How does loudness change

The pitch that a particular tuning fork generates depends on the length of its prongs. Each fork is stamped with the note it produces e. A and its frequency in Hertz e. Shorter prongs produce higher pitch frequency sounds than longer prongs. Long prongs will bend more readily and therefore tend to vibrate at a lower frequency when struck. Volume , or loudness, is related to the strength, intensity, pressure, or power of the sound. There are a few ways of varying the volume of a tuning fork.

Touching the vibrating fork to a table after being struck produces a louder sound. When both the table and the tuning fork vibrate, more air molecules are moved than by the tuning fork on its own. Touching a vibrating fork to clothes or your hand causes a damping effect on the vibrations reduction in size and the sound disappears. The energy from the vibrating fork is converted to moving your skin or clothes rather than moving air.

Resonance is the tendency of an object to vibrate at maximum amplitude size at a certain frequency. This frequency is known as the object's resonant frequency. Acoustic sound resonance is an important consideration for instrument builders, as most acoustic instruments use resonators think of the box of a guitar or a violin, or the hollow body of a drum.

Describe the properties of sound. Per Class: tuning forks rubber mallet or the rubber bottom of a shoe resonance box optional. If using this as an activity, provide the materials above for each pair of students.

Students should record the time and conditions at which they sampled the data. Using reliable books, articles, and websites, students research how sounds affect people and the natural environment.

They can examine both positive and negative effects of sounds of differing loudness, intensity, and duration. Students also investigate methods by which sound intensity can be reduced. Students go to the place where they will be examining the effects of sound, such as a nearby park. Students bring sound level meters preferably capable of measuring dBA to record sound intensities.

Students will listen and record all sounds heard over a 15 minute period. Students will listen and record only intrinsic sounds for 10 minutes those sounds typical of the park's daily operations , which may be natural and cultural like sound of a blacksmith's hammer at Herbert Hoover National Historic Site. Students listen and record extrinsic sounds not typical of the place such as nearby traffic, for 10 minutes. Record observations about weather conditions and characteristics of the place while recording the data.

Discuss which sounds contribute to the park's purpose and which are disruptive or not consistent with visitors' enjoyment of the park. Students may also want to determine which animals are native to the park and determine how the various sounds may affect them.

Use the students' data and research to assess how the sound levels and intensities may be impacting the place they visited. Compare the data to those already collected by others. Consider how the sound levels may affect the natural residents of the park or human visitors. Research more about impacts on the native species.

Discuss the impacts orally and write an outline or paper on the probable effects of different sounds on the residents and visitors, human or animal. Could the park experience be enhanced by eliminating or reducing certain sounds? If so, which sounds and how? Sounds that are natural to a park are considered natural resources. Birdsong, the bubbling of Hoover Creek, and the sounds of a blacksmith at work are sounds typical of Herbert Hoover National Historic Site. These sounds, both natural and cultural, were sounds Herbert Hoover heard as a boy in West Branch, Iowa.

Protecting and preserving them is part of the mission of the National Park Service. The A and C weightings are most often used since the former relates to normal everyday sound pressure levels and the latter relates to higher listening levels where the ear's response is nearly flat. We've covered some significant background, but how does all of that relate to the loudness control feature on an audio system?

Understanding how the ear perceives sound intensity versus frequency leads us directly to that loudness feature. The loudness control is simply intended to significantly boost low and high frequencies when listening at low levels so that the ear perceives an overall flatter sound pressure level. In other words, if the loudness contouring control is not enabled at low volume levels, bass and treble appear to be lacking. This effect corresponds to the recently described A-weighted condition where low and high frequencies require additional amplification so the audio "sounds good.

Since the ear's frequency response is relatively flat at high sound levels, the compensating effect of the loudness contouring control is not required. The loudness feature is a kind of equalizing function that, ideally, should adjust itself to have greater compensation effect at low sound pressure levels and less effect as sound pressure increases.

From Figure 4, you can see that the amount of power needed green shaded area bounded by LA curve to compensate for low frequencies is significant. For this reason, in home theater audio system design, it is not uncommon to use fairly large, separate amplification just for the low frequency channel. The shaded area within the high frequency range indicates relative compensation required for this portion of the spectrum when at a lower volume level. At high loudness levels, where the ear's response is nearly flat, compensation requirements decrease to nearly zero as shown by the LC curve.

The issue is whether the implementation of the loudness control feature merely boosts lows and highs using one fixed setting as some simplistic designs might do; or is it dynamic and capable of modifying the amount of equalization depending on the setting of the volume control? Historically, most loudness controls were analog implementations using discrete resistors, capacitors, and even inductors intended to approximate the compensation curve curve LA in Figure 4 for the A-weighting function.

Most were designed around the volume control. Figure 5 illustrates one simple approach using a volume control incorporating a fourth tap located about halfway through rotation.

Resistor-capacitor networks, when switched into the volume control circuit, provided amplitude compensation. For really low cost circuits, only the low end frequencies may have been boosted. Or, perhaps the midrange was "cut" to make it sound more like the level of the low end. Certainly, analog implementations of the loudness feature vary widely. Full compensation for the A-weighted response requires a relatively complex compensation network.

The basic approach with the circuit in Figure 5 is: 1 use C1 to boost high frequencies where it is connected across the top half of the volume control when the loudness switch is ON; 2 select the value of C2 so its reactance is lower at high and mid frequencies, and; 3 select R so that high and mid frequencies are attenuated; but, as frequency decreases, the reactance of C2 will rise and reduce attenuation of low frequencies.

This is a simple, low-cost design built totally around performance trade offs. Modern implementations of loudness equalization circuits fall comfortably into the realm of digital signal processing, or DSP. Within the vast possibilities afforded by digital processing, the creation of filters capable of replicating a near-exact compensating response is not only possible, but generally straightforward.

DSP-based algorithms allow for continuously adaptable functions that will compensate in real time as sound pressure level is varied over its normal excursion. High speed digital signal processing, in all its forms, provides the means for the best implementation of loudness compensation contouring in today's sophisticated audio systems.

With tools like this, engineers must return and study the fundamental knowledge base developed by researchers like Fletcher and Munson; et al. Taking a fresh look at "what once was" will ensure us the best shot at developing digital-based products that perform to the closest approximation of the original concept.

But, no matter what, all that you and I really care about is that when we push that loudness button, the system "sounds good. As an Extron Insider — Get product pricing, certification programs, downloads and more! It looks like you may be using an outdated browser that we no longer support. Extron uses the latest technology to make its website faster and easier to use. For the best experience, please use one of these supported browsers:.

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