Filter Design; Low Latency 96 Khz Studio Quality Filters; Measurements Of Two-Way Loudspeaker System - Crown DriveCore I-Tech 4x3500 HD Operation Manual

16 Application of FIR Filters to Loudspeaker Crossovers

16.10 Filter Design

IIR filters are typically based on an equivalent analog circuit. Because
of this, the IIR design process is a straightforward matter of converting
an analog filter frequency response specification into digital
coefficients. In contrast, FIR frequency response is usually specified in
terms of an ideal, though physically unrealizable filter, e.g. a brick wall
lowpass. The FIR filter design is the process of generating coefficients
that approximate the response of the ideal filter. The I-Tech HD FIR
filters are designed using a proprietary iterative algorithm using
state-of-the-art signal processing techniques. It yields linear response
and predictable low-noise operation over the entire audio
frequency range.
1600
1400
1200
1000
800
600
400
200
0
10
page 62

16.11 Low Latency 96 kHz Studio Quality Filters

Because of the extreme computational load imposed by high rolloff FIR
crossover filters, a potent DSP and highly optimized FFT Conbolution
algorithm are essential to low latency operation at 96 kHz. In-system
performance is equally dependent on the filter design process itself.
I-Tech HD's platform-optimized FFT Convolution algorithm and
state-of-the-art filter design methodology combine to deliver low
latency 96 kHz studio quality filters.
Required CPU Processing Power
IIR
FIR
FFT FIR
20 30 40 50 60
Crossover Rolloff Rate - dB/octave
Fig. 16.3 FFT convolution block diagram. here the input and filter impulse
responses are both individually FFT'd and multiplied and then inverse
FFT'd to genterate the output.
70 80 90 100
I-Tech HD DriveCore Series Power Amplifiers
Real World Benefits
16.12 Measurements of Two-way
Loudspeaker System
The practical advantages of using an FIR-based crossover can be
illustrated by comparing results with an IIR crossover when a two-way
loudspeaker is setup and measured. For measurement purposes, a
small two-way loudspeaker was driven by a Crown I-Tech 12000 HD
power amplifier controlled by Crown's HiQnetTM System ArchitectTM
software. the use of a small system in this application ensures that the
frequency response and angular coverage of the individual drivers has
sufficient overlap through the crossover region to properly illustrate
frequency response and crossover effects.
The following two sets of measurements show the results of using a
conventional IIR filter set up as a 4th-order Linquitz-Riley crossover
and a FIR filter set up as a linear-phase high-rolloff crossover. Each set
of measurements first show the magnitude and phase response of the
crossover alone and then follows the frequency response measure-
ments of the system itself showing individual driver responses, on-axis
responses with the crossover in and out of polarity, and a single
off-axis frequency response where the response exhibits a null due to
driver spacing.
The small two-way system measured here has a woofer and tweeter that
are separated by about 5.5" which creates an off-axis polar null at
about ±25° at the 3 kHz crossover frequency.
Operation Manual