man listening to music perceiving loudness.

Loudness and EQ

In the golden era of home audio, a myriad of features were designed to enhance the listening experience. One such feature, found in older stereo systems, is the “loudness” control. This feature has stirred up considerable discussions among audiophiles, some considering it a necessary tool while others deem it as a distortion of the original audio signal. In this article, we delve into the “loudness” feature, examining its purpose, operation, and its place in the modern audio landscape.

What is the Loudness Feature?

In essence, the loudness feature is a tone control function that alters the frequency response of the audio signal to emphasize the bass and treble regions, intending to create a perceived balanced sound at low volume levels. This feature is based on the Fletcher-Munson curves, which illustrate the human ear’s varying sensitivity to different frequencies at different loudness levels.

The Role of the Fletcher-Munson Curves

Derived from empirical studies by Harvey Fletcher and Wilden A. Munson in the early 20th century, these curves represent the frequency response of the human auditory system. According to their research, our perception of frequencies, especially the bass and treble, diminishes as the volume decreases. Therefore, at lower volumes, a flat frequency response would sound less full and less vibrant. Here is an article where we discuss the Fletcher-Munson Curves in more detail.

Operation of the Loudness Control

Traditionally, loudness controls were implemented using a potentiometer connected in the signal path, which allowed for an adjustable boost in bass and treble frequencies. The amount of boost applied would gradually decrease as the volume level increased, aiming to maintain a perceived balanced frequency response at varying volume levels.

The Benefits

  1. Enhanced Listening Experience: For listeners who prefer a richer, fuller sound at low volume levels, the loudness feature could offer a more pleasing auditory experience.
  2. Flexibility: The loudness control often allowed for adjustable settings, enabling listeners to tailor the sound signature according to their preferences.

The Drawbacks

  1. Altered Sound Signature: Purists argue that the loudness control alters the original sound signature, moving away from the audio as intended by the creators.
  2. Potential for Distortion: Applying a substantial boost to certain frequency regions could potentially introduce distortion, especially in systems with limited headroom.

The Loudness Feature in Modern Audio Systems

In the contemporary landscape, the loudness feature has largely been replaced by more sophisticated digital signal processing (DSP) technologies. These technologies allow for more precise control over the frequency response, offering personalized listening experiences without necessarily introducing distortion.

Moreover, modern playback devices often feature “loudness equalization” options, which work to maintain a consistent perceived loudness across different tracks and sources. This feature, although slightly different in operation, echoes the intentions of the loudness control, striving to offer a balanced, pleasing listening experience at all volume levels.


The loudness feature in older home stereos was designed with the intention of providing a rich, balanced sound at low volume levels, guided by the Fletcher-Munson curves. While it has faced criticism for potentially altering the original sound signature and introducing distortion, it holds a special place in the hearts of many audiophiles who grew up tweaking the loudness knob to find that “sweet spot” in their listening experience.

In the present day, while the loudness control may have faded into obsolescence, replaced by modern DSP technologies, it remains a fascinating topic of discussion, representing a bygone era of audio technology and the continual endeavor to enhance our auditory experiences through technological innovation.

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