A passive amplifier (or mechanical amplifier) is a device which amplifies sound without the use of power, it works like a sort of trumpet by changing the impedance of the air around the speaker to maximize the efficiency of your music player.
This passive amplifier was designed by me for my AS product design course at school. But I'll save you the hassle of writing notes after notes after notes, testing, analyzing, designing ideas, re-designing my designs and all the rest of the boring things I needed to do to get a good grade!
The project should only take a couple days to build, the amplifier is made from interlocking floor mats reinforced with resin (optional) with a 3D printed docking slot. The amplifier increases the sound from my IPad by about 30%! The total cost of the amp was about £30, but I had plenty of material left over to make another one.
YOU WILL NEED:
Foam Floor Mats- I bought a pack of 10 for £10 but only used 3 sheets (If you have the option of buying a non textured mat, the amp will have a better appearance).
Glue Gun- If you do not already have one I would recommend buying one, they are very useful!
Access To A 3D Printer- This is what I used to make the docking slot, this can be made in plenty of other ways, this is only the method I chose to use.
Resin (Optional)- This will be used to strengthen the rubber mats, it can be made without strengthening if you are only using a small device to play music from.
PVA Glue- Everyone's favourite adhesive and sealant!
Spray Paint- Choose your favourite colour to paint your amp with.
You will need some other tools such as disposable paintbrushes, craft knife (stanley knife) and a permanent marker.
Step 1: Cutting and Assembily
Start by drawing round the templates onto the foam using a permanent marker, try and put each shape close together as to not waste the foam.
Once all the pieces of the template are fully drawn out on the mat, you should have a total of 4 shapes (top bottom and two sides), use a craft knife to cut the shapes out, IMPORTANT... hold the craft knife at a 45 degree angle toward the inside of each shape, this will make sure the shapes sit 90 degrees to each other when assembled. I held the knife at an even smaller angle towards to front of the walls, this gave the front cross section curved inner walls.
You may need to do a dry fit of the parts to see if the angles are correct, if they are still too steep use a mouse sander to make the angle smaller.
Once all the pieces cave been cut out, we can glue them together. Get out your trusty glue gun and glue along each cut edge where it meets another shape, press the shape firmly in place and hold until the glue is dry. You may have to do this in stages because hot glue dries very fast so don't take on too much at once!
Step 2: Sealing and Reinforcing
Foam has a slightly rough surface to it, it has small bubbles and bumps which do not allow paints to sit well on the surface, especially if the paint is glossy or shiny; spraying straight onto the foam will result in a dull looking colour. Sealing the foam with PVA not only helps to create a nicer looking surface, but it also greatly increases the sound performance of the amplifier.
To seal the foam, simply paint layers of PVA glue onto the surface of the amplifier, leave each coat to dry completely, 3-4 coats work best with a final coat of slightly watered down glue. The amp should have a slightly shiny finish to it now and the glue will all dry clear.
Using Resin To Strengthen The Amp
If you are planning to use large devices in the amplifier such as tablets, the foam may not be strong enough to support the device. To increase the strength of the amp a layer or two of epoxy resin can be applied to the inside walls of the foam. Epoxy resin comes in a two part mixture which when combined sets into a solid plastic. Please read the quantities and ratios of your resin and note the setting time you have to work with.
Pouring half a cup of resin at a time into the amplifier and rotating it around will coat the inside of the amplifier with the resin, THIS IS A VERY DIFFICULT PROCESS but it will pay off in the end, ensure not to spill the resin on the floor, and to evenly coat the inside walls. Once set the amplifier should be very tough and able to hold larger devices.
I would recommend looking at another tutorial of slushcasting or using resin if this is your first time.
Step 3: Making the Docking Adapter
Click Here to open the 3D file in tinkercad for accommodating samsung phones.
Click Here to open the 3D file in tinkercad for accommodating an iPad.
After opening the file, save it to a file type which your 3D printer will accept, and print it! The docking port for the iPad comes in two pieces which can be glued together using the glue gun. If the part is too large for your phone to have a snug fit, you may want to consider adding a thin layer of craft foam which will also protect the device from scratching.
If you have a phone which is not supported by one of these attachments you can quite easily make your own; the aim of the adapter is to funnel as much sound as possible from the speakers on the phone to the rest of the amp (a tighter fit will have a larger amplification and will give the sound more bass) .
Once printed and assembled, the adapter can be glued into the gap on the rest of the amplifier, this should fit tightly with no air gaps, gaps are how amplification will be lost.
IF YOU DO NOT HAVE ACCESS TO A 3D PRINTER, do not worry, you can quite easily make a docking adapter using layers of wood or foam with a channel down the center, just use the measurements on the 3D file and make your own.
Step 4: Painting
Painting your amplifier is simple. Place your amp outside or in a well ventilated area on some cardboard or newspaper. Once you have selected the colour/finish you intend to use, follow the instructions on the side of the can as some paints may vary, shake the can well and spray 2-3 thin layers of paint onto the amplifier letting each layer dry in between. I would recommend using a textured paint such as the "stone effect" paint I used, this will hide any small imperfections in the foam and cover some of the gaps possibly left when gluing the pieces together.
Once dried, you're all set! Insert your device into the docking adapter and play some tunes, you will notice a large increase in volume. So put on your favourite playlist and sit back... You've made yourself a passive amplifier!
If you have any questions please ask in the comments!