First and foremost, the speaker must have a proper enclosure. The enclosure must seal (air tight) the back of the speaker from the front, and must NOT vibrate. Simply mounting it in a tender or freight car and using that as the enclosure will NOT provide any sound retention at all, and therefore is not even close to being a proper enclosure. Many people use a cut-off pill bottle or 35mm film container. While these will provide fairly good results for some speaker sizes, it won't suffice for all. And the material they are made of can vibrate slightly with speaker operation. We've found that the absolute best enclosure is made of thin sheet lead. It can be cut to size with household scissors, shaped with your fingers, soldered or glued (with Goo) to make it air tight, and absolutely will not vibrate.

The depth of the enclosure should be the same as the diameter (or width) of the speaker or smaller; i.e., for a one-inch speaker, the enclosure should be no more than 1 inch deep. While the enclosure can be as shallow as needed, it doesn't do any good to make it any deeper than the diameter. In fact, an extremely shallow enclosure that won't vibrate and is sealed air tight is far far better than a larger one that isn't sealed, or does vibrate.

The idea is to keep the sound waves emitted from the back of the speaker from reaching the sound waves at the front of the speaker. When the two get together, they cancel each other out and make it sound tinny. The better one side is sealed from the other, the more volume you will get and the better the entire frequency range will sound, especially the lows. There is one exception to this. We have found, quite by accident, that if the speaker enclosure is at the exact right shape and depth (dependent on a whole host of factors), and a hole is made in the enclosure at the exact right position, sound doesn't deteriorate and can actually improve. But finding all the exact factors is a hit-or-miss situation and would be extremely time-consuming to find unless you get lucky. We recommend against trying to find this and simply seal both sides from each other.

As we've all experienced, the bigger the speaker, the better the lows will sound. It's best to use the largest speaker you can fit into your sound car. However, our 1.1-inch by 1.5-inch oval speaker will fit most HO scale and larger, has more than twice the speaker surface as a typical 1-inch speaker, and is rated at 1 watt. And our LS-SO oval speaker does the same for smaller applications. You not only get better lows because of the larger surface area, but better sound due to the higher rating. Our LS-O speaker will easily out perform the 1.5-inch speaker and give a 2-inch speaker a good run for the money. With the typical round speaker being rated at 0.1 watt, this oval speaker is rated at 10 times that. With sound systems, equipment of higher power ratings is generally better-sounding at all volumes.

So, how large a speaker can you fit into a given loco? Unless the speaker comes with the sound unit for the application, the answer to that question depends upon you: your skills, time, desires, etc. In all cases, a very skillful person will be able to fit a larger speaker than an unskillful person. A person who doesn't mind cutting away some plastic or chassis will be able to get a larger speaker in than a person who wants to do as little cutting as possible. A patient person will get a larger speaker in than an impatient person. A person who want the absolute best sound will find a way to get a larger speaker in than a person who is satisfied with decent sound.

With all this in mind, you can see why it's not appropriate to ask us what speaker will fit a particular application. We don't know your skills, level of patience, or desires. So it's up to you to open the loco and scrutinize the available spaces. Decide where you'll put the sound decoder (their sizes are listed on the SoundTraxx index page), then decide where you'll put the speaker. Simply measure the spot to decide how large a speaker you can fit there.

The last consideration is capacitance for the speaker. For sound units that do not come with a speaker, Throttle Up! provides a general-purpose-sized capacitor rated for the size speaker most often used. However, your sound unit can be fine-tuned by changing the capacitance.

It's easy to overdrive a small speaker with lows. So, a capacitor is used to filter the lows out. The lower the capacitance, the more lows are filtered out. But this adds more resistance to the circuit and lowers the overall volume. You can, however, program the volume back up if you haven't already maxed it out.

So lower-capacitance filters more lows out (reducing distortion), but adds resistance which lowers the volume. Higher capacitance provides more volume and lets more lows through. If your speaker can handle the lows, the higher-capacitance capacitor is desirable.

What's optimum? Obviously you don't want to filter out anything that doesn't have to be. The optimum is the highest-value capacitor you can use in any given situation without distortion. If you have distortion, lower the volume and/or lower the capacitance.

Lastly, DSD-150 sound decoders can use polarized or bi-polar capacitors. DSX and LC sound units MUST have bi-polar capacitors. We carry spare capacitors that Throttle Up! offers, but don't have a wide variety. You can usually find a variety of capacitors at your local electronics store.