Getting the best possible performance from your sound decoders
(1) THE SOUND SYSTEM:
Sound adds a new dimension to the layout and is well worth considering as an extra “detail” on every layout, as it can do more for atmosphere and realism than you might expect!
Basically all Model railway sound systems are based on a simple chain of information and information processing. This is followed by loading into a decoder which stores and processes it on demand. This chain goes something like this:
Sound creation:
The sound is captured on an audio or video recorder
It is then transferred to computer software where it is extracted in a series of small, individual sound files, each specific to a particular type of sound. These files will then be processed into a form which is acceptable to the decoder software. This involves making all files mono, and then digitally processing them into an 8 or 16 bit sound to be “decoder compatible”
Some sounds will be made up of two or three sounds – the most common of these “multiple” sounds are steam loco “chuff” and “whistle or horn” sounds.
Creation of the “sound set”:
(d) This normally involves using special equipment such as the ESU “LokProgrammer”.
(e) Using the computer plus special hard/software, these sound files are then individually adjusted and matched for level and length, to allow them to fit into the available decoder memory AND to ensure that they harmonise well with each other. Where a sound nheeds two or three separate sounds to work together, these are carefully matched. For example, a steam “chuff” will have a start or “attack” file, a mid or “body” file and an end file, which will, if played in sequence, form a complete “chuff” cycle.
(f) The individual sounds are then loaded into a “project” file which forms the basis or the sound set for a specific locomotive. Utilising the brand specific software, these are then set out and allocated to “sound slots” in a particular pattern, according to the decoder logic.
The project files will now also include any “conditions” under which a sound will play, as well as the “sequence” in which they will play. This includes relating individual sounds to speed and other operating conditions. (For example, the “start sequence” which occurs when a loco is selected, or the “brake squeal” which will happen when a loco stops.)
Loading the sound files:
(g) The sounds are now able to be loaded into a decoder for testing. This is done either by plugging the decoder into a tester attached to the programmer, or perhaps placing a loco that has already had a sound decoder installed onto the programming track attached to the programmer. (TIP: loading sound files can take several minutes, so direct connection of sound decoder to a “decoder tester” attached to the programmer will give the most reliable results, as contact is not dependent on the sometimes tenuous contact between wheel and track)
(h) The Programmer will read the decoder, wipe any existing files, and then install the new files in their place. This will normally also result in all “control CV’s” being returned to their “ex factory” default settings… including address, which will revert to the standard ex factory “3”.
(i) The decoder will now be ready to go with its new sound set.
NOW, the decoder must “Process” the sound. This is a “chain” of events that goes as follows:
Start-up:
(j) On “Starting” or “Selecting” of the loco (you press the function key to start the sound) there may be a few seconds of loading time.
(k) During this time, the sound part of the decoder will “wake up”, digital sound files will be extracted from memory and fed into a multi-channel (polyphomic) processor to be turned from digital information into analog sound.
(l) This will then be fed into an analog audio amplifier, which will in turn increase the level and pass the sound to the loudspeaker. Both of these are not so different to any audio product – just smaller… and this gives special needs, as we will see later.
(m) The start-up sequence may, with a complex sound file, take several seconds. It is part of the process and cannot be bypassed – in fact, the loco may not move at all for these few seconds.
This is usually no big thing… A clever sound set will in any case make this procedure entertaining. ie: With a good sound set you may hear for example perhaps the sound of feet on gravel as the driver arrives at the loco. The sound of him entering the cab and the sound of the motor being started. When this sequence has loaded, the loco will be ready to go.
Operation:
(n) Now the decoder is “awake”, the loco can be driven. Motor or steam sounds will vary with speed settings, coupler clank, brake sounds etc will react proportionally with loco actions, and things like whistle or horn can be played at will.
This all depends of course on first installing it correctly. Here are a few thoughts on this – first the pre-planning and actuality of the install – then a few tips and tricks to make it work better.
Top
(2) INSTALLATION OF A SOUND DECODER:
Installation of a sound decoder is not so different to a normal “Loco drive decoder”. The same simple rules apply – red and black to the rails, Orange and Grey to the motor leads. The ONLY additional wiring in most cases will be two wires to the speaker system. Here are a few “guidelines” that may help you to install a sound decoder.
Planning - Think it through first:
(a) Think about BOTH decoder and speaker position before starting to do the installation. With Steam loco’s this will often be the tender OR side tanks OR cab. With Diesels this may be on the trucks OR in the cab (windows open?) OR under the fans OR behind the radiator OR perhaps under the fuel tanks. Look for speaker positions that will do the most to amplify any sound (like the tender or a hollow fuel tank or body) and also have a clear path to the “outside” of the body shell for the sound, so it is not muffled.
(b) Think about wiring positions before starting. Can you route the wires without fouling the drive system, will an installation in the cab be too ugly or too visible or will a decoder in the tender need the loco and tender to be permanently coupled? Pre-planning here makes things easier.
(c) The decoder position has no real need of any special consideration other than the fact that it should fit comfortably, not interfere with the mechanism and have reasonable access to free air for cooling (like any other decoder)…. BUT How about the speaker?
Will the speaker position allow any form of “enclosure” around the speaker to improve the sound and help volume level? Will there be sufficient “open space” in front of the speaker cone to permit sound to escape? Will it be possible to perhaps fit more than one speaker?
(d) Suggestion: BEFORE you start the installation, take off the body shell and service the mechanism. Clean off any old dirt and grease, clean the wheels, check ALL pickups are working OK, tighten any mounting screws, re-grease all universals and lightly oil the motor. Do test run the loco & ensure everything is as good as it can be before starting the installation.
Top
(3) SPEAKERS AND THEIR INSTALLATION:
Sound is governed by the laws of physics. There are FOUR factors that affect the potential level of sound as it applies to a locomotive install. Speakers are the MOST influential part of the equation, but to appreciate this we first need to look at ALL of the key factors. Most as you see relate to speakers anyway!
(a) The amp power: An amp is the thing that makes the speaker move, so it is an issue here… Amp power is normally fixed, and while it can be turned DOWN, it can rarely be turned UP very far. Normal power is between ½ and 1 watt RMS maximum.
(b) The speaker size: This is because volume is a relationship between the SPEED and the AREA of the cone. You have to move or influence the movement of air to make sound. Bigger cones move MORE sound. Sizes vary between 10 and 40mm.
(c) The Speaker impedance: ESU use a 100 ohm speaker as their “design spec”, Many others use 8 ohms. Occasionally, a manufacturer uses 30~33 ohms. Regard the impedance of the speaker as the “base” impedance for any install with the brand, and do NOT mix and match speaker brands unless the impedance is correct. Apart from that, it is ONLY important if you wish to use multiple speakers. For this discussion you need to know only three things:
a. Use the correct impedance as recommended by the manufacturer. The impedance MUST remain within a tolerance of no more than +/- 50% of the design spec of the built-in amp or the internal amplifier will get VERY hot and you WILL fry the decoder (or it will go into "protect" mode and not turn on). This kind of damage is obvious, and will not be warrantable, so do be careful. Adding a speaker in series will double the impedance. Adding one in parallel will HALVE the impedance.
b. The effect of changing the way speakers are wired is extreme in its effect.
• If you wire speakers in series you will DOUBLE the impedance - This makes the amplifier less loud.
• If you wire a second speaker in parallel, this will HALVE the impedance. This will in fact have the effect of doubling the available power delivery.
CAUTION: HALVING the impedance will take the amp to the edge of its design limits, and if you do this it is OK ONLY if you (a) don’t drive it at full volume (b) Do have good heat-sinking or air circulation around the decoder.
• Do NOT use a resistor to “Pad” the impedance level of speakers. Speaker impedance is quoted at a nominal level but in fact changes with frequency, so using a simple fixed resistor will have a negative result in relation to sound quality and as it “wastes: power, it will also reduce sound levels.
a. Consider the AIR mass or VOLUME of air the speaker is working with: Mounting the speaker properly will greatly affect the way it sounds, and the volume it can reproduce.
If you leave the speaker in the manufacturers own enclosure, it will be more efficient than in free air. (with no enclosure)
b. If you fail to add a baffle (a flat plate that the speaker is mounted to) and an enclosure, then you will allow air / sound waves to go from the front of the cone to the back with nothing between them. This will kill all bass sound and cancel much of the sound and therefore lower it to a very inefficient level.
c. If you use a space inside the loco as a “box” that will really help. Think of any home speaker with a sealed enclosure. If you can mount the speaker the same way in a proportionally tiny box, then you will get a much better and more balanced sound from it.
d. If you can’t make a box, then try to mount it on a bit of card or plastic so NO sound can get directly from the front to the back without traveling at least the cone diameter. In other words, a 20mm speaker should have 20mm of card each side, or for practical purposes, the card should span the width of the space and be appx 60mm long with the speaker in the middle.
e. Forget ported boxes or any “fancy” designs. They need a computer program to design well – and anyway are effectively impossible to design without knowing many of the speakers “thielle small” specifications and this is not practical in the tiny sizes we use. Stick to sealed boxes or simple baffles, and you WILL do well.
f. Let the speaker get the sound as directly to OUTSIDE the loco as you can: ie, on a diesel, use the fan position as it’s a natural “speaker Grille”. Or perhaps Drill LOTS of reasonably big holes in a tender floor – or even better cut out a speaker sized hole and mount the speaker straight to the tender bottom. Logically a speaker inside a body shell will be muffled. Put a stereo speaker inside a cupboard & turn it on and you will see what I mean.
g. Sometimes it IS hard to find a good space to add the speaker – Model loco’s aren’t made for audio really. Don’t panic, just do the best you can… there CAN be exceptions and there CAN be “lucky installs”. However, as a rule of thumb, if you try to stick to the recommendations above, you will be MUCH MORE LUCKY than those who don’t ?.
Top
(4) TIPS & TRICKS for BETTER SOUND
Sound & effects in Steam Locomotives:
(a) SOUND IS DIRECTIONAL - especially in the higher frequencies: For best results, try to keep the high frequency sound where it is generated. That means up front if possible for the “chuff”. Not so noticeable in 4mm scale and lower, but its obvious in 7mm/”O” scale and larger if all the sound is from the tender.
(b) NEAT TRICK #1: Put TWO tiny speakers back to back right up front in a steam loco. In this case the boxing is not that critical – we only want the hard mid/high sounds there. Wire these in SERIES and then PARALLEL these two with a large speaker in the tender, facing downwards towards the track. This series/parallel combination will have the effect of lowering the impedance to about 2/3 the design spec, so the volume will be louder…. It will also make the obvious “hard attack” of the “chuff” be very much at the loco front where it should be, while the larger tender speaker will have its highest frequencies slightly muffled by pointing down, leaving ONLY the heavier sounds coming from there, and these are actually far less directional. The result will be a steam loco that has a MUCH better sound quality, sound “imaging” and volume level.
(b) NEAT TRICK #2: Use the "coal space" as an open grille area for the sound to escape from. Drill lots of holes OR cut out most of the plastic coal, which is pretty unrealistic anyway. Add a fine grille made from "Tulle" (The stuff bridal veils are made from) or window flyscreen and paint it black. Add a sprinkling of fine coal with a little glue to hold it. and you'll have a good speaker grille that's totally invisible! (Make sure the "grille area" is not re-sealed by the glue that holds the coal)
(c) NEAT TRICK #3: Why not synchronise the random firebox glow with the sound of coal being shoveled by “fireman Fred”. ESU LokSound decoders and many other higher-end sound decoders will allow this, but you might have to look deeply into the instruction sheet.
Sound & effects in Diesel Locomotives:
(d) USE the FAN or GRILLE AREA if you can. These are usually either inset or see-through grilles, and are therefore natural “speaker grilles” too. Don’t be afraid to LIGHTLY spray paint the speaker if the colour offends you under the grille – or even paint the fan blades on the speaker if you like… the speaker won’t be damaged by a thin coat of paint. Another bonus is that there is MOSTLY clear area at the top of the body shell!
(e) USE the BIGGEST BOX YOU CAN. That’s usually the body shell itself. A flat “baffle” along the axis of the loco from side to side, sealed at the ends if possible (and using the body itself as the other three sides) will be the most effective box you can build… bigger is better with diesel speaker installs, as we really do want to get the depth and “mass” of the sound as big as we can, because a big diesel gives off huge energy which takes a LOT of reproducing. No need for a perfect shape if its hard to do - just use BLU-Tack or modelling clay/plastiscene to fill any gaps.
GENERAL tips for installing sound.
(f) Airtight boxes work best – but they can be hard to build in the small, weird shapes we have to work in. Don’t be afraid to use Blu-tack or modelling clay as a part of a speaker enclosure, and do use a sausage of the same stuff to provide a seal against the side of a tender or diesel body shell. The same stuff can be used to fit a speaker to a baffle… its secure enough to hold it well and won’t damage the speaker as long as its kept away from the cone area.
(g) THINK like a hi-fi person. The BEST speaker position will always be the one that gives the most direct relationship between speaker and ear. Obviously it’s not practical to mount speakers on the outside of the loco, but DO try to mount all speakers in a position that allows the sound to have a reasonably direct path to the outside world. Remember the effect of putting your Hi-Fi speaker in a cupboard!!
Top
Do you have any ideas or questions? Please feel free to email me at
Questions@DCCconcepts.com
