The importance of Kms(X) and BL(x) for mid-ranges

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#281
Hello @lrisbo and All,

In Sparkey’s Lab I have a Vifa P17WJ-00-08 (*) installed in a sealed ~14 liter enclosure. Sparkey is my cat.

Often this size driver is used in stand mount speakers with passive radiators.

The next set of tests will be this Vifa driver in the sealed enclosure and with passive radiators. I am curious to see what happens to in box pressures, Frequency Response, Harmonic Distortion, 2-Tone IMD’s. Anxious to see what the addition of passive radiators will do to the 2-Tone IMD test results.

(*) This driver I expect to see some warts that will hopefully show up potential issues in the test results.


Optional reading, Agenda and disclosures:

I do this for fun.

I have a similar size set of speakers on my bench that I use to listen to music and watch videos. These speakers are as large as will fit in my bench space. 8 inch drivers mean much larger enclosures. I also use a subwoofer tucked under the bench that sometimes I switch off when the household is asleep. The existing brand Peerless drivers sound nice at low to moderate SPL. To turn them up much louder than moderate levels they begin to sound pretty rough, that tests as increasing IMD’s. A high pass filter may help the Amplitude Modulation but I rather not use that option. I will test this option to see if or how much there is a reduction in measured Amplitude Modulation. I can do this filtering with the APx500 software generator setup.

Down the line for future testing, I do have a pair of SB17NBAC35-8 drivers with aluminum cones.

Also on the shelf is a pair of Purifi 6 ½ inch drivers.

Thanks DT
 
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#282
mikets42 said:
"I am not sure that I have correctly understood your arguments against viscoelastic creep."

If any mechanical effects were responsible for the observable non-linearities, there would be no differences in measurements for the amplitude of vibration was maintained the same for all (current linearizing) series resistors. But the differences are clearly observed.
Click to expand...
the first plot clearly shows the hysteresis distortion of the motor being reduced by increasing the series resistor. I assume you EQ’ed the stimulus to yield the same current/motion?

I agree that this should suppress any influence of the suspension nonlinear memeory effects (at least to first order)
 
#284
mikets42 said:
Lars, I do not understand how the current (so the force) linearization can affect the suspension non-linearity. Could you elaborate on this?
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yes. my impression is that you measured with different series resistors but also EQ’ed the stimulus so that the drivers response is the same (same current). This means the excursion is the same and this the influence from the suspension is the same across the sweeps with different resistors. Did I understand that correctly?
 
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#285
No, I did not EQ. I matched the levels in the middle. You can see in the graph that in the range of 200...3000Hz the FRs match closely - which can not be said about < 200 or >3000. If I measured IMD of 100Hz+5kHz, the results would be skewed beyond acceptability. But I am measuring 1450+1550 IMD and thus consider the lack of precise EQ-ing acceptable.

The excursion is about the same in the 200...3000Hz. I think the distortions due to suspension's non-linearity thus remain the same while the motor's distortions decrease. What do I miss?
 
#287
No, level up and down was with changing excitation, everything else was the same.
lenin=T*fs;
km=fs*T/2;
x=sin(2*pi*F1*(1:lenin)/fs)';
x=sin(2*pi*F2*(1:lenin)/fs)'+x;
for k=1:km
c=10^(-2.3*k/km);
x(km+1-k)=x(km+1-k)*c;
x(km+k)=x(km+k)*c;
end
 
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#288
lrisbo said:
Hi B_force,

I am not sure what you mean by the above? you mean when we have the general case where both Bl and Sd have both even and odd components?

cheers,
Lars
Click to expand...
https://dictionary.cambridge.org/dictionary/english/significance

https://www.merriam-webster.com/dictionary/significance

Sorry, but stop playing dumb and just show us some distortion numbers.

People asked that now multiple times and it's obvious you have them.

Again without REAL practical data it's just a lot of blablabla in circles and just a simple hypothesis.

That is NOT an opinion, but how fundamental science works.

Otherwise I am willing to scrape some money together with some people and just simply get a regular surround mounted on it professionally, measure it and share the data myself.
 
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#290
b_force said:
What's the question exactly?
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It was not a question. It was a statement.
b_force said:
One other thing I forgot to add, and going back to my brain fart earlier

BL(x), Km(x) or Cm(x) and Le(x) , means that all these parameters are a function of x.
So they are a function of the excursion.

So if there is no (or very little) excursion, it means they become constants.
Click to expand...

We are speaking of long throw drivers; B(l), S(d) ... are not constants.

For grins: https://www.mathworks.com/help/matlab/matlab_prog/local-functions-in-scripts.html

Thanks DT
 
#291
mikets42 said:
What do I miss?
Click to expand...
Caution please, loose collection (waffling) ;-)



The position of the voice coil is only loosely correlated with the position of the surface Sd.

in conjunction with

The position of the Sd is not where the microphone thinks it is. (... inherent HPF)

DC-Displacement [ Klippel ] comes to my mind too.

but

Bl(i) "works" without any position change.

and

The resistor does not linearize BL. (...over excursion)

It linearizes the phase (and impedance) (...over frequency)


Suspension creep... * haha*
 
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#292
yes, the resistor does not linearize Bl(x). IMHO, a series resistor linearises current only, and thus the force applied to the coil. In the first approximation, for the current drive,
Mms*d(d(x))/dt^2 = Bl(x)*I+Fsuspension(x, dx/dt)+Fair(x)+...;
At R=1m, p=a(...)Sd(x){ro/(2*pi*R^2)}; for wavelengths > diffusor's diameter.

About Sd(x), Bl(x), etc... For a 5.25-inch driver, the cone excursion with an amplitude of 0.25mm is sufficient to produce 94 dB SPL at 1m on 300Hz, and 100x smaller (1/f^2= 2.5mkm) on 3000Hz. How much do these Sd(x), Bl(x), etc change over 0.25mm, relative to Sd(0), Bl(0), typically?
 
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#297
phase_accurate said:
Well the purify is actually +- 2.9mm xmax
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No, Xlin is +/- 2.9mm Xmax is +/- 14.4mm. Let's try to be accurate and try not to change facts to accomodate what you said first.
phase_accurate said:
The other one is also not your typical midrange with its low fs and large Vas regarding its size.
Click to expand...
You where not asking about typical midrange, you ask for widrnage... 😉
 
#299
I was actually quite accurate by using xmax as the maximum linear excursion since this is the normal way to use it. The other one is maximum excursion before damage. To call it Xmax is a bit misleading. But they do at least explain what they meant. And yes, it is still not a long-throw driver since it is not intended to be used that way. While this large excursion before damage makes it very sturdy regarding short term abuse this is not the way it is intended to be used long term and it would not sound pleasing that way.

Regards

Charles
 
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#300
The Xlin and Xmax terms may be confusing, but no one in his right mind in this thread is interested in mechanical Xmax: everybody here means Xmax lin when Xmax is referred to. That context is clear as crystal, in particular because of the Bl(x) discussion.
 
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