distorsiuni mecanice woofer ?

[merck]

Lasa bre, ca vor mai apare si alti incepatori si doar nu o sa ne obosim cu fiecare cum am facut-o cu tine. Vor avea multe informatii adunate la un loc si se vor lumina in cele din urma.

Ceva ceva tot s-a prins de tine din tot topicul asta. Cand ai sa iti cumperi si un microfon pentru masurat difuzoare si ai sa incepi sa masori difuzoare de firma, ai sa vezi ca bagi xW in cutare difuzor si obtii ydB si se pupa cu pdf-ul producatorului si nu mai sunt asa mincinoase specificatiile producatorilor. Ai sa te lamuresti si cu chinezariile. Timp este pentru toate .... bani sa ai!

 

Nimeni nu s-a nascut invatat!

[franzm]

Acum 3 ore, sesebe a spus:

to @merck, @Mircea si @franzm, voi chiar va plictisiti si nu aveti ce face decit sa-i dati apa la moara? Voi nu vedeti ca omul deja este expert si stie mai multe ca oricine altcineva de pe forum? Credeti ca ii vei schimba in vre-un fel convingerile lui de youtube??? 

Nepoate, noi ne distram de minune si nu vrem sa se termine spectacolul fara sa vedem finalul. Asa ca, asaza-te comod, ia niste floricele, alune sau alte celea si o licoare care sa le ajute sa lunece si nu te mai încrunta atâta. Ca faci riduri înainte de termen.

Si gândeste-te ca, atât timp cât avem iesperti din astia, nu trebuie sa ne facem griji ca le-ar face cineva concurenta copiilor si nepotilor nostri.

Editat Septembrie 17, 2021 de franzm

[Florin_Eusebiu]

Acum 9 ore, merck a spus:

Lasa bre, ca vor mai apare si alti incepatori si doar nu o sa ne obosim cu fiecare cum am facut-o cu tine. Vor avea multe informatii adunate la un loc si se vor lumina in cele din urma.

Ceva ceva tot s-a prins de tine din tot topicul asta. Cand ai sa iti cumperi si un microfon pentru masurat difuzoare si ai sa incepi sa masori difuzoare de firma, ai sa vezi ca bagi xW in cutare difuzor si obtii ydB si se pupa cu pdf-ul producatorului si nu mai sunt asa mincinoase specificatiile producatorilor. Ai sa te lamuresti si cu chinezariile. Timp este pentru toate .... bani sa ai!

 

Nimeni nu s-a nascut invatat!

Deci :

 

1. cum se masoara (si unde)  Xmax-ul ?? 

 

2. Daca de exemplu in specificatiile unui producator de amplificator stereo (sau amplificatorului dedicat al unui bass activ sau boxa fullrange)  dispun doar de voltmetru ,si dau volum pana cand tensiunea de iesire la woofer ajunge pragul acela de voltaj calculat pentru wati rms dati de producator , este posibil sa existe distorsiuni si mai jos de acel voltaj ?  Sa zicem ca am 20 volti echivalentul a 50w 8ohmi declarat de producator . Poate sa existe distorsiuni mari sub acei 20 volti , daca ascult la  15 volti de exemplu ?

Editat Septembrie 18, 2021 de Florin_Eusebiu

[franzm]

Domnule, nu vrei sa întelegi ca notiunea de watt RMS nu are sens? A aparut cu ani în urma ca urmare a nestiintei celor din marketing.

Vrei cu adevarat sa afli câte ceva sau doar vrei sa ne scoti la tabla?

BTW, am laser (micro epsilon, al meu personal; Keyence - triangulatie si sistem 3D confocal) dar si câte ceva de la Klippel. Asa ca vin cu lectia învatata si temele de casa facute.

Editat Septembrie 18, 2021 de franzm

[Florin_Eusebiu]

Cum face aici ?

 

 

Acum 10 ore, franzm a spus:

Domnule, nu vrei sa întelegi ca notiunea de watt RMS nu are sens? A aparut cu ani în urma ca urmare a nestiintei celor din marketing.

Vrei cu adevarat sa afli câte ceva ..

Da ! Eu vreau sa aflu in ce fel ,tensiunea bagata intr-un difuzor , este influentata de distorsiuni . In raport cu ceea ce specifica producatorul (wati rms) , fara sa am alte aparate de masura , decat un voltmetru. Cursa Xdamage distruge un difuzor , nu Xmax , dar cum putem sti unde incep distorsiunile dupa calcul pentru difuzorul respectiv (de exemplu 10volti ori 10volti inpartit la 8 ohmi= 12,5 wati . Difuzoru are 12,5w rms in specificatiile producatorului - daca bag + 12 volti in difuzor , se aude cu dostorsiuni ???

 

Sa zicem ca am asa : 35volti fara distorsiuni , scosi din amplificator !  SPL-ul ne arata fiind liniar , cu exceptie intre 30-70 Hz ,  iar la Xmax , avem o cursa de 9,5 milimetri in 50 Hertzi !  Unde am eu distorsiuni in sunet daca difuzorul lucreaza cu acei 35 volti de exemplu ???

[icar]

 

[Florin_Eusebiu]

icar : discuti ceva concret sau doar esti mistocar de oameni ?

Editat Septembrie 18, 2021 de Florin_Eusebiu

[icar]

Nu te supara, ai auzit de anularea presiunii din fata membranei cu cea din spate, cand tii difuzorul in mana? Crezi ca asta e la misto?

Editat Septembrie 18, 2021 de icar

[franzm]

@Florin_Eusebiu: Sa le luam pe rând.

1. Termina cu aiureli precum Watt RMS. Este un termen inventat de oameni nestiutori.

2. Un difuzor nu are xy wati. Puterea data de producator este puterea în regim sinusoidal pe care o suporta acesta în conditiile specificate fara sa se distruga termic. Am aratat undeva mai la începutul topicului cât este curentul necesar pentru a atinge xmax specificat de producator în regim static. (De fapt, cifrele nu sunt exacte pt. ca fiecare producator determina xmax dinamic, care este mai mare decât valoarea statica.) Concluzia însa este ca, fara incinta, difuzoarele de basi (si nu numai) ating xmax la semnal mult mai mic decât cel rezultat din puterea nominala.

3. "Scurtcircuitul acustic" adica "anularea presiunii din fata membranei cu cea din spate" practic face inutilizabil difuzorul fara incinta sub o frecventa anume, data de dimensiunile sale. Chiar si un "open baffle" mareste lungimea de unda la care se manifesta anularea.

[merck]

Acum 46 minute, Florin_Eusebiu a spus:

icar : discuti ceva concret sau doar esti mistocar de oameni ?

Aceeasi intrebare ti-o pun si cei care nu-s paraleli cu audio si iti citesc posturile!

Peste ani, daca ai sa ajungi sa intelegi ceva din domeniul asta audio, ai sa te caci pe tine de ras cand ai sa-ti citesti propriile postari.

[Florin_Eusebiu]

Acum 7 ore, franzm a spus:

@Florin_Eusebiu: Sa le luam pe rând.

1. Termina cu aiureli precum Watt RMS. Este un termen inventat de oameni nestiutori.

2. Un difuzor nu are xy wati. Puterea data de producator este puterea în regim sinusoidal pe care o suporta acesta în conditiile specificate fara sa se distruga termic. Am aratat undeva mai la începutul topicului cât este curentul necesar pentru a atinge xmax specificat de producator în regim static. (De fapt, cifrele nu sunt exacte pt. ca fiecare producator determina xmax dinamic, care este mai mare decât valoarea statica.) Concluzia însa este ca, fara incinta, difuzoarele de basi (si nu numai) ating xmax la semnal mult mai mic decât cel rezultat din puterea nominala.

3. "Scurtcircuitul acustic" adica "anularea presiunii din fata membranei cu cea din spate" practic face inutilizabil difuzorul fara incinta sub o frecventa anume, data de dimensiunile sale. Chiar si un "open baffle" mareste lungimea de unda la care se manifesta anularea.

Asa , si deci graficul acela din poze  , cum este dat ?cu difuzorul in incinta sau cum ??

 

Care este curentul necesar pentru Xmax in specificatiile lui ? Acolo sus unde scrie 2.83 volti la 90.6 dB ?  Explica-mi te rog cati volti merg  bagati in difuzor pana ajunge in prag de distorsiuni .

 

Sau imi poti arata tu un print screen direct pe site cum am facut eu simularea  , sa vad cum arata diagrama Xmax si dB , in ce voltaj anume este el facut sa mearga normal pana la maxim

Editat Septembrie 18, 2021 de Florin_Eusebiu

[merck]

Acum 16 minute, Florin_Eusebiu a spus:

Asa , si deci graficul acela din poze  , cum este dat ?cu difuzorul in incinta sau cum ??

Exista un standard care se respecta de toti producatorii seriosi. In loc sa urlii ca prostu' ca producatorii seriosi mint in privinta parametrilor (in speta puterea, ca asta iti place tie) m-ai bine ai citit ce scriu in pdf. Uite ce spune Eminence:

Citat

 All speakers are tested at 1W/1m using a variety of test set-ups for the appropriate impedance | LMS using 0.25” supplied microphone (software calibrated) mounted 1m from wall/baffle mounted 1m from wall/baffle | 2 ft. x 2 ft. baffle is built into the wall with the speaker mounted flush against a steel ring for minimum diffraction | Carver PM-120 amplifier | 2700 cu.ft. chamber with fiberglass on all six surfaces (three with custom-made wedges).

 

Editat Septembrie 18, 2021 de merck

[Florin_Eusebiu]

Acum 57 minute, icar a spus:

Nu te supara, ai auzit de anularea presiunii din fata membranei cu cea din spate, cand tii difuzorul in mana? Crezi ca asta e la misto?

Domnule ! Am auzit de anularea aceea , dar spune-mi te rog eu , in ce voltaj merge difuzorul acela pana in pragul sa distorsioneze ! Spune-mi ce voltaj suporta si in cutie si afara in aer liber , unde vrei dumneata .Ai mai jos poza cu specificatiile lui :

Vreau sa stiu cum determin voltajul in functie de specificatii - adica pana in punctul ca difuzorul sa nu distorsioneze semnalul

Editat Septembrie 18, 2021 de Florin_Eusebiu

[merck]

Acum 19 minute, Florin_Eusebiu a spus:

explica-mi si ce inseamna toti parametrii aceia tehnici si TS ,pe rand

Explicatia parametrilor sunt pe net in nenumarate locuri la ... doar un clic distanta:

https://en.wikipedia.org/wiki/Thiele/Small_parameters

 

• S_d – Projected area of the driver diaphragm, in square metres.
• M_ms – Mass of the diaphragm/coil, including acoustic load, in kilograms. Mass of the diaphragm/coil alone is known as M_md
• C_ms – Compliance of the driver's suspension, in metres per newton (the reciprocal of its 'stiffness').
• R_ms – The mechanical resistance of a driver's suspension (i.e., 'lossiness'), in N·s/m
• L_e – Voice coil inductance, in millihenries (mH) (measured at 1 kHz).
• R_e – DC resistance of the voice coil, in ohms.
• Bl – The product of magnet field strength in the voice coil gap and the length of wire in the magnetic field, in tesla-metres (T·m).

F_s

Also called F_s, resonance frequency measured in hertz (Hz). The frequency at which the combination of the energy stored in the moving mass and suspension compliance is maximum, and results in maximum cone velocity. A more compliant suspension or a larger moving mass will cause a lower resonance frequency, and vice versa. Usually it is less efficient to produce output at frequencies below F_s, and input signals significantly below F_s can cause large excursions, mechanically endangering the driver. Woofers typically have an F_s in the range of 13–60 Hz. Midranges usually have an F_s in the range of 60–500 Hz and tweeters between 500 Hz and 4 kHz. A typical factory tolerance for F_s spec is ±15%.

Q_ts

A unitless measurement, characterizing the combined electric and mechanical damping of the driver. In electronics, Q is the inverse of the damping ratio. The value of Q_ts is proportional to the energy stored, divided by the energy dissipated, and is defined at resonance (F_s). Most drivers have Q_ts values between 0.2 and 0.5, but there are valid (if unusual) reasons to have a value outside this range.

Q_ms

A unitless measurement, characterizing the mechanical damping of the driver, that is, the losses in the suspension (surround and spider.) It varies roughly between 0.5 and 10, with a typical value around 3. High Q_ms indicates lower mechanical losses, and low Q_ms indicates higher losses. The main effect of Q_ms is on the impedance of the driver, with high Q_ms drivers displaying a higher impedance peak. One predictor for low Q_ms is a metallic voice coil former. These act as eddy-current brakes and increase damping, reducing Q_ms. They must be designed with an electrical break in the cylinder (so no conducting loop). Some speaker manufacturers have placed shorted turns at the top and bottom of the voice coil to prevent it leaving the gap, but the sharp noise created by this device when the driver is overdriven is alarming and was perceived as a problem by owners. High Q_ms drivers are often built with nonconductive formers made from paper or various plastics.

Q_es

A unitless measurement, describing the electrical damping of the loudspeaker. As the coil of wire moves through the magnetic field, it generates a current which opposes the motion of the coil. This so-called "Back-EMF" (proportional to Bl × velocity) decreases the total current through the coil near the resonance frequency, reducing cone movement and increasing impedance. In most drivers, Q_es is the dominant factor in the voice coil damping. Q_es depends on amplifier output impedance. The formula above assumes zero output impedance. When an amplifier with nonzero output impedance is used, its output impedance should be added to R_e for calculations involving Q_es.

Bl

Measured in tesla-metres (T·m). Technically this is B×l or B×l sin(θ) (a vector cross product), but the standard geometry of a circular coil in an annular voice coil gap gives sin(θ)=1. B×l is also known as the 'force factor' because the force on the coil imposed by the magnet is B×l multiplied by the current through the coil. The higher the B×l product, the larger the force that is generated by a given current flowing through the voice coil. B×l has a very strong effect on Q_es.

V_as

Measured in litres (L) or cubic metres, is an inverse measure of the 'stiffness' of the suspension with the driver mounted in free air. It represents the volume of air that has the same stiffness as the driver's suspension when acted on by a piston of the same area (S_d) as the cone. Larger values mean lower stiffness, and generally require larger enclosures. V_as varies with the square of the diameter. A typical factory tolerance for V_as spec is ±20–30%.

M_ms

Measured in grams (g) or kilograms (kg), this is the mass of the cone, coil and other moving parts of a driver, including the acoustic load imposed by the air in contact with the driver cone. M_md is the cone/coil mass without the acoustic load, and the two should not be confused. Some simulation software calculates M_ms when M_md is entered. M_md can be very closely controlled by the manufacturer.

R_ms

Units are not usually given for this parameter, but it is in mechanical 'ohms'. R_ms is a measurement of the losses, or damping, in a driver's suspension and moving system. It is the main factor in determining Q_ms. R_ms is influenced by suspension topology, materials, and by the voice coil former (bobbin) material.

C_ms

Measured in metres per newton (m/N). Describes the compliance (i.e., the inverse of stiffness) of the suspension. The more compliant a suspension system is, the lower its stiffness, so the higher the V_as will be. C_ms is proportional to V_as and thus has the same tolerance ranges.

R_e

Measured in ohms (Ω), this is the DC resistance (DCR) of the voice coil, best measured with the cone blocked, or prevented from moving or vibrating because otherwise the pickup of ambient sounds can cause the measurement to be unreliable. R_e should not be confused with the rated driver impedance, R_e can be tightly controlled by the manufacturer, while rated impedance values are often approximate at best. American EIA standard RS-299A specifies that R_e (or DCR) should be at least 80% of the rated driver impedance, so an 8-ohm rated driver should have a DC resistance of at least 6.4 ohms, and a 4-ohm unit should measure 3.2 ohms minimum. This standard is voluntary, and many 8-ohm drivers have resistances of ≈5.5 ohms, and proportionally lower for lower rated impedances.

L_e

Measured in millihenries (mH), this is the inductance of the voice coil. The coil is a lossy inductor, in part due to losses in the pole piece, so the apparent inductance changes with frequency. Large L_e values limit the high frequency output of the driver and cause response changes near cutoff. Simple modeling software often neglects L_e, and so does not include its consequences. Inductance varies with excursion because the voice coil moves relative to the polepiece, which acts as a sliding inductor core, increasing inductance on the inward stroke and decreasing it on the outward stroke in typical overhung coil arrangements. This inductance modulation is an important source of nonlinearity (distortion) in loudspeakers. Including a copper cap on the pole piece, or a copper shorting ring on it, can reduce the increase in impedance seen at higher frequencies in typical drivers, and also reduce the nonlinearity due to inductance modulation.

S_d

Measured in square metres (m²). The effective projected area of the cone or diaphragm. It is difficult to measure and depends largely on the shape and properties of the surround. Generally accepted as the cone body diameter plus one third to one half the width of the annulus (surround). Drivers with wide roll surrounds can have significantly less S_d than conventional types with the same frame diameter.

X_max

Specified in millimeters (mm). In the simplest form, subtract the height of the voice coil winding from the height of the magnetic gap, take the absolute value and divide by 2. This technique was suggested by JBL's Mark Gander in a 1981 AES paper, as an indicator of a loudspeaker motor's linear range. Although easily determined, it neglects magnetic and mechanical non-linearities and asymmetry, which are substantial for some drivers. Subsequently, a combined mechanical/acoustical measure was suggested, in which a driver is progressively driven to high levels at low frequencies, with X_max determined by measuring excursion at a level where 10% THD is measured in the output. This method better represents actual driver performance, but is more difficult and time-consuming to determine.

P_e

Specified in watts. Frequently two power ratings are given, an "RMS" rating and a "music" (or "peak", or "system") rating, usually peak is given as ≈2 times the RMS rating. Loudspeakers have complex behavior, and a single number is really unsatisfactory. There are two aspects of power handling, thermal and mechanical. The thermal capacity is related to coil temperature and the point where adhesives and coil insulation melt or change shape. The mechanical limit comes into play at low frequencies, where excursions are largest, and involves mechanical failure of some component. A speaker that can handle 200 watts thermally at 200 Hz, may sometimes be damaged by only a few watts at some very low frequency, like 10 Hz. Power handling specifications are usually generated destructively, by long term industry standard noise signals (IEC 268, for example) that filter out low frequencies and test only the thermal capability of the driver. Actual mechanical power handling depends greatly on the enclosure in which the driver is installed.

V_d

Specified in litres (L). The volume displaced by the cone, equal to the cone area (S_d) multiplied by X_max. A particular value may be achieved in any of several ways. For instance, by having a small cone with a large X_max, or a large cone with a small X_max. Comparing V_d values will give an indication of the maximum output of a driver at low frequencies. High X_max, small cone diameter drivers are likely to be inefficient, since much of the voice coil winding will be outside the magnetic gap at any one time and will therefore contribute little or nothing to cone motion. Likewise, large cone diameter, small X_max drivers are likely to be more efficient as they will not need, and so may not have, long voice coils.

η₀ – Reference Efficiency

Specified in percent (%). Comparing drivers by their calculated reference efficiency is often more useful than using 'sensitivity' since manufacturer sensitivity figures are too often optimistic.

Sensitivity

The sound pressure, in dB, produced by a speaker in response to a specified stimulus. Usually this is specified at an input of 1 watt or 2.83 volts (2.83 volts = 1 watt into an 8-ohm load) at a distance of one metre.

 

P.S. Formule banuiesc ca nu vrei ca la nivelul de logica pe care il ai sigur ai fost "tare" la matematica .

Editat Septembrie 18, 2021 de merck

[Florin_Eusebiu]

Ok, mersi mult . Vreau sa mai stiu , cum calculez voltajul necesar in functie de specificatiile difuzorului , adica cati volti suporta maxim pana in pragul de distorsiuni !  Cum calculez asta ?