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Loudness..

 

New member
Username: W00b

Post Number: 2
Registered: Mar-05
what is the purpose of the loudness button found on some receivers? i have it on mine and i find that when its enabled, i hear some extra bass.. but that's about it, im wondering if certain receivers don't have this, does that mean that it's always enabled? or it just doesn't have that capability? thanks.
 

nout
Unregistered guest
It's meant to compensate little or no bass performance at low listening levels. Many amps perform better when the volume is cranked up: more presence and better bass.

It can be very useful, with bass-shy recordings too.
 

Gold Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 3259
Registered: May-04



As volume decreases, you hearing is less senitive to low and high frequencies. This is the Doppler Effect and is proven by a passing train. When the train is in the distance, you do not hear the rumble of the wheels. As the train nears and then passes you, you hear not only more volume but also more bass and treble. As the train leaves, you hear less bass and treble.

Loudness compensation is meant to give a boost to frequencies when you lower the volume. Some controls use only bass boost, while some boost both ends. Some controls give large amounts of boost, while others are more modest in the efforts. Some are fixed at a certain amount of boost, while others have a variable amount of boost depending on the volume level. Some pre amps do away with loudness compensation believing any additional circuitry will affect the sound negatively. If your pre amp or receiver has loudness compensation, the system is set up to roll out the compensation as the volume rises. At about 12 O'Clock on a traditional rotary control, loudness compensation is out of the circuit.




 

Gold Member
Username: John_a

Post Number: 2908
Registered: Dec-03
This is correct, Jan, but it is not "The Doppler Effect". The Doppler Effect is the change in frequency of a waveform, such as sound, which arises when the source is moving relative to the observer, or listener. Sound travels at about 1000 ft/sec. If a source of sound is travelling towards you at 100 ft/sec then you hear its frequency 10 % higher than it is heard at the same speed as the source. 10 ft/sec give 1 % higher. When the sound moves away, you subtract the speeds; the sound has a frequency 10% lower for 100 ft/sec; 1% lower for 1 ft/sec.

The Doppler effect is familar as the sudden drop of pitch of sirens on emergency vehicles; whistles on trains, etc.; as they pass you.
 

Gold Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 3261
Registered: May-04



John - I may have misstated the case somewhat, but maybe I need more assistance here. The Fletcher- Munson Equal Loudness Curves are (usually) the basis for the amount of loudness compensation at any one volume setting when using a variable loudness contour. It has been years since I had to discuss loudness compensation, but my memory (such as it is) tells me the F-M curves were developed from the concept of the Doppler effect and share similar values. I understand Doppler involves a moving source and F-M curves relate to stationary objects. My understanding though is Doppler is related to frequency and level where F-M is stricly level vs. sensitivity. Where have I gone wrong?

It should be noted for the original questioner, the Doppler effect has found wide spread use in other areas of science such as physics, astronomy and meterology. As far as I know, F-M curves are useful only in the study of audiology.


http://www.sfu.ca/sonic-studio/handbook/Equal_Loudness_Contours.html


 

Gold Member
Username: John_a

Post Number: 2913
Registered: Dec-03
Jan,

What you say is correct and I also recall something called the Weber-Fechner curve or similar. The sensitivity of human hearing falls off more steeply with decreasing amplitude at higher and lower frequencies than it does at frequencies in the middle of the audible spectrum.

"Loudness" controls are designed to compensate for this effect, and are intended for "night-time listening": the result is to enhance the bass and treble at the expense of the midrange. Some people like this effect even when playing at normal volumes.

This phenomenon has nothing to do with "The Doppler Effect". Yes, the latter is widely seen, or experienced, with all wave forms, including sound and light. It is the basis of the "Red Shift" in astronomy, where the frequency of light is decreased (and so the colour is shifted to the red) if the object (say, a galaxy) is moving away from the observer. In fact the speed of recession, and therefore the amount of red-shift, is proportional to the distance of the object. The constant in there is the "Hubble constant".

Searching, I found a brilliant little applet illustrating the Doppler Effect, for a police car siren, here:

http://www.colorado.edu/physics/2000/applets/doppler.html

I have queried your use of "Doppler Effect" before. I think I see the misunderstanding, now. I really do not think it has anything to do with hi-fi. Not directly, and not unless we had our loudspeakers whirling around the room or something.
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