Intro: DJ Subwoofer
I will show you how me and my friend Charlie Entwistle built a subwoofer for Djing purposes! Whether you are a professional gigging DJ, or just a bedroom DJ starting out, this will work well for you! It was the first time we had done something like this, and we made a few mistakes, all of which I will point out during the instructable, but it works incredibly well, and has a very nice, loud sound. It ended up costing us about 600 dollars for everything, including the amplifier and cross over. You will need a fair bit of space to do this, and we ended up working outside in my backyard for most of the build.
Enjoy making it, and if you have any questions feel free to ask!
Step 1: Parts (part 1 - Wood and Electronics)
The first step obviously is to plan what you want to make the subwoofer out of. We decided to make it out of 3/8" particle board, as particle board won't resonate with the speaker driver and shake itself apart.
The next steps are going to be picking out what driver(subwoofer), amplifier, and crossover/lowpass filter you use. Each one of these depends on each other, and the size of the actual cabinet you build also depends on these. When choosing your driver, pick a name brand that you know is reliable, and because you are making this for DJing purposes and it will need to be loud, you are going to want a driver that has a fairly high RMS and even higher peak power rating.
The RMS is the amount of power that it can handle on a steady basis, and the peak power rating is the amount it can handle in very short bursts of time(accidentally start with the volume turned up way to high etc.). We ended up buying the Eminence Delta Pro 18-A which can be found here. We decided on this because it has a fairly high RMS rating (500), was reasonably priced, and from a reliable speaker dealer.
Once you decide on the driver you buy, you can look at the stats in order to determine the size of the cabinet you need to build. For the Delta Pro driver, it recommended a cabinet volume of 3-10.5 cubic feet, with a vent. Depending on the driver you buy, the supplier will recommend a vented or sealed enclosure, so be sure to check for that as well.
Now that you have decided on the driver you want to buy, its time to decide on the amplifier. The amplifier can be a little bit tricky because there are so many crappy amplifier brands out there, so again try to find a brand you have had good experiences with. You want the amplifier to have an RMS rating equal to or slightly higher than that of the driver. Slightly higher is probably better, so the amplifier isn't always working as hard as it can, but because we were on a tight budget, we went with the PQA4100 which has an RMS of 500 watts for an 8 ohm driver.
The resistance of the driver is another factor you have to look for when buying the amplifier and driver, because the RMS rating of the amplifier will change depending on how much resistance the driver has. The Delta Pro has a resistance of 8 ohms, so we made sure that our amplifier has an RMS of 500 at 8 ohms.
To sum up all of the above steps briefly, you want to buy a good quality driver with a high RMS and peak power rating, and then buy an amplifier that has a slightly higher RMS and peak power rating at a resistance equal to that of the driver.
The next step is to find what kind of crossover or lowpass filter you want to buy. Depending on how you wire up your entire speaker system, one might work better for you than the other, but in general the crossover can be used as just a lowpass filter if need be, so thats what we ended up getting. The function of the crossover is to separate the high frequencies from the low frequencies so that the subwoofer only plays the low end sounds, while your mid-range speakers and tweeters play all the higher frequency sounds. There are two types of crossovers that you can buy, active, or passive. Active ones are powered, and therefore you need an extra plug for them. Other than that, the only real difference between an active and passive crossover is that when wiring up an active crossover, the order is: source --> crossover --> amplifier --> speakers, whereas a passive crossover goes source --> amplifier --crossover --> speakers. Another thing to be aware of when buying a crossover is to make sure that you aren't buying a crossover that is meant to be put in a car for a car sub-woofer. We made this mistake, and had to take a wall transformer from some old piece of electronics that had the proper voltage output to power the crossover. If you are fine with getting a transformer and having a little messy wiring, you can go with the crossover we chose here, or you can do your own research to find a proper one with a wall plug included.
Step 2: Parts (part 2 - Other Stuff)
Apart from the main electronics and wood, you are gonna need a lot of other stuff as listed here:
- L brackets - around 20 to 25, depending on where you use them.
-wheels - 4
-felt - we got 3 yards from Joanne Fabrics and had some to spare
-wire mesh - we found this in the masonry section at Lowes
-about 5 feet of 12 gauge speaker wire
-quarter inch wall jack
-assorted other audio cables for connecting crossover, amplifier, and driver together
-Staple gun with a ton of staples
- 1.5 " wooden dowel for vertical support
-nuts and bolts to secure driver to the cabinet
- a short segment of 2 by 4
-lots of tools
Step 3: Designing the Cabinet
Obviously I would recommend starting out by drawing your ideas out on paper to make sure your measurements are right and whatnot. We ended up decided on building a 4th order Ported design (you can learn all about what that means here) due to its recommendation as a good design for DJing needs. The dimensions you need for the cabinet will obviously vary depending on the recommended enclosure volume, and because a 3-10 cubic foot enclosure was recommended for our driver we designed our cabinet around those specifications.
One thing we did which may or may not have been a mistake, was assuming that only the space directly behind the driver, and not the entire space including the venting passage counted in terms of the volume. Our total volume including the venting passage was around 13 cubic feet, while the volume only behind the driver was around 10, as recommended.
If the dimensions in the drawing aren't exactly right, I apologize, but here are the size of the pieces we ended up cutting out and using:
2 - 30 by 30
3- 25 by 30
2 - 25 by 25 (one of these that you use for the front will probably have to be trimmed a bit down to account for thickness of the wood)
1 - 20 by 25
Step 4: Building!
Here comes the fun part! We took our circular saw and table saw outside and got to work cutting out the pieces!
Because we wanted the L brackets on the inside, we had to use a dremel tool to cut off the ends of the screws that were sticking out of the wood once we were done.
As you go along and start putting the pieces together, I would suggest using caulk or wood filler in between the pieces of wood to keep things as tight as possible. It isn't a necessity though, because everything will be covered with felt afterwords.
As we put the pieces together, we started with the L brackets, and then used thin nails and screws along the edges as necessary.
We used a dowel in the center pointing up to give a bit more vertical support to the cabinet.
Attach everything together but the front and a side wall, you will put those on later! The side wall of your choosing will go on last.
Be wary that you will be unable to put L brackets on the last piece of wood that you put on, so make sure you secure that piece with screws, or L brackets on the outside, which is what we did.
Step 5: Cutting the Hole
This is a very difficult part, as it is generally hard to cut enormous holes in pieces of wood. In order to determine the size of the hole you need to cut, look at the specifications for the driver you bought. For the Delta Pro 18-A, it suggested a baffle hole diameter of 16.57 inches, so we rounded that up to 16.6 inches.
In order to mark out the hole, what we did was take a piece of wood, and drill a screw though it, so just a small bit was sticking out. Then we measured 8.3 inches away from that screw's tip, and drilled another screw through so a small bit poked through. Then we found the center of the board we were going to cut the hole in, placed one of the screw tips in the center, and then pressed down and turned the piece of wood to gouge a perfectly circular 16.6 inch diameter circle into the wood.
If none of that made sense to you, watch this video, and it explains how to mark a big circle.
Then we used a scroll saw to cut out the circle.
Step 6: Wheels, Wall Jack, Speaker Hook Up
For the wheels, we cut out an extra layer of particle board so they would have a bit more support from wobbling, and then put them on the wall opposite of the speaker. You don't want the wheels on the side that the speaker will be sitting on when in use because then it will vibrate itself all over the place. Having the wheels on the back side is easy enough, because you can just flip it over onto its side and then roll it wherever you want.
Solder your 5 foot cable to the wall jack, and then drill a 1 inch diameter hole in the center of the back panel, (same panel the wheels are on), and then screw it in using the two holes that should be provided. We bought a wall panel with two jacks because thats all they had, but all you need is one. I would highly suggest soldering the cable before you screw the jack on, as soldering with the jack already in will be very difficult.
We named the speaker Ms. Jackson, which is why you see it engraved on the wall jack.
For mounting the speaker, place it in the baffle hole you cut out for it, poke a pencil through the mounting holes to mark where you need to drill, and then drill the holes. Only once you have done this should you attach the front piece to the rest of the cabinet. Once you have attached the front piece, you can then mount the speaker into the big hole with the holes you have drilled.
When the speaker has been mounted, wrap the wire around the vertical dowel so there isn't too much slack banging around, and then solder the other end of the wire to the speaker. At this point I would highly recommend plugging in your amp and crossover, and testing your entire system to make sure that all your connections are solid.
If everything is working, then you can put on the final wall, or if not, pull out your multimeter and figure out what isn't working.
Step 7: Tightening Things Up/Felt/Grill/Handles
We went around with a hot glue gun and glued in between all the cracks to make things more airtight. We also used some extra L brackets on the front outside (you can kind of see them sticking out from the felt in the first picture) to secure it even more and ensure the front wouldn't shake itself off.
The next step is covering everything up with felt so it looks professional. We decided we would do it in 3 pieces. One piece that wrapped from one side wall, over the top, and over the second side wall as well. Another piece that covered just the front, and a final piece that covered both the back and the bottom. It was pretty annoying cutting everything out just right, but was fairly manageable. Make sure that you stretch the felt really tight, and then staple it down along the edges. Use hot glue for any loose flaps you can't staple. For the front piece, you can see we covered up the speaker, stapled all around it, and then cut off the piece over the speaker so we got a pretty clean hole that wouldn't stretch out and show the wood beneath it. We also put some felt inside of the vent to give a more professional appearance.
When felting the back piece, cut slits to put the wheels though, just big enough that you can slip them through, and then once they are through the felt, staple the slits back together as close to the wheel as possible to get a clean look. To cut a hole out for the wall jack do the same thing that you did for the speaker: staple all around it, and then cut out the piece covering. Once you have felted everywhere, go around with a glue gun to put any loose flaps down.
For the grill, cut out a piece that is a little bit bigger than the hole for the vent. Lay it flat on the bottom of the vent so it is sticking out, and secure it to the bottom of the vent with staples, nails, or else whatever you choose. Then bend it up and attach it to the outside edge of the top piece with staples, and then cover over the edges of the grill with felt so the edges are smooth.
The very last step would to be put handles along the sides to make it easier to pick up.
After that, you are done! Enjoy!!