The loudness button

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How many of you remember back when every receiver, preamp and integrated had a loudness button? I remember with great fondness my first Kenwood integrated amplifier in the early 1970's and right on the front panel was a magical button labeled loudness. Funny thing was whenever I pushed it on nothing got louder. There seemed to be more bass but no more loudness. The button was a complete mystery to me for years but whatever it did meant better sound and I liked that. Many of you understand that this button was actually a bass and treble boost that varied with the volume control - hence the name "loudness" as the amount of bass and treble boost varied with the loudness control. Whoa. Remember in yesterday's post I was rambling about how any electronics designer would be run out of town on a rail should he decide to make an amplifier that was not flat? Well, here you are: the loudness button permitted amp designers to add bass and treble boost depending on the volume level listeners chose. Because this was user selectable it was ok and, it actually has a basis in acoustics and one we'll discuss in this post. Back in 1933 two audio engineers,Harvey Fletcherand Wilden A. Munson, published a paper that later became known as the Fletcher-Munson curve that this loudness control was fashioned after. What they discovered is that our perception of flat really depends on volume - and the lower the volume our ears seem to think that bass and treble are rolled off - despite the fact they are actually not. The lower the volume the greater this effect. Fletcher and Munson published a set of curves describing the amount of bass and treble increase necessary to satisfy the ear's deficiency as a measurement tool. Receiver and preamp designers in the 1970's added this feature to just about everything they made and, if left on, music would have the proper amount of perceived bass and treble for any volume level you played it. You've probably noticed this effect in your system: if the music is playing in the background there simply isn't any bass to speak of. You have to turn up the music to get the proper bass response - yet the sound is actually flat. One of the problems in these older designs is the curve was implemented relative to the volume control's position - not actually the loudness. So, for example, if you had an efficient pair of loudspeaker connected to your receiver you might hear an overlyexaggerated set of frequency extremes for any given volume setting with the loudness button engaged - the opposite being true for an inefficient pair of speakers. Today it should be a simple matter for designers to add back this wonderful control and make it relative not only to the volume control position but the actual loudness of the speaker in the room. Sadly, no one has done this that I am aware of. See what I mean? Flatness isn't always a great standard to live by because "flat" is in the ear of the beholder.
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Paul McGowan

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