Intro: Bent Plywood Speakers
Hello, my name is Dave and I'm an audiophile.
I love an awesome set of speakers or headphones. In fact I love them enough that I spent an entire summer building them while interning in Chicago, at Specimen Products. These are the same people that make all of Andrew Bird's speakers and various other musicians audio gear.
While interning I wanted to build my own set of speakers using similar techniques, and In doing so I learned a lot about how to make a really killer set of speakers, as well as some of the science behind making them.
So here is what you need:
1) Wood, the thicker and denser the better. Use at minimum 3/4" thick pieces of wood, also your best options for wood are also the cheapest! Go with MDF or if you want them to be a little lighter and look a little prettier go with some Baltic Birch Plywood and make sure to get the good stuff with as many layers of real wood as possible.
2) You also need a method of cutting wood, I used a table saw but if you have access to a CNC that will make your life so much easier.
3) Wood glue
4) At least one driver per speaker, since this was my first one I wanted to as simple as possible. Adding more requires a crossover and various other components that get real complicated real quick.
4.5) Also get some terminals, these and the drivers can be found at Madisound
5) A power drill, if you have one a drill press is nice too.
6) Some screws, also do not buy brass screws, I broke at least 3 or 4 heads off of them while making these.
7) Tape measure or a ruler, really you should always use these when doing any kind of hands-on project.
8) Epoxy putty, lets be honest this stuff is magical.
9) Sandpaper, another one of those "you should always have" things
10) Bending ply, for these speakers I wanted a little flair so I used some bending ply. If you want just a basic set of speakers just use more of whatever material you used for the rest of the body.
11) A disk/belt sander, in order to get the sides flush faster.
12) A jig-saw or any other saw that will allow you to cut internal shapes.
13) About 12 clamps, if you don't have any or are looking to buy some I cannot recommend quick grips enough!
14) Optional paint
There may be more things that I left out so feel free to shoot me any questions you might have!
Step 1: Making a Bending Form
To start, you should probably draw out what you are going to be making. I unfortunatly do not have those drawings anymore so I will be skipping that step, Its really just a lot of simple math.
Anyway the first thing I worked on was the bending ply, after figuring out just how big I wanted the speakers to be I cut out multiple strips of bending ply until their combined thickness was at least 3/4".
Then I started to stack up pieces of mdf and made a block that was about as thick as the bending ply was wide. I glued the stack together and gave a radius to each corner the bending ply would be in contact. By doing this we make sure that the bending ply wont bend too far and snap. Also be generous with your radius, mine were a little small so the end shape was a little more warped than I wanted.
PROTIP: If I was to do this again I would have made a lip around the edge of the form in order to keep the bending ply from shifting or twisting as it set. If you cannot tell already, that happened slightly to mine. It didn't impact the sound, but it did make working on it a little more frustrating.
Step 2: Bending the Ply
Ok so once you have your bending form take your ply and do a test run with no glue between the layers, just to make sure that everything works right. This allows you to correct errors before they happen. The glue will set fairly quick so you really won't have a chance to adjust a lot as you work.
When you have your routine down apply a layer of glue between each sheet of bending ply and clamp it down. Normally If you were to use woodglue on a woodworking project you would want a really thin layer of glue because it actually doesn't take much to have a strong connection. However when you are using bending ply, side on having excess glue, delamination is is not something you want to deal with.
There are a lot of ways to clamp these pieces down, the best method involves a positive and negative form squishing the ply together. However this can be expensive if you are doing something large, but it can be used multiple times.
The way I approached this was by using a vacuum bag. This method is great but requires a good bit of finesse as the vacuum starts because the bag may want to go in-between your ply and your form which could make your ply go all wibbly wobbly in a bad way.
The last method takes a bit more running around, but it will work great. Simply make a form that you can clamp all the way around with. Then try to clamp down as much surface area as possible.
However you decide to go about this, after you have everything glued up and clamped down let it rest overnight. The next day don't be afraid to run to your ply like a kid on Christmas morning!
PROTIP: At some point before doing the final run, add masking tape around the
form, this will help you so much when you pull the bent piece off after all the glue is dry.
Step 3: Building the Box
Alright now before I go any further you should know a couple things about how speakers and sound work.
First off the part that creates sound on a speaker is the called a driver. Drivers work by pushing air around really quickly which, causes the vibrations we call soundwaves. They come in a variety types and emphasize different sections of the sound spectrum. For example a subwoofer will hit deep bassy notes but will not hit the high pitched tones that tweeters will hit.
For these speakers I used full-range drivers and the only downside to full-range drivers is that they won't always hit those deep bass notes or those high notes as well as a speaker with multiple drivers would. Unless you are looking to have music that shakes your house you don't really need to have a speaker that goes that low.
Since we want the driver to produce a specific range of sounds we need to make sure that there are no excess vibrations. Any extra vibrations can begin to alter the sound and even negate some frequencies, leaving you with audio quality similar to putting your cell on speakerphone. This is why most high quality speakers are made from mdf or thick plywood as they are great at absorbing vibration and giving you nice clean audio. If you want to go the extra mile you can put some insulation on the inside of the speaker in order to soak up even more vibration. Drivers also require a certain amount of air in their box in order to function optimally and in order to figure out how much internal space you need you can plug in your drivers' specs into a calculator like this *click* . Then use basic math to determine your boxes dimensions based off the volume of air required (volume=length*width*height).
The last thing to learn for now is that there are multiple types of speaker enclosures. What I built was an "acustic suspention" enclosure, which is basically a tightly sealed box that produces a very clean sound. However if you wanted to add a little flavor to the sound you could add an opening and channel the sound through it. The resulting speaker would sound warmer and possibly have a little more bass. Types that use this method would include horn speakers (thats what Specimen uses) or bass reflex (most boom boxes use this style). The last major style of speaker is an open baffle, which has no enclosure at all. Imagine a plank of wood with a driver smack-dab in the middle of it... yupp... that basically sums up open baffles.
Congratulations! You now know a little bit more about speakers!
Step 4: Tricks to Building a Box
When I was designing this box I had originally thought I would be using
the bent ply for both the top and front panels of the speaker, but life happened and the bent ply wasn't done as perfectly as I wanted, no worries though! I am a pro at adapting to these sorts of situations, in other words I just cut up one more panel.
In order to make a nice sleek and clean looking box I add some dado cuts to the sides. This creates a little bit of a stronger connection, as well as making the box easier to assemble. The width of the dado should be the same as the thickness of the material you use for your box and as for the depth, I think I only went in an 1/8". Make sure you account for this depth when you are writing down your measurements for each panel!
After all the dados are made, Its time to glue up the box! To do this you want to add glue along all the dados and add one clamp on each corner of each square. It will be a pain to do, and as always do a dry run first and then move onto your final glue up.
Once the glue has dried sand each side of the box flush. Try and avoid sanding deep into plywood as you will be creating more work for yourself than necessary. If you do, paint is a pretty appealing way to disguise the horrors you create.
It should be noted that I added 2 holes to the back panel for the terminals that route power to the driver.
Step 5: Putting Things Together
When my bending ply had finished drying I found that it had been warped a little bit, to correct this I simply brought it over to a belt sander with a nice broad, flat platen and sanded the faces until they were suitably flat and perfect.
I then whipped out a jigsaw and cut a hole for the driver to go in. I could have used a hole saw but I don't think we had one the right size at the time. Four holes were popped into the bent ply that lined up with the center of each panel of the box, and if you can't guess I used those holes to screw the bent ply to the box. I also used some wood glue and made sure to fill in any gaps with woodglue and sawdust, I could have also used some other kind of filler but the sawdust worked great.
While working I kept doing test fits of the driver and found that there would be a little gap beneath it. To fix this I used some epoxy putty, making sure not to get any on the face of the driver, and filled in the gap.
Step 6: Paint
After everything had been securely attached together and I was now working with one solid entity It was time for paint. To be honest I wanted to avoid using paint, but when I was sanding down the box to make everything flush I had gone through a bit too much of the ply and it started to look pretty bad. Moral of the story, I made a lot of mistakes while working on this, but there is always a way to fix or hide your errors! The next set I make I will be able to see these obstacles much quicker and prepare for them accordingly.
Anyway I made sure to go into a well ventilated area and then attack the speakers with a coat of primer and then a coat of awesome turquoise, or perhaps its more of a sea-foam green who really can say?
PROTIP: Make sure sure you pay attention to how you apply the paint as it will probably make streaks. If you can try and keep your strokes all in the same direction.
Step 7: Installing the Driver
Ok so you got your speaker all painted up, now all that's left is to install the drivers!
I have a bit of experience soldering things but when it came to soldering wires to the drivers I was super nervous! Overheat the terminal and you may seriously damage the driver. Also as you solder it make sure that you lay the face flat on a CLEAN table, anything on the face of the driver will change how it sounds so treat it like a delicate little flower...of glass.
Once you have those all soldered up you are pretty much home free! There are some cool terminals that you can order off websites like Madisound, and assembling them is really easy, especially with that fancy little diagram I drew!
Step 8: The Final Product
After its all wired up, just screw in the driver to the box, plug it into an amp, plug the amp into your music playing gizmo, turn it up, and jam out!
Hope you learned some stuff and if you have any questions feel free to ask!