Filters and Frequency Tables
18.0Filters and Frequency Tables
18.1 Standard
Filters
18.2 Full Range
Frequency Card
Fig 18.1 Frequency and
Component Function
The standard filter provided for the FDS-360 is of the Linkwitz-Riley response based on two second order Butterworth circuits in series. The response is a 24dB/OCT slope with a 'corner' frequency where the output of the filter if 6dB down from its pass band level. The use of these filter realisations has been well documented and provides the best possible phase and amplitude response for driving large speaker systems.
Table 17.1 lists the component values for various frequencies and should be used in conjunction with the drawing for the FDS-360F frequency card (See Figure 18.3). Blank cards, or ready made cards can be provided by any BSS dealer.
All resistors should be ΒΌW metal film 2% tolerance or better. Capacitors should be 5% tolerance or better. Figure 18.1 shows how these components relate to the separate filter blocks to assist in making mixed frequency cards that might be needed for speaker systems that require gaps or overlaps in the amplitude response of the filters. Other filter responses can also be realised using these frequency cards, and your dealer will be able to supply these to order.
Should the fourth band output be required to work as a full range buffered output (See section 14.1), a full range frequency card is required to be inserted into FC3 position. This card removes all filtering associated with the third frequency point. The limiter setting capacitor C10 should be chosen to suit the lowest frequency in the band, which would normally be 30Hz. Figure 18.4 shows the frequency card modified for this result.
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