HASIB'S ARTICLES AND AUDIO PROJECT REVIEWS

• 6-CHANNEL POWER AMPLIFIER
• STEREO POWER AMPLIFIER - 120 WATT (4 OHM)
• BLOCK DIAGRAM FOR MY HT SETUP
• 3-WAY ACTIVE CROSSOVER/STEREO SUBWOOFER CONTROLLER
• MULTICHANNEL POWER AMPLIFIER 35 WATT RMS x 6 CHANNEL
• 2-WAY CENTER SPEAKER
• 12" PASSIVE VENTED SUBWOOFER
• 3-WAY MAIN SPEAKER SYSTEM
• 10" SEALED SUBWOOFER (PART 1)
• 10" SEALED SUBWOOFER (PART 2)
• 12" SEALED SUBWOOFER
• 120-WATT PLATE POWER AMP
• SURROUND SPEAKER
• KENWOOD SS3300 AV PROCESSOR MODIFICATIONS
• TRI-AMP MAIN SPEAKER AMPLIFICATIONS
• 3-WAY ACTIVE CROSSOVER/STEREO SUBWOOFER CONTROLLER EAS MKII
• PICTURES GALLERY OF HASIB'S TRI AMP AUDIO SYSTEM

12" PASSIVE VENTED SUBWOOFER

Introduction

This subwoofer project started out as a subwoofer for my home theater and for music too. Along the way I learned few things about working with subwoofer enclosure. It is my first time in designing my own subwoofer system. 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 that the frequency has been cutted about 80 Hz.

The design is straight forward, no special techniques available in making this subwoofer enclosure. During the construction I made several mistakes. I will avoid them the next time around in making my another "true" subwoofer enclosure. I started this project in the middle 1999. Before I begin this construction I only have little information on how to make good subwoofer boxes. Since before the information on how to make the good subwoofer are hard to find on the Internet, I try my own. Now, there are many pages available on the line today that make life a little easier.

Design Goals and Criteria

As with all my projects, I start with a list of goals, which then guides my design.

1. Low cost. When I started this project, I did have real need for another subwoofer since my another subwoofer does not match with good subwoofer criteria. It only has criteria for woofer only. Since this was targeted for home theater use and not for high
   fidelity, I was willing to sacrifice some quality to keep cost down. Overall costs is about RM 120.
2. Easy to build. Nothing overly fancy. The enclosure is about as simple as it gets; though it turned out to be more difficult to work because it is my first time working on subwoofer enclosure.
3. Use existing parts where possible. If you like making stuff, you know what I mean when I say that I always seem to have "stuff lying around" wanting to be used. This goal is also consistent with 31 above. I already have the 12" woofer, feeds for the subwoofer and speaker terminal.
4. Decent SPL capabilities. It needs to have enough output to enjoy movies.

The Driver

I already have a 12" woofer lying dusty and decided to make it as subwoofer driver. I have not much information's on this driver, the specifications that only I have is, maximum power handling is 60-watt, 4 Ohm of input impedance, treated paper-cone with a foam surround. I believe this driver manufactured in China based on the label on top of the magnet structure. I have listened the sound coming through this woofer with raw setup and it good for subwoofer driver. The X-max is not long enough so I fed it with small power amplifier. If I fed it with large power, it tends to bottoms up because the driver has limited eqursion. No Small-Thiele parameters (fs, Qts, Vas etc) involved in this construction. That's the problem when you use cheap driver, usually the manufacturer didn't include that important parameters. You can measure them yourself if you have tools (ie frequency sweeper, DVM, frequency meter etc). I'm unable to do that since I don't have frequency meter/frequency counter handy. I just build the box and have a listen. If you have that 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 rough surface 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 liters. I gone to ported enclosure for achieving 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 heightening the height; I cuts 12-mm plywood measures 5-cm x 5-cmfor 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 cube 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 nail 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 at the 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 with no first layered background 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. I found the original feet-base lying around and use it in this speaker project. 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 for:

The Grill

Grill included in these project caused the front panel/sub driver looks 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?

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. After hearing heavy pounding bass with dance tracks, 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 too. Although the EAS subwoofer controller is not designed for vented sub is still work but not as good as sealed sub.

The Costs

No	Items and Quantity	Price in (RM)
1	11-mm x 1200-mm x 2400-mm plywood x 1 sheet	42.00
2	12" woofer (already available)	30.00
3	Binding post speaker terminal x 1	05.00
4	Flat black spray paint x 2	10.00
5	Miscellaneous	30.00
Total Costs		117.00

Lessons Learned

In making good enclosure for subwoofer, the enclosure
needs internal bracing cause the subwoofer has bad press inside the enclosure that makes panels vibrate (especially front/back panel). The panel thickness from 22-mm plywood are good but the enclosure still need internal bracing. It comes very annoying when the box will vibrate during listening period that kills our joy. Adding mass to the top decreased the vibrations; sitting on it removed all of it. Vent also needs serious tuning for letting the reinforcement air not coming through it that makes a lot of noises and worstly wrongly tuned the sound that gives boomy bass. From my experience if use vented speaker configuration please select larger port, this will keep the rushing air noise coming out from it.

Tweaking

I put some kind of hard/ thick masking tape behind the subwoofer's feet to keep the enclosure from rocking and introduce vibrations from the panels. Yeah, it's work.

Links to ESP page

1. EAS subwoofer controller
2. Measuring loudspeaker driver parameters

Author

Muhammad Hasib Md. Nor 1999

Any Comment And Question Email to : hasib_tangkak@yahoo.com