MAKING SUBLIMINALS

I've been making my own subliminals and I am quite confused which speed of affirmation is more effective. 2x or 4x? Some say 2x so it can still be understood by the subconscious. While others said 4x speed is more effective so ONLY the subconscious can understand. Which is more effective and recommended? Which is better? And does both speed really have a big difference??