I have a Digitrax SDH Round Speaker and just wondering what everyone thinks is the best kind of Box to build for a little speaker like this.
Cary
That depends mostly on the type of locomotive you’re putting it in.
Generally, the front and back of the speaker need to be sealed off from each other, so there’s no way the sound waves from the front can interfere with those coming off the speaker cone at the back and cancel out.
Can you provide a description/photos of where you will be putting the speaker?
It’s going in an Athearn P42 and it seems like lots of space in the back. I kind of made a speaker box out of styrene but has to be placed on an angle with speaker aimed to the top. I did notice someone has used PVC Pipe Cap; threaded pipe. Has anyone else used this or any other ideas out there?
Once I get this done I’ll put a small Vid on Photobucket to see what you guys think.
thanks again, Cary
I use to work for James B. Lansing Sound back in the early 1980s in the engineering department, I will tell you you need a port tube in the wall of the speaker box you are making. This can be made from a small soda straw about a half inch long glued into a separate hole same size in the box. Also be sure to put some insulation such as a small wad of fiberglass also inside the box. Build your speaker box from styrene thick enough so it will not resonate, .040 thick should do. Doing these steps will result in better sound quality.
This is contrary to all that we have been told by the decoder manufacturers and installers. We have been told that the speaker box or enclosure should be sealed tight. This has always bothered me a little but I have been doing it and getting acceptable sound levels on the tiny speakers we use. Can you elaborate a little more about the port tube?
OK, you already have your speakers but Railmaster Hobbies makes them fully enclosed and ported with very good bass sound. The owner and his wife are both in the National Guard, I beleive, so are away at times but you get good service at a good price. He is introducing new speakers all the time in different sizes and configurations. I actually bought a few from him on ebay with free shipping. I am going to do my first installation as soon as a friend gets a frame milled for me. (No, the milling is not to fit the speaker but to redo the fuel tank.)
As big as you can make it and make sure it’s a tight seal.
Big speakers put a material similar to fiberglass, or batting inside the speaker to help absorb the backwave of higher frequencies. I’m not sure that would help here given the small size. But it’s worth a try if you have extra.
Port tubes are designed to extend bass by bumping up a narrow frequency range. They are “tuned” to a specific frequency, typically -3 to -6dB from the cut off of a sealed speaker.
It takes very careful planning to properly “tune” a port speaker. Don’t even try it unless you design speakers and or have the proper software and know the response characteristics of your speaker.
Trust me on this. My other side hobby is home theater and speaker design. I built my own designed amps in college.
I was working on a “folded-horn” type design which is in many ways superior to just a simple “port” But even with an Allegheny HO tender, my software told me it wasn’t worth it.
Thanks for all the Great info guys. I bookmarked Railmasters for future use. I did make one on an angle out of .040 styrene and was thinking silicone to Seal it in good??? (could drill a hole out the front beside the speaker like my Home Speakers) and also another idea; spent .67 on 1" PVC threaded pipe that has an opening on both ends (would have to open up a bit with the Dremel for a Good fit).
My little speaker box that I built probably won’t fit any fiberglass, insulation etc. but the PVC pipe should.
I’m going to try and test these tonight and see how it goes.
Consider just a plain bare speaker hanging in free air. Put juice to it and the cone moves back and forth making sound. Thing is, we get sound off the front of the speaker cone, and off the back as well. If you think about it, the front wave will be 180 degrees out of phase from the back wave. If the front wave and the back wave are allowed to meet, they cancel each other. In the real world the cancellation isn’t perfect, but the sound does get weaker. And the amount of sound the tiny speakers that can fit inside HO rolling stock isn’t great, anything we can do improve the loudness is a good thing.
Simplest improvement is a speaker enclosure of the “infinite baffle” design. The speaker is mounted in a good tight enclosure, stuffed with sound absorbing material and the back wave is absorbed, leaving the front wave to do all the work.
A trickier speaker enclosure is the “bass reflex” design. The speaker is mounted in a good tight enclosure with a “port” (hole) in it. As the speaker cone moves backwards it compresses the air in the enclosure, which puffs out the port. If the port size and the enclosure size are just right, the sound wave from the port re enforces the front wave and the speaker makes more sound for the same amount of juice put into it. Bass reflex enclosures can be designed for sizable stereo speakers (8 inch speaker, several cubic feet of enclosure), but getting the idea to work on a 1 inch speaker in a couple of cubic inch enclosure is beyond the state of the art.
Stick with the “infinite baffle” design.
Well; I did what I could tonight and I uploaded a Video on Photobucket to hear the Sounds. It is the Digitrax SDH164D and the Basic SD38 what is pre-programmed for this decoder. I am wondering how I would get the Ditch Lights going with the other Functions as there was nothing in the Decoder Manual and I’m not a programming Guru yet that has gone through that Digitrax Manual and understands it.
Please excuse the Video.
http://s244.photobucket.com/albums/gg34/cjham/?action=view¤t=2010-Jan-P42sound.mp4
img\http://s244.photobucket.com/albums/gg34/cjham/?action=view¤t=2010-Jan-P42sound.mp4img/