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Investing amplifier circuit frequency response in speakers

By Diksha Nama, contributor, Engineers Garage. An audio system is designed to receive audio signals via microphone , record audio in some storage, transmit audio through wired or wireless communication channels , and reproduce audio signals via speakers. So, the audio circuits perform signal processing for representing the sound in the form of electrical signals, manipulate the electrical audio signals like amplifying, filtering, or mixing, reproduce sound from the audio signals, store audio into computer files or reproduce audio from an audio file. The following block diagram can represent a general audio system. Like microphones or audio sources and speakers, audio filters are also the basic building block of an audio system.


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WATCH RELATED VIDEO: Speaker Size \u0026 Frequency Response

What is an Active Low Pass Filter : Working and Its Applications


Effective date : A primary amplifier is coupled to receive one of the variety of frequency response shapes from the adjustable high pass filter and includes a main operational amplifier op-amp with the inverting input coupled to the adjustable high pass filter through a series connected input capacitor and input resistor.

The primary amplifier provides low frequency signal gain and shaping of the received frequency response shape. A high frequency signal shaping circuit includes a feedback op-amp coupled to the inverting input of the main op-amp through a feedback resistor and a feedback capacitor.

Provisional Patent Application Ser. This invention generally relates to analog signal conditioning in audio systems. Research has shown that the response of the human ear is very dependent on the frequency content of the sound. The ear has peak response around 2, Hz to 4, Hz and significantly less response at lower and higher frequencies. In other words, a sound with a frequency between 2, Hz and 4, Hz will be perceived as louder to the ear than sounds below and above this range.

Additionally, the ear's ability to perceive low and high frequencies varies with sound intensity i. This explains why soft music seems to sound less rich than music played at higher volume. Turning to FIG. Curves on the bottom represent quieter volume levels and curves on the top represent louder volume levels. By examining these curves it will be observed that the quieter a volume level the greater the difference in sound intensity level sound energy required for the ear to hear low and high frequencies.

Thus, it is desirable for a sound system to compensate for the natural inadequacies of the ear. Furthermore, the ability of a typical speaker to reproduce sound diminishes rolls-off at low and high frequencies resulting in a reduction of sound content conveyed to the ear. A significant reduction of sound intensity occurs as the signal frequency decreases from Hz down to 20 Hz and again as the frequency increases from 4, Hz to 20, Hz.

See for example the typical speaker frequency response illustrated graphically in FIG. This roll-off results in diminished loudness and thus audibility as perceived by the human ear. Subwoofer systems, specifically designed to accentuate lower frequencies, are incorporated with standard stereo systems to compensate for the low frequency roll-off.

A major problem is that commonly obtainable audio subwoofer systems for reproducing low frequency sound are constructed in such an embodiment that their form is bulky and therefore cannot be easily transported for personal use, for example with an MP3 player when walking or exercising. Additionally, commercially obtainable subwoofer systems consume sizeable electrical current, require ventilation for heat removal, can be complex and difficult to connect and operate, are costly to obtain, present a potential for electrical shock when exposed in damp or wet environments, and as a result are not able to be proliferated widely or easily.

To date, audio engineers have been unable to produce extreme low frequency sound i. In fact, it is commonly believed by audio engineers that it is physically impossible to produce extreme low frequency sound with small speakers and other audio sound devices.

It would be highly advantageous, therefore, to remedy the foregoing and other deficiencies inherent in the prior art. Accordingly, it is an object of the present invention to provide a new and improved subwoofer sound synthesizer.

It is a further object of the present invention to provide a new and improved dynamic contoured sound system that substantially compensates for the natural inadequacy of the human ear at either or both the low frequencies and the high frequencies. It is a further object of the present invention to provide a new and improved dynamic contoured sound system that substantially compensates for the roll-off effects of standard speakers and other sound producing devices.

It is a further object of the present invention to provide a new and improved subwoofer sound synthesizer that is capable of being used with substantially any sound producing devices, including speakers, small speakers, earpieces, hearing aids, etc.

The high pass filter is designed to provide a variety of frequency response shapes in response to adjustments of an adjustable component. A primary amplifier is coupled to receive a frequency response shape of the variety of frequency response shapes from the adjustable high pass filter. The primary amplifier includes a plurality of feedback components designed and connected to produce low and high frequency signal gain and shaping.

The primary amplifier provides low and high frequency signal gain and shaping of the received frequency response shape to the output terminal. An adjustable high pass filter is coupled to the input terminal and includes an adjustable component. The high pass filter is designed to provide a variety of frequency response shapes in response to adjustments of the adjustable component.

The primary amplifier includes a main operational amplifier having an inverting input, a non-inverting input, and a signal output. The inverting input is coupled to the adjustable high pass filter through a series connected input capacitor and input resistor to receive the frequency response shape of the variety of frequency response shapes. The primary amplifier further includes a first feedback resistor coupled between the signal output of the main operational amplifier and the inverting input.

A high frequency signal shaping circuit includes a feedback operational amplifier having an inverting input, a non-inverting input, and a signal output. The high frequency signal shaping circuit further includes a second feedback resistor and a feedback capacitor with the feedback operational amplifier coupled to the inverting input of the main operational amplifier through the second feedback resistor and the feedback capacitor. The inverting input of the feedback operational amplifier is coupled to the signal output of the main operational amplifier through a first differential gain resistor, and the non-inverting input of the feedback operational amplifier is coupled to the signal output of the main operational amplifier through a second differential gain resistor with a resistance value different than a resistance value of the first differential gain resistor.

A capacitor, resistor, and adjustable component, coupled with the non-inverting input of the feedback operational amplifier and output of the second differential gain resistor forms an adjustable simulated inductor. The desired objects of the instant invention are further realized in accordance with a method of contouring sound and synthesizing subwoofer sound in a sound producing device including the step of providing an adjustable high pass filter having a plurality of step settings and constructed with each setting having a different frequency of emphasis and the frequency of emphasis for each setting occurring at a lower frequency than a prior setting and each setting having a different magnitude of gain change, for each setting the magnitude of gain change is greater than a prior setting.

The method further includes the step of applying audio signals to the adjustable high pass filter for controlling the amount of subwoofer synthesis of the audio signals, each step setting providing a different frequency response shape, and selecting a step setting of the high pass filter to provide a preferred frequency response shape of the different frequency response shapes. The method further includes the step of receiving the preferred frequency response shape of the different frequency response shapes from the adjustable high pass filter and amplifying the preferred frequency response shape to provide low frequency signal gain and shaping of the preferred frequency response shape.

The desired objects of the instant invention are further realized in accordance with a method of contouring sound in a sound producing device including the step of providing an adjustable simulated inductor having a plurality of step settings and constructed with each setting having a different frequency of emphasis and the frequency of emphasis for each setting occurring at a higher frequency than a prior setting and each setting having a different magnitude of gain change, for each setting the magnitude of gain change is greater than a prior setting.

The method further includes the step of applying audio signals from the output of the primary amplifier to the adjustable simulated inductor for controlling the amount of high frequency contoured sound of the audio signals, each step setting providing a different frequency response shape, and selecting a step setting of the simulated inductor to provide a preferred frequency response shape of the different frequency response shapes.

The method further includes the step of receiving the preferred frequency response shape of the different frequency response shapes from the output of the primary amplifier and amplifying the preferred frequency response shape to provide high frequency signal gain and shaping of the preferred frequency response shape.

The method thereby controls the amount of contoured sound, subwoofer synthesis, and high frequency signal shaping that substantially compensates for the roll-off effects of sound producing devices at low audio frequencies and at high audio frequencies.

Furthermore, the method counterbalances the natural inadequacies of the human ear and significantly compensates the ear's ability to perceive low and high frequency sounds. The foregoing and further and more specific objects and advantages of the instant invention will become readily apparent to those skilled in the art from the following detailed description of a preferred embodiment thereof taken in conjunction with the drawings, in which:.

Turning now to FIG. Sound system 20 includes passive and active electronic components formulated and configured to filter input signal frequency and contour output signal magnitude in calculated proportion with frequency characteristics of the input signal. It should be noted that FIG. Referring additionally to FIG. While approximately 12 contours are illustrated for this example, the specific embodiment of sound system 20 is constructed to provide 32 unique low frequency shapes or contours and 32 independent high frequency shapes or contours, resulting in a total of 32 2 unique controller response shapes.

It will of course be understood that 32 shapes is simply for purposes of explanation and more or less low frequency and high frequency contours can be provided if desired. Also, it can be seen that each contour or controller setting, has a different magnitude of gain change, i.

This is true for both the unique low frequency shapes or contours and the independent high frequency shapes or contours. It should also be noted that the low frequency contours have a much greater effect on the overall response and are a primary subject of the present invention. While high frequencies are affected by both the human ear and speakers, as illustrated in FIGS.

It will of course be understood that each section influences each of the other sections but for purposes of understanding the overall operation or function of the sections will be discussed individually. Referring specifically to FIG. The opposite end of resistor R 7 is connected to one side of a filter input capacitor C 5. The opposite side of capacitor C 5 represents the output of section A and is also connected to one end of a 32 step digital potentiometer A 1.

Resistor R 7 creates a voltage divider with potentiometer A 1 and resistor R Capacitor C 5 , potentiometer A 1 , and resistor R 10 form a high pass filter. Section A is a high pass filter configuration responsible for controlling the amplitude of audio signals passed-thru to the primary amplifier section B. By changing the value setting of digital potentiometer A 1 , a variety of frequency response shapes are obtained, as illustrated in FIG.

Without section A, the low frequency response of sound system 20 would appear as shown in FIG. Section B includes an input capacitor C 1 , the input side of which is connected to receive the output signals from section A.

The opposite side of capacitor C 1 is connected to one side of an input resistor R 1. The opposite side of resistor R 1 is connected to the inverting input of an operational amplifier X 2. The positive or non-inverting input of operational amplifier X 2 is connected to an amplifier bias supply V 3. Power is provided to the positive terminal of operational amplifier X 2 by a DC voltage supply V 1 and the negative terminal is connected to the common or ground.

It will be understood that bias supply V 3 and DC voltage supply V 1 along with other bias supplies included herein may be simply batteries or might be connections through a voltage divider network to a common supply source, as will be understood by those skilled in the art.

The output of operational amplifier X 2 is the signal output of section B. Section B is the primary amplifier including feedback components producing low frequency signal gain and shaping. The feedback components include a feedback resistor R 4 an input end of which receives a signal from the output of operational amplifier X 2 see FIG. The input end of resistor R 3 is connected to an output of section C and the output ends of resistor R 4 and capacitor C 3 are connected to the inverting input of operational amplifier X 2.

Capacitor C 1 and resistor R 1 form a band pass filter that sets the bandwidth of frequencies passed to operational amplifier X 2. Resistors R 1 , R 3 , R 4 and capacitor C 3 form a high pass filter that sets the voltage gain of operational amplifier X 2. Capacitor C 3 reacts in proportion to signal frequency and dynamically changes the combined impedance of components forming the voltage feedback loop.

The circuit included in section B, by itself, produces the signal shape illustrated in FIG. Section C includes an operational amplifier X 1 the inverting input of which has an output terminal of a differential gain resistor R 5 connected thereto and the non-inverting or positive input of which has an output terminal of a second differential gain resistor R 6 connected thereto.

The input side of a differential gain capacitor C 4 is connected to the non-inverting or positive input of operational amplifier X 1 and the output end is connected to the input of section D. Power is provided to the positive terminal of operational amplifier X 1 by a DC voltage supply V 4 and the negative terminal is connected to the common or ground.

The output of operational amplifier X 1 is connected directly to the inverting input thereof and is also connected through a high frequency shaping capacitor C 6 to the junction of series connected capacitor C 3 and resistor R 3 in section B. Section C is a feedback servo amplifier, further simulating the electrical characteristics of an inductor, that produces high frequency signal shaping.

The impedance of capacitor C 4 changes in proportion to the applied signal frequency from the output of operational amplifier X 2. Resistor R 6 and capacitor C 4 form a dynamic voltage divider at the non-inverting input of operational amplifier X 1. Operational amplifier X 1 changes the output voltage thereof in proportion to the difference voltage between the inverting and non-inverting inputs thereof.

The output voltage from operational amplifier X 1 is applied to the inverting input of operational amplifier X 2 to produce the frequency response shape illustrated in FIG.

The impedance of capacitor C 6 changes in proportion to the applied frequency from the output of operational amplifier X 1. Basically, the inputs of operational amplifier X 1 are connected to maintain operation at a mid point between upper and lower limits to ensure that no clipping and the consequent sound aberrations occurs.

The variable tap of potentiometer A 2 is connected to the input end thereof i. Basically, potentiometer A 2 and resistor R 11 are added to the dynamic voltage divider i. Resistor R 11 provides a fixed resistance to the dynamic side of the voltage divider and sets the attainable high frequency gain. Capacitor C 4 , potentiometer A 2 , and resistor R 11 form an adjustable simulated inductor.


Basics of audio filters

In previous tutorials, we discussed two of the most important building blocks of an audio system: microphones and speakers. Audio circuits perform signal processing, essentially transforming sound waves into electrical signals, which can further be altered through amplifying, filtering, or mixing. These signals can also be stored and reproduced. Audio filters are one part of this system, working as amplifiers or passive circuits with distinct frequency responses. Much like microphones and speakers, these filters are an important part of the basic building blocks of an audio system. They can amplify or attenuate a range of frequencies from the audio input. However, these filters are distinct from a simple audio amplifier or input source, which does not have a frequency-dependent functioning.

Amplifier circuits that drive ceramic speakers have different if the frequency response of the audio signal passed to the speaker can be.

Active op amp high pass filter circuit


Electronics for altering the audio frequency response of a micro-speaker without modifying the micro-speaker itself are used to provide a selected frequency response of the micro-speaker. The micro-speaker has a resonant peak region, from which the response declines for both higher and lower frequencies. In one embodiment the electronics includes a first circuit for modifying the frequency response curve up to the resonant peak region, and a second circuit for modifying the frequency response curve for audio frequencies higher than this region. Each filter yields an integer multiple of 6 dB per octave slope. This application is a Continuation In Part of patent application Ser. This invention pertains to the electronic compensation of the existing micro-speakers contained in earphones or earbud headsets. The compensation is designed to modify the normal micro-speaker output as a function of acoustic frequency so as to: 1 produce a desired response that can compensate for the hearing deficiency of users, usually elderly, that suffer from presbycusus, or age-related hearing loss, which is characterized by a hearing loss that becomes more severe as the acoustic frequency moves to higher tones. Other chosen frequency characteristics can be similarly provided. He describes the generally known speaker in col.

Audio Filters: Understanding the filters – Part 5

investing amplifier circuit frequency response in speakers

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Regular price R Designed for satellite application, it sustains high level of total ionized dose TID and immunity to heavy ions effects.

Electronically compensated micro-speakers


This article is dedicated to methods of boosting bass for systems where it's desired by adding circuits before the amplifier. Bass is a troublesome frequency, but we feel dissatisfied when listening to a setup that just doesn't have enough bass. I've now setup and used a number of bass boost circuits, and they can lift the low-end for systems which use small speakers i. Remembering that small, portable, speakers need to have some efficiency so they can respond with low, battery powered amplifiers. Otherwise, at their size, they'd overheat with big amplifiers. For small 'hi-fi' speakers, i.

-3dB frequency estimation for basic OpAmp configurations

In earlier work, we examined the concept of negative feedback. Here, a portion of the output signal is sent back to the input and summed out of phase with the input signal. The difference between the two signals then, is what is amplified. The result is stability in the circuit response because the large open-loop gain effectively forces the difference signal to be very small. In this case, the combined signal looks just like the output signal. As long as the open-loop gain of the amplifier is larger than the feedback factor, the signal can be constantly regenerated.

The 1uF must be added to the end of the R Update: If you want to improve the low frequency response change the 1uF on the R to 10uF.

Op-Amps: A Beginners Guide

Effective date : A primary amplifier is coupled to receive one of the variety of frequency response shapes from the adjustable high pass filter and includes a main operational amplifier op-amp with the inverting input coupled to the adjustable high pass filter through a series connected input capacitor and input resistor. The primary amplifier provides low frequency signal gain and shaping of the received frequency response shape. A high frequency signal shaping circuit includes a feedback op-amp coupled to the inverting input of the main op-amp through a feedback resistor and a feedback capacitor.

9.2: Op Amp Oscillators

RELATED VIDEO: Measure Your Audio Gear with REW: Pt. 2 Frequency Response

Back from the Analog computers era, Op-Amps have been used for mathematical operations with analog voltages hence the name operational amplifier. Till date Op-Amps are extensively used for voltage comparison, differentiation , integration , summation and many other things. Needless to say, the Operational Amplifier circuits are very easy to implement for different purposes but it has few limitations that often leads to complexity. The major challenge is to improve the stability of an op-amp in a wide bandwidth of applications. The solution is to compensate the amplifier in terms of frequency response, by using a frequency compensation circuit across the operational amplifier. The stability of an amplifier is highly dependent on different parameters.

Acoustic refers to sounds other than human language and music, including the sound of the natural environment, the sound of animals, the sound of machine tools, and various sounds emitted by human actions. This paper first introduces the schematic diagram and working principle of the audio circuit.

Spice Amplifier Tutorial using (.DC, .OP, .AC, .TRAN, .FOUR, .SUBCKT)

In the previous tutorial, we have seen about Passive Filter i. As the name suggests, a High Pass Filter allows only high frequency components of a signal while restricting low frequency components. A high pass filter will allow the frequencies which are higher than the cut-off frequency and attenuate the frequencies lower than the cut off frequency. The amount of attenuation or the pass band range will depend on the designing parameters of the filter. The pass band gain of an active filter is more than unity gain. The operation of the active high pass filter is same as passive high pass filter, but the main difference is that the active high pass filter uses operational amplifier, which provides amplification of the output signals and controls gain.

Bass Boost circuits

University of California at Berkeley. Donald A. Glaser Physics A.




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