Sound systems

Sound systems in G scale have challenges, but the good thing is that it's nowhere near the challenge of a smaller scale. You have enough electrical power for a good amplifier, enough room for an adequate speaker, and a circuit that has a reasonable amount of ram and memory.

I'm not going to cover all the low end systems that really are not realistic, or polyphonic. Polyphonic means capable of making multiple sounds at the same time. Many cheaper sound systems will "lose" the sound of the locomotive engine when blowing the horn, for example. Crummy. There are many sounds on both steam and diesel prototypes that happen at the same time.

All the quality systems are now (as of 2009) based on DCC, and some have some "DC capability". More on this later. This all makes sense since G scale is way smaller than the HO market, where the bulk of the DCC technology is coming from. It's a lot easier to "scale up" an HO sound system, than to develop one ONLY for G scale from scratch. 

The following sections will cover some of the basics.

Speakers

The basic rule is pick one as big as you can possibly fit. Normally people put speakers for steam locos in the tender, but in large scale you can put reasonable speakers in the boilers of larger locos.

See my page on the Aristo Mallet, this loco is so long, that a speaker in the tender sounded funny, because the sound comes from a place nowhere near the stack.

When you put a speaker in a loco or tender, you most often want to make a sealed enclosure for it. There are two reasons: One is that sound actually comes from both sides of a speaker cone. But, since when the front side of the speaker is moving out, the back side is moving in. Thus, two out of phase pressure waves are created. If they mix, they cancel each other. So you want to isolate the front from the back.

The second reason for an enclosure is that bass frequencies try to make the cone move a lot. When the cone moves too far, like at high volumes or low frequencies, it eventually stops due to the mechanical limits of the speaker. This abrupt stopping causes distortion, and makes the sound bad. You also want to limit the motion (called the excursion) of the cone to protect from actual damage to the speaker. A sealed enclosure acts very much like a shock absorber and spring on your car's suspension. When it trys to go too far, the spring and the shock absorber serve to smoothly stop the motion before the mechanical limits of  the suspension is reached.

Another commonly misunderstood item is speaker "impedance". Impedance is like resistance, but measured in the AC domain, which a sound signal is. The lower the impedance, the more current a speaker draws from the sound board. Draw too much current, and you distort, and draw way too much current an you destroy the output amplifier in your sound board.

Most sound systems have NO protection from too low an impedance speaker.  The impedance of speakers connected together in series or parallel follows the same rules as resistors.... put them in series, and the impedance is the SUM of the two. Parallel 2 speakers of the same impedance, and the resulting impedance is HALF the impedance of one speaker. DANGER! This will typically destroy a sound board. DON'T DO IT!

***need*** section on triggering sounds, sound volumes, etc.

What are "sound triggers"?

In the world before DCC, where the commands are directly received by the sound board, people first used reed switches triggered by magnets between the rails. When you passed over the magnet, it moves a small arm in the reed switch (the reed) to make contact. Closing a circuit to the sound board is called "triggering" the sound board.

From a practical sense, you could run a maximum of 2 different triggers, with the magnets offset towards one rail or the other.

As R/C systems progressed, they were built with multiple "outputs" which could be connected to the "trigger inputs" of the sound board. This is of course limiting, since every sound controlled needs a physical wire between the R/C system and the sound board.

What is all this about wattage?

There's no real magic here, and it's exactly the same as the home stereo market. Sound volume is measured in decibels, and one decibel was meant to be the smallest increment / change in volume that humans could perceive. In reality, most people can only discriminate between 2 or 3 db (decibels) in change. 

It takes DOUBLE the wattage to increase the sound level by 2 db. Read that again!

What this tells you is that the difference between a 2 watt system and 3 watt system will be NOTHING. If you are expecting to get your loco "louder" with wattage, you need to increase the wattage by a factor of TEN. This does not exist. 

To get a louder loco, you need to get a more efficient speaker, whether the speaker itself, or the effects of an enclosure. 

Phoenix sound systems:

P5 - Basically a DCC only board. It seems that this is being discontinued, 6 watts, no trigger inputs.

P5T - $45 list - adds trigger inputs and motor speed inputs so it can be controlled by R/C systems, and sense motor speed. It has 6 trigger inputs.

P8 - $195 list - This product is the combination of the P5 & P5T basically, an all in one that has trigger inputs as well as DCC functionality. It has 5 trigger inputs, 6 watts.

PB9 - $245 list - this is the replacement for the 2K2 decoder (which is being discontinued)  - 4 triggers and 3 watts, low voltage operation - 3v (big boost) built in.

Bigboost - $45 list - allows the system to run at lower voltage, 3v (switching power supply)