Earth Lift
The Earth Lift button ensures the Seismix can be connected to a wide range of stereo amplifiers / AV receivers. Should a humming noise be evident when the Seismix is connected, push the Earth Lift button (see figure 1) which interrupts the current that may be circulating from the subwoofer’s signal ground through the mains earth wiring (see figure 4). Note: The Earth Lift button does not break the mains earth connection to the subwoofer, only the connection between the subwoofer’s signal ground and the mains earth. To guard against electric shock NEVER disconnect the mains earth from any appliance.
Low Pass (Hz)
The Low Pass control (see figure 1) adjusts the total bass content from the Seismix. This control allows you to adjust the upper limit of the Seismix’s frequency range between 60
Hi / Lo Gain
The Hi / Lo Gain button (see figure 1) is positioned below the blue Power / Standby LED, this button allows you to increase or decrease the sensitivity of the subwoofer without adjusting other settings. In the ’Lo’ gain position, a much higher input signal is required, and you will need to increase the main volume control to reach maximum output.
In the ’Hi’ gain position the output of the subwoofer is increased by approximately 20dB, requiring a lower input signal, meaning you will not need to increase the main volume control to achieve the same amount of output.
Phase
Signal phase can be left at '0°', or shifted 180° (inverted), by pressing the Phase button (see figure 1). This applies to the output of the subwoofer compared to its input.
To get the most from all of your speakers they must be operating in Phase. That is the signals must all be positive going or negative going simultaneously. If this is not the case and one signal is positive going and the other is negative going the result will be a cancellation of signal and the sound at those particular frequencies will be perceived as quite 'empty' sounding and lacking potential impact.
The setting of the Phase button (ie. 0° or 180°) and the resulting sound is dependant on where the subwoofer is positioned in relation to the main speakers. The best way to find the correct setting is through trial and error during set up by comparative listening tests. In most cases the effect will be subtle and there won't be a complete lack of bass. If no difference can be heard, the position of the button is not crucial.
The effect of phase can best be shown with the representation of a sine wave (see figure 5). The effect shown in the lower diagram is with the signals 'out of phase' and this can be rectified by changing the position of the Phase button. This will invert the negative going
Figure 4 Earth lift button
Mains power outlets
Circulating ground currents
Earth lift button
Signal connection
Subwoofer
Figure 5 Phase
Denotes chassis Earth
Denotes signal ground
Receiver / Amplifier
signal and the result will be the same as the first, 'In Phase', example.
Line Level Inputs
Line level inputs (see figure 1 or 2) need to be connected to the ‘PRE OUT’ or 'SUB OUT’ from your stereo amplifier / AV receiver.
The line level stereo input performs a summing function adding the left and right signals where applicable, to give a mono (L+R) signal. This mono signal is filtered and then amplified before being sent to the subwoofer driver.
Speaker Level Inputs
The speaker level stereo inputs combine
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1 | + | 1 | = In Phase | = | 1 |
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Positive | Negative going |
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1 | + | 1 |
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0 | 0 | 180° out | = | 0 | (No output) | |
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= of phase |
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the signal going to the main left and right speakers providing a mono (L+R) signal to the subwoofer driver. This mono signal is filtered and then amplified in the same way as the line level input signal before being sent to the loudspeaker. Two pairs of terminals are provided so that the speaker level signals can “pass through” the subwoofer on the way to the main speakers (see figure 1 or 3).
