BardP

Umm..Did you do the calculation?The speed of sound in air is much lower than the speed of light you use when calculating for RF. 343 m/s is the standard value. If 1/4 wavelength is 1 in, a full wavelength is 4 in, which comes out to about 3.4 kHz. Right in the audio spectrum.In any case, if they get a good enough result without doing any additional changes to the box, there is no need to add more work.

This type of lens could be an option.https://www.instructables.com/id/DIY-Adjustable-Fo...(Not sure if this would require adding cooling to the lens liquid to avoid cooking the lens...)

Quick and dirty way of making something similar: (The result will of course not be as nice as this, but you get a working tool much faster.)- Buy a cheap set of lathe tools with decent handles. Amazon have some that cost less than $20 for an 8-pack, shipping included. Or use some old useless tools you already have.- Remove the temper if necessary. Cheap tools may be untempered already.- Grind away the cutting edge and whatever other metal you want to remove.- Drill and thread a hole.- Mount the carbide bit.Done!

Done wrong, you could blow up a battery with a spot welder. (As you could with the soldering method shown in this instructable.)Done right, it is safe.Battery spot welders are designed to connect both contactsof the welder to the same side of the battery, so none of the welding currentgoes through the battery. The current only goes through the metal at the end ofthe battery.Each side of the battery done separately, of course. Do a search for “battery spot welder” on this site and youfind several DIY designs.

Good advice on the screws.I found a couple of tables here showing screw diameters and pilot holes for both straight and tapered drill bits:https://www.boltdepot.com/fastener-information/Woo...https://www.boltdepot.com/fastener-information/Woo...Another option that removes the problem of pre-drilling completely, are self drilling structural screws.My favorite screws for these kind of projects are now the screws made by GRK Fasteners. They are expensive, but are real time savers. They are much thinner (for the same load bearing capability) than regular wood screws, so I have had no problems with them splitting wood.Home Depot and other stores carry themhttps://www.homedepot.com/s/grk?NCNI-5

Even if they did file a patent for it way back when, it would be expired long time ago. Someone further down mentioned buying this 50 years ago, patents last only 20 years. After that everything is in the public domain.

My 2 cents here:I built a similar setup in my garage, using old laptop power supplies as the power source. (I modified the supplies to output slightly more than 12V, so I got the right amount of current for my strings. I also added wiring to avoid voltage drops along the length of the strings.) This created some interference on my garage radio, as the LED strips act as a large antenna for the noise coming from the switching power supplies. So I have to add additional filtering, the PC supplies were not designed for this purpose. (And my radio is right next to the lights.)Possible solutions for those who get similar problems:-Listen only to strong radio stations ;-) (or use WiFi radio). I am currently at this stage when using my lights, the following is on the to-do list for when I have ...

My 2 cents here:I built a similar setup in my garage, using old laptop power supplies as the power source. (I modified the supplies to output slightly more than 12V, so I got the right amount of current for my strings. I also added wiring to avoid voltage drops along the length of the strings.) This created some interference on my garage radio, as the LED strips act as a large antenna for the noise coming from the switching power supplies. So I have to add additional filtering, the PC supplies were not designed for this purpose. (And my radio is right next to the lights.)Possible solutions for those who get similar problems:-Listen only to strong radio stations ;-) (or use WiFi radio). I am currently at this stage when using my lights, the following is on the to-do list for when I have too much time on my hands.-Add extra RF filtering to the DC power. RF chokes and RF decoupling capacitors will be the right medicine here. Place the filters as close to the power supply as possible, noise should always be treated as close to the source as possible.-Use a better power supply. If you have one of the old fashion, heavy, transformer based power supplies available, you get the noise on the mains power frequency and nothing on the RF bands. The led strings are way to short to act as antenna for mains mains power frequencies, so this will not be any worse than the noise from the DC power itself. Make sure you get true DC, though. Some older "DC" power supplies are rectified AC with poor filtering, so the voltage has a strong AC component. This is OK for many applications, like car battery chargers, but not for LEDs. Too high voltage, even for just a short amount of time, is the one of the best ways to reduce the life of your LEDs. (Heat is the other one, but that it not much of a problem for these LED strings.) And be aware that many of the 12V power supplies used for halogen lights are 12V AC, you need a rectifier, decoupling caps and a voltage regulator to use these for 12V LED strings.-If necessary, add RF shielding to the LED strings. Start by shielding the DC cable between the power supply and the LED strings if the cable is not already shielded. (Laptop power supplies are usually shielded already.) The shield should be connected to the shield of the power supply at one point (and one point only) if the power supply has a shield. Connect to 0V (or GND on the DC side) if not. Adding a layer of aluminum tape behind the lights should reduce the radiation from the led strings. The alu-tape should be connected to the cable shield (again, at only one point). This can be done more elaborate by also adding insulating tape over the strings (unless you use strings that are already insulated) and then an additional layer of alu-tape over that, (not covering the LEDs themselves, of course), effectively creating a Faraday cage. Small holes in the shield to let the light out will not decrease the efficiency of the shield significantly at these frequencies. Just make sure you get good metal-to metal contact between the two layers of alu-tape, the glue on most of these tapes is not conductive and can create gaps in the shield.

The internal wiring in the strips is thin, so there is significant voltage (and light) loss in the far end of a long strip. I run extra wiring parallel to my strips and connect it to the strip every meter or so.