mobile phones have revolutionized music listeningonce again, but unless you're wearing headphones they simply don't have enough oompf to getthe party started. you can of course jack them into your stereosystem of choice, but there are definitely more elegant ways of pumping up the volume,like with an acoustic amplifier. don't let the term "acoustic amplifier" scareyou off, it's literally just a funnel which
wood branding irons custom, will amplify the sound coming out of yourphone. no electronics required! in this video we'll be making an amplifierfor the iphone 6, but this could be easily modified to work with many other mobile phones.
we'll start with an old horn picked up ata flea market, a sturdy piece of walnut and of course the phone. cut the walnut down roughly to size and splitthe final slab into two separate boards. if you only have access to thinner piecesof wood you can of course use two individual pieces as well. using one thick slab will make sure the splitwill be less noticeable in the end. don't worry, it will all make sense soon. sand out the rough saw marks using a discor belt sander. the surfaces should be perfectly flat onceyou're done.
prop up your top board at an angle in thevice. this is purely for aesthetics, giving thephone a bit of a lean back in the final amplifier. using a ball ended endmill mill a groove thesame width as your phone, and down into the board, but importantly not through it! it's only supposed to hold your phone in placeand a snug fit is even better. since the iphone has its speaker at the bottom,follow through with a smaller endmill and mill a slot all the way through the boardjust where the speaker sits. we also need a bigger hole further back throughthe board, which is easily drilled using a forstner bit.
double check that the speaker and the slotyou milled lines up well with the speaker on your phone. place the top and bottom boards together againand transfer the speaker slot and the hole you drilled onto the bottom board. connect the slot and the hole to mark whicharea you need to remove more material. you can use a multitude of tools for this,like a chisel or a dremel, i chose to mount an end mill on a drill press and manuallymove it around until i had removed the desired material. the idea is to create a channel from the speakerslot to the hole.
you can also file a bit on the top board toopen up the area near the exit hole. i know there are a lot of audiophiles whichwill have issues with the acoustic properties of this construction. if you require high quality amplification,this is not the route to take anyway. sand the surfaces completely smooth, makingsure there are no loose splinters or anything around the holes. time to rejoin the boards again, and you reallydon't want to use more glue than required. to be fair, i used far too much glue thanwas needed, and was worried that the squeezeout would clog up the channel between the holes.
you of course need to use enough glue to jointhe pieces well, and to make sure the glue joint in between the boards become as invisibleas possible in the final product. remember though, you can never have enoughclamps! the following day once the glue has dried you can test the amplifierfor the first time. play something on your phone and put it intothe slot. if sound is coming out the hole you're wellon your way. don't worry though, it won't be amplifiedby much yet, but we're soon going to remedy that.
let's continue to finish up the base. sand down the top, the bottom and the sidesto their final dimensions. you're likely going to be filling up the amplifierwith sawdust, but a quick burst of air should clear that right up! we can now turn our attention over to thefunnel. remember that horn from the beginning of thevideo? we're starting by disassembling it the bestwe can, and since it's just soldered together some heat and a big screwdriver comes in veryhandy. since you're going to heat up the funnel afair bit, use some heat resistant gloves as
well so you can handle it without burningyourself. remember, safety third! on this horn we lucked out and had a solderjoint which could be easily swiveled around to form the s-curve shape we're after. make sure it's aligned straight, and add alittle more solder to make sure the joint is solid. you can now also use some solder wick to removesome of the remaining solder elsewhere on the funnel. solder wick is super useful if you're workingwith electronics as well, as it makes removing
parts from circuit boards very easy. figure out where you want the funnel to exitthe base and mark it with a pen. the easiest way to cut it off is probablywith a small pipe cutter. it works by basically forcing a circular cuttingwheel into the pipe cutting it little by little with every turn you make. take note how i'm actually cutting the hornoff about a centimeter below the mark i made. that's because i want it to sit slightly downinside the hole in the base. next we're going to make a flange to holdthe horn to the wood. start by forming a small sheet of thin brassinto a cylinder, it helps immensely if you
have a piece of pipe the same diameter asthe horn to form it around. place it in a vise and peen it with a hammerto force the brass out, creating a small lip. don't smash it, just slowly and lightly workit out. once out of the vise you can fine tune itwith a pair of pliers. place it over the pipe again and use the pipecutter to cut it down to length. take a square piece of thicker brass and markout the center. measure the diameter of the horn, togetherwith the small flange you just made, and drill a hole through the thicker brass to that diameter. don't drill the final diameter at once, butwork your way up with progressively larger
drill bits instead. since we don't want a square flange we'regoing to have to round it off somehow. you could for sure use a belt sander for this,but i really want to get it perfect, so the lathe seems like the right way to go. however, to minimize time in the lathe wecan remove some of the excess material using a hacksaw. since it's a bit difficult to start a hacksawon a angled surface, you can always file a tiny ledge for the hacksaw to grab on to. to hold the brass in the lathe we need toform a mandrel to affix it to.
using some steel rod stock start by turningdown a small ledge with a step of the same diameter as the hole in your brass plate. drill and tap a hole for a bolt to fit, whichwill hold the brass in place. now we can affix the brass plate to the mandrel. using some double sided sticky tape also ensuresit won't spin off while turning. add a bolt and a washer to really keep itin place. using small incremental steps start to removematerial until it's finally completely round. file the edges to remove any burs and removefrom the lathe. we also need a way to mount the flange tothe base, using a protractor you can easily
mark out where you want your mounting holesto be. finally we can put our horn assembly together. put the smaller flange through the brass plate,and put the horn through the flange. make sure you push it down to where you previouslymarked. place it into the base and make sure it sitsstraight, and that your holes are situated where you want them to be. break out the torch and solder again and solderit all together. the idea is to heat up the brass enough forit to melt the solder, you don't want the torch to melt the solder otherwise it willjust bead up on the surface and not actually
wick into the joint. you can see an example of just that just asi begin to solder it together. once cool we can clean the horn assembly upa bit. it's up to you how shiny you want it to be. i'm using a chrome polishing paste just toknock the worst grime off the horn, but being careful not to take it all off as i stillwant a patina on the horn that tells a bit of a story of its previous life. make sure you clean off the polishing compoundwith some soap and water. scrub the joints well with a stiff brush toalso clean off the flux from the soldering
wire. it's a quite corrosive compound, and you canalready see how it has tarnished the brass around the joints. i'm deliberately not removing that tarnishthough, as i want the brass to also build up a new story and a new patina in my home. now, there are a few things we still needto finish up on the base. as the small flange we made protrudes slightlyunder the thicker brass plate we need to remove a little wood around the exit hole so thehorn will mount flush to the base. again, you can use a chisel or dremel here,i just chose to use a big endmill as it was
quicker and easier. and now it sits nice and flush with the wood. the front and the back of the base is stillunfinished, and i think we can make them a bit more interesting than just cutting themat a right angle. the front will match the same angle as thephone will lean in its slot, and the back will just have an arbitrary angle which ithink will look nice. set your table saw to the right angles andsimply cut the front and back off. using a piece of wood as a backer piece willprevent any tearout which may occur from the table saw.
do you like sanding? because we're about to do a lot of it! smooth out all the surfaces using progressivelyfiner grits of sand paper. i started with 80 grit and worked myself downto 220. make sure all the marks from the previousgrit are gone before moving on to the next. while you can sand in any directon, i findit useful to sand diagonally against the last direction you sanded in, especially duringthe coarser grits. sanding with the grain in with the final gritof sandpaper also helps to hide any tiny marks you may still have once you move on to thevarnish.
remember to break the corners as well, itdoesn't have to be by much, but at least enough to catch the light. also, varnish doesn't stick well to a supersharp 90 degree corner, so even a tiny bit of a roundover helps a lot. finally it's time to make the wood pop! take a scrap piece of wood and double sidedsticky tape it to the bottom. this gives you something to hold on to whilevarnishing. i'm using a satin polyurethane varnish whichi've thinned down a bit with mineral spirits to make it spread a bit more easily.
the key here is many thin layers of varnish. varnish the entire base, but be careful notto get a lot of varnish down into the phone slot, as it may build up and your phone maynot fit in the end. i only did one coat of varnish in the slot,to at least give the wood a little lustre. the first coat will probably not look greatonce it's dried. still, take some 600 grit sand paper and sandit down, not to remove the varnish, but to knock down any high spots from grain whichmight have risen. don't worry if the surface looks dull afterwards,the next coat of varnish will take care of repeat this process 3-4 times for a nice andrich coat.
i generally don't sand between the last twocoats, as that way i won't end up with a dull spot in the varnish should i accidentallymiss a part. now you may need to clean out the little recesswe made using a chisel before putting the funnel in place and marking the holes. use a scribe or a centre punch and give theholes a small divot to help guide the drill when predrilling for the screws. putting a piece of tape on the drill helpsensure you won't go in too deep. it's finally time to put it all together. put the horn in the hole and screw it downwith some matching screws.
to help keep the entire amplifier more stableyou can also put some rubber feet on the bottom so it won't slide around so easily. now all that's left is just to sit down, poursome of your favourite libation, que up something good and enjoy. how much does it actually amplify though? i don't actually have a decibel meter, butyou can be the judge yourself. thanks for watching! why don't you cue up one of the other videosfrom switch and lever and pump it through your new amplifier?
also remember to follow switch and lever onfacebook and instagram. i have a surprise for when i reach 1000 followerson instagram! until next time!
