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HASIB'S ARTICLES AND AUDIO PROJECT REVIEWS
12” SEALED SUBWOOFER Introduction This subwoofer project started out as a subwoofer for my home theater and for music too. This is an absolutely passive subwoofer system (with no passive filter at all, so there will be no crossover detail) that powered externally using 35-watt rms power amp (based on TDA 2050 IC). The signal feeds from EAS subwoofer processor/controller. Back to history this is the ported subwoofer for my very old HT system. Because the EAS subwoofer controller need a sealed subwoofer to work properly so I must block the port and derived to sealed alignment. Using tools to measure Small-Thiele parameters I’m able to obtain its. Design Goals And Criteria As with all my projects, I start with a list of goals, which then guides my design.
The Driver (update) This is very old 12” driver that I found in my store room and I decide to make a subwoofer driver. On the beginning of this project I’m unable to measure the parameters (just beginners). At last (on early 2001) I’m able to measure its myself. I found that the driver is suitable for sealed box alignment. I’m very lucky that I can still use this driver for my current project. Here are it Small-Thiele parameters
If you have tools handy and want do the measurements yourself follow this link Measuring loudspeaker driver parameters ESP The Enclosure The enclosure is made by two sheets of 11-mm thickness plywood with that layered together to give thickness of 22-mm. The external dimensions are by 42.5-cm high by 42-cm wide and by 44.5-cm deep. Internal volume is 1.789 cubic feet or 51 litres. I gone to ported enclosure for archieving maximum bass output capabilities. Building the enclosure was straight forward. I increase the height about 3.6 cm cause I want maintained the golden ratio for the enclosure that may look nice. Procedures in heightning the height; I cuts 12-mm plywood measures 5-cm x 5-cm for three of them (I got it height about 3.6-cm), nailed them together and nailed it at bottom of the enclosure; these 5-cm x 5-cm plywood cubes will act as the holder for the subwoofer’s feet. I cut the 12-mm plywood about 46-cm for the front panel x 1 and 45-cm for the side panel x 2. I attached it to another plywood, still measured the same and nailed it at the bottom of the subwoofer enclosure. I cut the plywood with the external dimension shown above and attached the joint using nails and lots of wood glue. I glued all the joints for avoiding leaky air. After the glue dried I attached the front panel and using heavy-duty knife/rough and medium pile to remove the rough joints. I cut the hole for the driver and the vent where it will be sat on the front panel - using jig saw. I clean the cutting edges using file and sandpaper. The vent measured by 8-cm diameter and 12-cm long. It’s actually tune to 40Hz. The speaker terminal located on back panel. After finishing the enclosure box I sealed all joints using masking tape to keep it from uglying my eyes. I spray the enclosure with flat black spray paint. I attached the driver, vent and speaker terminal after the paint dries. The driver needs large wood screws for secure the driver tightly to the front panel for keep it from vibrates. Say, I just finish the subwoofer! No heavy sweat running for making this subwoofer unless for cutting the panels and working with pile. For the subwoofer’s feet I use PVC that diameter about 8-cm, 10-cm long and put original feet-base under the PVC and lastly screwed with long screws for three of them. For the speaker terminal I use binding post terminal because it’s joints more solid than spring clip terminal. Here is the driver/port and speaker terminal arrangements:
The grill Grill included in these project caused the front panel/sub driverlooks ugly enough without the grill. I just made simple grill but the side’s cutted about quarter round for keeping the grill look nice. I keep the grill about 5 mm away from the side front’s panel to keep it fits the front panel neatly. I know I made one mistake here, the grill covers the port that blocked the air coming out. Remake new grill is not the answer. If I push the sub hard I will pull-out the grill. What a mess isn’t it? Enclosure Updates After I have found that the driver is good for sealed box, I take out the port and sealed the port hole with thick plywood and use lots of wood glue to secure it. Just that? Actually no, again I’m very lucky that from optimum sealed box calculations, I need to reduce internal volume about 4 liters. It is easy to make the volume smaller by adding suitable packing but to make it larger, that would be difficult. The Result As I mentioned earlier, this is my first subwoofer project and I don’t expect much by it performance. No measurements were ever made. Instead I simply listened, looked and felt the result. I connect this subwoofer to the amplifier and hit music. At first I experienced boomy bass coming through it and with a lot of midbass/midrange. I tuned the EAS controller for more pleasant output. Sound well defined now. I turn to video mode. During T-Rex munching in Jurassic Park, this subwoofer gives me good bass that I really feel the T-Rex footsteps. After several weeks experienced with my new subwoofer, I felt the subwoofer is good for movies and music's too. Completed Project Pictures
Fig1 - !2" Sealed Subwoofer (Front View)
Updates I have several modifications on this subwoofer system. I mount 120-watt(4-ohm) plate power amplifier/EAS subwoofer controller at the back panel. So it didn’t need external power amplifier. You can read the article for 120-watt (4-ohm) plate power amplifier that published somewhere in my article column. 6/5/2002
Fig2 - !2" Sealed Subwoofer (Rear View) Muhammad Hasib bin Md. Nor 1999 Any Comment And Question Email to : hasib_tangkak@yahoo.com
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