A system designed and built in early 2019 which was given away to a friend who really liked them. Two notch filters were added to compensate for his room acoustics which, according to calculations, would have had a severe hump in the bass response of the order of about 10dB.. Given his musical preferences, that eventually proved to be unnecessary but the filters were left in anyway.
The sides were held in a jig until the glue at their junction set, after which these braces were installed.
At the bottom, the input terminals.
At the top, the two bypass switches. They are in bypass mode, down, 55hz on the right and 110hz on the left.
|The crossovers. The 55hz notch filter is in the upper right corner; inductor, resistor, capacitor from top to bottom. The 110hz notch filter is top center; resistor, capacitor, inductor from left to right. The L-pad is the pair of resistors to the left of the inductor at the lower right corner.|
The finished pair.
Total cost of materials, about US$700.
Response of each section, in dBV measured across a resistive load equal to the nominal impedance of the drivers at the crossover frequencies.
This doesn't show the actual speaker outputs; it's purpose is to show the effect of the notch filters. The brown curve is without the notch filters in and the red curve is with both filters in.
Actual responses. The band above 300hz is measured at 1w1m, gated to reduce the room effects. The woofer section below 300hz is measured near field. Blue, no notch filters applied; red, notch filters applied.
The fixed L-pad is applied in the mid-section. None is used for the tweeter. While the 5dB rise above 10khz may be objectionable to a listener younger than 40 years of age, it would be beneficial to one over 40, in this case, well over 65.
The crossover, three way, second order, Butterworth.
The notch filters are shown on the left side above the woofer. The bypass switches, SW1 & SW2 are shown to the right of these filters.
The fixed L-pad to the mid-range is encircled in green. It attenuates about 4dB.
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