Can you give us some real life examples where these magical properties are demonstrated?
I've designed drive units using aluminium, titanium, a diamond-like-ceramic, low modulus polymers, unique fibrous material and engineered plastics which I've specified and had produced. My favourites are the last two.
My speakers certainly don't sound 'veiled in comparison to stiff membranes'.
Ref #96. What happens to amp output z as the phase of the signal from speaker resonance goes from + to zero to - degrees?
[testing 🙂 ]
Thx-RNmarsh
[testing 🙂 ]
Thx-RNmarsh
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Variable Amplifier Impedance
Per Rod Elliot, your circuit output impedance is 6.3 ohms, (0.3* (20k + 1k)/1k). That would be independent of frequency and speaker impedance/reactance.
What are the phase angles are involved?
I didnt see my topology on his Elliots' site.
-RM
Your circuit is figure 2 on Rod's Variable Amplifier Impedance page. You draw it differently but its the same circuit. You place the components under the (-) of the op amp, Rod places the components under/near the speaker.
I am not sure what your phase angle question is asking. The output impedance, 6.3 ohms, of your amp is resistive which would have zero phase angle. The current in the load and thereby the amp output impedance would be a function of the total load on the amplifier. The total load would be the vector addition of the complex load impedance plus the 6.3 ohms amp output resistance.
Your circuit has 6R3 Output Resistance ie phase is zero.
If done correctly, this will not change with what the speaker is doing unless it overloads.
But the very finite Output Resistance means the output voltage will change depending on the load and what its doing.
Fig 2 in the link I posted in #111
At the end of his article, Rod Elliott mentions a dubious patent by the Tymphany Corporation about manipulation of the output impedance of a power amplifier using some current derived negative feedback (rigorously called CFB in a previous century).
Why not patent the attached circuit which is a bit more original ?
It shows a very simple way to achieve negative output resistance to lower the Qes of a driver.
Looking carefully, one may observe that it is a bridge.
Preceding it with an op-amp providing bass-boost by its negative feedback network, it is a smart way to make closed subs.
.
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Yamaha AST/YST technology does not use an elementary EQ to bring the bass back up. This woud well apply to a closed box but not for a driver in a bass reflex enclosure which what they use.
In Stahl's concept, there is a second feedback loop derived from the sensed current passing through the driver to define a complex output impedance.
So, if we put 6.3 Ohm series R with a standard (low Zo) VFAmp will the distortion be lowered?
So, explain the action of distortion reduction, exactly how.
Thx-RNMarsh
So, explain the action of distortion reduction, exactly how.
Thx-RNMarsh
'Elementary' is in the eye of the beholder.
Because we were already doing loadsa fancy EQ, we consider the Yamaha EQ elementary. This is a complex issue.
But if the target design is an overdamped passive 4th order Vented Box with a 2nd order electronic filter (ie a 6th order system like Thiele's B6), the 'fancy' EQ is actually quite 'elementary' and not that more complex than for a Closed Box .. often simpler than the dreaded Linkwitz transform which is itself quite crude EQ.
If you are starting off with a poor drive unit which is badly matched to the box in the first place, then the EQ required might be a lot more complex.
Stahl is much more sophisticated cos the 'EQ' is reduced to 'designing' the parameters you want in the drive unit with electronic voodoo.
That circuit appears in Elliot, Birt, Mills & Hawkesford and perhaps even Voigt.
.. and that Ladies & Gentlemen, is what Yamaha AST/YST is all about if you strip away the marketing.
Please don't think I'm dissing Yamaha. They were very brave to try this when they did and made some excellent systems.
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Yes. Provided the amp doesn't clip or the resistor smokes, you will have exactly the same THD reduction and response changes.RNMarsh said:
For mostly the same reasons that Merilainen yaks about. (Caveat: some of his claims, but not all, are rubbish). Mills & Hawkesford is more accurate and best is Klippel.
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I believe that there is a significant distortion current produced by the back emf plying into the low amplifier Z out. The added R reduces the back emf current thereby reducing distorted cone motion thereby reducing acoustic output distortion.
The back emf voltage is out of phase with the forward drive current. This makes the back emf current out of phase causing distorted movement.
Wouldn't it be more Pure to have an intrinsic high
output Z, rather than contriving it with dubious
feedback schemes ?
output Z, rather than contriving it with dubious
feedback schemes ?
An externally hosted image should be here but it was not working when we last tested it.
Putting a resistor in series with a driver increases its Qes, & consequently its Qts, & therefore puts a hump in the response @ fs. = more Bass !
@ Joachim Gerhard
Yes it reduces the effeciency, but it does alter Qes & Qts etc.
More here Simple Network Lowers f3
Yes it reduces the effeciency, but it does alter Qes & Qts etc.
More here Simple Network Lowers f3
Problems arise with full range current drive (or even just non-zero drive impedance) where mechanical resonance causes a rise in acoustic output along with an increase in load impedance. In this case, and at such frequencies where this occurs, the speaker ends up drawing more power and the peak is accentuated. Whether distortion is decreased, response flatness is not inherently improved. Are we considering only woofers or assuming pistonic cone response?