I’m wondering how one would go about retro-fitting a sound decoder in a P2K or Atlas diesel locomotive? Steam is easy since you can stuff the speaker in the tender. Would you have the weight milled to make room or remove the weight (not acceptable) or try to purchase a new weight from Atlas or P2K (Walthers) if available.
Or is there another option I haven’t thought of?
Bob DeWoody
I squeased a speaker into the middle of the hood on a Athearn GP38-2, right above the motor. It didn’t have a baffle box tho so it’s sound was average.
Ken.
Top firing - several (4) tiny 1/2" speakers under each of the cooling/dynamic brake fans.
Down firing - remove the weight over the truck and put the speaker(s) pointing down so the sound gets out around the trucks.
Side firing - use bigger speaker(s) angled or tepeed into the shell near the trucks to get more sound.
If multiple speakers are used, be certain to matrix them, since wiring speakers in parallel decreases the effective ohm rating.
Bob,
I’ve done this in an RSD-4 where there is no room at all. I milled out the weight to have space for the 1/2" speaker, the capacitor, and the wire! The speaker fits directly under the cooling fan, facing up. There is no baffle and there is very little sound. Most of my sound installations have baffles and they sound great. The one or two that don’t have baffles can be heard when they are running alone, but not very well with any background noise (other engines or crew members). You’ll have to decide whether you really want sound if there is little or no place to put a speaker and baffle. It took several weeks to figure out where it was all going to fit, and I’m not really satisfied with the results of the RSD-4.
Mark C.
Laast night I squeesed one into a GP-38 with the speaker box. But to answere the question, I was prepared to cut out some of the weight, take out the optical crystal, and reroute the rear lighting. Didn’t have to luckily. Just fit.
Bob,
Which Proto 2000 or Atlas diesel are you thinking about retrofitting sound into?
Tom
I have been eyeing the Atlas RS1’s myself and they dont look as to give very many options for sound. Ultimately I think either Atlas or BLI might release these in factory installed sound with DCC.
Mark,
If I am understanding what you said, are you certain you don’t have the opposite problem? If the milled out weight is exactly the size of the speaker that would mean the weight forms an enclosure(what I believe you are calling a baffle). Unless you removed the strip of foam from around the weight it could be pretty air tight. I would guess that when the speaker tries to retract it can’t because the air is compressed too much behind it, and when trying to extend it can’t because a vacuum forms behind it. So the sound is greatly diminished.
For top firing speakers the locomotive body should be plenty of baffle. All a baffle does is prevent the air from rushing from the front of the speaker around to the back and vice versa. When the air is just moving back and forth around the speaker it doesn’t project much sound.
On the other hand, according to current acoustic thought, the smallest speaker enclosure is 2.5 times the area of the speaker cone. So a 1/2" speaker needs a minimum baffle volume of 1.963 cubic inches. The “ideal” enclosure for that speaker and sound processor is going to depend on their combined harmonics. So far I have not found a formula to determine that. I often make a variable volume enclosure and keep adjusting it until it sounds best.
Here’s an installation in an Atlas C30-7. I’ve got two Proto1K C-Liners which I’ve been working on, but I’m considering removing the circuit boards to improve the space available inside, so I haven’t finished/posted them.
http://www.geocities.com/bpickeri/C30-7.htm
Enjoy, however you decide to do it. I’m quite happy with my GE.
Brian Pickering
Texas Zephyr,
The weight fills the ends of the carbody. The RS series has a very narrow, low hood. Just to mount the speaker I had to drill out a hole in the weight to the shape of the back side (magnet) of the speaker. A baffle is typically an enclosed area where the sound is trapped and keeps the sound waves from one side of the speaker from reaching around and cancelling those from the other side. But the baffle must be large enough to allow the trapped air to compress a little. For a 1" speaker, the recommended minimum baffle size is 1 cubic inch (1" x 1" x 1"). My speaker was 1/2" diameter and there is absolutely no room behind it.
I have another engine where I built a baffle into the shell using styrene strips. The oval speaker fits snug in the baffle when the shell is attached to the chassis. The sound level is fine even though the baffle is a little small.
One other comment - you don’t have to seal the “back side” of the speaker to get the sound to improve. It is often much easier to seal (baffle) the front of the speaker, especially since you don’t have to ruin the baffle effect by drilling holes for the wires in the baffle. The sound is just as loud from the back side of the speaker as it is from the front!
Mark C.
Yup, very familiar with that particular unit. Which is why I commented.
Yup, yup, Good point. And an additional benefit of a “rear firing” speaker is that the magnet doesn’t consume enclosure space. Often people will forget to deduct the magnet volume in their computation of enclosure size.
The speaker shown below has a great sound, I think largely due to the large magent allowing the cone to have lots of travel. The problem is the magnet consumes 0.15 cubic inches of any enclosure it is installed in. The solution is to mount it backward. It will never make it into a locomotive though since it is only 0.1 watt, sigh. I wish I could find a 1 watt with similar dimensions for installations in dummy “B” units.
The loco’s I’m considering are the Atlas GP38 & GP40 and the P2K GP38-2 and GP60
Bob DeWoody
Texas Zephyr,
What is that baffle - 1/2" PVC pipe fittings?
Mark C.
Close, that particular one is 3/4". It is strong so it doesn’t vibrate and waste sound out the “sides”. They are readily available, cheap, and can be easily cut to and fitted to any size/length. I like mounting the speaker in a junction and then using an enclosed regular pipe to seal the other end. The pipe can be slid forward and back slowly while the speaker is in operation until its harmonic “sweet” spot is found. I found with Soundtraxx there is one position where the engine main sound is stronger and a different one that highlights the background “chug”. Sort of hard to describe in words. The point is, it is very simple for a person to vary the sound to make it sound best for their ears.
This one was eventually installed into a Stewart FTB. I get lots of comments because the sound is so much different (more bass) than the stock BLI or typical Sountraxx installations. Here the speaker is forward fireing because the enclosure was big reguardless and it wouldn’t fit in the shell with the magnet poking out the front.
The bigger the pipe the harder to fit. Here is a 1" pipe trimmed to fit inside a B body.
http://www.walkersquawker.net/images/filed%20pipe.JPG
My overall goal is improved low frequency via chambers / vents / ports etc. After disecting some Advent, Klipsh, and especially Bose speakers, then pouring over equations for a year I got frustrated and just started building monstrosites. I’ve got like 10 different ideas in orbit now.
Texas Zephyr,
Thanks for the insight into another way to improve the sound in engines. What are you using to “cap” the end of the baffle opposite the speaker? I don’t see a PVC pipe cap - it would be kinda large. PVC sheet, maybe, glued over the opening?
Do you glue the two pieces together once you have found the “sweet spot” or are they friction-tight enough to stay where you want them?
Mark C.
I just put a Soundtrax in the GP-38 and the speaker dropped right in above the decoder in the pop out section in the center. It even have a speaker enclosure. Really pretty simple. Weathering it was harder.
A thick styrene sheet. I tried and rejected the cap because of the size issue. Don’t forget to put something sound deadening on the inside “flat” of the cap. Otherwise sound could bounce off it causing an unwanted echo.
They might be tight enough but I glue them anyway.
Texas Zephyr,
Thanks for the info. I’ve copied it all and made a nice 3-page reference for the next time I install a sound decoder in an engine.
What are your other 10 projects???
Mark C.
I think we have hijacked modlerbob’s thread.
The PVC concept but with variations that include internal chambers and/or ports pointing up where the locomotives vents would be, elbows instead of straight fittings, speakers at either end with and without an internal baffle between them. And I just found these (below) that I am trying to find suitable enclosures for. It is a three watt speaker and has a great surface area. In this case I cut the bottom of the fuel tank out and made the body of the locomotive into an enclosure.
Oh yeah, concerning the caps, the pipe doesn’t have to make an enclosure. I got a really good sound with a pipe about 18" long with no cap. Unfortunately that obviously wouldn’t fit in any HO locomotive. It depends on the sound your ear likes. Also remember that the unit will sound different with a locomotive shell over it. I had one I really liked but when it was installed in the loco it went flat or something. So I continue to experiment.
