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robertbartsch
06-12-2009, 01:26 PM
So this is a measure of the motor strength in the VC gap; right?

So what are the benefits of a higher reading design?

All things being equal, I assume you would get a better flatter response and higher sensativity or is it more complicated than that?

Hoerninger
06-12-2009, 01:50 PM
guass



... or is it more complicated than that?
Yes.

O.k., the strength is given by Bxl (in Tesla x Meter). It has quite different influences, it can't be said with a few words, look here:

The equations:
* Qm, fres, Cms, Rms
Qm := 1/(2*pi*fres*Cms*Rms);
* Qe, fres, Mms, Re, Bxl
Qe := 2*pi*fres*Mms*Re/power(Bxl,2);
* Rme, Bxl, Re
Rme := power(Bxl,2)/Re;
* Rme, fres, Mms, Qe
Rme := 2*pi*fres*Mms/Qe;
* Qt, Qe, Qm
Qt := 1/(1/Qm+1/Qe);
* Df, Qt
Df := 1/(2*Qt);
* Dd, Sd
Sd := pi/4*power(Dd,2);
* Mcost, Rme, Xmax, Hc or Hg
Mcost := Rme*(H+Xmax)/H; where H is the smallest of either Hc or Hg
* Mpow, Bxl, Re
Mpow := Bxl/root(2,Re);
* Mpow, Rme
Mpow := root(2,Rme);
* f4pi, Sd
f4pi := c*root(2,1/(4*pi*Sd));
* f2pi, Dd
f2pi := 2*c/(pi*Dd);
* f2pi, f4pi
f2pi := 2*f4pi;
* fpist, Dh
fpist := c/(10*Dh);
* fmax, Dd
fmax := c/Dd;
* Cms, Sd, Vas
Cms := Vas/(power(Sd,2)*rho*power(c,2));
* Mms, Cms, fres
Mms := 1/(power(2*pi*fres,2)*Cms);
* Mair, Dd
Mair := rho/3*power(Dd,3);
or (when measuring),
Mair := 8/3*rho*power(Sd/PI,1.5);
* Mvac, Mair, Mms
Mvac := Mms - Mair;
* Zres, Re, Bxl, fres, Qm, Cms
Zres := Re + power(Bxl,2)*2*pi*fres*Qm*Cms;
* EBP, fres, Qe
EBP := fres/Qe;
* Bxl, Mms, Gamma (the acceleration factor)
Gamma := Bxl/Mms;
* no, fres, Vas, Qe
no := power(2*pi,2)/power(c,3)*power(fres,3)/Qe*Vas;
* no, Mms, Bxl, Re, Sd
no := rho*power(Sd*Bxl,2)/(power(Mms,2)*2*pi*c*Re);
* Pn, SPL
SPL := 96 - 10*log10(Pn);
* no, SPL
SPL := SPL_ref + 10*log10(no);
where SPL_ref = approx. 112.2 dB in 2*pi space is given as:
SPL_ref := 10*log10(rho*c/(2*pi*power(pref,2)))
where pref = 20 uPa reference pressure for 0 dB SPL.
* SPLmx, Pe, SPL
SPLmx := SPL + 10*log10(Pe) - 3;
* USPL, Sd, Bxl, Re, Mms
USPL := 20*log10(USPL_Volts*rho*Sd*Bxl/(2*pi*pref*Re*Mms));
where USPL_Volts = 2.83 Volt (equals 1 watt into 8 ohm load),
but can be changed to eg. 1 Volt by modifying DPC.INI.
* SPL, USPL, Re
SPL := USPL + 10*log10(Re/power(USPL_Volts,2));
* Hc, Hg, Xmax
Xmax := abs(Hc-Hg)/2;
Here abs means absolute value, ie. the value must be positive
* Gloss, Xmax, fres
Gloss := (g/(2*pi*fres)^2)/Xmax;
where g = 9.81 m/s2 but can be changed to eg. 9.82 g by
modifying DPC.INI.
* Vd, Xmax, Sd
Vd := Xmax*Sd;
* Dvol, Dd, Depth, MagDpt, Magnet, VCd
Dvol := pi/4*((Depth-MagDpt)/3*(power(Dd,2)+power(VCd,2)+Dd*VCd)+MagDpt*power(M agnet,2));
* Dvol, Outer (simplified method)
Dvol := 0.4*power(Outer,4);
* Res, Zres, Re
Res := Zres - Re;
* Res, Rms, Bxl
Res := power(Bxl,2)/Rms;
* Ces, Mms, Bxl
Ces := Mms/power(Bxl,2);
* Ces, Qm, fres, Res
Ces := Qm/(2*PI*fres*Res);
* Les, Cms, Bxl
Les := Cms*power(Bxl,2);
* Les, fres, Ces
Les := 1/(power(2*PI*fres,2)*Ces);
* Les, Res, Qm, fres
Les := Res/(2*PI*fres*Qm);
* Res, Re, Qm, Qe
Qe := Qm*Re/Res;
* Le, fLe, KLe
KLe := Le*root(2,2*pi*fLe);

All these formulas are checked in DPC (http://home1.stofanet.dk/cfuttrup/dpc/dpc.htm)'s calculation routine in all possible combinations of known and unknown variables.
____________
Peter

robertbartsch
06-12-2009, 02:09 PM
...some of the drivers I enjoy most have a relatively low gauss specification and carry alumium not Ti frames, for example. I could only assume this low spec is offset by lighter frams or some other factor that allows them to sound good.

Hoerninger
06-12-2009, 02:41 PM
A loudspeaker is always a compromise by many aspects.

Simply said a stronger motor will give more efficiency but a higher cut off for the lows. The lack of bass can be circumvent in a horn (about QTS <= 0,25).
____________
Peter