Modelling Sound

Bob Backway


Sound may be described as the last frontier of realism for the model railroader. Yes, it is true that sound systems for model locos date back almost to the first powered models themselves. But it wasn't until the age of miniature electronics and digital sound that this aspect of modelling could be considered practical and realistic on the average layout. As prices are driven down by technological advances we can expect to see sound become the "norm" in our future models.

Another driving force is the introduction of new Command Control systems, particularly the NMRA's DCC Standard. These new systems have the ability to control more than a loco's speed and direction having several "Function" outputs just begging to control lights, animation and sound. DCC decoders share similar technology to digital sound modules. The logical combination of the two will result in economies of scale and price.

An otherwise "dead" layout is brought to life with the help of sound giving it a feeling that the train is running through an environment, not just a base board, plaster and ground foam. Sound can also fill in the gaps, the natural or man made world of the layout that could not be modelled for lack of time and space.

Often when sound is used with a layout little thought is applied to its use and it is rarely modelled accurately. This is intriguing given that the techniques to accurately record and reproduce sound have been around for half a century.


Analog Sound

A real sound copied onto a device such as a tape recorder. With analog recording methods the information stored is subject to the degradation of the record/copying/play system and recording media. Analog sound can be used effectively on the layout but can't fit in a loco!

Synthesized Sound

A sound made using electronic circuits. Usually a mix of primary sound generators followed by various envelope generators and filters attempting to manipulate the sound to imitate the original. Synthesis used to sound as good as vinyl did before CD's came along!

Digital Sound

A real sound stored in a coded form by sampling the real thing. The sample is an accurately reproducible copy of the original within the limits of the reproduction system. Further copying does not degrade the sound quality.

Where can sound be found on today's layout?

Sound can be applied to a layout in different ways. There is no best way, each one having it's pros & cons.

"Under" the baseboard

In/under/near a lineside structure

In a locomotive

In a piece of rolling stock

Using sound


Entering the exhibition and the first thing you hear is a poorly synthesized ding dong "noise" coming from the other end of the hall. Sound is always around us but we unconsciously filter most of it out while having at the same time the ability to detect important sounds from within high noise levels. This complex capability of our ear must be kept in mind when modelling sound.

Ambient or Background Sound

Sounds that are present intermittently in the background that add a "live" feeling to your layout. Ambient sounds should be heard only during quiet periods such as pauses in conversation or when particularly listened for.

Background sounds should be gentle, subliminal and non-repetitive. Even a busy part of the layout should "bustle" quietly.

Intermediate sound

Sounds that imply action and identify with an object on a layout. They should appear to come from or only be clearly heard in the vicinity of their modelled source.

An intermediate sound such as "ding dongs" should be heard during conversation but should not dominate the other end of a large layout.

Feature Sound

Generally sounds emitting from the locos, after all they're what we're here for. They can also be scenario related sounds which give the layout purpose and flair.

A feature sound such as the loco at the centre of attention should be louder, but not too louder, than the intermediate sounds. If the overall effect is too loud you will soon annoy the viewers and drive the operators up the wall by the end of an exhibition.

It is difficult to adjust sound levels in an exhibition as noise levels will vary during the day so an easily accessible volume control is mandatory.


Most of us have been to a scenery planning clinic where the use of guiding lines and scene division have been used to paint a picture or tell a story. The same concepts are as important when using sound. With sound it's best to place yourself as an observer on a nearby hill. Here you will only get a hint of sound from the scene spread before you. Sitting there you may here a mill saw start, a dog bark, a truck squeal to a halt. Each time you will look in that direction and expect to see what you heard, a mill, a house with a kennel or dog, paws up on the fence, a truck just stopped outside the general store.

This effect is important, but don't over do it. Whether you use a tape and switched speakers or digital effects you may like to try a sequencer. This is an electronic device that uses timers to space sounds in a certain order at a preset time interval.

A typical scenario would be:

"Loco enters night scene and whistles for road crossing, dog barks, wakes baby, dad swears at dog, light goes on and baby stops crying."

The whole sequence could be triggered by a track detector. The icing on the cake is to make the whole sequence occur only every 4 or 5 passes. This has two consequences. First the sequence is infrequent enough not to annoy and secondly when the viewer has finally convinced their partner to wait and listen, it won't happen!


Getting the best out of your sound system

Speakers, the critical part of the system

Size & sources

Miniature speakers can be found in many consumer items from toys to audio equipment and home computers. Headphones in $2.00 shops provide a small speaker suitable for high pitched sounds such as chuff and whistle for a logging loco. Better quality headphones have larger speaker sizes and hence a wider frequency response. These are cheaper bought separately at an electronic parts shop such as Jaycar, Dick Smith or Tandy. Obsolete computer modem boards have the smallest speakers I've seen but they are rather inefficient.

Once you're into sound you find yourself collecting various speakers in your travels and will soon have samples of many shapes and sizes to experiment with. Various speakers have different parts of the frequency spectrum that they work best in. The only generalization being that normally the larger the diameter the lower the frequency response. They also vary in the amount of power they can take without distorting, or in extreme cases, dismantling themselves.

It pays to try a range of speakers temporarily installed in their final situation (see below re baffles etc) before making up your mind. The differences can be substantial.

Cut & Paste

Sometimes it may be necessary to "doctor" a speaker to fit it in a model. Any outer cover or mounting brackets that are not used can be cut off. The only important part is to ensure that the cone is supported in the voice coil. Sometimes the cone has to be cut to fit in the model. While lowering output and affecting frequency response, this can sometimes give a better result than using a smaller speaker. It is important however to make the cut sides a good fit in the "box" and run glue lightly along the edge so it is fixed to the box. Without the unattached area of cone flapping around the sound is cleaner.

Yes, you have to be rough sometimes!

Baffles, enclosures & sealing

All speakers convert electrical energy into sound waves by moving a surface, the cone in the case of a conventional speaker. The movement is greatly influenced and in fact enhanced by the speakers surrounding environment. To put it simply a speaker will perform better if the sound waves emerging from the front cannot be interfered with by those from the rear of the cone. Interference reduces the volume because the front and rear waves are opposite in phase and cancel each other when they meet. Ideally the surface through on a speaker mounts should be hard, flat and infinite in dimensions. Obviously we'll need to compromise! At least try and provide a hole through which the speaker transmits its energy. For example through a floor or a loco grill.

A speaker also works better if it's in an enclosure. This has an effect of reinforcing the sound, particularly the lower, bass, frequencies. Normally the enclosure size is calculated using the resonant frequency of the speaker, in a model it's do what you can. From cut down film canisters to utilizing blocked off sections of the model body. The simplest and crudest reinforcement is a piece of foam plastic jammed behind the speaker. An ideal situation is a speaker through the floor of a box car filled with dacron wadding.

Sealing the enclosure prevents out of phase sound waves from "leaking" out from the speakers rear.

Brass & plastic resonance

All materials have a resonant frequency at which they vibrate when sound of that frequency is applied. Brass models, just like the brass section of the orchestra, make a sound appear "tinny". This is the biggest complaint of brass model owners who've used sound. Similarly plastic models can develop an annoying buzz.

The following tips help cure this problem:

Electrical noise

Electrically speaking a sound unit is operating in a very noisy environment. With motor commutators nearby radiating radio frequency energy and noise spikes coming via track power from other locos by way of a delicate contact system.

If you have problems with noise try reducing it by using capacitors across your motor leads or the power leads of your sound unit. I keep a range of small ceramic capacitors from 100 picofarad to 0.1 microfarad for motors and 0.1 to 1000 microfarad for power supplies. The larger values are usually tantalum (small) or standard electrolytic capacitors and are polarised so remember to put the + end to the + wire of your power lead.

In general the smaller value capacitors get rid of radio frequency noise and electrolytics the lower frequency audio noise. For a power lead you may need protection for both ie a 0.1 and a 100 microfarad capacitor.

The common wires (called earth or ground) for all electrical units in your system should be kept separate from each other to a point as close as possible to where the ground first appears in the model. This prevents "earth loops", noise created in a device by large earth currents from another device.

Tailoring sound


We have seen how to improve the output from a speaker. Some of these tips can also be used to tailor the sound to suit a particular application. Placing plastic foam against a speaker tends to "kill" high frequencies and deepen a sound such as a chuff.

Projecting a speakers output through a tube can give it depth as well as ensure that all available energy is pointed in the direction of the listener. Tunnelling the sound is important in scenario planning

Using computer software

As user recordable sound modules become more common so will the use of computers to tailor sound. Computer programs are available that have all the capabilities of a major recording studio. The sound can be altered to cope with poor speakers, given depth and mixed, extended and enveloped without any loss of quality. A sound card or a direct digital connection can then "program" the sound module.


Sound quality is in the ears of the listener. Use the tips above to experiment and obtain the sound that you want.

Sound units currently advertised

Dallee Electronics


Remote Control Systems

Box 1118 Bayswater Vic 3153

Tel/FAX (03) 9762 7785

Mobile 014 029 083

United States:


Dallee Electronics Inc.

10 Witmer Rd, Depot C, Lancaster PA 17602

Phone: (717) 392 1705 FAX: (717) 392 4694


Phoenix Sound Systems

United States:


Watts' Train Shop

Phone: (317) 873 6524 FAX: (317) 873 6522



United States:

Speed, Direction & SOUND Inc.

Dept. NGG-97

1840 E Warner Road, Suite A105-260, Tempe, Arizona 85284

Phone: (602) 705 4544



Real Rail Effects

United States:


RRE, POB 1672 Highland, IN, 46322

Phone: (773) 202 9931




United States:



555H Burbank Street, Broomfield, CO 80020

Phone: (303) 465 4435

FAX: (303) 465 4191


Tony's Train Xchange

24 Corduroy Road Essex Jct, VT 05452

FAX: 802 878 7684




United States:



3800 SW Cedar Hills Blvd, Ste 224, Beaverton, OR 97005

Phone: 503 350 0595 FAX:503 626 9995

Sound units steam or diesel



The Signal Box

Shop 3/457 Great western Highway Faulcanbridge 2776

Phone: 02 4751 2088 FAX: 02 4751 4503