Thiel Small Parameters?

[lynkage]

I am wondering if any of you gurus can tell me about different names for t/s params. It seems as though some manufacturers use slightly different names (as in Re) for the different parameters. This is unclear to me as I am new to this. I would like to use speaker workshop to model box/crossover design. I have built a few boxes based on T/S and done ok but it looks as though in the crossover is were it is at.

Please go easy on me as I am unknowing but willing to listen and learn.
Thanks Shane

[kelticwizard]

Re is the simple resistance of the driver, measured when you unhook the driver from the amp and just measure the resistance between the speaker terminals with a multimeter. It is also labelled DCR.

Vas is sometimes called "equivalent volume".

Be careful of this one: excursion. Linear excursion is the amount of travel the speaker can do without going into distortion. It is supposed to be measured from the center to the extreme. So a driver with 6 mm linear excursion is supposed to be able to go from rest to a point 6 mm forward and back to rest again linearly. This is also sometimes called "peak excursion", not "Peak-to-peak".

However, some manufacturers list their excursion as being "peak-to-peak". That means the distance traveled coming all the way back to all the way front. This way of measuring yields a number twice as large as the normal way to state linear excursion.

Then there is Mechanical excursion, or max mechanical excursion, which is how far the driver can go without suffering mechanical damage, regardless of the distortion. In hi fi drivers it is safe to assume that Mechanical excursion is at least 1.5 times the linear excursion, usually somewhat more. PA drivers can have mechanical excursion four times the linear excursions.

Any others you would like to list?

[AGGEMAM]

In regards to Xdam (maximum mechanical exursion).

If you have the air gap height and the voice coil height you can calculate the Xdam by subtracting the former from the latter. This is the peak-to-peak Xdam or Xdam(p-p).

This is not an exact figure but can be used if it is not spefied on the parameter sheet.

[Ron E]

The following are the main parameters listed in a somewhat abbreviated form to allow you to interpret most parameters correctly. Different manufacturers may modify these terms slightly, and they may use different units (like cubic meters instead of liters, etc..) So you have to be aware of a lot of things.

Major Variables:
F = frequency
Q = Q factor
V = Volume
S = Area
R = Resistance
L = inductance
C = capacitance or compliance
M = mass

Subscripts (Modifyers):
a = acoustic
s = speaker
e = electrical
m = mechanical
t = total
c = combined (or sometimes closed box or cutoff)
b = box
l = loss
p = port
d = diaphragm
vc = voice coil (seen sometimes with R and L - equivalent to "e")

Some examples:
Fs = Resonant frequency of speaker
Fb = resonant frequency of box
Fc = combined box/speaker resonance (for sealed - also called Fb in some texts)
Qes = Q electrical of speaker
Qec = Q electrical of speaker box system (closed speakers)
Vas = Equivalent acoustic volume of speaker compliance
Re = electrical resistance
Le = electrical inductance
Sd = diaphragm area

[lynkage]

Thanks for all of your input!!
It looks as though the program is asking for:
Voice coil series (L1)
Voice coil series (R1)

If I am correct from the info given L1 should be the equivalent of Le
and R1 should be Re correct ?
Thanks Shane

[454Casull]

All this time and I still haven't figured out what Q really means...

[sreten]

Originally posted by 454Casull
All this time and I still haven't figured out what Q really means...

I believe its from radio circuits where very narrow filters were
required, Q's of >100, and that Q is an abbreviation of Quality
Factor related to the peak value and the width of the radio filter.

Doesn't make much intuitive sense when applied to loudspeaker Q's.

sreten.

[Ron E]

Q = energy stored/energy dissipated (defined at resonance).

Speaker workshop uses a slightly enhanced driver model, which consists of a fixed inductance and resistance, in series with a component that consists of an inductor and resistor in parallel. Look for help on "set equivalence", although this may confuse you more because the nomenclature is inconsistent. The best thing to do is measure the driver with speaker workshop and let it do it's thing. L1 and R1 (and Re and Le for that matter) are under the heading "calculated", so you don't need to enter these. The model is still a rough model of driver inductance (measurements are better) and cannot fully account for the variation in inductance with frequency, and there is no way to guess values for the extra components.

The only reason to enter Re is if speaker workshop is indicating really wacky values, in which case the other measurements may be suspect as well.

[Svante]

Originally posted by Ron E

Speaker workshop uses a slightly enhanced driver model, which consists of a fixed inductance and resistance, in series with a component that consists of an inductor and resistor in parallel.

What are the general opinions on this model? I have seen this, and also another where the impedance of the inductance goes like

Zl=w^n * L, where n usually is 0.6 .. 0.8 for most drivers.

(The normal inductor would of course be Zl=w*L)

Has anybody tried to match either or both of these models to real driver data?

[Pjotr]

Originally posted by sreten

I believe its from radio circuits where very narrow filters were
required, Q's of >100, and that Q is an abbreviation of Quality
Factor related to the peak value and the width of the radio filter.

Doesn't make much intuitive sense when applied to loudspeaker Q's.

Think you are close by. It means “Quality factor” but tells you nothing about the actual overall quality of the speaker. In radio circuits it says something about the frequency discriminating capabilities of a tuned circuit.

A loudspeaker is a mass-spring system and also a tuned system in some sense. Same laws apply. It tells something about the inherent capabilities of the speaker how quickly the fundamental resonance (Fs) dies out. The total Q factor Qt is the inverse of damping factor D. Damping factor comes from control theory and feedback systems, but since loudspeakers are handled mostly by EE’s (like Thiele and Small) which are more familiar with Q they keep using Q. Qt is the total result of mechanical damping (1/Qm) and electrical damping (1/Qe).

Cheers