Improving WPC sound balance

There are three speakers in WPC games: one big at the bottom of cabinet, and two smaller in the backbox. The right backbox speaker is connected via 10 uF series capacitor, to make it only active at high frequencies. The other two speakers are full range.

In home use, with low volumes the sound appears to come only from backbox speakers and the cabinet speaker is very quiet. This degrades low frequency response. For example, in Twilight Zone the sounds are quite thin and bass almost nonexistent at low volumes.

By adding two resistors, the bottom speaker can be given more power than the backbox speakers. This improves low frequency response, and gives more depth to game sounds.

Speaker wiring before and after

Backbox speakers are in parallel. The right one has a high-pass filter, in the form of a 10 uF capacitor. Cabinet bottom speaker is then in series with the backbox speakers. The modification adds one 4.7 ohm resistor in parallel of backbox speakers, to bypass power from those to the bottom speaker. There is also another 4.7 ohm resistor in series with the right speaker, to reduce high frequencies slightly.

Location of the added resistors

Left speaker has a resistor soldered directly across its terminals. The right speakers coupling capacitor has been disconnected from other end, and a resistor added between.

After this modification, the backbox speakers will be a little quieter. Volume can be set 1-2 steps higher, and then also the bottom speaker can be heard. If you use high volume settings, say over 10, it is probably best to use 5 W resistors instead of 2 watts used in my prototype. The modification makes speaker impedance a little lower, and in theory increases load on sound board amplifier. But in practice it doesn't matter. Adding the two resistors will not do any damage to the sound board in normal volume settings. If you use very high volume, you won't probably need this modification anyway.

Note that this modification applies to older WPC games with pre-DCS sound board only (Twilight Zone and older). The DCS games have a different arrangement of speaker connections and this modification doesn't work in them.

This modification is fully compatible with the startup/shutdown pop remover (the No-Pop board).