How is the DCX crossover used to attain subjective tightness?
The Behringer DCX2496 is more than a digital electronic crossover. It is a parametric equalizer, capable of digitally setting up numerous notch filters. These notch filters can be used in the low frequency range to smooth out the in-room bass response.
When a speaker is put into a room with walls, floor and a ceiling, reflected sounds can cancel or reinforce one another which further alters the frequency response. At higher frequencies, hundreds of small peaks and dips can be measured in the frequency response. Trying to remove all these small deviations with a parametric EQ would result in colorations to the sound that may not be desirable. The characteristic sound that made a particular speaker attractive could be completely lost. Even if the hundreds of small peaks and dips were to be adjusted, it would only be correct for a single position in the room. Moving your head just a few inches would require a completely different set of corrections.
At low frequencies, the picture is different. There are fewer peaks and dips, but they are much more dramatic. The peaks and dips persist over a much larger portion of the listening area. Dips can't be corrected electronically. Putting out more power at the dip frequency won't help. If the original and reflected waves cancel each other, they will cancel at 1 watt or 1000 watts. If you have major dips in the frequency response you can try repositioning your speakers, particularly the subwoofer. Fortunately, dips in the bass response are typically not that noticeable. When an instrument plays that particular frequency, the bass is lost, but the higher harmonics of the instruments tone are still there. To some degree, your ear and brain will fill in the missing information.
The situation is different for large low-frequency peaks. These peaks are what tend to shake the knick-knacks off the shelves and result in an overall tubby sound to the bass. Often one or two large peaks dominate the bass sound. People tend to adjust the volume of their subwoofers based on these peaks, getting what is called “one note bass”.
Fortunately, this can be remedied electronically without drastically altering the characteristic sound of your speakers. A room may have several (typically 3) large peaks due to the distance between the front/back walls, left/right walls, and the floor/ceiling. Notch filters can address each of these peaks. You must be able to identify the frequency and magnitude of these in-room bass peaks. There are a variety of ways to measure this, and the DCX2496 can help do this, but I don‘t own one and am not certain of this.
Typically one uses a test tone generator to generate a frequency tone sweep between 20-300 Hz and measures the in-room SPL response. A frequency response curve can be plotted on paper or on a program such as Excel. The worst offending bass peaks will be easily seen. The DCX2496 can then be used to create notch filters to flatten or partially flatten each these peaks. Each notch filter can be customized by adjusting the filter’s center frequency, frequency width, and height.
The result will be a smoother, tighter sounding bass.
