinear hearing aids with speech tests and Glasgow Hearing Aid Benefit Profile (GHABP) questionnaires. The majority of subjects preferred the WDRC nonlinear hearing aids compared to the linear hearing aids. They showed better scores on speech tests, had better speech recognition, and preferred the overall listening experience with the WDRC hearing aids. WDRC hearing aids can be programmed with fast or slow attack and release times or a combination as this can be adjusted for different channels. In this study the researchers found that there was more of a preference for slow attack and release times for the most comfort and satisfaction compared to fast WDRC (Gatehouse, et. al., 2006). In comparison, Shi and Doherty (2008) found better speech recognition scores for both slow and fast, attack and release times compared to linear hearing aids, however found no difference between scores for slow and fast times in WDRC. When attack and release times are shorter the soft speech sounds are amplified more than the louder ones. If the release time is long then the soft and loud speech sounds are amplified at the same level, which may result in the softer phonemes being masked by the louder ones (Valente, et. al., 2008). Where to set attack and release times may be different for each patient depending on their preference; however in these studies it has been shown that having attack and release times using WDRC improves speech recognition scores compared to linear hearing aids.
WDRC multi-channel hearing aids have a distinct advantage over single channel hearing aids because they have the ability to use BILL and TILL (features of WDRC) at the same time (Sandlin, 2000). BILL is the “bass increase at low levels” and TILL is “the treble increase at low levels” (Dillon, 2001, pp 169). BILL will tend to go into compression a lot more with low frequency sounds and not as much with high frequency sounds. The strategy of BILL is to allow the hearing aid wearer to hear better in background noise. TILL will go into compression more often with high frequency sounds and not as much with low frequency sounds. The strategy of TILL is to increase audibility of high frequency sounds. Both BILL and TILL used in conjunction can create a good fitting strategy for a flat moderate high frequency sensorineural hearing loss (Venema, 1998).
Dillon (2000) described two problems that can arise with WDRC hearing aids. The first problem is that while WDRC hearing aids amplify very soft speech well, they also amplify very soft background noises such as the clock ticking or the sound of clothes moving (Dillon, 2000). Fortunately with newer digital technology, hearing aids are able to separate speech from background noise more intuitively than with analogue technology. A way to deal with these very low level background noises is to use expansion. Expansion is the opposite of compression and aims to make the weakest sounds in the quietest environments unnoticeable as it is below the listener’s aided threshold (Valente, et. al., 2008). The second disadvantage is the problem of feedback being introduced when the hearing aid wearer is in a quiet environment and the gain is increased (Dillon, 2000; Valente, et. al., 2008). In the past few years digital feedback suppression/cancellation has become more sophisticated and this does not seem to be a problem with WDRC in hearing aid wearers as long as a suitable earmould is fitted.
Wide dynamic range compression has been shown to have advantages over linear amplification using compression limiting and peak clipping circuits. In some researchers opinions it has still not been unequivocally proven that WDRC is the best fitting strategy for all types of hearing loss. As levels gets worse than moderate sensorineural hearing loss, the loss of outer and inner hair cell function causes temporal cues to worsen. It is unclear whether fast WDRC may be causing distortion in speech signals due to this. What is clear is that for mild to moderate sensorineural hearing loss, most commonly observed with presbyacusis, WDRC seems to improve speech recognition in quiet, in noise, overall comfort and it is easier to acclimatise to wearing hearing aids. There is not a great amount of recent literature on the subject of the benefits of WDRC in the moderate sensorineural hearing loss category. It would be interesting to see new research conducted to determine whether there are more benefits in multichannel WDRC with newer, more intuitive, digital technology hearing aids.
 

Compression and Extension Rates of a Linear-piecewise Damper

Vibrations Lab Report

Summary

 

A Vehicle suspension system is a device that allows the car to compress and extend in response to road irregularities while keeping the body of the car stable. This gives the passengers more comfort along an irregular road. Dampers are used to absorb the energy of such shocks and dissipates them in the form of heat. This experiment investigates the compression and extension rates of a linear-piecewise damper when used on a mountain bike suspension. Investigations were carried on different configurations that have different speeds or compression values and the Force-Velocity and Force-Displacement graphs were determined using a Spring Dynamometer. The extension and compression rates were calculated linearly from a F-V graph and by integrating the area of a F-D graph and were then compared. It was found that finding the compression and extension damping rates using the energy dissipation method is more accurate as it considers each data rather than the linear method which takes the average best-fit line. The spring constant was found to be 69880 N/m with a discrepancy of 14% to the actual value.

 

 

Table of Contents

Summary

1.Introduction

2.Theory – Method

3.Results

3.1. Velocity-Voltage Calibration Factor

3.2. Spring Stiffness / Pre-Load

3.3. Spring – Damper Response at Different Speeds

3.4. Compression and Rebound Rates

3.5. Damper Response at Different Compression Rates

4.Discussion

5.Conclusion

6.References

7.Appendix

7.1. Appendix A – Force-Velocity Graphs Script

7.2. Appendix B – Force-Displacement Graphs Script

List of Tables

Table 1: Configurations for the different sets

Table 2:Energy Dissipated in Bound and Rebound and the respective Bound/Rebound Rates

Table 3:Compression and Extension Rates from F-V Diagram

Table 4: Summary of Bound and Rebound Rates using the two methods

List of Figures

Figure 1:Force vs Displacement and Force vs. Velocity for a Spring-Damper System

Figure 2: Schematic Diagram of Mono-Tube Damper

Figure 3: Amplitudes vs. Time for Set 2

Figure 4: dx/dt – Velocity Graph for Configuration 2

Figure 5: Force-Displacement for Configuration 1

Figure 6: Force-Displacement graphs for Configuration 1 and 6

Figure 7 (a)-(d): Force-Displacement Graph for Configurations 2-5

Figure 8(a)-(d): Force-Velocity Graph for Configurations 2-5

Figure 9: Force-Displacement for Configuration 5 and 7

Figure 10: Force-Velocity for Configurations 5 and 7

Vibrations occur on many mechanical systems when the system is excited or is forced to vibrate due to an external disturbance. This is mainly due to the mass, elastic and damping properties that these systems acquire. The Mechanical Vibrations are responsible for the transfer of energy between kinetic and potential energy. These vibrations may highly impact the performance and lifespan of the system. Therefore, all systems undergo vibration testing in order to assess their quality. One way of limiting these vibrations is by adding a damper. A damper dissipates the energy of the vibrations in the form of heat to avoid failures in the mechanical structures. One such example of the use of dampers is in the suspensions of a bicycle to overcome the vibration that occurs due to irregularities on the road. This report will analyze the key characteristics of a mountain bike suspension unit. [1]

The main objectives of this experiment:

To determine the Force-Displacement and Force-Velocity characteristics of the spring-damper system under sinusoidal motion cycles.

Calculate the Spring Stiffness and the Damping coefficients linearly and by calculating the energy dissipation.

Identify the non-ideal behaviours of the suspension system and to state what are the reasons behind this behaviour

Dampers used in the suspension system are designed to have different dampening rates for the rebound and compression. This gives two different gradients on a Force vs. Velocity graph where Cr is the slope of the rebound (Extension) in the negative region of the velocity and CB is the slope of the Bump (Compression) in the positive region of the velocity as shown in Figure 1. Also, on a Force-Displacement Diagram the area under the graph for the positive force represents the energy dissipated over compression and the area enclosed by the negative force represents the extension as shown in Figure 1. The negative values represent that the force is opposing the direction of motion. In this, damping coefficients are calculated both linearly and through energy dissipation. This damper is referred to as an idealized piecewise-linear damper system which is shown in Figure 2.

Figure 1:Force vs Displacement and Force vs. Velocity for a Spring-Damper System

Figure 2: Schematic Diagram of Mono-Tube Damper

Using a Suspension Dynamometer, the spring/damper is subjected to a sinusoidal displacement cycle where the frequency, compression, rebound and speed can be adjusted whereas the displacement is fixed. The compression damping absorbs all vibrations as the wheels move upward whereas the extension damping returns the wheel to its original position. This helps in making the journey of the cyclist as smooth as possible. [2]

Table 1 shows the 7 configurations which were used to evaluate the Spring-Damper System under the Suspension Dynamometer. Configuration 1includes a spring along with the damper whereas Configuration 2-5 do not have a spring. Configuration 6 and 7 are additional measurements used to be compared with Configuration 1 and Configuration 5 respectively.

Table 1: Configurations for the different sets

 

Damper Settings

 

Spring Constant

Air Pressure (psi)

Speed Setting

Compression

Extension

1

350 lbf-in /

61294 N/m

50

2

0

0

2

None

2

0

0

3

0

4

4

3.66

0

5

4

0

0

6

350 lbf-in /

61294 N/m

4

0

0

7

None

4

4

0

3.1. Velocity-Voltage Calibration Factor

The Suspension Dynamometer gives the velocity of the spring-damper system in the form of Voltage. Therefore, a calibration factor must be deduced that transfers the velocity from voltage to its S.I Unit meters per second. This was done by two methods; one method is by plotting the data given from the Suspension Dynamometer on a graph, shown in Figure 3, and the actual frequency was computed by finding the period of the sinusoidal curve. Using Equation 1, the frequency was calculated. Using Equation 2, the angular speed was calculated which was used to find the velocity in meters per second by multiplying it with the amplitude (A) as in Equation 3. Then, a calibration factor was calculated by taking the ratio of the velocity in voltage and the velocity in meters per second as shown in Equation 4.

Figure 3: Amplitudes vs. Time for Set 2
f=1T=10.6773=1.476 
Hz        Equation 1
ω=2πf=2π*1.476=9.276
rad/sec     Equation 2
V=ωA=9.276* 12.62×10–3
= 0.11707 m/s    Equation 3
Callibration Factor=Velocity in m/sVelocity in Voltage=0.11707 m/s1.892 V=0.0618
  Equation 4  

Since this method is valid for a pure sine curve only, a different method was done by differentiating the displacement numerically and plotting it against the velocity in voltage. Figure 4 shows that relationship and the calibration factor was found to be 0.0605. However, this method is prone to noise ,therefore, an average of Method 1 and Method 2 was taken to represent the calibration factor to reduce uncertainties.

Figure 4: dx/dt – Velocity Graph for Configuration 2

The average calibration factor was found by averaging the values of both methods.

Method 1: 0.0618

Method 2: 0.0605

Thus, the average value was found to be 0.0612.

3.2. Spring Stiffness / Pre-Load

Using Configuration 1, a Force – Displacement graph was plotted, as shown in Figure 5, to calculate the spring stiffness. A line of best fit was plotted, and the slope was found to be 0.06988 kN/mm. Therefore, the spring constant is 69880 N/m. It was given that the spring constant in Table 1 is 61294 N/m. This shows that there is a discrepancy of 14%.

Figure 5: Force-Displacement for Configuration 1

According to the Equation of the line, the line is a straight line that does not pass through the origin and has a y-intercept. This means that the spring has a Pre-Load of 1.33 kN. Therefore, in further calculations of a Spring-Damper, this offset needs to be compensated when processing further results.

3.3. Spring – Damper Response at Different Speeds

On a similar graph, the responses of both Configurations 1 and 6 were plotted as a form of comparison. Figure 6 shows both configurations. Using configuration 6, the slope of the line was found to be 0.07229 kN/mm. Therefore, the spring constant is 72290 N/m. The change of speed has increased the discrepancy to 17.94%.

Figure 6: Force-Displacement graphs for Configuration 1 and 6

3.4. Compression and Rebound Rates

The Compression and Rebound Rates can be calculated graphically in two different ways. Either by integrating the two enclosed areas of the ellipse that are above and below the velocity axis in a Force-Velocity graph or linearly where the two slopes of the best fit lines are calculated of a Force-Displacement graph. Both methods will be used to calculate the rates in order to identify possible sources of error and inaccuracies.

The energy dissipation method is calculated by integrating the areas enclosed by the ellipses and halving their sum. This is given by the following equation:
EPiece–wise,1–Cycle=12(πCbA2ω+ πCrA2ω)
      Equation 4

After finding the areas of both halves, it was noticed that there is a sudden change in force while there was no change in displacement. If this is to be regarded, then it will lead to significant inaccuracies in the compression rate. Therefore, the area of this rectangular gap is computed and subtracted from the area of the upper ellipse. This rectangular gap represents non-ideal behaviours such as the Coulombs friction at seals or due to thermal effects. Figure 7 (a)-(d) shows the Force-Displacement graphs for Configurations 2-5. Using a MATLAB script –Appendix A, the areas were computed and are tabulated in Table 3.

Figure 7 (a)-(d): Force-Displacement Graph for Configurations 2-5

Table 2:Energy Dissipated in Bound and Rebound and the respective Bound/Rebound Rates

 

Total Energy (J)

Lower Ellipse Energy (J)

Upper Ellipse Energy (J)

Coulombs Friction Energy (J)

Upper Energy- Coulombs Friction (J)

CB (Ns/m)

CR (Ns/m)

2

10.9092

5.0042

5.9050

4.0186

1.8864

396.9

1052.8

3

27.9345

22.1268

5.8077

3.9050

1.9027

403.5

4692.2

4

11.753

4.7904

6.9626

4.0790

2.8836

611.5

1015.8

5

34.7721

27.2220

7.5501

4.7777

2.7724

587.9

5772.7

The other method is then used to calculate the compression and extension rates which is linearly through the Force-Velocity Graph. As stated above, the compression and extension rates are different as compression damping helps the suspension absorbs road irregularity as the wheel moves upward in the stroke and Rebound damping helps the suspension to return to the proper position, after a bump or other irregularity causes the fork to compress, in a smooth and controlled motion. By taking two lines of best fit, one for the negative region of the velocity and one for the positive region of the velocity, the Extension rate and Compression rate will be deduced respectively.

Figures 8 (a)-(d) shows the relationship between Force and Velocity for Configurations 2-5 respectively. The rates are then tabulated in Table 3.

Figure 8(a)-(d): Force-Velocity Graph for Configurations 2-5

Table 3:Compression and Extension Rates from F-V Diagram

 

Slope of +ve Region

Slope of -ve Region

CB (Ns/m)

CR (Ns/m)

2

0.5845

3.3343

584.5

3334.30

3

0.5945

12.1386

594.5

12138.6

4

1.146

3.072

1146

3072.1

5

0.5432

9.8575

543.2

9857.5

Table 4 summarises the Bound and Rebound Rates using both methods, Linearly and using the energy dissipation method.

Table 4: Summary of Bound and Rebound Rates using the two methods

 

Energy Dissipation Method from Force-Displacement graph

Linear Method from Force-Velocity graph

 

CB (Ns/m)

CR (Ns/m)

CB (Ns/m)

CR (Ns/m)

2

396.9

1052.8

584.5

3334.30

3

403.5

4692.2

594.5

12138.6

4

611.5

1015.8

1146

3072.1

5

587.9

5772.7

543.2

9857.5

3.5. Damper Response at Different Compression Rates

Configuration 7 is an altered version of Configuration 5 where the compression rate has been increased from 0 to 4. This was done to compare the dampers response at different compression rates. Figure 9 shows the Force-Displacement of both configurations and Figure 10 shows the Force-Velocity of both configurations.

Figure 9: Force-Displacement for Configuration 5 and 7

In Configuration 1, the spring was found to have a pre-load of 1.33kN which has caused an offset. Therefore, it was compensated for when the results where being processed. Moreover, the preload is what makes the suspension of the bicycle work. As this allows the bicycle to push the tires down on big jumps and makes travel over terrain easier. Also, under compression, the spring load increases the contact pressure which improves traction. [3]

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The spring constant was calculated in configuration 1 by finding the slope of the linear region in the Force-Displacement graph, it was found to be 69880 N/m which has a discrepancy of 14%. The reason behind this may be defined as since the spring can’t be tested alone and the damper used has a spring-like characteristic, so the damper has contributed in changing this value. The force exerted has compressed the spring as well as the air in the damper as at high pressures, the compressibility effects of air in the damper becomes significant. This explains the discrepancy in the values as the compressed air increases the energy and gives a deviated spring constant. Moreover, when configurations 1 and 6 were compared in Figure 6, the lower ellipse of Configuration 6 was deformed which illustrated that at higher frequencies the air in the damper gets compressed more and has led to a greater discrepancy in the spring constant. This has illustrated the characteristics of the damper where it has spring-like characteristics at high frequencies as the air inside is compressible. [4]

The Coefficients of Bump and Rebound were found in two different methods, Linearly and using the Energy dissipation method using the Force-Velocity and the Force-Displacement graphs respectively.  Table 4 shows that the coefficient of bump i.e. the damping coefficient upon compression using the two methods was approximately the same, whereas the coefficient of the extension was found to vary considerably between the two methods. This is because the negative region of the Force-Velocity Graphs followed a linear behaviour whereas the positive region had deviated away from the linear region as a result from the non-ideal behaviour, as shown in Figure 8 (a)-(d). Since the linear approximation methods finds the line of best fit for half-cycle where the slopes represent the damping coefficient of extension and compression, Cb was found to differ significantly. On the other hand, the energy dissipation method finds the area of the half-cycle and the damping coefficients are deduced. This is more accurate as it takes each set of data into account rather than taking the average best fit line.

The Force-Displacement and the Force-Velocity graphs shown in Figures 8 and 9 do not match the ideal graphs that are shown in Figure 1. As the damper was changing from an extension to a compression, the Force-Displacement graph shows there is a sudden rise in the force at a constant displacement which resulted in a rectangular area between the ellipses. Also, in the Force-Velocity graphs there was a gap between the two linear regions. This was due to the non-ideal behaviour of the Spring-Damper system such as coulombs friction which is the friction that occurs between the piston and seal as shown in Figure 2. Another non-ideal behaviour was the increase in the compression damping rate which was due to the increase in pressure as there was an axial load acting on the damper called the piston side force. [5]

Table 4 shows that the Rebound Coefficient in 5 is much larger than that of Configuration 2, this explains the response of the damper at different frequencies. At a high speed, the damper underwent agitation much faster than Configuration 2, which generated a high force and air in the damper was compressed. Since the force is related to the acceleration and this has led to the deficiency of oil flow. Also, Configuration 3 has a higher extension rate which has also increased agitation and has led to a high Rebound coefficient  compared to configuration 2. [6]

When Configuration 5 and 7 were compared, Configuration 7 showed a greater area enclosed for both the upper and lower ellipse. Also, the rebound and bump slopes from the force-velocity graph were higher as the slope was steeper. This shows that at a higher compression turns, air is more readily compressed in the damper and this increases the energy giving inaccurate coefficients.

Although the procedure in calculating the coefficients included two methods, the two methods have resulted in varying values and the energy dissipation method was proven to be a better approach. A further step to improve accuracy is to add lubrication between the piston and seal to overcome the Columb’s Friction. Moreover, replace the damper with a one that has a higher damping effect and air inside doesn’t compress easily. Another step that must be done is to repeat each configuration more than once and take an average of the values to improve the accuracy

 

 

 

[1]Ngowmpo, R., 2018. University of Bath. [online] Moodle.bath.ac.uk. Available from: https://moodle.bath.ac.uk/pluginfile.php/785983/mod_resource/content/6/Section1_Elements_of_vibration_systems.pdf [Accessed 13 Nov. 2018].

 

[2]Pan, M., 2018. University of Bath. [online] Moodle.bath.ac.uk. Available from: https://moodle.bath.ac.uk/pluginfile.php/1253929/mod_resource/content/1/SolidMech3_Lab_guidance_notes-2018.pdf [Accessed 13 Nov. 2018].

 

[3]Anon, 2018. [online] Available from: http://accutuneoffroad.com/articles/spring-preload-matters/. [Accessed 17 Nov. 2018].

 

[4]Dixon, J., 2008. The Shock Absorber Handbook. Hoboken: John Wiley & Sons, Ltd.

 

[5]Reimpell, J., Stoll, H. and Betzler, J., 2001. The automotive chassis. Oxford: Butterworth Heinemann.

 

[6]Dixon, J., 2008. The Shock Absorber Handbook. Hoboken: John Wiley & Sons, Ltd.

 

7.1. Appendix A – Force-Velocity Graphs Script

 

 

7.2. Appendix B – Force-Displacement Graphs Script