Designing an Enclosure for DCC Sound Decoder Speakers

There are now many options for adding sound to DCC locomotives but, with the limited space often found inside N Scale locomotives, fitting in all the parts can be a problem.  Apart from the actual DCC decoder the speaker is one of the larger problems and in this post I will share with you my design for a customizable speaker enclosure.

When you buy a DCC sound decoder it normally looks something like this.


This sound decoder, model SDN136, is made by Digitrax and is designed to fit into N Scale locomotives.  The standard 8 pin plug is attached to the wires coming out of the left hand side.  The right side has wires attached to the speaker and a capacitor which is used to keep continuos power to the decoder when crossing dirty track.  This prevents the sound from stuttering.

The speaker has a sticky area with white peel-off paper. This can be stuck to the inside of a locomotive shell, preferably in an area which has some holes to allow the sound to come out.  Although this works it can be very quiet as the speaker is small and not capable of making lots of sound.  Or it may simply sound tinny.

To improve the sound volume the speaker can be placed inside an enclosure.  This works in the same way as speakers used for home stereo systems. The speaker is fixed to the front of the enclosure facing outwards. The air inside the enclosure acts like a spring returning the speaker cone to the ‘zero’ position more efficiently than if it was surrounded by open space.  Not only does this reduce noise from the back of the speaker but it amplifies the sound from the front.

Several companies sell speakers already mounted on enclosures and these can easily be used to replace stock speakers.  However the speaker is now getting bigger and finding space for it can be an issue.

A speaker which has been regularly used by members of my local club is the Zimo LS8X12.  This speaker comes with an enclosure as you can see in the images below.

Zimo LS8x12-1

The speaker simply fits into the recessed top of the enclosure.

Zimo LS8x12-2

Because the enclosure is fairly deep by N Scale standards, it doesn’t fit into some of the locomotives. To get around this the modeller tends to file or cut down the enclosure.  Because it is tapered this then creates the problem that the speaker no longer fits properly and may leave gaps around the edge preventing the enclosure from working effectively.

To solve this I have designed an enclosure that is built up in layers allowing the modeller to make it as deep as they want in 1.5mm steps.

Zimo Speaker Enclosure 1

The enclosure is made from two different types of part.  The first is the base and the second is a wall.  They are both shown below from top and bottom. The recesses in the tops of both allow the speaker to be fitted, even in the base.

Zimo Speaker Enclosure 2

The walls push together creating a 1.5mm extension to the enclosure.  Once it’s at the required size the speaker will simply fit into the top wall section.

There is a tolerance gap between the flange that fits them together to allow a small amount of glue.  This will hold the parts together and ensure a good airtight fit.

I have now ordered a test set of these enclosure parts in Shapeways ‘Frosted Ultra Detail’ material and I should have an actual working enclosure to share with you soon.