Operation Manual
I-Tech HD DriveCore Series Power Amplifiers
page 64
I-Tech HD DriveCore Series Power Amplifiers
Operation Manual
page 65
Fig. 16.6 Reversed-polarity on-axis response (left) and ±25° off-axis
response of a two-way system with a 4th-order 3 kHz crossover.
The remaining two LR crossover graphs in Fig. 17.6 show the
reversed-polarity on-axis response and the ±25° off-axis response.
note that when the tweeter leads are reversed, the response exibits a
deep null at the 3 kHz crossover. However, the null is also accompa-
nied by a wide two-octave depression in response. The second graph
of the pair shows the 25° off-axis null due to driver spacing. Not
surprisingly, the response is similar to the on-axis response when the
polarity is reversed.
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16 Application of FIR Filters to Loudspeaker Crossovers
16.13 FIR Measurements
The Crown I-Tech HD amplifier was used to create a linear-phase FIR
crossover with a 3.67 ms latency. This latency allows crossovers to be
created with filters whose corner frequencies can extend down 500 Hz.
Selections of higher latencies allow sharper cutoff filters to be created
with correspondingly lower corner frequencies. FIR filters with
latencies from 0.92 ms up to 29.33 ms can be created with the
amplifier’s software with minimum corner frequencies ranging from 2
kHz down to 62.5 Hz. the 3.67 ms latency FIR filter provides a relatively
sharp rolloff filter with reasonably short latency.
Figure 7 shows two graphs illustrating the measured frequency
response magnitude (left) and phase (right of the 3.67 ms latency FIR 3
kHz crossover generated by the HD amplifier. The right graph shows
the measured phase of the crossover with the phase rotation due to the
latency and speaker-to-microphone transit time subtracted out. It
shows a linear zero-phase characteristic over most the measured
range.
Note the extremely fast filter rolloffs in the left graph which approach
150 dB/octave and the exceptionally-narrow one-third octave
crossover span.
Figure 16.8 shows the measured individual driver responses of the
same two-way system driven by the FIR crossover as produced by the
Crown I-Tech HD amplifier and the resultant summed 1m on-axis
response. Note the extremely sharp filter rolloffs in the left magnitude
graph. Note also that the right on-axis response is essentially identical
to the previous LR on-axis response.
Fig. 16.7 Magnitude (left) and phase (right) of a 3.66 ms latency 3 kHz
FIR crossover filter generated by an I-Tech HD amplifier.
Fig. 16.8 Measured individual driver responses (left ) and overall
summed on-axis response (right) of the two-way system of Fig. 5
driven with 3.67 ms latency 3 kHz FIR crossover filter generated by an
I-Tech HD amplifier.
Fig. 16.9 Reversed-polarity on-axis response (left) and ±25° off-axis
response of the two-way system of Fig. 5 driven with 3.67 ms latency 3
kHz FIR crossover filter generated by an I-Tech HD amplifier.
16 Application of FIR Filters to Loudspeaker Crossovers
Figure 16.8 shows the measured individual driver responses of the
same two-way system driven by the FIR crossover as produced by the
Crown I-Tech HD amplifier and the resultant summed 1m on-axis
response. Note the extremely sharp filter rolloffs in the left magnitude
graph. Note also that the right on-axis response is essentially identical
to the previous LR on-axis response.
The final two graphs, shown in Fig. 17.9, illustrate the reversed-
polarity on-axis response and the ±25° off axis response for the FIR
crossed-over system. Note the extremely narrow crossover regions due
to the rapid filter rolloff of the FIR filter. Psycho acoustic tests reveal
that these narrow high-Q dips in the response are much less audible
than low-Q wider dips.
16.14 Conclusions
Crown’s powerful DSP processing power in the latest I-Tech HD Series
amplifiers allow sophisticated crossovers to be implemented using
Finite Impulse Response (FIR) filters. FIR filters offer a number of very
strong advantages when used to implement DSP electronic
loudspeaker crossovers.
16.15 Refereces
For those who want a more in depth treatment of the topics in this white
paper, here are three good reverences.
[1.] A.V. Oppenheim, R. W. Schafer, Digital Signal Processing,
(Prentice Hall, Englewood Cliffes, NJ, 1975).
[2] E.C. Ifeachor, B.W. Jervis,
Digital Signal Processing,
A Practical
Approach (Addison-Wesley Publishers, Reading, MA, 1996).
[3] G. J. Krauss, “Advantages of FIR Filters in Digital Loudspeaker
Controllers,” Presented at the 120
th
convention of the Aud. Eng. Soc.,
Convention Paper 6779. (May 2006, Paris)
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