I. BACKGROUND:

1. Situation:

• I and my father own a motorcycle Harley Davidson Softail Low Rider and we enjoy listening to songs during our ride. My motorcycle had a Boss speaker system on it, but it was not built to produce good bass. So, I need to have a pair of sub-woofers to increase the amplitude of bass of the overall sound, especially essential for my playlist (including songs that require good bass).
• I have found no subwoofer in my motorcycle model (2018 Harley Davidson Softail Low Rider). Sub-woofers are only applied for another Harley Davidson model – Touring. However, I and my father did not choose the Touring model due to its overwhelming size and weight, which are not suitable for traffic in my country-Vietnam as well as not suitable for my father. I also could not buy the sub-woofers of Harley Davidson model – Touring to mount for my motor because of the different design. Therefore, I decide to create a pair of sub-woofers in my own way.

2. Objective:

• It must maintain the good quality of the input signal of the existing boss speakers and make the input signal quality of the (added) sub-woofers as good as that of boss speakers.
• Boss speakers and sub-woofers can be turned on/off at the same time.
• The appearance and the positions of the sub-woofers must be harmonious with those of the existing bass speakers, it should not destroy the original design. The positions must ensure that the sound of the sub-woofers is heard as well as the existing bass speakers and be convenient for electrical connection.

II. Implementation:

1. Summary:

1.1. Set up Sub-woofer cabinets and the inside:

I outline the process of setting up the sub-woofer as below:

1.1.1. Identify suitable sub-woofer position: to meet the requirement as above mention

Figure 1: Position of subwoofer (this is captured after having done the project)

1.1.2. Sub-woofer cabinets: Prepare a sample cabinet for testing, and a pair of official cabinets.

Figure 2: This shows a pair of sub-woofer cabinets.

1.1.3. Pair of sub-woofer drivers: Finding a suitable one (in terms of size and power, try to fit it in the cabinet)

Figure 3: This shows a speaker driver.

1.1.4. Pair of sub-woofer Amplifiers: Finding a suitable one (in terms of size and power, try to fit it in the cabinet)

Figure 4: This shows a sub-woofer amplifier.

1.1.5. Pair of passive bass radiators: Finding a suitable one (in terms of size, test with different size for the best performance, try to fit it in the cabinet)

Figure 5: This shows a passive bass radiative

1.2. Assembly Sub-woofer cabinet:

All the above steps were done on a sample cabinet. After all, the parts that has been tested and adjusted to fit the sample cabinet would be assembled into the official cabinets.

Figure 6: This summary how the official pair of subwoofers is made

1.3. Set up input signal for the sub-woofer system (music signal):

Connecting signal between the boss speakers and the sub-woofer amplifiers. However, the output voltage of the speakers was too high compared to the limit of the input of the amplifiers, and to address this issue, the high to low signal converter has been used.

1.4. Set up power source for the sub-woofer system (power from battery):

Connecting the sub-woofers to motor battery via a relay so that when the switch of the boss speaker (mid-treb speaker) was turned on, the sub-woofer was also turned on.