Enthalpy

Here' a bassoon system evolved from Oct 22, 2017. It keeps two keys for each front finger acting at different phalanges, and one key per half-tone, but spreads the hands' action according to the bassoon's joints: The left thumb opens three or more high side holes at the wing joint; The left front fingers' proximal or middle phalanges open four side holes at the wing joint; The right front fingers' proximal or middle phalanges open four side holes at the boot; The right fingers', including the thumb's, distal phalanges close five side holes at the boot; The left front fingers' distal phalanges close four side holes at the long joint; The left thumb closes two side holes at the bell. The boot is one hole longer than usual, both wings are correspondingly shorter, and the bell with optional two covers can ease the transport. Movements pass only to the bell cover(s), and maybe to the register key(s) if the right thumb moves them. This improves a lot over my previous attempt. The keys are quite simpler than for a Heckel system and hopefully more silent. The resulting fingerings seem easier now. Cross-fingerings still let move many fingers, but the actions for individual notes are healthier. A bassoon and its small side holes won't follow the sketched flute logic, but if the intervals between open holes are kept, for instance if the instrument sounds all cross-fingerings a semitone higher, then the simple fingerings are kept and only shifted. With narrow side holes at locations differing from the Heckel system, this system needs a redesign of the instrument, lengthy to tune properly since the adequate cross-fingerings are still unknown. It can be worth it as the keys are simple and enable very uniform and perfect hole combinations. Marc Schaefer, aka Enthalpy

I'm always wary about genetics. One time the experts say "Neanderthals didn't interbreed with us" and next time "they did". And so on. Imagine that the magic feature appears in one individual only if both parents carry the rare mutation that has no consequence for them. Then, evolution will not amplify the mutation, even if it's very favourable. It's the symmetric situation from cystic fibrosis: deadly even before the patient has children, but the mutation has no effect on the parents, so there is no selection pressure against it. I don't take that as an element to make my opinion. I'd prefer "Various agencies said they collaborated with him". "Agency" includes many people, not necessarily the best scientists. Less so in a so-called intelligence agency. Some people are curious and want to try, that's normal. It does not mean that they observed something. In a science journal, not up to now. It's nearly certain that reviewers would exclude a paper just based on the topic, whatever its hypothetical qualities about the method, the statistical strength, the possibilities to reproduce the experiment. Big scientists investigated such topics, and this is more important to my eyes than any journal, because they know better than about any journal reviewer how to make experiments and what is science. For instance Yves Rocard investigated if and how some people detect underground water https://fr.wikipedia.org/wiki/Sourcier (no English version) and put his observations and thoughts in a book. But as Rocard had previously developed the French hydrogen bomb, he was fully surrounded by the French intelligence agencies, so all people taking part in the experiments would have fooled the scientist. Sad for the science.

Most sources claim that we discern the direction of a sound source by the relative phase at our ears, and after experimenting, I agree. Has everyone noticed? TutSter.exe in the archive runs in Windows' Cmd.exe to create the stereo TutSter.wav that play identical sounds at right and left but with propagation delays that result from the command p <float> The source is 1m before the listener, the signed number is a lateral distance in metres. Direction.7z The hardware matters at computers. Headphones are far better here, and connecting them directly to the sound board can be better than through the loudspeakers' amplifier, though this cuts the low frequencies. Many sound boards and amplifiers demand a balance adjustment, as we infer the source's direction much from the relative intensity. And, err, different computer hardware swaps right and left at random. These sounds play a sine 5m on side A, centered, 5m on side B, and again: Dir_A_E082sine_m5z0p5m5z0p5.wav at 82.4Hz, I perceive no direction. Dir_B_A110sine_m5z0p5m5z0p5.wav at 110Hz, a direction is perceptible. The phase shift is only 0.1*lambda. Dir_C_E330sine_m5z0p5m5z0p5.wav at 330Hz lets still perceive the direction. 0.3*lambda. Dir_D_A440sine_m5z0p5m5z0p5.wav at 440Hz, 0.4*lambda and Dir_E_E659sine_m5z0p5m5z0p5.wav at 659Hz, 0.6*lambda are unreliable. Plus or minus a half-wave is undecidable. Dir_F_A880sine_m5z0p5m5z0p5.wav at 880Hz, I perceive no direction at all. It would be meaningless anyway. Added harmonics help if some have a useful frequency. # 1 2 3 4 5 6 7 8 dB 0 0 0 0 -3 -8 -12 -20 Dir_G_E082harm_m5z0p5m5z0p5.wav at 82.4Hz, now the direction is clear. Dir_H_A880harm_m5z0p5m5z0p5.wav at 880Hz (strident!), no improvement. At at favourable fundamental frequency, we perceive a more accurate direction with harmonics. Here 0.3m on side A, 0.3m on side B, and again: Dir_I_A220SineHarm_m03p03m03p03.wav at 220Hz, pure sine then with harmonics. At least up to 330Hz, our (hair cells?) detectors must transmit the raw signal to the brains rather than the detected amplitude - unless someone has a better explanation to the directivity. I didn't expect it, because we are insensitive to the phase of the harmonics versus fundamental, and because it needs very wideband nerves. Marc Schaefer, aka Enthalpy

Maybe F/2, F/3... undertones help us perceive the pitch of the highest notes? Like overtones help us for contrabass notes. The pitch of the highest notes isn't very clear at the piano but while we perceive it easily at the piccolo flute (high C like a grand piano) and the violin (higher with "harmonic" sounds). A difference is that the piccolo and the violin can produce weak undertones at these notes. An other difference: I played them both, but the piano very shortly, so it can result from practice. This archive has notes in the piano's last octave, and I believe to perceive the pitch better with undertones. Unpleasant height, adjust the volume. HighNotesUndertones.7z High_C_NotesNoUndertones.wav has only sines. High_D_NotesUndertones.wav adds F/2 at -50dB to the high C. This undertone is not strongly perceived as a distinct note. The piano might add (or not?) such undertones to its highest notes, say above G, by playing them "harmonic" like on plucked and bowed strings. These strings would be an integer number of times longer and have the equivalent of a finger, possibly of silicone rubber, mildly applied at a fundamental's vibration node. Marc Schaefer, aka Enthalpy

Here I compare the payload mass in geosynchronous orbit with electric versus sunheat engines. ----------- Ariane 64 and Hall ----------- Fakel's Spt140D has been used on Eutelsat 172b http://www.fakel-russia.com/images/content/products/fakel_spd_en_print.pdf and Ariane VA237 put it on the usual GTO: 250km*35706km*6°, from where a 1465m/s short kick would achieve Gso. This Hall thruster offers Isp=1770s=17360m/s and 0.29N from 4500W, so the 3550kg satellite's 13kW (end-of-life?) solar panels feed 3 engines for 0.87N or 245µm/s2. 4714m/s spiralling from Leo would need 8.5 months, and even longer for heavier satellites, but in 4 months the Hall thrusters achieved Gso from Gto. To save delays, the apogee pushes are very long hence inefficent. Let's say they must provide 1.2*1465=1758m/s: the payload is 0.90* as heavy once in Gso. Scaling up to 11500kg in Gto for Ariane 64, 1108kg xenon are consumed, plus 83kg for a bigger tank, and 85kg for 10 Hall thrusters. This leaves 10220kg in Gso for the satellites and a dual launch adapter. Other transfer orbits would improve. The long pushes raise the apogee too, so a lower one is better. A perigee higher than 1000km would reduce the risk of collisions. A mid-high circular orbit would let the electric satellite spiral to Gso. Ariane 6's user's manual gives masses to these orbits. But as long as chemical satellites buy half-launches, Ariane will target the usual Gto, maybe Gso (5000kg there). ------------ Falcon 9 and Hall ----------- The outdated but documented Falcon 9 v1.0 put 4536kg to Gto 185km*35786km*28.5°, from where a short 1826m/s kick achieves Gso. Let's take 2191m/s with Hall thrusters: the payload weighs 3998kg in Gso, minus 40kg tank and 34kg thrusters, that's 3924kg in Gso. ---------- Ariane 6 and sunheat ---------- As estimated on Apr 15 & 19, 2018, Ariane 64 and a sunheat stage would put 13.1t at Gso in 3 months or less. This 2880kg or 28% improvement over Hall thrusters starting from Gto is worth 25M$, plus the saved delay. Ariane 62 and a sunheat stage would put 6.1t at Gso in 2 months, that's 1251kg or 26% better than Hall thrusters. Worth 18M$ or 20M$, the price of upgrading to Ariane 64. The transfer time is one month for 360kg or 120kg less payload. ---------- Falcon 9 and sunheat ---------- Falcon 9 v1.0 put 10000kg at 400km*28.5°, from where I estimate imprecisely to 5552m/s the cost to spiral to Gso and suppress the inclination simultaneously. This leaves 6396kg at Gso, of which 1016kg are the dry sunheat stage (282kg/t as for Ariane) and 5380kg the payload at Gso in 2 months. That's 37% heavier than Hall thrusters, a bigger advantage because Gto in two stages is demanding. At 56M$ per launch (?) the gain is 21M$. Marc Schaefer, aka Enthalpy

Here's a more detailed mass estimate of the sunheat stage for Ariane 6. Computed to break at 2.2MN*m (6.4t on A62) or 8.6MN*m (13.7t on A64) and to work at 1.5atm (boiling 2K warmer than 1atm). The truss is cold at A64. kg kg 190 360 290µm or 370µm steel balloon with brazed seams 74 94 22mm or 17mm foam for 1000s after trickle hydrogen removed 61 76 25 or 19 plies of 13µm MLI for additional 7 idle days in vacuum 10 20 Polymer straps holding the balloon 250 700 Welded truss of Di=80mm e=1,4mm AA6082 or Di=98mm e=2,6mm AA7022 no 83 Upper short insulating truss of Di=116mm e=4,4mm glass fibre epoxy no 0 Lower insulating truss already thrown away 120 180 4 or 6 engines 20 30 Engines' deployment and orientation no 0 Shell already thrown away 100 100 Equipment if not in the spacecraft 30 30 1.5 remaining separation belts 50 50 Undetailed ---------- 905 1723 kg dry stage 282 and 254kg per ton of propellant is heavy but would improve at a lighter space probe. The 5* denser couple with oxygen would scale it as 56 and 51kg/t, outperforming the projected Esc-B. I wouldn't be surprised if Ariane 6, whose manual tells masses landed on the Moon, uses the already suggested insulation stack http://www.scienceforums.net/topic/60359-extruded-rocket-structure/?do=findComment&comment=761740 At the A62's truss, tubes of isogrid AA7022 would improve over smooth AA6082. At the A64's truss, tubes of isogrid Ti-Al6V4 would improve over AA7022, be weldable, and could replace the glass fibre trusses too. Everywhere, balloons and trusses made of graphite composite would be half as heavy, and the walls of graphite tubes could be a balsa sandwich to save more mass. These sandwich tubes could replace the glass fibre trusses too. The throwaway windshield shells are already described http://www.scienceforums.net/topic/60359-extruded-rocket-structure/?do=findComment&comment=764231 Marc Schaefer, aka Enthalpy

An ion thruster would accelerate itself and its solar panels enough. Geosynchronous telecom satellites weigh about 4 to 7 tons in Gto, or 2.5 to 5 tons in Gso. Their 15kW take a few 100kg panels, but the claimed 150W/kg would take just 100kg, so there is margin. Fakel's Spt140D takes 15kW/N so the absolute limit would be 10mm/s2, enough for most missions. For the sunheat engine, this limit or factor-of-merit is 2.4N/30kg or 80mm/s2. This comparison is more important farther from the Sun. The hardest limit to ion propulsion is the cost of the solar panels.

The first user's manual for Ariane 6 is published and it details preliminary performance to varied orbits, nice. Once put on low-Earth-orbit by Ariane 6, heavier satellites can attain the geosynchronous orbit using sunheat engine. The sunheat stage would spiral from 400km 6° to 35800km 0°. This costs 4700m/s, 500m/s more than a Hohmann transfer, but saves a year. With Ariane 62, the fairing can house the 3.2t hydrogen and the payload. This brings no higher stresses on the previous stages, but needs trickle hydrogen under the fairing at pre-launch. The satellite owner can operate the sunheat stage, use the existing sensors and electronics. I take 120kg of structural tank per ton of hydrogen, 4 engines of 17kg for 2 months transfer, 100kg equipment if the launch company operates this stage. With Ariane 64 (or for missions of higher energy), 6.8t hydrogen need a tank outside the fairing and probably common to both customers. This suggests operation by the launch company. The stresses on the previous stages increase. I take 120kg of structural tank per ton of hydrogen, 6 engines of 17kg for 3 months transfer, 100kg equipment. Marc Schaefer, aka Enthalpy

Wiki has an articke about absolute ear, also called absolute pitch https://en.wikipedia.org/wiki/Absolute_pitch compiling studies made with method and on more people than the few musicians I heard, so their opinion is more reliable than the one I expressed in the present thread https://www.scienceforums.net/topic/113243-sound-perception/?do=findComment&comment=1038890

Baroque trumpets and natural horns used even in Beethoven's symphonies: https://www.youtube.com/watch?v=fhHcty9OM-0 at 6:34, 7:42, 7:59, 8:45, 14:57, 26:06, 47:48 etc. If I see properly, the HR Sinfonieorchester afforded specialists to sound the baroque instrument for Beethoven's symphonies. Most orchestra don't. A much easier semibaroque trumpet, with two valves, would need some reasonable adaptation time for the easy Beethoven scores, and avoid the difficult specific techniques of intonation correction. More orchestra could then use instruments close to the original ones.

Private enterprises do exist in Venezuela. Some differences are qualitative, others quantitative: - The Venezuelan government announced that it wanted a socialist economy, and renamed many organisations accordingly. - The country exports only oil, which is fully controlled by the armed forces and the government. - Access to foreign currencies, import, export... are fully controlled by the gov. - Something (I ignore what) prevents the Venezuelan economic actors from taking initiative and filling the needs of the country. Everyone would want meat, but to breed rabbits it needs a governmental initiative. An other difference with Norway is the extent of corruption. Mean reports can be read about that. Experience tells this is not linked with socialism, but does put an economy down quite efficiently.

The experiment in Vienna had bins some 2µm wide and 10mm high which got around 1000 hits of 1nm molecules. This makes around 5*10-8 molecular layer. Even over many runs, there is margin. I'm confident that 100 molecules per second, each filling 5*10-11 of the target area, don't collide. I made microscopic accelerometers during the paleomonolithic era, and we got good sensitivities. The noise energy drops with the size, and achieving kT is natural for small sensors. Confining the kT noise energy outside the measurement frequency band needs engineering and thinking. Converting the movements of the sensing element into a signal without added noise tends to be feasible. That's why I suggested microphones. But it needs more detailed thoughts with figures, sure. I have to think more at the rest.

Our perception of height for contrabass sounds is imperfect. It's a joke topic in orchestras. Some sources want to tune the piano's lowest octave stretched. The joined sounds show a more subtle picture. ContrabassC.7z CB_6_SinglePeak.wav in the previous message goes to 23.1Hz F#, lower than the contrabassoon and piano, and I perceive all notes in tune. But CB_A_Bb29HzOnePeakTwoPeaksOddHarm.wav contains the same 29.1Hz Bb played with different harmonic spectra, and I perceive the third one too high. Starting with a measured euphonium spectrum enriched at ranks 10 to 20: The first note has phases for one peak per period; The second for two peaks; The third has no even harmonics (and two peaks per period). Waveform.xls draws a period from a harmonic spectrum. The instructions in CB_Make.txt can be pasted in the running TutF.exe by a right click. # | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 ------------------------------------------------------------------------------------ dB | -15 -1 -1 0 -1 -6 -8 0 -7 -10 -12 -13 -15 -16 -18 -20 -22 -24 -27 -30 ° | 90 -90 90 -90 90 -90 90 -90 90 -90 90 -90 90 -90 90 -90 90 -90 90 -90 ------------------------------------------------------------------------------------ dB | -15 -1 -1 0 -1 -6 -8 0 -7 -10 -12 -13 -15 -16 -18 -20 -22 -24 -27 -30 ° | 90 -90 -90 90 90 -90 -90 90 90 -90 -90 90 90 -90 -90 90 90 -90 -90 90 ------------------------------------------------------------------------------------ dB | -15 -1 -1 -8 -7 -12 -15 -18 -22 -27 ° | 90 90 90 90 90 90 90 90 90 90 ------------------------------------------------------------------------------------ We hear that (or at least I do): Two peaks let hear faster beats than one but don't change the perceived height; Without the even harmonics, the third note seems much higher. So our hearing would not rely on the beat repetition rate to assess a contrabass note height. The difference between the harmonics, which makes their interference frequency, may become important at low notes, more so than some GCD that would have told the exact height. The next sounds play Bb 116.5 - F 87.3 - Bb 58.3 - F 43.7 - Bb 29.1 - F 21.8 Hz with the three spectra: CB_B_OnePeakDescentBbF.wav with one peak sounds in tune even at 21.8Hz; CB_C_TwoPeaksDescentBbF.wav with two peaks, too; but CB_D_OddHarmDescentBbF.wav seems too high at 29.1 and 21.8Hz, even at 43.7Hz a bit; the perceived error is a variable amount, not a fixed octave. Other trials not supplied here tell that the explanation isn't only an interference of harmonics. For instance at 21.8Hz, when suppressing the (even and odd pairs) highest harmonics progressively, a euphonium note seems higher without its harmonics 7 and 8 while a flat spectrum doesn't. Bad loudspeakers too influence the perceived height, logically as they deform the harmonic spectrum. More experiments and interpretations would be needed, but I have no such plan. Since the spectrum influences the perceived height of contrabass notes, and the position of the hammer impact changes the spectrum of a piano note, maybe hammers hitting the strings at a different position would let us hear the first octave in tune. Presently the position is said to be 1/7th of the string length to reduce this harmonic - the one that must remain at the euphonium note. Marc Schaefer, aka Enthalpy

Thank you JC! I was surprised too that they used no velocity filter, that's why I proposed one. But the idea is immediate enough, sure. Possibly the group in Vienna hoped only to see the first sidelobes, and for that the unfiltered speed distribution is good enough. Hi Swansont, thanks for your interest! The essential factor the determines the number of molecules observed at the detector is the angle filter composed of both 10µm slits at 1m interval (+-10µm, not +-20µm, my bad). If a means lets reduce the emission angle, like a nozzle or a moving emission surface, a bigger proportion of the molecules have the proper direction, so fewer can be emitted, at a lower temperature - by how much remains to be checked. A nozzle would reduce much the temperature of the emitted molecules, both as a lengthwise random speed (which influences the fringe quality) and as a transverse speed (which determines what proportion of the flux can be kept). But it does increase the width of the emitting source, yes. A paper by chemists on fullerene properties: http://www.dtic.mil/get-tr-doc/pdf?AD=ADA292726 Adsorption on the microscopic microphones isn't a worry to my eyes, with 103 molecules impinging per second. The molecules can just stay where they arrived. Collisions are so improbable that they're negligible. 6kT (Boltzmann's constant) is just to compare with the achievable thermal noise at the microphone. kT can be a noise energy at a microphone; some designs put this energy outside the measurement frequency band. So comparing the expected event energy with kT gives a first idea if the signal can be discriminated from the noise.

Many telecom satellites use presently electric thrusters to raise the perigee from the transfer to the geosynchronous orbit. To achieve it in 4 to 7 months but save solar panels, the thrusters eject more propellant but slower than the Vasimr cited on Aug 19, 2017. For instance the Hall thruster PPS-1350-G in the table there https://en.wikipedia.org/wiki/Ion_thruster achieves 90mN at 1660s=16.3km/s from 1.5kW. This makes the solar panels 0.35* as huge as previously. The visual comparison with the sunheat engine becomes :

The perceived beats in a contrabass sound depend on the number of peaks per period. I use here three waveforms with the same harmonic amplitude but different phases to vary the period shape: # 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 dB 0 0 0 0 0 0 0 0 0 0 0 -3 -6 -9 -12 -18 -24 -30 -40 -50 ° 90 -90 90 -90 90 -90 90 -90 90 -90 90 -90 90 -90 90 -90 90 -90 90 -90 ° 90 180 -90 0 90 180 -90 0 90 180 -90 0 90 180 -90 0 90 180 -90 0 ° 90 -90 -90 90 90 -90 -90 90 90 -90 -90 90 90 -90 -90 90 90 -90 -90 90 In this archive: ContrabassB.7z CB_6_SinglePeak.wav has a single strong peak per period. CB_7_TwoPeaksClose.wav has two close arches. CB_8_TwoPeaksDistant.wav has two strong peaks well separated. These three sounds play D=73.4Hz - Bb=58.3 - F#=46.3 - D=36.7 - Bb=29.1 - F#=23.1Hz, and At 73Hz the phase makes no difference for me, as already observed at 440Hz. Two close arches per period sound like a single one. But they help bad loudspeakers or amplifiers. I hear individual periods from 58Hz down with one peak or two close arches, but two distant peaks need 29Hz to beat as clearly. Again as quick as the reaction time already observed, 70Hz or 50Hz. At 29 and 23Hz, the two peaks per period beat more quickly than one peak or two close arches. To make it patent, this sound contains the three waveforms at 29.1Hz: CB_9_Bb29Hz_OnePk2close2dist.wav These observations are compatible with amplitude detectors, for instance the hair cells in charge of the harmonics around 300Hz, that discern the waveform's peaks individually if their repetition is slow enough. Marc Schaefer, aka Enthalpy

Here's how a mechanical chopper could look like to pick only the molecules within a narrow speed distribution. In optics, similar choopers are often pairs of teethed disks, 50% solid, with the proper distance and relative phase. Here I suggest instead a helix (and didn't check if I'm the first, of course). It can be long for increased speed selectivity without letting other speed domains pass through. The helix can be thin to let most molecules with adequate speed pass through. Just 5mm groove width and 200mm helix length would leave +-2.5% speed tolerance, and the corresponding fraction of the beam intensity, sure. Alloys achieve peripheral speeds like 400 to >600m/s, and turbine superalloy can be baked for vacuum operation. The design must prevent dynamic flexural instability. Some ceramic bearings can run in vacuum, and magnetic bearings of course. The peripheral speed, angle and number of threads let accommodate varied molecule speeds. A high peripheral speed lets evacuate to the sides the molecules with bad speed. After short thinking, building the chopper between the slits seems feasible. If not, it can fit before the slits. Marc Schaefer, aka Enthalpy

Hello you all! Experiments are built to observe the wave nature of ever heavier objects. It was done around 1999 with C60 fullerene at the Vienna Center for Quantum Science and Technology, short description there www.univie.ac.at/qfp/research/matterwave/c60/ from which this sketch is adapted: I resembles what one expects from a diffraction setup, but the wavelength differs from optics, hence so do the distances, grating's period, fringes separation. The light beam is strong and concentrated to ionize the molecules on its path, and a detector senses the charges, around 1 to 100 per second. The description doesn't detail all subtleties. Science has progressed meanwhile, as interferences were obtained with heavier objects like proteins, but the experiment with fullerenes remains admirable. ==================== Maybe some improvements can be brought to similar experiments ? At least on the sketch, the oven resembles a barrel with a hole. A true and good nozzle would expand and cool the fullerene better, to obtain a narrower velocity distribution. Authentic De Laval, at least down to a pressure where the mean free path is smaller than the divergent. The narrow throat may need special fabrication. Seek a high pressure ratio, by a big oven pressure if needed. Try optionally to mimic the gas temperature at the nozzle's walls. Heat the fullerene after it sublimates, before the expansion. This shall limit its condensation during the expansion. Add a gas to the fullerene in the oven to make the expansion more efficient? Argon, methane… Problem: I don't know how to remove the gas from the beam. Maybe the detector can discriminate the fullerene from the gas? Add mechanical choppers on the path, especially near the collimation slits, to keep only the fullerene molecules with nearly the mean velocity. You lose some beam intensity but improve the diffraction pattern. Use a mechanical speed to impart the 200m/s or more. Up to 500m/s are easily accessible to a rotating disk of metal, more with carbon fibres. Heat the fullerene very little, just enough for slow sublimation at the rotating part. The emission is more in the plane, so less heat achieves the same beam intensity, and the speed is more uniform. Use microphones as detectors. The kinetic energy is 6kT at 300K, so cold microphones are better. With a piezoelectric or piezoresistive material, with micromachined silicon or with electrets, you can cover an area with microphones, so the experiment is faster than by scanning the diffraction pattern area. I feel microphones easier than the power laser too. Marc Schaefer, aka Enthalpy

Here are some sounds and thoughts about our perception of contrabass notes. -------------------- We hear low frequency sines very badly. In CB_1_DescentSine.wav of this archive ContrabassA.7z if the volume is set for 370Hz, the 9th sound at 58Hz is quite weak despite my loudspeakers resonate around 50Hz. Frequencies are: 370, 294, 233, 185, 147, 117, 92.5, 73.4, 58.3, 46.3, 36.7, 29.1, 23.1Hz. The conventional frequency limits of our ears aren't defined by a mild damping like -3dB, but as when a wave gets painful before we hear a sound. So we're very insensitive well before the often cited 20Hz and 20kHz. Knowingly, we hear low musical sounds by their partials. A (nearly bass tuba) euphonium spectrum measured on Bb=58Hz is http://hyperphysics.phy-astr.gsu.edu/hbase/Music/euph.html # 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 dB 15 -1 -1 0 -1 -6 -8 0 -7 -16 -22 -13 -15 -19 -34 -40 CB_2_DescentEuphonium.wav uses it to synthesize by TutE.exe sounds well audible at D=73.4, Bb=58.3, F#=46.3, D=36.7, Bb=29.1, F#=23.1Hz. The bassoon reaches Bb=58.3Hz, the piano A=27.5Hz, the contrabassoon Bb=29.1Hz or A=27.5Hz. CB_3_RemoveLowHarmonics.wav contains sounds at Bb=29.1 and Bb=58.3Hz with harmonics 1 to 15 equally strong and higher ones dropping. Then it removes the harmonics 1 to 6 from the 29.1Hz sound and 1 to 4 from 58.3Hz. I hear a small difference when removing the harmonic 5 of 29.1Hz or the harmonic 3 of 58.3Hz, both around 160Hz. Maybe our lowest hair cell is centered on such a frequency, and only its residual sensitivity to lower frequencies extends our range down. Or maybe not. The radiation resistance of a small acoustic source varies like F2, so low frequency components are hard to emit. While the contrabass tuba achieves it, the contrabassoon doesn't even try. Here a measured contrabassoon spectrum http://www.berliozhistoricalbrass.org/29-4%20Sum02.pdf # 1 2 3 4 5 6 7 8 9 10 11 12 dB -19 -22 -13 -10 -8 -2 0 -2 -1 -2 -6 -19 -------------------- If they have audible partials, we perceive musical sounds at very low frequency, with no clear limit, but as individual periods more than a sound if the frequency is low. CB_4_PeriodsOrSound.wav plays a note at 10, 30, 50, 70, 90Hz. Its spectrum is wide: # 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 23 25 27 29 31 dB -14 -4 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 -2 -4 -6 -8 -10 -12 I hear individual periods up to some 70Hz. This is but more than the 50Hz tremolo of the 880Hz sine of Mar 18, 2018 in this thread https://www.scienceforums.net/topic/113243-sound-perception/?do=findComment&comment=1043295 CB_5_PeriodsOrSound.wav plays a note at the same frequencies, but the spectrum is flat from harmonic 1 to 4 and zero above. Now I hear individual periods up to 50Hz, again but more than the 30Hz tremolo on the 131Hz sine. The stronger modulation depth can make the difference. So I propose (...and may not be the first) that, when hearing a contrabass sound, we notice individual periods if enough harmonics interfere within a frequency band (like the bandwidth of individual hair cells) to let the amplitude wobble there, and not too quickly. -------------------- Acoustics is a means and music the goal, so here are records of contrabass woodwinds: contrabassoon https://www.vsl.co.at/en/Woodwinds/Contrabassoon contrabass clarinet youtube v=d-aqcHlSFEI and youtube v=wUNZjNVFMkY Marc Schaefer, aka Enthalpy

April's fool: the slag heap was not made by earthlings.

April's fool!

Other nice address: https://www.vsl.co.at/en/Percussions/Celesta

Very nice records of wagnertuben, chosen to highlight the instrument https://www.vsl.co.at/en/Brass/Wagner_tuba The site also tells ranges, notation and more. Not only for this instrument, but also the bass trombone, contrabassoon, celesta, marimba and pretty much all usual instruments of a symphonic orchestra. Definitely worth bookmarking!

You thought Nasa would be first, or a company like Deep Space Industries or Planetary Resources? India has been faster, with less resources but with innovative thinking. No scale is given, but it doesn't look small. Without data about how compact the soil is, it's difficult to estimate how much of the opencast mine was usable ore and what proportion landed on the slag heap. Well done!

Anything can happen. The EPR has just made a successful start at Tianshan, producing heat by the chain reaction and converting it to electricity. The customer has declared "to be fully satisfied with the results" and the manufacturer "that the test confirm the good design of the product, called to a bright future".