II. Implementation (continued)
2. Details:
2.1. Set up Sub-woofer cabinets and the inside:
2.1.1. Identify suitable sub-woofer position: to meet the requirement as above mentioned
I added a pair of sub-woofer cabinets to the position marked red in Figure 7
Figure 7: This shows the position of the sub-woofer being marked red.
This position is suitable as it coincide the concept of the Boss speaker, it does not change the design of other parts, and it is convenient to hang the sub-woofer (to the engine guard) as well as connecting wires, as it is close to the Boss speaker. The follwing parts of the project would explain for this.
2.1.2. Sub-woofer cabinets: Prepare a sample cabinet for testing, and a pair of official cabinets
I have used speakers which have quite big cabinets, and I would design a subwoofer with that.
Figure 8: This shows a pair of subwoofers cabinet.[1]
Figure 9 & Figure 10 shows the wiring and structure of GoHawk Speaker, whose cabinets were reused for the sub-woofer. According to these figures, there are 3 sets of wires coming out from the right GHS, and 1 from the left GHS. In the following sections, some will refer to these figures.
Figure 9: This shows the wiring and struture of the GoHawk Speaker
Figure 10: This shows the GoHawk speakers in reality.
From now until the end of 2.1.5 page 13, the pair of sub-woofer that would be used was the one in the worse condition (which has scratches), within this pair, I only used the left GHS, reason will be explained in 2.1.5 page 13. This was to test and see if everything fitted, and then came up with final solution. Then the official design would be applied on the same pair of GoHawk Speaker being in better condition (no scratches).
2.1.3. Pair of sub-woofer drivers: Finding a suitable one (in terms of size and power, try to fit it in the cabinet)
Opening the sub-woofer cabinets to measure the suitable size of the driver:
Figure 11: This shows the front of the left GHS
I firstly used my finger to pop the covering ring out. See Figure 12.
Figure 12
After taking the ring out, we can see 4 holes where 4 screws are located (See Figure 13). I then used the phillips screwdriver to unscrew them, and took the whole head which was attached to the speaker driver out.
Figure 13
Figure 14 Figure 15
After pulling the head out (See Figure 14), I used Phillips screwdriver to unscrew four screws that attached the driver to the frame (being marked red in Figure 14). After unscrewing, I measured the diameter for the driver, which was also the distance between two oppsite holes (see Figure 15), which was approx. 11.25cm, which was just below 4.5inch. So I looked for 4.5 inch sub-woofer driver (in Vietnamese, with key words ‘loa trầm 4.5 inch’, which means ‘4.5 inch bass driver’)
Figure 16[2]
Accoding to the results (see Figure 16), the red-circled one has the thickest front surround suspension
Figure 17[3]
This driver has the 100mm internal diameter (see Figure 17), which means the edge can be cut and grind (where needed) to fit the (head) frame. I will buy this one and see if it is possible.
Figure 18
This is the result after cutting and grinding at totally 8 positions, and fit the driver into the frame (see Figure 18).
2.1.4. Pair of sub-woofer Amplifiers: Finding a suitable one (in terms of size and power, try to fit it in the cabinet)
Figure 19 Figure 20
After attaching the driver to the frame (cabinet) successfully, I bought amplifiers for sub-woofer (see Figure 20). They had the dimenssion approximately fit the magnet at the back of the driver, which had the diameter of 88mm (see Figure 19 & Figure 21).
The amplifier has two rotary switch, a crossover switch[4] and a volume switch. Crossover switch would be adjusted to select the widest range of bass (from approx 250Hz to the lowest). Volume switch is set at maximum, as I cannot adjust this switch after closing the cabinet. An external volume switch (later in this project would be called Boss switch) is used to adjust the volume for the subwoofer (will be mentioned in ‘Output’, page 44).
Figure 21[5]
After purchasing them, I sticked them to the back of the drivers (see Figure 22), and connected the two wires from the terminals of the driver to the output port of the amplifier (see 1 in Figure 22 and see Figure 23) in a specified order: black wire for positive, and grey wire for negative (see 1 in Figure 22). This specification would avoid the phase cancellation in case two sub-woofers were connected in reverse order. The two rotary switches have been cut to fit in the cabinet. (see 2 & 3 in Figure 22)
Figure 22
Figure 23
After this, I closed the cabinet and saw if it fitted, and it fitted.
2.1.5. 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)
More specification on passive bass radiator and the reason I choose it can be found at Speaker Enclosure page 108 and Passive (bass) radiator page 111.
In this section, I would try to test which bass radiator suit the cabinet the most, in terms of size, design, performance. I used the left GHS (see Figure 9) to test.
2.1.5.1. First test
Firstly, I measured the total height of the speaker and the amplifier, then I estimated the maximum diameter of passive radiator that I was able to put in(so that when it vibrated, it would not touch the amplifier).
In Figure 24, the cyan dotted line passing through the top of the amplifier and cutting the cabinet shows the height of the speaker and the amplifier when the cabinet is closed. The yellow dotted line is the range for the passive radiator to vibrate (approx. 1cm each side). After measurring 90mm was roughly the maximum diameter which satisfy the requirement for vibrating (red dotted line).
But to make sure nothing went wrong such as the rubber suspension of the passive bass radiator, I used 85mm passive radiator (see Figure 25)
Figure 24
Figure 25
Figure 26 shows searching results for 85mm passive radiator (in Vietnamese) from shoppee.
Figure 26[6]
Figure 27 shows the one that I bought.
Figure 27[7]
After this I drilled a 85mm hole on my cabinet (see Figure 28).
Figure 28
And then I put the passive radiator inside, I measured the height from 4 positions to ensure that the bass radiator was not awry (see Figure 29). Then I used a hot melt glue gun to fix it in place (see Figure 30). While the glue was still hot, I then re-measured the height (similar to Figure 29) to make sure it was in the correct position. Then I waited for it to dry. Figure 31 shows the result.
Figure 29
Figure 30
Figure 31
After this, I disconnected the speaker wires from the amplifier (see Figure 32).
Figure 32
Then I connected 2 wires from speaker termanal to the wires in the cabinet (see Figure 33). At the junction of one of wires I covered it by the insulation tape, so that the circuit would not be a short circuit in case the 2 wires touch each other (see Figure 34). And then I closed the cabinet.
Figure 33
Figure 34
The other end of the wire (the wire originally in the left GHS cabinet) was the rca analog type (see Figure 35 & Figure 9), and I remembered I had a amplifer in a speaker system that connected to the sub-woofer by this type (Figure 36, S.W. stands for sub-woofer), so I decided to connect my sub-woofer to the amplifier to test it (Figure 38).
Figure 35
Figure 36
Figure 37
Figure 38
Before connecting the wire from my subwoofer, I unpluged the original wire of the speaker system first (the S.W one) (Figure 37). I then plugged my sub-woofer wire in (Figure 38).
I tested by choosing a song that has a lot of bass, I turned the bass volume to maximum (see Figure 39).
Figure 39
On testing, I found 3 problems:
There was some high-pitched noise coming from the passive radiator, and as I tried to use my finger to knock on it, there was a high-pitched noise.
The bass radiator was moving too much as it was expected which may damage the suspension, this also explain the reason for the first problem.
With this design, the hole was quite large, and the edge, when being drilled, ofcourse, would not be perfectly shaped, there might be some scratches, and the bigger the hole, the easier the scratch would be seen.
Solution:
Therefore, I decided to add some mass on the passive radiator to restrain its movement, the mass should have a plastic layer outside so that it would not generate high-pitched noise, the size of the passive radiator was kept the same. A smaller hole would be drilled.
2.1.5.2. Second Test
In order to perform the next step, I disconnected the wire from the amplifier (see Figure 40), detached the wire of the driver and the wire from the cabinet (see Figure 41), and then detached the current passive radiator by using heating gun to melt the glue (see Figure 42) (the heating gun was very hot, so I just turned it on for a few seconds, and didn’t keep it at a position for too long)
Figure 40
Figure 41
On this sample cabinet, because I has already drilled a big hole, I took the part of the cabinet that was drilled, and drilled a small hole on it (see Figure 43), and attached it back to the cabinet where I drilled by hot melt glue gun (see Figure 44).
Figure 43 Figure 44
After this, I added mass on the passive radiator, by buying the jbl extreme 2 passive radiator (see Figure 45), but this one has a too big total diameter to fit my cabinet (95mm, see in Figure 45). So I cut out the rubber suspension, took only the mass in the middle, grinded the edge of it and sticked it to my passive radiator by the hot melt glue gun (see Figure 46).
Figure 45[8]
Figure 46
And then, the passive radiator would be assemble to the cabinet (similar to the steps in Figure 29 & Figure 30 and the description just above these figures).After this, I connected them to the wires in the cabinet (similar to Figure 33 & Figure 34 and the description above these figures). And then I close the box.I then plugged my sub-woofer rca plug into the amplifier (similar to Figure 37 & Figure 38 and the description just above these figures).
I tested by choosing a song with a lot of bass, I turned the bass volume to maximum(see Figure 47).
Figure 47
Conclusion:
This test appeared to be perfect. So after this I would drill a small hole in the official cabinet, assemble the passive radiator in. I did the similar steps with both cabinets.
[1]: https://www.google.com/url?sa=i&url=https%3A%2F%2Fwww.aliexpress.com%2Fitem%2F4001359843779.html&psig=AOvVaw1tewAErDCHsnDwrnAgyjzn&ust=1673185996101000&source=images&cd=vfe&ved=0CBAQjhxqFwoTCPC4otnNtfwCFQAAAAAdAAAAABAR
[2]: https://shopee.vn/search?keyword=loa%20trầm%204.5%20inch
[3]: https://shopee.vn/Loa-siêu-trầm-4.5-inch-i.40226055.4018511408?sp_atk=e222dc56-abf9-48d2-8641-b4bdb9a5858c&xptdk=e222dc56-abf9-48d2-8641-b4bdb9a5858c
[4] Crossover switch: This is used to select the frequency range for the output of the sub-woofer amplifer.
[5] https://shopee.vn/Bảng-mạch-núm-xoay-khuếch-đại-âm-thanh-Tpa3116-100w-Tpa3116D2-Dc12-24V-i.844616927.23207024545?sp_atk=d199bee0-6541-406b-865b-f2382b4e6655&xptdk=d199bee0-6541-406b-865b-f2382b4e6655
[6] https://shopee.vn/search?keyword=màng%20thụ%20động%2085mm
[7] https://shopee.vn/Màng-loa-cộng-hưởng-bass-thụ-động-85mm-i.314046418.10108473208?sp_atk=d05359c9-2530-4a00-93a6-1f22f928960c&xptdk=d05359c9-2530-4a00-93a6-1f22f928960c
[8] https://shopee.vn/Màng-loa-Cộng-hưởng-JBL-Extreme-2-i.121774202.8908163566 | I choose this beacuse I reminded of my JBL potable speaker, and I decided to buy this.
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