Unwanted Audio Intensity Decrease

I have a c# windows form project with the following c# code which uses BiQuadFilter class of NAudio library to implement low pass filter. The problem I am facing is that the intensity of the sound is also dropping along with the frequency thus making the volume barely audible. How can I fix this?

My Code:

    private ISampleProvider sourceProvider;
    private BiQuadFilter[] filters;
    private int channels,cutOffFreq;

    //Constructor
    public MyFilter(ISampleProvider sourceProvider,int cutOffFreq)
    {
        this.sourceProvider = sourceProvider;
        this.cutOffFreq = cutOffFreq;

        channels = sourceProvider.WaveFormat.Channels;
        filters = new BiQuadFilter[channels];
        CreateFilters();
    }

    private void CreateFilters()
    {
        for (int n = 0; n < channels; n++)
            if (filters[n] == null)
                filters[n] = BiQuadFilter.LowPassFilter(44100, cutOffFreq, 1);
            else
                filters[n].SetLowPassFilter(44100, cutOffFreq, 1);
    }

    public WaveFormat WaveFormat { get { return sourceProvider.WaveFormat; } }

    public int Read(float[] buffer, int offset, int count)
    {
        int samplesRead = sourceProvider.Read(buffer, offset, count);

        for (int i = 0; i < samplesRead; i++)
            buffer[offset + i] = filters[(i % channels)].Transform(buffer[offset + i]);

        return samplesRead;
    }

This is how I am using it:

    waveOut.Init(new MyFilter(new AudioFileReader(path + "\\Audio_Tracks\\" + topic + "\\" + currentTrack + ".wav"), 750));

    waveOut.Play();