DaBaller504

06-02-2003, 02:20 AM

Alrite, is there a site that will help me to figure out what to tune and what dimensions to build a ported box to? I have built with the help of other people ported box but I want to figure out how to decide what to tune your box too. Also i want to understand like Vas, Qes, and all of those terms. Is there a site???

bigred78797

06-02-2003, 02:34 AM

Well i don't know about a site... there is one but i cant remember the url, but ill give it a shot. This is the help file in win ISD PRO.

ok

Thiele/Small-Parameters section

Qes

Electrical Q (=damping), lower value means higher damping. It describes a drivers ability to resonate at fs based on electrical means.

Qms

Mechanical Q (=damping, lower value means higher damping). It describes a drivers ability to resonate at fs based on mechanical means.

Qts

Total damping (parallel coupling of Qms and Qes).

Vas

Equivalent Volume of air to Cms.

Fs

Free air resonance frequency of driver.

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Electro-Mechanical parameter section

Mms

Mechanical Mass of the vibrating part of the driver including air load.

Cms

Compliance of driver (inverse of spring stiffness).

Rms

Mechanical damping, gives you the mechanical damping of the diaphragm arising from mechanical friction, including the resistive part of the radiation load. Rms can be compared to Rme, and Rms is similarly related to Qms. Larger Qms gives smaller Rms. For woofers this is normally desired because the suspension then operates closer to a perfect spring.

Re

DC-resistance of voice coil.

BL

Magnetic Induction crossed with wire length in the airgap. (crossing = cross product, a mathematical vector-operation)

Dd

Diameter of Diaphragm.

Le

Voice coil inductance.

Sd

Surface-area of Diaphragm.

fLe

The frequency at which Le and KLe is to be determined.

KLe

Voice coil semi-inductance in [H·sqrt(Hz)], after Vanderkooy

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Large-Signal Parameter section

Xmax

Max linear excursion, usually calculated as abs(Hc-Hg)/2, and sometimes multiplied by a factor (1.15 or 0.87, depending on how much distortion is accepted). WinISD does not multiply with any of these factors. Some manufacturers erroneously gives you Xmax as the damage limit, see Xlim. WinISD needs this as peak value.

Xlim

Damage limit excursion, also a peak value.

Hc

Height of coil.

Hg

Height of airgap.

Vd

Volume Displacement, how much air the driver can move in its linear range.

Pe

Thermal limited max. continuous electric power handling. If a driver is driven continuously above Pe, then it will eventually fail.

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Miscellaneous parameters section

no

Efficiency (n should be the greek letter "eta") in percent [%].

Znom

Nominal impedance of the driver (not used in simulation).

USPL

efficiency in deciBell (SPL = sound pressure level) in [dB/2.83V] dB per 2.83 Volt (similar to 1W into an 8 ohm load). This SPL-measurement is similar to SPL (see above), but gives different values. This shows you the difficulties about matching drivers. With 8 ohm drivers 2.83 Volt gives you 1 Watt and the two figures (SPL and USPL) will be similar, but at lower impedance levels the USPL level will increase. USPL is the socalled voltage sensitivity and is closer to application with voltage amplifiers. To a limited extent you could match drivers for a loudspeaker system with this factor.

SPL

Efficiency in deciBell (SPL = sound pressure level) in [dB] per Watt directly related to no, but definately not an "accurate" figure in applications. In other words, if a speaker driver is specified by the manufacturer to some other value, do not use that value for WinISD unless you need it to calculate some Thiele-Small parameters and approximate values are better than no values at all. WinISD assumes distance 1 meter, radiation into halfspace (2*pi), and voltage driv. SPL is the so-called power-sensitivity, not really related to application, normally voltage amplifiers are used, but can become relevant if you want to compare two similar drivers with different nominal impedance levels.

Voicecoils

Voicecoils is a descriptive parameter. It just tells how many voicecoils there are. So ordinary drivers have 1, DVC drivers have 2 etc.

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"figure of merits" parameters section

SPLmaxLF

SPLmaxLF gives how loud driver can play in closed box or infinite baffle into half-space at maximum excursion at 20 Hz. Distance from this imaginary baffle is 1 meter. It gives "feeling" on Vd. Note also, that it doesn't apply to vented or any other assisted enclosure.

SPLmax

Maximum thermal limited SPL in [dB] (at maximum Pe, assuming power compression = 3 dB) playing into 2pi space

Rme

Electromagnetic Damping Factor in [N·s/m] (the unit for viscosity), gives you the mechanical control/damping of the diaphragm arising from the electro-magnetic motor system. Rme is related to Qes in a way similar to how Rms is related to Qms. Rme is often used as a measure for power of the magnetic motor system, see Mpow and Mcost.

Gamma

The acceleration factor (acceleration per ampere) in [m/(s²·A)].

Mpow

Motor power-factor in Newton per square-root Watt [N/sqrt(W)]. Similar to Mcost. I have seen Rme as a measure of motor power, but this is simply the square-root of Rme, and it provides a simple measure in Newton, which I (Claus Futtrup) prefer, and which seems to relate the actual (subjectively perceived) power in a linear way. The square-root Watt unit can be difficult to understand, but should be interpreted as square-root of Volt * Ampere. In this respect it becomes clear that Mpow is independent of the drivers impedance level, and therefore does not prioritize high or low impedance drivers. Mpow is purely a motor system power-factor.

Mcost

Motor cost-factor in [N·s/m] (or [kg/s]). Mcost expresses how powerful the motor system is (based on Rme, Xmax and either Hc or Hg depending on whether the voice coil is overhung or underhung), and the Xmax value includes an indicator of how much efficiency is "lost" in the design. This factor is therefore a description of how expensive the motor system is. This is an indicator on the price of the driver, but please forget about the unit. Other factors comes in, like diaphragm material, manufacturing tolerances etc. This version of Mcost (instead of using Rme) is based on an extension suggested by T. L. Clarke, where the cost of getting a high Bl at low impedance must be even higher when the driver is significantly overhung or underhung.

EBP

Efficiency-Bandwidth-Product in [Hz]

Gloss

Gloss tells how many percent of Xmax driver cone will sag, if driver is mounted horizontally. This figure is only approximate, because surrounding air shifts resonance frequency to somewhat lower value. So result is somewhat over-pessimistic by some amount. Generally, figures of more than five percent tell you that driver in question shouldn't be mounted horizontally. Value of gravity acceleration used when calculating sag is 9.80665 m/s².