Introduction: Stage Monitor
Today we build some stage monitor boxes and here are some things we need.
brad nailer (air compressor)
paint brush and roller
4 sheets of plywood
truck bed liner paint
4 pole mount brackets
4 15" speakers
4 horns and compression drivers
Step 1: Planning
First things first these layouts were originally intended for my eyes only hence them being so crude. I apologize for my illegible handwriting and scribbled designs.
This is the hardest part of the project, a lot of research, and math involved. Firstly figure out what you want out of your project. What materials you already have or would like to use? (speakers, horns, wood, handles, hardware, etc.) What designs are going to be suitable for your needs, budget, and performance of the speakers you are using. All speakers have Specs. that you can usually find online some place, you need to know them to get the best performance out of your speaker.
That being said, In my own project I had some JBL TR 225 speakers laying around that weren't getting used, so I decided to take them apart and build monitors out of them. Therefor making a copy of the monitor in the same TR line saved me some time on air space calculations and port tuning as the horns I am using have them built in. I did not find the plans for the box itself, so I had to reverse engineer it from only the measurements found in the manual pdf I found on line and adjust for the type of wood I planned on using.
Getting these measurements down can be time consuming, and will most likely wrack your brain with some geometry questions you have long forgotten. So do your self a favor and brush up on your triangle calculations. All angles in a triangle will equal 180 degrees, and base x height =area of triangle. If you have three measurements, either angle degrees, or length of the sides, you can find all other measurements of your triangular wedge. This instructable is pretty straight forward, all 45's and 90's so cuts and math is fairly simple.
Determine how big all sides of your boxes are, by first figuring out what pieces will be on the outside that all other pieces will attach to. These will be the only pieces true to their original measurements. Then by taking the total box size and subtracting the thickness of your material from that, this will give you the width of all inside boards. For instance 3/4" plywood = 1 1/2" off the inside box width. Once again outside boards measured as-is no subtraction needed.
Once you have all your side measurements, make a cut list in order to fully utilize your sheets of plywood, and to determine how many sheets you will need.
Step 2: Cutting
Note: I got excited on 1 box and slapped it together before I cut the hole for the speaker... bad idea... way harder to cut once it is built.
First things first lay out your cut list on a piece of paper to see how it best fits the pieces of wood you have. Then measure out the pieces on your plywood. Use a chalk line to get fast straight lines but remember what bob says. "measure once cut twice" ...oh wait no that's not it "measure twice cut once" ah whatever just don't screw up it costs money.
My cut list consisted of:
4 fronts, 16.75" x 28.25" with inset holes cut out for the horn, ports and 15" speaker
8 long sides, (inside) 28.25" x 6.25"
8 short sides,(outside) 18" x 15.25" ( I cut the 15.25 a little long knowing I was going to trim later maybe 16")
4 longer backs (one long side cut at 45° angle), 28.25" x 13"
4 shorter backs that have been trimmed material thickness shorter in order to make an even 90° (one long side cut at 45° angle) 28.25" x 12 3/8"
Step 3: Building the Box
Now all the cutting is done and its time to make it look like something resembling a box. Lets start by marking a chalk line across all 4 sides of the box at 2 3/8 inches. (this was the measurement I needed in order to get enough clearance for my horn to be protected by the edge of the box yours may be different) This line will be for drilling holes in the sides to connect to the front. I used 4 screws for the short sides and 5 for the longer ones. Use your discretion on how many you want to use but use a countersink bit, and wood glue on all your holes and seams.
We can start by gluing and screwing the long sides of the box making sure the ends are flush to the front.
Then the short sides to the front, flush with the long sides.
And then the short sides to the long sides, you can guess the center of the depth for this one.
Next we screw the two flat ends of the backs together, leaving the 45° angles open to sit flush with the sides of the box.
Slip the back into place making sure to glue the long edges of the sides before hand so you can get at them.
Once you place the back you want to screw the panel in a way that will keep the back as flush to the sides as possible, this can be tricky due to any mis-cuts or board warping. On the same note do this quick before the glue dries, so you can use the air nailer to secure the back to the long sides.
Next we trim the short sides to the back of the box with a jig saw or a flush bit for the router.
Finally we take the round over bit on the router and trim all of the edges. If you have never used a router before, practice on scrap wood to get the depth of your bit correct, know the direction you need to move, and how to keep your router flush to the surface you are cutting.
Step 4: Painting the Box
Painting the box will involve a few steps but lets start with the items we will need to do so.
1. 1 gallon flat black primer
2. a can of Bondo
3. calking gun and calk (2 full tubes maybe 3 should do it)
4. paint brush, small roller, and paint tray
5. 1 gallon roll on truck bed liner
6. sander and sand paper
7. putty knife
After finishing my boxes I realized I would have taken a different approach to this process given a second build. The boxes turned out great, but by using the wood that I did I would have liked to spread a thin layer of bondo over the whole box before painting in order to get rid of the cracks in the wood itself, or use a different type of plywood. That being said I will instruct you as how I think I should have done things.
Step 1. Bondo, mix up your bondo to specifications on the can only mix enough for 1 or 2 boxes it dries quicker than you think, so work fast. First go around the box and fill on any screw holes or gaps in your seams. Then come back and do a light coat to smooth over any imperfections in the wood. Don't worry too much about getting things perfectly smooth, but don't leave pits either you will be coming back to sand this once it dries. Don't bondo the inside of the boxes, sealing those comes in the next step.
Step 2. Calking, place a nice bead of calk on all seams on the inside of the box and smooth with a wet finger. (you will not stay clean during this process, for the calking gun won't fit in all crevices of the box so you will have to smear some by hand into the places it won't reach.) By doing this you are creating an air tight seal so the speakers and ports function optimally.
Step 3. Primer, once all is dried and sanded (possibly vacuumed for dust) pop open that can of flat black primer and get started painting the inside corners of the boxes first with a 1 1/4" brush then come back with a 2" roller for good coverage. you can do 1 or 2 coats here but I suggest 2 because primer is much cheaper than the truck bed liner.
Step 4. Duraflex or truck bed liner, be safe kids this is some potent smelling stuff, so get ventilated. If you are working with this read the instructions on dry times mine was 3 hours to recoat or be dry enough to flip and do the other side, and 5 days for full cure, you may want to recoat for extra durability but not necessary. Also no need to do the inside of the box with this either it can actually cause an odd resonance in the box.
Step 5: Hardware
Each set of handles, crossovers, amps, and pole mounts, is a little different so figure out how big of holes you need to cut before starting, and lay out as see fit. (careful not to cut too big) My handle cut out was 6.5" by 4.75" and crossover cut out was 3.25" x 4.75". As far as the pole mount goes, I set the speaker box on top of a tripod to find out where it was most stable from front to back. Then measured to the center of the pole and centered to the sides, and used my hole cutter at that cross-point .
T-nuts are a great invention, they have few spikes that lock the nut in place and also give you much more strength and stability in your projects. I used them on the pole mounts, the handles, and for speaker mounting.
Corner caps / protectors these will help keep the box from getting damaged with the bumps and bangs of the road. Usually corner caps have two or three screws depending on the type you are using, some are meant for flush 3 sides they will look like a cube and have 3 holes. Others will have 2 sides and a rounded over edge, these will have 2 screws and are used for the type of corners you see when a speaker front is recessed like the ones we are building. There are other specialty caps like 45° round overs and others, but these are the most common.
We are building monitor boxes, so the chances of someone thinking they are a rockstar from 1980 with hair flying in the wind and singing to 30,000 people with their foot firmly pressed against your speaker, is pretty high. So we need to have durable METAL grill covers for our speakers. Remember you need enough clearance so your speaker will move with out hitting the grill. (at least 5/8" from the board the speaker is mounted to)
I always try to put some foam barrier tape below my grill to dampen some noise as well, just around the outside edge where it is screwed down.
Step 6: Wiring
I used jbl crossovers pre-wired with yellow green wires. A 2way crossover meaning it cuts off certain frequencies above or below a speakers optimal range, for instance a tweeter may deliver high frequencies very well but lower ones will blow the driver itself. On the other hand the woofer may distort at higher frequencies but when crossed over it becomes stable again. There are many crossovers available, full sound systems are mostly crossed over in a 4 way system highs (tweeters), high mids(woofer), low mids (woofers), sub lows (subwoofers). most monitors will be a two way system because the bass is a sound wave that travels in a 360 degree range as to where highs and mids are more directional, therefor the person on stage needs to hear more of the (directional) sounds to create a more well rounded sound on stage behind the speaker stacks.
Anyway enough of that if you don't know why you need a monitor you will probably not be reading this Instructable soon to the next. Back to the wires on the jbl yellow is going to the tweeter green is going to the mid woofer, and if you are using a 3 way white is going to the low mid woofer.
I used double sided mounting tape on the horn and then screwed them down for two reasons one durability and two for any residual buzz from vibration of the speaker.
Also I filled the inside of the boxes loosely with polyfill in order to dampen any reverberations inside the box that may cause feedback or low level hums. ISH my ears hurt just typing that.
And time to put your speakers back in the box and see how they sound. CHECK CHECK 1 --- 2, MICROPHONE CHECK 3 --- 4
Step 7: Finished
All done, now you have some monitors you can use on stage as a floor wedge, or a side wash, or you can use them as a main pole mounted speaker for small events or parties. Thanks for the read, can't wait to see what you make next.
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