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Subwoofer Filter
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Active X-over

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L C Audio Technology
H.C. Andersensvej 56
8230 Aabyhoej

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or Gert Frederiksen
+45 6062 9017

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    Active Speaker X-over [Discontinued]

    The 2 way active x-over board has been discontinued. This page is for existing owners who want to reconfigure and experiment with the filter frequencies, slopes etc.
    The Bass section is made with the NE5532 bipolar opamp, which has good properties for frequencies up to 5 kHz. For the high pass section a discrete circuit with single end class A amplifiers is used as the best solution. See schematics below!

    This is the basic setup of an active X-Over system. Each speaker unit is connected DIRECTLY to the output of an amplifier, with no x-over components in the signal path. You need 4 amplifier channels to drive a complete system. 2 Channels for high section can be low power, and the bass amplifier only needs to have good sound in the bass regions, but bigger output power. The division of tone frequencies is done before the power amplifier rather than after, as is the case in a passive x-over setup. There are many advantages: The driver units see a constant low impedance from the amplifier, in a passive x-over the impedance is typically very high in the x-over frequency range, so there is no damping factor at all. You can adjust the level of each driver separately without loss of sound quality. Real high quality capacitors cost around 1$ for this type of filter, it would cost 100-200$ for a passive filter.
    The sound of this setup is incredible!

    Bass Correction.

    As an extra feature, we have built in a bass correction that inverts the roll-off curve of your loudspeaker [optional], and adds half or one octave of frequency to the bottom end of the frequency scale without sacrificing dynamics or power handling. Signal is gradually added in the beginning of the roll-off area, but when the roll-off is too much, and the effective sound is 9-12dB down, a steep low-cut filter removes all signals that would otherwise only generate vibrations and not sound. This turns out to make the speaker sound bigger than it is, by extending the bass performance in both frequency and acoustic output. >

    The BLUE curve shown natural roll off of this typical 14 litre speaker. The ORANGE curve shows the corrected bass signal, adapted for this particular speaker. The bass roll-off is inverted in the signal until -9dB, then the lower frequencies are cut off with a 12dB/oct low cut filter. The GREEN curve shows the resulting bass performance of this speaker. You can correct even further, depending on the only trade-off in this method: available amplifier power. With modern power amplifiers like ZAPpulse Power should not be a problem though.

    This correction circuit is integrated on the module, and can be activated or not as you wish. 2 resistors configure the frequency and lift rate for this filter, so it is very easy and cheap to experiment with to find the best match for your speakers and your listening room.

    Gainer Configuration

    Gain in Centre Frequency: Centre Frequency: Hz

    Here is a sample setup of an active X-over filter setup. The Filter board, and 4 ZAPpulse modules with a power supply make up a complete system to drive the speaker directly. The drivers used here are the Scanspeak 15W8530-00 and the Scan Speak Revelator D2905-990000 tweeter. For the tweeter we used ZAPpulse 2.1 Special Edition for best sound quality, and for the bass'es we used ZAPpulse 2.1 standard modules, as they perform great at lower frequencies. This sounds amazing!

    Filter Configuration

    Bass Section Frequency: Hz
    Treble Section Frequency: Hz

    The Low Pass section for a 24dB/oct. filter. Note OPA2134 shown here, but we use NE5532 for this section.

    The High Pass section in our filter is made with single end Class A buffers.

    Note in these two cases that capacitors are configured as two chained Butterworth sections, to make a 24dB Linkwitz Riley filter. To read more about Linkwitz-Riley filters, click here: []

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