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Rumble measurement

Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (December 2009)

Rumble measurement is carried out on turntables (for vinyl recordings) which tend to generate very low frequency noise originating from the centre bearing and from drive pulleys or belts, as well as from irregularities in the record disc itself.

It can be heard as low-frequency noise, and becomes a serious problem when playing records on audio systems with a good low-frequency response. Even when not audible, rumble can cause intermodulation, modulating the amplitude of other frequencies. The nweighted response curve is intended for use in assessing the level of inaudible rumble with such intermodulation in mind.

Turntable design

One way to reduce rumble is to make the turntable very heavy, so that it acts as mechanical damper or low-pass filter, but even with the best turntables a lot of rumble tends to be generated by warped records or pressing irregularities sometimes visible as obbles in the surface. An important factor affecting rumble is low-frequency resonance resulting from pickup arm mass bouncing against stylus compliance. This resonance is usually in the 1030 Hz region, and will increase rumble as well as reducing tracking ability if not well-damped. Good pickup arms incorporate viscous damping aimed at eliminating such resonance.

Rumble filters

Because these effects generate a mostly vertical component at the stylus, which corresponds to a difference signal in stereo reproduction, the incorporation of a high-pass filter operating only on the channel difference can be very effective in reducing rumble without loss of bass. Such a filter merges the two channels to mono at very low frequencies, which is not generally considered to have any effect on stereo perception, though it can change the sound balance (often for the better) by altering the way in which resonant room modes are stimulated (reducing corner to corner stimulation). The original circuit was designed in 1978 by Jeff Macaulay and featured as a circuit idea in Wireless World. Most so-called rumble filters work by simply rolling off the low-frequency response, which is detrimental to sound quality.

Though several standards exist that define how rumble should be measured, they all have a common basis, and use the weighting curves shown here. DIN 45539 (1971) and IEC98-1964 both cover rumble measurement. BS4852: Part 1 (1972) is specific in requiring that a slow rectifier be used, which shall reach 99% of its steady indication in 5s +-0.5s with not more than 10% overshoot.

See also

Audio quality measurement

Noise measurement

Headroom

Wow & flutter measurement

Crosstalk measurement

ITU-R 468 noise weighting

A-weighting

Weighting filter

Equal-loudness contour

Fletcher-Munson curves

Categories: Audio engineering | Broadcast engineering | Sound production technology | Sound recording | Sound | TurntablesHidden categories: Articles lacking sources from December 2009 | All articles lacking sources
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question 14. how many connecting rods bolt to each crankshaft jounal in a v-type engine?

a.one
b.two
c.three
d.four

question 15.

which of the following is used to control the high-frequency movement that results from crankshaft twisting?

a. vibration damper
b. crankshaft pulley
c. harmonic balancer
d. both a and c

question 16.

all of the following are basic types of camshaft drives exceot:

a. rod drive
b.belt drive
c.gear drive
d. chain drive

question 17.

a camshaft drive must turn the camshaft at?
b.crankshaft speed
c.one-half crankshaft speed
d.none of the above

question 18.

engine size is determined by:

a. cylinder diameter
b.number of cylinder
c.piston travel per stroke
d. all of the above

question 19

the distance a piston moves from tdc to bdc is called:

a.piston taper
b.piston stroke
c.piston clearance
d.piston displacement

question 20.

piston displacement times the number of engine cylinders equals:

a.engine size
b.cylinder bore
c.engine torque
d.compression ratio

question is done now

answer to #14- one
answer to #15- harmonic balancer
answer to #16- rod drive
answer to #17- one half the crankshaft speed
answer to #18- all of the above
answer to #19- piston stroke
answer to#20- engine size
t

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