#Power of sound reference power full

SBN is measured by attaching an accelerometer to the frame of the fan and creating a spectrum plot with an FFT analyzer or similar equipment. One factor is the balance of the rotating component of the unit, however, there are several other factors which affect many other frequency ranges of the total signature. There are many causes of SBN, some of which are similar to acoustical noise. This type of noise, while related, is often significantly different from acoustical 'airborne noise'.

Smaller spikes at blade passing frequencies + harmonicsДue to the increased emphasis on systems which are difficult to detect with sonar equipment, primarily for undersea platforms, there has been a great deal of research dedicated to reducing noise which is 'structure borne' or transmitted through solid media, such as mountings and cabinet frames.

Most SBN at rotational frequency + harmonics.

This will create another fundamental frequency

Filters can dampen noise (EMI + Air Filters).

Put fan as far away from noise critical area as possible.

Keep sharp objects away from prop / rotor.

Filters can damp noise (EMI + Air Filters).

Fundamental noise freq must not equal mounting structure natural freq.

Be aware of blade passing freq and harmonics.Pick a fan that will operate at peak efficiency.Control speed of air through the fan by changes in geometry.Vary # of stationary vanes in vaneaxial fans.Modify trailing edge of blade to control vortex shedding noise.Vary # of blades to shift blade passing frequency.

#Power of sound reference power full

Typical Full Octave Band Typical 1/3 Octave Band 1/3 Octave band measurement simply divide each octave band into thirds.Typical curves are full octave bands with center frequencies from 63 to 8,000 Hz.

Analyzer - Takes amplified pressure fluctuations and processes the information into useful information.Microphone - Measures pressure fluctuations.two identical fans) add to produce a 3 dB increase.Дў- Two decibel values differing by 6 dB add to produce a 1 dB increase Normal range of hearing is 20 Hz to 10,000 Hz.Speed of sound in air is 1,130 ft/sec (340 m/sec).Sound is a change in pressure with respect to atmosphere.The SWL quoted by the manufacturer is often an average over a particular range. This method of rating speakers using SWL is often deceiving because most speakers produce very different SWLs at different frequencies of sound, often varying as much as в‘0 dB throughout the speaker's usable frequency range (it generally varies less in higher quality speakers). This measurement can also be represented as a strict efficiency ratio of audio output ( sound power) to electrical input (electrical power), but this is far less common. The SWL is then measured and the product labeled, something like 'SWL: 93 dB 1 W/1 m'. Then a particular sound (usually white noise or pink noise) is played through the source at a particular intensity so that the source is consuming one watt of power. The most common means is measuring the sound power level from the speaker with the measuring device placed directly in front of and one meter away from the source. Most audio manufacturers use SWL to describe the efficiency of their speakers. One of the advantages of expressing the noise level of a source in terms of its power level is that one does not have to note any distance from the source. As noise is unwanted sound the trumpet can be perceived to be acceptable when listened to as music but at the same sound power level may be perceived to be noisy if one is trying to sleep. The Trumpet and excavator both have the same sound power of 0.3 watts, but may be judged psychoacoustically to be different levels. Table: Sound power level and sound power of some sound sources Situation 1 Table: Sound power level and sound power of some sound sources.