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Thread: Thiele-Small Parameters definitions...

  1. #1
    Senior Member remusr's Avatar
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    Thiele-Small Parameters definitions...

    Thiele-Small Parameters
    B
    Magnetic flux density in gap, in Tesla-meters (TM)
    BL
    The magnetic strength of the motor structure. "Expressed in Tesla meters, this is a measurement of the motor strength of a speaker. Think of this as how good a weightlifter the transducer is. A measured mass is applied to the cone forcing it back while the current required for the motor to force the mass back is measured. The formula is mass in grams divided by the current in amperes. A high BL figure indicates a very strong transducer that moves the cone with authority!"
    C
    Propagation velocity of sound at STP, approx. 342 m/s
    Cas
    Acoustical equivalent of Cms
    Cmes
    The electrical capacitive equivalent of Mms, in farads
    Cms
    The driver's mechanical compliance (reciprocal of stiffness), in m/N
    D
    Effective diameter of driver, in meters
    F3
    -3 dB cutoff frequency, in Hz
    Fb
    Enclosure resonance (usually for bass reflex systems), in Hz
    Fc
    System resonance (usually for sealed box systems), in Hz
    Fs
    Driver free air resonance, in Hz. This is the point at which driver impedance is maximum. "This parameter is the free-air resonant frequency of a speaker. Simply stated, it is the point at which the weight of the moving parts of the speaker becomes balanced with the force of the speaker suspension when in motion. If you've ever seen a piece of string start humming uncontrollably in the wind, you have seen the effect of reaching a resonant frequency. It is important to know this information so that you can prevent your enclosure from 'ringing'. With a loudspeaker, the mass of the moving parts, and the stiffness of the suspension (surround and spider) are the key elements that affect the resonant frequency. As a general rule of thumb, a lower Fs indicates a woofer that would be better for low-frequency reproduction than a woofer with a higher Fs. This is not always the case though, because other parameters affect the ultimate performance as well."
    L
    Length of wire immersed in magnetic field, in meters
    Lces
    The electrical inductive equivalent of Cms, in henries
    Le
    "This is the voice coil inductance measured in millihenries (mH). The industry standard is to measure inductance at 1,000 Hz. As frequencies get higher there will be a rise in impedance above Re. This is because the voice coil is acting as an inductor. Consequently, the impedance of a speaker is not a fixed resistance, but can be represented as a curve that changes as the input frequency changes. Maximum impedance (Zmax) occurs at Fs. "
    Ms
    The total moving mass of the loudspeaker cone.
    Mmd
    Diaphram mass, in grams
    Mms
    The driver's effective mechanical mass (including air load), in kg. "This parameter is the combination of the weight of the cone assembly plus the ‘driver radiation mass load’. The weight of the cone assembly is easy: it’s just the sum of the weight of the cone assembly components. The driver radiation mass load is the confusing part. In simple terminology, it is the weight of the air (the amount calculated in Vd) that the cone will have to push."
    n0
    The reference efficiency of the system (eta sub 0) dimensionless, usually expressed as %
    p
    (rho) Density of air at STP 1.18 kg/m^3
    Pa
    Acoustical power
    Pe
    Electrical power
    Q
    The relative damping of a loudspeaker
    Q Parameters
    "Qms, Qes, and Qts are measurements related to the control of a transducer's suspension when it reaches the resonant frequency (Fs). The suspension must prevent any lateral motion that might allow the voice coil and pole to touch (this would destroy the loudspeaker). The suspension must also act like a shock absorber. Qms is a measurement of the control coming from the speaker's mechanical suspension system (the surround and spider). View these components like springs. Qes is a measurement of the control coming from the speaker's electrical suspension system (the voice coil and magnet). Opposing forces from the mechanical and electrical suspensions act to absorb shock. Qts is called the 'Total Q' of the driver and is derived from an equation where Qes is multiplied by Qms and the result is divided by the sum of the same.

    As a general guideline, Qts of 0.4 or below indicates a transducer well suited to a vented enclosure. Qts between 0.4 and 0.7 indicates suitability for a sealed enclosure. Qts of 0.7 or above indicates suitability for free-air or infinite baffle applications. However, there are exceptions! The Eminence Kilomax 18 has a Qts of 0.56. This suggests a sealed enclosure, but in reality it works extremely well in a ported enclosure. Please consider all the parameters when selecting loudspeakers. If you are in any doubt, contact your Eminence representative for technical assistance."
    Qa
    The system's Q at Fb, due to absorption losses; dimensionless
    Qec
    The system's Q at resonance (Fc), due to electrical losses; dimensionless
    Qes
    The driver's Q at resonance (Fs), due to electrical losses; dimensionless. "A measurement of the control coming from the speaker's electrical suspension system (the voice coil and magnet). Opposing forces from the mechanical and electrical suspensions act to absorb shock."
    Ql
    The system's Q at Fb, due to leakage losses; dimensionless
    Qmc
    The system's Q at resonance (Fc), due to mechanical losses; dimensionless
    Qms
    The driver's Q at resonance (Fs), due to mechanical losses; dimensionless. "A measurement of the control coming from the speaker's mechanical suspension system (the surround and spider). View these components like springs."
    Qp
    The system's Q at Fb, due to port losses (turbulence, viscousity, etc.); dimensionless
    Qtc
    The system's Q at resonance (Fc), due to all losses; dimensionless
    Qts
    The driver's Q at resonance (Fs), due to all losses; dimensionless. "The 'Total Q' of the driver and is derived from an equation where Qes is multiplied by Qms and the result is divided by the sum of the same."
    R
    Ripple, in dB
    Re
    "This is the DC resistance of the driver measured with an ohm meter and it is often referred to as the 'DCR'. This measurement will almost always be less than the driver's nominal impedance. Consumers sometimes get concerned the Re is less than the published impedance and fear that amplifiers will be overloaded. Due to the fact that the inductance of a speaker rises with a rise in frequency, it is unlikely that the amplifier will often see the DC resistance as its load."
    Ras
    Acoustical equivalent of Rms
    Res
    The electrical resistive equivalent of Rms, in ohms
    Rms
    "This parameter represents the mechanical resistance of a driver’s suspension losses. It is a measurement of the absorption qualities of the speaker suspension and is stated in N*sec/m."
    Revc
    DC voice coil resistance, in ohms
    Rg
    Amplifier source resistance (includes leads, crossover, etc.), in ohms
    Rms
    The driver's mechanical losses, in kg/s
    Sd
    Effective piston radiating area of driver, in square centimeters. "This is the actual surface area of the cone, normally given in square cm."
    SPLo
    Sound Pressure Level, usually measured at 1 watt, at 1 meter in front of the loudspeaker
    Vas/Cms
    "Equivalent volume of compliance", this is a volume of air whose compliance is the same as a driver's acoustical compliance Cms (q.v.), in cubic meters. "Vas represents the volume of air that when compressed to one cubic meter exerts the same force as the compliance (Cms) of the suspension in a particular speaker. Vas is one of the trickiest parameters to measure because air pressure changes relative to humidity and temperature — a precisely controlled lab environment is essential. Cms is measured in meters per Newton. Cms is the force exerted by the mechanical suspension of the speaker. It is simply a measurement of its stiffness. Considering stiffness (Cms), in conjunction with the Q parameters gives rise to the kind of subjective decisions made by car manufacturers when tuning cars between comfort to carry the president and precision to go racing. Think of the peaks and valleys of audio signals like a road surface then consider that the ideal speaker suspension is like car suspension that can traverse the rockiest terrain with race-car precision and sensitivity at the speed of a fighter plane. It’s quite a challenge because focusing on any one discipline tends to have a detrimental effect on the others. "
    Vd
    Maximum linear volume of displacement of the driver (product of Sd times Xmax), in cubic meters. "This parameter is the Peak Diaphragm Displacement Volume — in other words the volume of air the cone will move. It is calculated by multipying Xmax (Voice Coil Overhang of the driver) by Sd (Surface area of the cone). Vd is noted in cc. The highest Vd figure is desirable for a sub-bass transducer."
    Xmax/Xmech
    Maximum peak linear excursion of driver, in meters. "Short for Maximum Linear Excursion. Speaker output becomes non-linear when the voice coil begins to leave the magnetic gap. Although suspensions can create non-linearity in output, the point at which the number of turns in the gap (see BL) begins to decrease is when distortion starts to increase. Eminence has historically been very conservative with this measurement and indicated only the voice coil overhang (Xmax: Voice coil height minus top plate thickness, divided by 2). Xmech is expressed by Eminence as the lowest of four potential failure condition measurements times 2: Spider crashing on top plate; Voice coil bottoming on back plate; Voice coil coming out of gap above core; Physical limitation of cone. Take the lowest of these measurements then multiply it by two. This gives a distance that describes the maximum mechanical movement of the cone."
    Zmax
    "This parameter represents the speaker’s impedance at resonance."

  2. #2
    Senior Member Hoerninger's Avatar
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  3. #3
    Senior Member Hoerninger's Avatar
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    TSP in a rush for closed box design

    Some JBL speakers can well be driven in a closed box as Zilch Labs have worked out. Some theorie may encourage you.
    ____________
    Peter
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  4. #4
    Senior Member Hoerninger's Avatar
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    TSP and Horn Design

    Although a horn can't be designed with TSP alone, these parameters can give you a prediction of frequency limits, as D.B.Keele has pointed out.
    A short summarization you find in JBLs Tech Note Volume 1, #24: "JBL's New Maximum Output Midrange/Low Frequency Transducers" (page 3).
    The theorie behind is published in an AES paper (preprint):
    D.B.Keele: "Low-Frequency Horn Design Using Thiele/Small Driver Parameters" www.xlrtechs.com/dbkeele.com/PDF/Keele%20(1977-05%20AES%20Preprint)%20-%20LF%20Horn%20Design%20Using%20TS%20Paras.pdf

    The frequency limits are related to a straight horn. With bends arise limitations. Dr.Bruce Edgar has made some investigations which are published in Speaker Builder 3/93 p.13. A legalized copy is on Volvotreters site with "The Monolith Horn, page 2":
    http://www.volvotreter.de/dl-section.htm
    ____________
    Peter

  5. #5
    Senior Member Hoerninger's Avatar
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    TSP and Bass Reflex Design

    TSP have made bass reflex design easy.
    D.B.Keele discusses a modern design "A New Set of Sixth-Order Vented-Box Loudspeaker System Alignments" using TSP, which you can find on his homepage:
    http://www.xlrtechs.com/dbkeele.com/PDF/Keele%20(1975-07%20AES%20Published)%20-%20New%20Set%20of%20VB%20Alignments.pdf

    For a special bass reflex enclosure you need not only the TSP alone but also the alignment parameters as well. In the AES preprint by D.B.Keele "The Vented Loudspeaker: A Restatement", you will find a thorough investigation, many tables and graphs visualizing the results:
    http://www.xlrtechs.com/dbkeele.com/PDF/Keele%20(1972-05%20AES%20Preprint)%20-%20Vented%20Loudspeaker%20A%20Restatement.pdf
    Although it is very mathematical not using TSP it is worth looking at it.

    *******

    A bit OT here, the new statement speaker seems to be an interesting example of bass reflex design.
    The published frequency curves show a 6dB/oct decrease to lower frequencies for speaker LF2 starting at a remarkable high frequency . May be it is a sixth-order butterworth alignment. Speaker LF1, same type and same enclosure, shows instead a decrease to higher frequencies with 6dB/oct. It must be remembered that speaker LF2 is connected via a lowpass in the deviding network. Both speakers together sum up to a frequency response down to 53 Hz (-3dB) according to the graph.

    For me it is an interesting approach using two speakers in a smaller enclosure. At low frequencies the cone areas of both speakers are active.
    __________
    Peter
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  6. #6
    Senior Member Hoerninger's Avatar
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    errata

    In post#3 I made a writing error - missing power 2:

    VB = VAS / [ (QTC/QTS)^2 - 1 ]

    ____________
    Peter

  7. #7
    Senior Señor boputnam's Avatar
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    Hey, Peter...

    If you can edit / correct the original image attachement, and then imbed it again here, I'll copy it and insert it into Post #3.


  8. #8
    JBL 4645
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    Found this on youtube thought I’d add to this thread for historical use.

    AES Oral History 074: Neville Thiele
    http://www.youtube.com/watch?v=T3BbyYBrCJ8

  9. #9
    pdemondo
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    Some good info thanks!

  10. #10
    Senior Member ivica's Avatar
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    Quote Originally Posted by Hoerninger View Post
    Although a horn can't be designed with TSP alone, these parameters can give you a prediction of frequency limits, as D.B.Keele has pointed out.
    A short summarization you find in JBLs Tech Note Volume 1, #24: "JBL's New Maximum Output Midrange/Low Frequency Transducers" (page 3).
    The theorie behind is published in an AES paper (preprint):
    D.B.Keele: "Low-Frequency Horn Design Using Thiele/Small Driver Parameters" www.xlrtechs.com/dbkeele.com/PDF/Keele%20(1977-05%20AES%20Preprint)%20-%20LF%20Horn%20Design%20Using%20TS%20Paras.pdf

    The frequency limits are related to a straight horn. With bends arise limitations. Dr.Bruce Edgar has made some investigations which are published in Speaker Builder 3/93 p.13. A legalized copy is on Volvotreters site with "The Monolith Horn, page 2":
    http://www.volvotreter.de/dl-section.htm
    ____________
    Peter
    I have got it from:


    http://diy-audio.narod.ru/litr/Keele...g_TS_Paras.pdf

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