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Play the record back with an elliptical or line-contact stylus that has a smaller tip radius. Keep the recorded volume to a reasonable level (read: On scale on the meters) is the first thing. What can be done about it? Many things have been tried, but there is no “magic bullet”. The problems start when the curvature of the groove equals or exceeds the diameter of the playback stylus. The result is actually a loss in high frequencies, and increase in distortion as the groove moves to the center. That 1.8 seconds at a 12” diameter is covering a lot more territory than at the minimum 4.75” diameter. Yes, it is still turning at 33 1/3 revolutions per minute, but consider: one revolution takes 1.8 seconds. Curvature isn’t usually a problem, per se, on the outside of a 12” 33 1/3 record, but as the groove moves toward the center, its relative speed slows down and curvature increases. Why 45, you ask? Because it sounds better! In record mastering, the higher the recorded level and frequency, the greater the groove curvature. 180 gram virgin vinyl pressings were the next development, and last but not least, around the late 70s, 45 rpm 12” LPs started to appear. Digital computers arrived on the scene in their best role: Out of the audio chain, but doing machine-control to adjust the groove spacing on the record for maximum playing time and recorded volume. The most unfortunate thing about the LP is that it was really starting to flourish back in the mid 80s, just as the record companies tried to kill it.Īdvances in cutterheads (the device that etches the groove in the master lacquer disk) and cutting electronics reached a pinnacle in the early 80s. It has a solid, palpable, satisfying sound that no digital format has yet equaled, let alone surpassed. But you'll mostly encounter that on turboprops.Why 45 rpm? by Kevin Gray, AcousTech MasteringĪfter 60 years the good ol’ analog LP is still one of the highest resolution sources of music distribution available. This is further complicated in beta range (reverse thrust) where the power lever switches to controlling pitch directly while throttle is controlled by another governor to maintain RPM. There were some variable pitch propellers where the pilot directly controlled the pitch, but the governor is a fairly simple hydromechanical device (weight on spring measures the centrifugal force and directly controls hydraulic valve that adjusts the pitch) and results in so much more practical handling that it quickly prevailed. If the throttle is too closed, even the finest possible pitch might have too much drag and the RPM will be lower than selected. If the propeller is too slow, the governor decreases the pitch, thus reducing the thrust and associated resistance until the engine can keep up, if it is too fast, it increases the pitch until the propeller absorbs all the power the engine is providing. You are setting the desired RPM, which the governor will try to attain by adjusting the propeller pitch. If we move prop lever we are changing blade pitch and then rpm adjust to it or we are changing engine rpm and blade angle adjust to new rpm It is still aircraft-dependent, because some engines go up to values like 102.5% and the spread between maximum and most efficient also varies.ģ. If it instead said 31, it would make no difference.īecause of this, turbine RPM is only reported in percent, which sometimes extends to the propeller on turboprops too. In one aircraft the POH might say that maximum RPM (more can't be selected anyway) is 2500 and most efficient for cruise is 2100, but on another aircraft it might say that 2750 is for take off, but for 2 minutes only, 2600 is maximum for continuous operation and 2300 is most efficient. But it does not really matter, because the gear ratio is always fixed and because the pilot does not have any other use for the value than comparing it to some nominal values in the operating handbook, which are aircraft-specific anyway. Usually propeller, but may depend on the aircraft. Is tachometer on constant speed prop reading engine rpm or prop rpm? Sounds like very basic knowledge but I heard a lot of versions and I want to reassure. Fuel flow is a better indicator of power as long as you keep the engine properly leaned.Ģ. There is less contention for the air from intake manifold so the manifold pressure will increase a bit and each power stroke will deliver a bit more energy, but not nearly enough to compensate the overall lower number of power strokes.įor this reason, manifold power can only be related to power for constant RPM, and it's still complicated by other things, especially the density altitude. Power is energy per unit of time, and since there is fewer revolutions, there is fewer power strokes to release that energy. Why if we decrease RPM and maintain throttle lever setting the power output decrease?
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