Is that acid paste flux on your desk? I hope it isn't as it is a no no when soldering electronics. You can get lightweight MDF now that should help lighten the load on the whole thing. You can also go with a bit thinner wood if you use the right bracing. MDF would also be the easiest to work with and if you have a router you can easily make the shapes you want.
Whats wrong with acid paste flux? Other than I'm sure its bad for my lungs. This Rosin Core solder doesn't adhere to things when I'm trying to solder wires for example. Breadboards work fine without it but if I'm soldering two wires together they won't solder unless I use some flux.
You can use relatively light & thin mdf, say 12mm, and the bracing can also double as a compartment for the electronics, such as a small cube at approximately the centre of the boom box. I'd have the heatsinks exposed to the exterior, and the edges of the heatsinks snugly fit & sealed to the box. I'd also lightly fill the bass chamber with soft quilt wadding, to improove sound quality, including improoving bass. At the end of the day tho, there's not alot of point making a perfect box, if you don't have the specs of the speakers, so that the box & ports can be made to maximise performance. Those speakers probably sound good, but they aren't 20wrms, it looks more like 7wrms, so you wouldn't wanna give them more than about ~10wrms. It would be nice to get some good woofers, that can handle ~20-30wrms, with as good a effeciency & as low a resonant frequency you can find/afford, and some matchable soft dome tweeters, and then the box & port can be made to maximse bass! 2 x 20wrms can make an ok amount of bass with 2 x good 4", and some pretty good bass with 2 x good 6"
You must be doing something wrong then, or using severely oxidised wire. Are you over/underheating the joint?
Well the acid part is what is wrong with acid paste flux. Solder tips have various coatings of metals on the tips (depends on brand) and the acid in the flux will eat that coating and cause solder wetting issues (like you are having with the wire). The wetting issue will also cause less heat to flow to he joint causing soldering problems and cold solder joints. Also tip selection is important depending on what you are doing. Personally I use the standard tip that comes with an iron for 90% of my work (including smt), a heavy tip for large wires and a small tip for tiny smt rework. If you have any soldering questions feel free to drop me a line, I have been doing electronics manufacturing/prototyping/repair for a long time so I should be able to point you in the right direction.
Well, firefox just flipped out and I lost all I had written, so I'll be brief in my rewrite. Its all radioshack stuff, 60/40 solder and a 25W iron. It works for now, in the fall I will buy a new one for school. @mvagusta, I know what you're saying, but getting real woofers for a boombox results in a sore shoulder and I need to keep it light. But how do I keep the power to these current speakers to around 10W? I know they are 7W speakers, but I figured since I hook them up to the same spots on my Hi-Fi as a big stack that they just take what they need. The speakers currently have a moderate amount of bass, and I'm really not a fan of bass if it drowns out the finer points of the music (ie all the other instruments) as we so often hear from cheap imports with unpainted body kits rolling down our neighborhood streets. In short I think I'm set in terms of speakers, at the very least I will do the project with these ones and see how I feel about the result afterward.
You can limit the output power to approx 10w by reducing the gain of the amps, or just not going over a certain level on your mp3 player. Just remember to not put the volume up so loud that the bass isn't reproduced clearly, and the speakers will be safe. If you want to reduce the gain of the amps, then a bit of trial and error using the same method will find the correct gain setting. There are other ways to find the 'correct' gain level involving measurements and/or calculations. And btw, using a 20w amp to only output 10w and drive a 7w speaker, is the sort of thing an audiophile would do! Seriously, as this way, the signal and sound is as clear as possible, so the speakers themselves are the weakest link People are usually more likely to blow a 20w speaker with a 10w amp, then the other way round, as the signal becomes distorted much more easily with less power, so the sound starts becoming like dc alot more easily, which burns out speakers. Your biggest danger would be having it so loud that the bass is making the speakers physically move too much, so that the bass isn't clear. Like this the coil can bottom out/crash into the inside of the magnet, killing the speaker. As for solder not sticking, just make sure the metal is clean, be it wire, track, component, etc, using alcohol, and as long as there is a good level of heat, the solder will stick. edit: Oh, and if you don't want to maximse bass, just have it all nice & clear, then make the box sealed, meaning no ports. There's no worries about speaker specs like this either, unless you wanted to see a graph of exactly what would be happening, as sealed boxes are simple. The general rule is that the bigger the sealed box, the deeper the bass response, and seeing the size of those speakers, your boom box looks liek a good size. Sealed boxes also give smoother & more natural/audiophile style bass response.
Thanks for the insight. I'll be sealing the speaker portions of the box and putting the insulation that was in their original boxes in as well.
Mvagusta is right on all accounts. Under driving a speaker is more likely to damage a speaker then overpowering it as the voice coil struggles to move hence less air to cool it. Putting pollyfill (like the stuff in pillows) will make the box look larger for the low end drivers hence cleaner and tighter bass. PS You are likely only hearing bass from those cars as low frequencies penetrate solid objects easier then high frequencies.
Today I built a cardboard mockup of the boombox. I did it to get an idea of how much wood I would need before I go to the store tomorrow. I'm rethinking the built-in handle only because I have relatively limited time to complete this mod before school starts. I think I will be simply bolting on a handle and shoulder strap to keep it simple, and it will help me cut a good 6cm off the height. I'm amazed at the sheer size of the coils and magnets on these speakers. I've never seen ones so large in proportion to the cones. For the corners, due to the difficulty of getting a nice curve like I want, will be capped with these plastic corner protectors. I will either use ones stolen from my guitar amp or ones bought from the hardware if I can find any. I've never seen these for sale though so I'm thinking cannibalism will be in order. I would like to run this device off 120V mains right into the back, which means I need a PSU that will output 12V at 4A to get 48W of power available. This will be plenty of juice, yes? I've been running it off my 300W variable supply for testing so this hasn't been an issue until now. My latest redesign, which doesn't look nearly as good but at least will be do-able instead of some sort of distant dream.
Today was probably the most work I've ever done in a day of modding. I cut all the pieces for the sides, front, back, top, bottom, and internal sections, and drilled and mounted L-brackets for everything except the internal section pieces. Tomorrow I will begin cutting the holes for the speakers and the MP3 box. The L-brackets that hold it all together along with 3/16 x 3/4 stove bolts. I'm thinking about upholstering the entire thing the way that the guys at Metku Mods did their boombox. They used fake leather. A lot of guitar amps I've seen are coated in a thin textured rubber skin, I'm wondering if thats something that can be bought at a hardware or craft store somewhere. If anyone has any ideas at all on what I could use to cover this system please let me know. Its very important that I cover it and seal it because the MDF will be ruined by any water.
To seal the box airtight, make sure all the cuts are true and that all the pieces fit snugly. Predrill for long self tapping wood screws, say one every ~15-20 cm, and run a nice line of wood glue along the joins. When you screw each join down excess glue will squeeze out, which you can smooth along with your finger. The wood will suck in the glue, and once this happens, if you want to thicken up the seal, you can run another line of glue along the join line, smooth again, and allow the glue to suck in again. The box will take a little while to screw together like this, but it will be 100% airtight and extremly strong. Leave it overnight to dry, and forget ever opening it again without using a hammer. If you want a less permanent way to seal the box, run some silicon along each join and the screw each join down, and smooth off the squeezed out excess silicon. As for waterproofing the box, a few layers of paint will do it. No need for any fancy paint, just be aware that mdf will suck in alot of paint, so just one coat, let it dry for hours at least, re-coat, wait hours, etc. About 3-4 coats on smooth sides, and cut ends will need a couple more coats. If you use a thick filler primer, etc, then a coat or two less will be required. That ghetto cardboard boom box mockup looked pretty funky btw
Todays progress: I must say this MDF certainly is soft, I drilled the starter holes for the speakers, the hole I need to get the jig bit into the wood, using a screwdriver and a 1" spade bit and it only took about a minute to do. The jigsaw eats it like its nothing too.
I normally make boxes without brackets. To prevent splitting & bulging you have to predrill & get them dead center, and as long as the screws are long, the strength is excellent. If you seal with glue the join becomes even stronger than the wood! Silicon seals are still good enough tho, and has it's advantages for something like this, so probably best... not much is needed as it all gets squeezed like thermal paste when the box is screwed together. The other thing about brackets, is that you can't bolt all the sides from the inside! and it would be lighter without them, whilst still being at least as strong. I might also mention that mdf isn't the healthiest thing to touch or breath in the dust of, so don't forget to wear a dust mask & washup afterwards
If you are using MDF get a counter sink/drill bit and use drywall screws it will make the box a 100% stronger. Also use lots of wood glue as MDF soaks it right up.
Since I want (ie need) to be able to disassemble this thing, glue isn't an option for nearly everything. Some has been used on some inside compartments, but thats it. Its all nuts and bolts. I forgot to pick up some lock washers when I was there, but I'm going to get some when I go back to buy some more bolts, just in case the bass vibrates the nuts off the bolts. I was wondering if these here connectors from the amp board can handle the amount of current for these speakers? and could these USB pins that I harvested be able to work as suitable connectors for the speakers? I would need to use a small portion of the small wire out of the connector that will then be soldered to some higher gauge wire, but I'm worried that this stuff can't handle the current and will fail at volume. standard PC screw for size. And could a mod please move this thread to the Project Logs section now that I'm doing work? Thanks.
You can use a little loctite, or just put a little paint on the thread just before you put the nut on. I had an idea actually.. how about mounting all those shiny corner brackets from the outside? It might not be the look you're going for, but it would make the boom look tough i think! For the last panel, the nuts can be glued in posistion on the inside, and then screwed together from the outside. Those connectors & wire would handle the current fine, they wouldn't heat up, but you'd definitely be loosing a tiny bit of power due to resistance at full volume. The tiny bit i'm talking about might not be noticeable however, so if you did go and put some beefy connectors with thick wire, you might notice a tiny improovement in volume and maybe a bit more bass... but maybe not, since it's not like your speakers are big subwoofers, so they probably don't reproduce much deep bass. A simple upgrade would be to use a little thicker wire, say ~1mm core, and solder the wire to both the speakers & those pins/or remove the pins and solder to the pcb. This would mean no loss in signal even at full volume, but i can't garantee the improovement would be noticeable.
Electrical is 98% done aside from the PSU which I think will be a modified PC PSU since I can't find one running 12V at the required wattage. I will take a look at the local electronics store though. Most of the wood has been cut, I just need to devise a way to attach the back that will still allow for easy, tool-less access to the interior. The sound is good but with little bass right now without a back, I think once it is sealed up it will sound brilliant though. I'll need to figure out a way to seal the back piece airtight without permanently attaching it. I think two large rubber O-rings could work... Or actually, I could just cut the back plate into three pieces and permanently seal the speaker portions of the unit but not the electronics centre portion. Comments?
