KT66 Posted January 21, 2005 Share Posted January 21, 2005 Does any know of any performance degradation that may result from using Khorns at 8,000+ feet (Bogota and other high Andian cities) - horn LF cutoff depends on air density and pressure. Quote Link to comment Share on other sites More sharing options...
D-MAN Posted January 21, 2005 Share Posted January 21, 2005 No, only the speed of sound changes with altitude (and temperature). The low frequency response would remain the same, however, efficiency MIGHT go up a measurable amount, I would think, being that the air is thinner and therefore easier to move.. DM Quote Link to comment Share on other sites More sharing options...
yaffstone Posted January 21, 2005 Share Posted January 21, 2005 Is the decible a function of the air preasure change in the sound wave? If so, you would need to move the diaphragm further to move the same number of air molecules at lower air preassure. PV=nRT (preassure times volume = number of molecules times a constant times the temperature) Therefore if the pressure drops you have to increase the volume (number of cubic centemeters, not the knob) to move the same number of molecules and make a sound wave. The efficiency might be very high in a vacuum, but you couldn't hear a thing. Quote Link to comment Share on other sites More sharing options...
D-MAN Posted January 21, 2005 Share Posted January 21, 2005 Wait - consider this: 1) the limitations of the cone mass still applies 2) the speed of sound has increased due to altitude or slightly decreased density 3) the horn itself remains constant in size and shape The results being that the cone would NATURALLY move further than it would in denser air. The AMOUNT of air moved BY VOLUME is virtually the SAME, it just moves a MICRO-METER or 2 further in both directions within the maximum excursion limits imposed by the mechanics of the driver. This should be apparent as a slight (maybe so slight as to be unnoticeable) increase in efficiency. If the air was so thin as to effect the transmission of sound you would be dead unless you were wearing a space suit. DM Quote Link to comment Share on other sites More sharing options...
Istari Posted January 21, 2005 Share Posted January 21, 2005 I immediately thought "Nearer My God To Thee".... Quote Link to comment Share on other sites More sharing options...
ZAKO Posted January 22, 2005 Share Posted January 22, 2005 Do you think it means a natsass difference sitting 15 feet away? Quote Link to comment Share on other sites More sharing options...
KT66 Posted January 24, 2005 Author Share Posted January 24, 2005 A horn's LF cut-off is given by: w=m.c w=2.pi.f where, w=angular freq, rad/s f=frequency, Hz m=horn flare constant c=speed of sound, m/s the cut-off at altitude would therefore (favourably) drop slightly because c reduces with altitude. However the efficiency, which depends on horn throat impedance, is more complicated to predict off-hand as it depends on a mix of c, air density and pressure. My question was weather any one had real experience using horns in high places. thanks for all replies further comments welcome. Quote Link to comment Share on other sites More sharing options...
SilverSport Posted January 24, 2005 Share Posted January 24, 2005 I LOVE this place! Quantum Physics for $400, Alex! ;-) Bill Quote Link to comment Share on other sites More sharing options...
D-MAN Posted January 24, 2005 Share Posted January 24, 2005 ---------------- On 1/24/2005 6:07:06 AM KT66 wrote: My question was weather any one had real experience using horns in high places. ---------------- Anyone in Denver? That's a mile high. They should know. {edit} Do you REALLY think that Khorns go lower in Denver?! NOT! DM Quote Link to comment Share on other sites More sharing options...
yaffstone Posted January 24, 2005 Share Posted January 24, 2005 Denver's only 5280 ft, significantly lower than 8000 asked. As I recall (it's been a long time) the air pressure there was around 640 mmHg rather than the normal 760 at sea level. I can not believe the air pressure will have any significant impact on the enjoyment level of these speakers other than the fact that before getting aclimatized to the altitude, it takes a lot less beer to notice! Unfortunately this has all been clasical physics, we have not reached the quantum physics arguements yet. That discussion would be to calculate the probability that all the air molecules in the room suddenly moved to one side leaving no sound at the other. Yes, quantum mechanics does indeed say that this could happen. That's why auto mechanics usually make more money Quote Link to comment Share on other sites More sharing options...
D-MAN Posted January 24, 2005 Share Posted January 24, 2005 The change in altitude from sea level would be significant enough to adequately disclose an answer to the question posed. One mile should suffice, as that is 2/3 of the 8000. DM Quote Link to comment Share on other sites More sharing options...
yaffstone Posted January 24, 2005 Share Posted January 24, 2005 There was recently a set of K-horns on e-bay from Englewood CO (accross the street from Denver) Item number was 5739590934 Perhaps someone could contact the original owner and ask him how the speakers sounded. This would almost certainly be a quantitative cure for our quizical quantum querey. If this seller won't answer, we'll have to set up a room sized vacuum or pressure chamber. They have these for hyperbaric oxygen treatment of various maladies. Perhaps some large medical center would loan us one for a sound test. Quote Link to comment Share on other sites More sharing options...
KT66 Posted January 25, 2005 Author Share Posted January 25, 2005 You mean hypobaric surely .. Maybe a kindly moderator would intervene and answer this question with some authority. BTW, I've heard a pair of rather BIG JBL Hartsfield's at 8,000 ft nearer the stars .. not bad at all, but I lacked an A/B test switch to comapre with sea level. Quote Link to comment Share on other sites More sharing options...
yaffstone Posted January 25, 2005 Share Posted January 25, 2005 Actually hyperbaric (high pressure oxygen). But back to the point of the thread: Air pressure is lower, speed of sound is lower, mass of air moved is lower. Mass of diaphragm doesn't change. Frequency doesn't change. Sincd the diaphragm mass is constant, the ratio of diaphragm weight movement to mass of air movement must determine the efficiency. (power in to power out). For the same volume, you have to have the same mass of air but since the air is less dense you have to move the diaphragm further to get the same air movement. Therefore, more energy into the diaphram for the same volume. But I still predict the effect is negligable. Quote Link to comment Share on other sites More sharing options...
D-MAN Posted January 25, 2005 Share Posted January 25, 2005 I guess that I'm just like a dog with a bone. Speed of sound increases with lower density air. The speed of sound at sea level is considered to be a constant with temperature and humidity taken into account. Wavelengths in sound stay constant. Frequency stays constant. Fc of the horn stays constant, however the reactance at the throat will decrease slightly as the air in the horn "weighs" less. However, the differences are very small. Amplitude will increase slightly. Noticable? I don't know. Theorectically, the sound generated should also carry farther for given input. DM Quote Link to comment Share on other sites More sharing options...
yaffstone Posted January 25, 2005 Share Posted January 25, 2005 I finally looked this up instead of relying on physicial intuition. The speed of sound c=sqrt(p/d *k) c=speed of sound sqrt =square root p = air pressure d = air density k = constant of proportionality since p and d are proportional to each other at the same temperature, only the temperature changes the speed of sound. A temperature change will change the air density but not the pressure since the world is an open system. I think I am agreeing with you D-Man! Quote Link to comment Share on other sites More sharing options...
KT66 Posted January 26, 2005 Author Share Posted January 26, 2005 Lets agree on this .. - Sound speed DEcreases with altitude(fact) - so wavelength decreases at a given frequency as you go higher - it follows then that a horn's cutoff freq goes down - however slightly - sound attenuates quicker in thinner air (fact) - Both density AND pressure DEcrease with altitude (fact) - Atmosphere is far from being at constant pressure ( changes continually with altitude and weather ..) ( just look at a weather forecast barro pressure map) Taking things to the limit, at very high altitudes sound ceases to propagate completely (i.e. infinite attenuation) so no sound power can be produced by any source. Thin air means less air mass available for a diaphragm to push so at a given diaphragm velocity (or equivalently at a given cone amplitude excursion as the two are simply related by frequency) less momentum or engergy is imparted to the air the radaited sound power therfore drops suggesting lower efficiency. ( Radiated power is propotional to air radiation resistance x air velocity squared). This suggests horn throat impedance ( resistive in a horn loaded diaphragm) drops with air pressure and density signifying a drop in efficiency - however slight at 8Kfeet - but goes to zero at space shuttle hights. Doesn't the Klipsch speaker design dept read these forum ?? Quote Link to comment Share on other sites More sharing options...
yaffstone Posted January 26, 2005 Share Posted January 26, 2005 Nope, Can't agree on the decrease of speed with altitude. According to the equation given the speed of sound is a function of temperature, not pressure. Check out http://hyperphysics.phy-astr.gsu.edu/hbase/sound/souspe3.html#c1 The speed of sound in air is only a function of temperature, not pressure. Quote Link to comment Share on other sites More sharing options...
KT66 Posted January 27, 2005 Author Share Posted January 27, 2005 Well, sound propagates faster in denser media - that is why in water it propagates so much faster than in air and goes so much further ( i.e. less attenuation) , a swim in a pool should convince you. Ask any submariner about sonar and related physics. Also check out the definition of Mach number involving speed of sound at flight altitudes. Indeed at sea level sound propagates faster the colder the air. Air gets colder as you climb yet sound travels slower because the air gets thinner. Quote Link to comment Share on other sites More sharing options...
yaffstone Posted January 27, 2005 Share Posted January 27, 2005 KT66, that's exactly what I thought on first blush, however, see the formula for the speed of sound (above). Speed of sound is a function of the ratio of the density to pressure. Density changes with temperature however, density and pressure scale with each other. Therefore only the temperature survives as a driver for the speed of sound. Remember for air, the medium stays the same so you can't compare the speed of sound in air to that in water. The density term is vastly different for fluid versus gas. This topic is not as obvious as it would appear. Quote Link to comment Share on other sites More sharing options...
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