I carry a hundred different kinds of speakers. So which one is the best? The one that fits, right?
Choosing the best speaker is more about physical size and matching the rating to the decoder than the quality of the speaker. We are not trying to fine tune a $1000 Hi-Fi stereo system. We are trying to get as much noise as possible from the smallest source we can find. Don't get me wrong, quality is important. Junk is junk and broke is broke. I am simply saying that at some point, size becomes the limiting factor until the technology over comes that.
That said, the best speakers for our applications will have a low frequency response range. A speaker with a low frequency repsonse range is best for model trains since the locomotive sound are heavy with bass. The lower the frequency response range, the better job the speaker will do to reproduce it.
The physical size of the speaker is pretty straight forward. Bigger is almost always better. The larger the surface area of the diaphram, the louder the speaker will be.
One way to increase the surface area if you are limited by space is to use multiple speakers
Speakers and the amplifier on a decoder are rated by Watts of Power and Ohms of Impedance. It is very important to try to match this. A mis-matched configuration will definitely affect the volume and could fatally damage the decoders amplifier.
Watts of Power
The Watts of Power rating for current production decoders varies by manufacturer and model. It is best to review the specs for your appliction to be sure what your decoder is rated at. Most are rated at 1 Watt. This will be the basis for our discussion.
Matching the wattage of the speaker to amp is important because a mismatch can cause poor sound quality and premature failure of the speaker.
In general, a higher the wattage will produce a louder the installation. That's why the rock stars want more power. What was it Terrible Ted said... "If it's too loud, you're too old"...
The actual value of wattage delivered to the speaker is determined by the rating of the amp, the wiring circuit, and the volume setting for playback.
A 1.0 watt amp will deliver 1.0 watts to a single speaker when the volume is set to 100%.
A 1.0 watt amp will deliver 0.5 watts to a single speaker when the volume is set to 50%.
Multiple speakers affect this calculation even further. There are a number of sites on the web that discuss the formula for calculating this. I like to leverage the knowledge of the web and have found an easy way to do the math. Read on...
Ohms of Impedance
The Ohms of Impedance rating for current production decoders varies by manufacturer and model. Again, it is best to review the specs for your appliction to be sure what your decoder is rated at. Most are rated at 8 Ohms. This will be the basis for our discussion.
Matching the impedance of the speaker to the amp is important because a mismatch can cause poor volume and premature failure of the amplifier.
In general, a lower impedance will produce a louder installation. But be careful! This is also the quickest way to smoke the amp. If the impedance is too low, it will over-drive the amp and cause rapid failure. The high road here is to be equal to or higher than the actual rating of the amp.
The actual value of impedance of the installation is determined by the rating of the speaker and the wiring circuit.
A single 8-ohm speaker will create 8-ohms of resistance.
Two 8-ohm speakers wired in parallel will create 4-ohms of resistance.
Two 8-ohm speakers wired in series will create 16-ohms of resistance.
Multiple speakers affect this calculation even further. There are a number of sites on the web that discuss the formula for calculating this. As stated previously, I like to leverage the knowledge of the web and have found an easy way to do the math.
There is a free excel spreadsheet download available from Duncan Amps that will do the math for you and allow you to experiment with speaker ratings to determine how they will affect the final configuration.
While not mathematically perfect, you can also simply measure the impedance of a speaker(s) with a multimeter set to read resistance. It's close enough for our needs. This will tell you the ohm's of resistance of the circuit and is a great way to double check your wiring before connecting them to the amp.
A Picture Is Worth A Thousand Words
They say a picture is worth a thousand words... Looks like deflation is working hard here 'cause I was a bit windy today.
To make things even easier, here are examples of the most common circuits I use... in pictures.
