![]() ![]() 707, which results in a very simple resistor calculation represented by R2=R1*2.įor my application I wanted to reduce the FLAT response so that the corner of the filter is somewhere below 20Hz, or the same frequency that corresponds to the point where by sub begins to reach xmax. Since am trying to achieve a maximally flat response, I will shoot for a Q =. Damping is represented by Q and is calculated by the formula: Q = 1/2*(R1/R2)^0.5 where C1=C2. The calculation for determining the f3 (or -3dB point) of an active 12dB/octave filter such as this is represented by the formula: f3 = 1/((2*pi*(R1*R2*C1*C2)^0.5). It’s just an underdamped, i.e., high-Q, high pass filter which creates a peak is the response at a calculated frequency. This is the basic function for many bass boost circuits found in a lot of plate amps. The peak amplitude is approximately 6 dB.” The peak frequency is noted in the swtich markings on the front panel. Once past the peak frequency, the curve falls at 12 dB/octave. In an underdamped second order filter, a peak occurs in the frequency response just before the curve breaks away from a flat response. At other positions, U2 (1) becomes an underdamped high pass filter. In the FLAT position, U2 (1) becomes a second order (12 dB/oct.) high pass filter. ![]() S2, the LF EQ switch, controls the cutoff frequency. This is how the high pass filter and boost work according to the service manual: The one op-amp is for the 18 dB/octave low pass section and the other is for the high pass section. The filter for the low pass section is made up of a single-chip dual op-amp. This is what I learned while looking over the schematic. The service manual has the schematic for the unit which is key into figuring out how to adjust the high pass circuitry. They had a link to both the manual and the service manual. I found it in an unlikely place – someone’s eBay auction that had ended months ago. The first thing I needed to find was the service manual for this unit. The EV XEQ-2 is the perfect crossover for achieving this. An ideal subsonic filter is achieved by setting the cutoff frequency to be low enough to have a negligible impact on the acoustic response of the driver/enclosure while still maintaining just the right amount of safety margin below tuning for the driver so that it does not exceed xmax. It is either too high, in which case it negatively impacts the natural frequency response of the driver/enclosure, or it’s too low and still allows the driver to exceed its rated excursion capability. However, the problem with most rumble/subsonic filters is the cutoff frequency is arbitrarily chosen and usually does not represent the ideal cutoff frequency for the subwoofer to which it is connected. Any vented subwoofer will essentially unload below tuning which can cause the driver to exceed its rated xmax (or even xmech) causing potential damage to the driver. And this is how I did it.įirst off, why put a high pass filter on a subwoofer at all? Commonly referred to as a rumble filter or subsonic filter, the idea is to remove frequencies below that which you can’t hear or those frequencies below where your sub can adequately produce, in an effort to reduce driver excursion and reduce stresses put on your amplifier. What I really wanted was to do was adjust the filter for a predetermined cutoff frequency that corresponded exactly to the maximum excursion capability of my new Audiopulse vented subwoofer. Definitely not optimized for HT and certainly not for a subwoofer that is, by design, flat to 20 Hz. Each click of the switch adds +6 dB boost at varying frequencies from 29Hz to 60Hz. Worse than that, the options for adjusting this filter don’t offer any solutions. The one thing I always disliked about this EQ was the 30-Hz built-in high pass filter. I’ve got an old XEQ-2 active crossover made by EV that I’ve been using for the crossover on my subwoofer for my home theater. ![]()
0 Comments
Leave a Reply. |