Sunday, May 1, 2016

Upgrading the Athearn RTR SD40 with an iPhone 4 Speaker

When I first tried out my two N&W Athearn RTR SD40's with Soundtraxx DCC sound, I was happy with their performance and detail but felt the speakers left much to be desired. Most factory equipped sound units have speakers or speaker enclosures that can't produce a rich sound with at least the impression of low frequencies. I'd seen online where people using cell phone or tablet speakers have had surprising success making their model train engines sound more like the real thing. This thread in Model Railroad Hobbyist and others furthered my interest in these small speakers that might help my N&W SD40s sound more like their big brothers.

Last week I finally bought a couple
iPhone 4 replacement speakers off eBay for $2.00 each to experiment with. Today they arrived so I installed one of them, took some pictures and made a comparison video to share along the way.

Factory Athearn speaker at top, iPhone 4 speaker at bottom.
The iPhone 4 speakers were way smaller than I thought which gave me hope they would easily fit inside the SD40's long hood. I guess I've forgotten how tiny the iPhone 4 was since getting my iPhone 6.

Testing the iPhone speaker out.
From the moment I temporarily hooked up the iPhone speaker to the SD40's decoder I was blown away at the amount and quality of sound this little thing was producing! And this was without the engine shell enclosing the speaker which would only help deepen the diesel sound.

A perfect fit on top the old speaker location. More weight could be added in the hole left by removing the factory speaker.
Just enough room to route the speaker and power truck wires around the speaker enclosure so they don't interfere with the shell.

Now for the video comparison, but first some disclaimers!
  • The only programming these Athearn units had was their address changed to their respective engine number. 
  • I have not changed any other CV values like EQ settings or volume. I will change the volume level soon because out of the box these engines are way too loud.
  • The N&W SD40 1613 has the factory equipped Soundtraxx "Onboard RTR Sound" DCC Decoder and a factory speaker.
  • The N&W SD40 1611 has the factory equipped Soundtraxx "Onboard RTR Sound" DCC Decoder and a new iPhone 4 replacement speaker. I soldered all contacts and taped the speaker unit to the metal weight where the old speaker was located.
  • This is my first real YouTube video, how embarrassing!

In my opinion the factory speaker sounds really high pitched compared to the fuller more dimensional sound of the iPhone speaker. For only $2.00 the iPhone speaker was a big upgrade that will only get better once I play with the decoder settings. Especially once I lower that volume! Wow Athearn, let's revisit some of those factory settings!

I know some people disagree with using cell phone/sugar cube speakers over traditional cone speakers for sound fidelity reasons, but for tight installs and based on my what's left of my ears, this two dollar speaker wins hands down!

I do have some iPhone 5 speakers on the way to try out also. I've seen some mixed reviews on those in modeling forums, so I'll be sure to report my findings as well.


  1. Chris,

    What a difference the iPhone 4 speaker makes!!

    I'm going to have to experiment with some of those to compare them to the "sugar cube" speakers currently in use.

    1. Yep I will certainly be ordering more. Sugar cubes are great too because you can fit them in to just about anything. They don't have that premade enclosure to contend with like the iPhone speakers. I saw somewhere a guy wired four sugar cubes together and mounted them on some styrene for an EMD SD unit, it sounded really good too.

  2. Yeah that sound is amazing, and for the price I think they would be hard to beat. The housing looks like it was made to fit inside an HO scale shell.

    I thought I'd seen somewhere how somebody removed the actual speaker from that housing and it was incredibly small. Not sure where it was though.

    1. It has to be a very tiny speaker in that iPhone part. Goes to show what a good enclosure can do for the sound output.

      I should've recorded the differences between all the speakers outside and inside the engine shell. The various levels of sound and quality were remarkable. I can't wait to try the iPhone 4 speaker in a steam engine tender, even though I could put a much larger regular cone type speaker inside.

  3. Awesome work. The difference is night and day and the iPhone speaker sounds much deeper with still very good highs. I have a couple of questions... 1. Which prong is the positive speaker lead? 2. Do you know what the ohm rating is on these?

    I just came across a few of these and I'd like to do multiple speakers, thanks and good job again!


    1. Answers;

      1. Unfortunately I have no idea.
      2. Again I don't know, but a lot of people have used them with success. Even Rapido the model train company uses them in their DDC/Sound models.

  4. Nice article, thanks for sharing.

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