C#: Removing common invalid characters from a string: improve this algorithm

Question

Consider the requirement to strip invalid characters from a string. The characters just need to be removed and replace with blank or string.Empty.

Answer 1

This one is faster than HashSet. Also, if you have to perform this action often, please consider the foundations for this question I asked here.

private static readonly bool[] BadCharValues;

static StaticConstructor()
{
    BadCharValues = new bool[char.MaxValue+1];
    char[] badChars = { '!', '@', '#', '$', '%', '_' };
    foreach (char c in badChars)
        BadCharValues[c] = true;
}

public static string CleanString(string str)
{
    var result = new StringBuilder(str.Length);
    for (int i = 0; i < str.Length; i++)
    {
        if (!BadCharValues[str[i]])
            result.Append(str[i]);
    }
    return result.ToString();
}