Another Speaker Transplant for the IM SD40-2

[jdcolombo]

Hi folks.

While upgrading (?) my SD40-2 to alternating ditch lights, I decided to try a second speaker transplant.  This time, I used a 9x16mm speaker (a Knowles Fox, no longer made, but you can buy a CUI or Soberton 9x16 from Digikey) mounted lengthwise in an enclosure the size of the cutout.  This meant that there was 3mm of unused space inside the enclosure to improve the inside air volume.  I also mounted this one so that the speaker was facing up, firing into the chassis.

The 9x16 conversion sounds best to my ears.  A bit more treble than the 8x12 conversion (this may partly be because of the speaker orientation: firing up into the chassis rather than down at the track), but still much more "heft" than the stock speaker.

Here is the video, which is basically the original video I posted, now with the Fox conversion also added for comparison - so you'll get three sequences for each sound: the original, the first transplant (using an 8x12 speaker firing down at the track) and the second transplant (9x16 speaker firing up into the chassis). 

I can see using this kind of speaker orientation (mounted in fuel tank area, firing up into the chassis) in other installs; I think it sounds quite good.  But it would require major milling of the frame, and would be harder to mill by hand (now that I have a small milling machine, I could do this pretty easily, but I sure wouldn't want to try with a Dremel in my hand).

John C.

[wazzou]

Yeah, that sounds much, much better.

[drgw0579]

The next F7B conversion I do will have a Fox in the fuel tank pointing up and the shell/frame sealed as much as possible to try to use the entire inside of the body as the enclosure.  Will use silicon caulk to seal the gap between the two frame halves. It won't be possible to seal where the trucks mount to the frame, but maybe the path for the air to exit there is long enough that it won't matter.  I tried that in the past with some success, but we'll see if some of the recent ideas helps the sound.

Bill Kepner

[jdcolombo]

The next F7B conversion I do will have a Fox in the fuel tank pointing up and the shell/frame sealed as much as possible to try to use the entire inside of the body as the enclosure.  Will use silicon caulk to seal the gap between the two frame halves. It won't be possible to seal where the trucks mount to the frame, but maybe the path for the air to exit there is long enough that it won't matter.  I tried that in the past with some success, but we'll see if some of the recent ideas helps the sound.

Bill Kepner

Hi Bill.

Just to clarify, I'm not using the shell as the enclosure.  The Fox is in a separate sealed enclosure that is about 5.25mm high, 13mm wide, and 17mm long (made out of .020 styrene).  That size JUST BARELY fits in the factory cutout (I had to sand down the short sides a tiny bit to get it to slip into the cutout).  But by having the speaker firing up through the chassis, what I am doing is having the shell serve as a sort of reverberation chamber.  That gives the sound a bit more heft, and the additional reverb I think really helps the sound of the horn and bell.

The enclosure is basically the same design as for the 8x12 that I posted earlier - the only difference, really, is that the Fox is oriented N-S, instead of E-W.  So the empty air space is on the long side of the Fox, running front to back on the locomotive axis.  This seems to give the Fox enough enclosure air space to provide fairly good frequency response, and using the shell as a bit of a reverb chamber allows the sound to "bloom" a bit before reaching your ears.

I really think this is about as good as I could do, short of milling out more of the fuel tank and trying to get a 13x18mm speaker in that space.  It probably isn't worth trying that, anyway - I don't think the sound would be much, if any, better.

John C.

[RBrodzinsky]

Better with each iteration!

[Santa Fe Guy]

And the winner is Number 3. Great job as always John.
Rod.

[davefoxx]

Excellent work, John!  But, I must add that you're killing me, because my SCL SD40-2 is expected to be in the second delivery, which isn't until at least February.  I'm dying here!

DFF

[jdcolombo]

Excellent work, John!  But, I must add that you're killing me, because my SCL SD40-2 is expected to be in the second delivery, which isn't until at least February.  I'm dying here!

DFF

Well, if it helps any, by then we'll also know where to attach keep-alive wires . . .

I really don't know what I'm going to do with this SD40-2.  My layout is set in 1957; I model the NKP; having this thing around is a bit . . . weird.   But this is the second manufacturer to ask ESU to do a custom board (Atlas S-2 was first; the Rapdio Trains GMD-1 uses a standard LokSound Select micro) and is, I think, a harbinger of things to come.  If this board becomes popular, more speakers will end up in the fuel tank.  And if that happens, I want them to pay attention to what I've done.  The manufacturers ARE paying attention so far - IM did a darn good job with the factory sound install; they just needed to have something that did not require hand-soldering, which means they faced some limitations that I don't.  But I hope that I can convince them (and others planning a similar path) that you can do better if you're willing to push the envelope a bit and pay attention to basic speaker design theory (e.g., having sufficient internal air volume in an enclosure).  There's not any particular reason you couldn't re-create my Fox enclosure commercially (I'm sure you could 3D print it in a heartbeat), and instead of using wires, use contact pads on  the outside of the enclosure (sealed off from the inside by some sort of glue - rubber cement, maybe?).  These contact pads could serve the same purpose as the current IM stock speaker design (no hand-soldering), and the sound would be better.  So maybe when it's time for IM or Atlas to do a new design, they will think about my experiments.

And in the meantime, pretty much anyone can re-create what I did with some .020 x .188 styrene strip; a 9x16mm speaker; gel CA; a bit of wire, and a willingness to do a little modification to the bottom of the motor mount surround where the stock speaker sits.  Takes about an hour after you've ginned up the courage to completely disassemble your new prize and start hacking away at some plastic . . .

John C.

[Cajonpassfan]

That's great, John, thank you, I do hope the manufacturers are paying attention. I like the way you spliced the three samples for comparison purposes. What a difference!
Otto K.

[cnw mike]

Wow, that does sound way better. Any chance of getting a pic of the installation?

Thanks!

[jdcolombo]

Wow, that does sound way better. Any chance of getting a pic of the installation?

Thanks!

Well, I didn't take photos of this one, because I was in a hurry to do it so I could send the decoder board off to Peteski who is going to try to find a place to hook up a keep-alive. 

BUT . . . the basic installation is exactly the same as what I did for the 8x12mm in my prior thread.  All I did was use a 9x16mm speaker, instead of an 8x12, oriented to the long side of the enclosure, instead of the short side.  I threaded the wires for the speaker out the same side of the enclosure as the speaker front (remember that there is 3mm of space between the long edge of the speaker and the edge of the enclosure, because the speaker is 9mm wide, but the cutout is 13mm wide - the remaining 1mm is the width of the two pieces of .020 styrene making up the enclosure sides) instead of the back, put the speaker/enclosure in the cutout with the speaker facing up instead of down, soldered the wires to the speaker leads wrapping around the motor, and then put the other half of the frame on and clipped everything together.

When I get time, I'll build a second enclosure like this and take photos.  But my other speaker transplant thread shows the basic techniques. 

John C.

[cnw mike]

Ok, thanks for the rundown. I think I get the idea now.

But yeah, if you do get a chance to take pictures next time time I'd sure appreciate it, I'm sure I'm not the only one.

My sound installs in diesels have been hit or miss, mostly miss...lol. The only one I've done that sounds good is an old Kato RS3 that I never really run, go figure. Really looking for some new ideas.

[AKNscale]

You could also get the SBS speaker. I used a 9X16 in my SD50 LOKsound install. I believe it's a zimo.

[jdcolombo]

OK, here are front and back photos of the speaker enclosure I built for the 9x16mm speaker.  All that's left is to glue the back on, then the whole thing sits in the cutout of the fuel tank with the speaker facing up toward the motor.  The wires get soldered to the speaker leads that wrap around the motor to the top of the frame, where the decoder board sits.  You'll probably have to sand down the short sides of the enclosure a bit to get the enclosure to fit in the frame cutout; I ended up sanding each side to thin it by about .005, or .010 total for both sides. 





The sides of the enclosure are .020 x .188 styrene; the "extra space" on the long side of the speaker is sealed by using a strip of .030 styrene.  I use gel CA cement to glue the styrene strip to the speaker; styrene-to-styrene joints (including the bottom, which will also be .020 styrene) are done with regular liquid styrene cement.  I lightly sand the sides of the speaker and the styrene strip to rough up the surface before applying the CA cement.  The whole construction project shouldn't take more than an hour, though you will want to let the cement dry overnight to fully cure (both the styrene cement and the CA).

John C.

[jdcolombo]

You could also get the SBS speaker. I used a 9X16 in my SD50 LOKsound install. I believe it's a zimo.

or you can order bare speakers from Digikey for less than $3 each . . . since you're not going to use the enclosure provided with the SBS or Zimo speakers anyway, no reason to pay extra for that.

John C.