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Old 3rd June 2003, 12:15 PM   #1
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Default speakerworkshop, meaning of L1 and R1?

I have finally gotten SW 1.06 to run and calibrate. I've been doing TSP measurements by the added mass method.

Q, f_s and V_as values are surprisingly close to manufacturer's specs except for Peerless CSC217R, which does not really come to a surprise.


The major difference is that (whether I enter R_e manually or have it determined automatically), L_e is at best half as big as per specs or magazine test articles. Now, SW computes R1 and L1 additionally. I suspect these are electrical equivalents in some standard loudspeaker model, but none of the texts I have handy uses the same nomenclature.

How do I compute anything anything similar to standard TSP L_e? How do I obtain m_ms and Bxl directly?

Regards,

Eric
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Old 3rd June 2003, 02:15 PM   #2
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I'm pretty sure you have to enter Re manually, as a typical soundcard cannot accurately measure DC resistance...only AC impedance. If you accurately measure Re with a good multimeter and enter this value and still get wrong Le, try measuring just an inductor of known value. I have found that if I use SW to measure a 1mH choke, it will show as 1mH in SW, within 1 or 2%. If SW will not accurately measure a known inductor, then something is wrong.
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Old 3rd June 2003, 02:23 PM   #3
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I have this problem also with manually entered R_dc. There was somebody else on the SW forum having the same problem, but it was never answered satisfactorily (the forum is kind of dead).

It will measure most inductors very accurately, even small devices (0.18 mH/ 0.4R air core). There is one air core inductor that has relatively high resistance (0.6 mH / 1 R) resistance that it will treat stubbornly as a resistor, wrongly reporting 0.2 R and no inductance. I guess this is more a problem with the software making the wrong decision which algorithm to use.

Regards,

Eric
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Old 3rd June 2003, 04:21 PM   #4
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Out of curiosity, what resistors do you use for the series R and calibration resistors? I use 8.0 for the series Resistor, and 1.0 and 15.0 for the calibration resistors. I also use a small power amp as the source...not just a soundcard line level output.

So far I have never gotten a result out of the ordinary, but then I don't use it that frequently, either.

By the way, after you measure the driver's parameters, under the DRIVER tab, there is a "set driver equivalence". When you select this, it should produce an impedance graph that looks like the measured FREE AIR Impedance graph. If they look the same, it proves your parameters are correct. If your Le is way off, it will show a much different impedance as the frequency gets higher.
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Old 3rd June 2003, 07:25 PM   #5
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Capslock,

I can't offer any advise about your Le problem but I've found that changing the sample rate value (under the options/prefs/measurements tab) can give better measurements for caps and inductors.

As for your other question, I believe that the R1 and L1 values are used execlusively by LEAP.

Now, a question for you! I've never had particulary good results when measuring TS parameters with Speaker Workshop. I've detailed my problems in this thread:
T/S measurements with Speaker Workshop

Do your Vas and Fs values show a similar trend?

Nice one,
David.
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Old 3rd June 2003, 10:18 PM   #6
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daatkins,
I went over and read your other post that you linked. I just wanted to say that Audax are notorious for not being like their published specs, usually requiring a much larger box than planned. They have some great sounding cones, but I won't use them anymore due to the phony specs they publish.
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Old 3rd June 2003, 10:53 PM   #7
Ron E is offline Ron E  United States
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R1 and L1 are an additional pair of components that help approximate the value of voice coil inductance. The pair are connected in parallel and added in series with the constant portion of voice coil inductance.

However much you would like there to be one, there is no single value for voice coil inductance, it changes with frequency and with most drivers it even changes with excursion. Any single value is a fallacy.

So how does one design Zobels? Either by experiment, trial and error circuit analysis with measured impedance data or by using software that can optimize...like speaker workshop...
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Old 4th June 2003, 08:28 AM   #8
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@ron:
thanks, that was the answer I was looking for

@daatkins:
My peerless drivers CSC217R measure somewhat differently from specs. The Audax HT300G0 measure right on spec, as do many other drivers (Tang Band W3-881S, Raveland AXX1515, Vifa XT18WO09).

I have problems measuring Scan 21W8555-00 and 01. The Q_es and Q_ts values are almost double the manufacturer specs. These drivers have fairly low resonance, extremely high Q_ms and low inductance. Maybe the algorithm is having trouble...

I am using 3 and 15 R calibration resistors and a 7.6 R reference resistor, and an LM3886 as a power amp.

Regards,

Eric
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Old 4th June 2003, 11:09 AM   #9
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Well, I compared simulation and measurement, and they look very much identical, especially in the HF region. I think the resolution of roughly 1 Hz may be a little too low for high-Q, low fs drivers like the Scan. I will remeasure with a lower sample rate.

As for the L1 and R1 definitions, the nomenclature is not really consistent within SW. In the "set equivalence" dialog box, what was Le in the driver menu now seems to be L1b, and what was L1 now is L1a. Then there are L2, C2, R2 which I assume are the electrical equivalents of the mechanical oscillator. I assume that R2 would be proportional to R_ms, and C2 to m_ms, the factor largely governed by Bxl which should also tumble out of these measurements (unless I want to measure it with a weight and a ruler...)
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Old 5th June 2003, 07:55 AM   #10
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I have gone to 11 kHz and 256 ksamples. I now can measure the high resistance inductor correctly.

Remeasuring the 21W8555-00 now gives a very good impedance plot, and simulation and measurement agree extremely well. Unfortunately, Q_ts is still 50% too high...
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