Direct Digital Speaker Volume Control Using Filter Selection
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Solution Overview
Problem
Direct digital speakers lack effective volume control methods, as their frequency response is not flat across the entire frequency range, leading to undesirable sound level changes when frequency is increased, unlike analog speakers which maintain constant sound pressure level.
Innovation Solution
A direct digital speaker volume control system using multiple filters with distinct cutoff frequencies, where a selector chooses the appropriate filter based on desired volume and frequency, ensuring the speaker exhibits a flat response across its frequency range by applying the filtered signal to the input.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the frequency of direct digital speakers is increased, then the sound pressure level increases, but the frequency response becomes non-flat
Solution Approach 1:
The patent applies filters to the input signal before it reaches the speaker elements. By pre-processing the signal with appropriate filters (low-pass, high-pass, band-pass, or notch filters) based on the desired frequency and volume, the system compensates for the inherent non-flat frequency response of direct digital speakers, ensuring flat overall output across the frequency range.
Solution Approach 2:
The system changes the parameters of the input signal by applying different filters with distinct cutoff frequencies. The selector chooses among multiple filter options (low-pass, high-pass, band-pass, notch) and adjusts the cutoff frequency parameter to compensate for the speaker's frequency response characteristics, thereby achieving flat response despite frequency changes.
2Measurement precision
If multiple filters are added to control volume, then volume control precision improves, but device complexity increases
Solution Approach 1:
The system makes the filter selection dynamic rather than static. The selector automatically chooses the appropriate filter and cutoff frequency based on the desired volume and frequency parameters, allowing the system to adapt to different operating conditions without requiring manual configuration or complex fixed architecture.
Solution Approach 2:
The filter bank is designed to be universal, handling multiple functions with a single set of components. The same set of filters (low-pass, high-pass, band-pass, notch) serves different purposes depending on the selected filter type and cutoff frequency, enabling comprehensive volume and frequency control without requiring separate dedicated circuits for each function.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system allows for precise control of sound pressure level and frequency response, maintaining a flat sound level across the entire frequency range, addressing the volume control challenges in direct digital speakers.
Implementation Method 1
each filter exhibits substantially no attenuation below its cutoff frequency and an attenuation response above said filter's cutoff frequency
Data Source
Figure 1A
Figure 1B
Figure 1C~1G
AI summary
A system that includes a direct digital speaker volume control device configured to be coupled to a direct digital speaker. The direct digital speaker include many pressure producing elements being adapted to generate a sound at a sound pressure level (SPL) and at a given frequency in response to an input signal, without using digital to analog converter. The direct digital speaker inherently exhibits a frequency response throughout its entire frequency range. The direct digital speaker volume control device includes a module for providing few filters each having a distinct cutoff frequency such that each filter exhibits no attenuation below its cutoff frequency and an attenuation response above the filter's cutoff frequency. And a selector for selecting one of the filters according to a selection criterion that depends on a desired volume and frequency of generated sound, and applying the filter to the input signal for generating a filtered signal that fed to the speaker.