To determine the number of types of speakers Genevieve can choose from, let’s denote the number of types of speakers as \( S \).
Genevieve has 5 types of stereos and 2 types of amplifiers. The total number of combinations she can create with these components is given by the formula:
\[ \text{Total Choices} = (\text{Number of Stereos}) \times (\text{Number of Amplifiers}) \times (\text{Number of Speakers}) \]
Plugging in the values we have:
\[ 30 = 5 \times 2 \times S \]
This simplifies to:
\[ 30 = 10S \]
To find \( S \), divide both sides by 10:
\[ S = \frac{30}{10} = 3 \]
Thus, the number of types of speakers must be \( \boxed{3} \).