John Curl's Blowtorch preamplifier part III

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#3,841
Joe Rasmussen said:
While the current is what the device (a driver is a current device) actually responds to, it is the current times voltage (the power dissipated in the voice coil) that determines the dB-SPL.
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At 1Hz? There's a small problem of the actual radiated power of a finite baffled piston in the way.

Please start your own thread for this stuff.

Guess we won't be talking much about how speakers work.
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#3,845
Markw4 said:
Agreed, and also trying to be nice about it. No ill will intended towards Joe, who seems like a good guy.
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Hang on just a minute...he's not nice to me:
"This is too silly to answer in detail "
"and an intelligent person should be able to grasp that, OK?"
😡

Joe seems to talk as if no one here understands how to analyze a resistor in series with an inductor. All this about the voltage across the resistor defining the coil current rather than the voltage across both is a muddled way of expressing the thing.

I detect two main conjectures in this turgid series of diatribes:
1) That the less electrical damping a drive unit has the less THD it exhibits.
2) Amplifiers distort less with non-reactive loading.

I think these are worthy of discussion but it would be more fun without all the arrogance and BS.
 
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#3,847
traderbam said:
I'd say you are being less general. You are talking about phase shifted sinusoids. The instantaneous power is always VI or i * deltav if you prefer.
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I thought we were talking about speakers and sine waves, sorry. With a speaker I'm not sure anything else is really useful.

BTW I don't think THD has been addressed at all and it could be of interest. I looked at that other site, some people like to be outsiders and the AES conferences since they are very weakly peer reviewed are a good forum for them.
 
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#3,848
@traderbam, Okay. Hopefully, that takes care of payback.

I would agree there could be some interesting things to discuss. Not going to happen though unless Joe wants to learn some electronics. Unless I am mistaken my impression is that he has no interest. Joe?
 
#3,849
scott wurcer said:
To be general V and I have relative phase and the real part of the product is the power.

Apologies to Joe I should have said maybe he is disappointed that more folks are not paying attention to this way of designing speakers. You could eliminate all the wrong and/or confusing stuff and underneath there is a valid design process. There is no "breaking down" of Kirchhoff or any of the other nonsense.
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Er not really V and I have no phase issues. The upper case letters refer to DC.

v and i would require phase information to calculate power.

Scott, do you float? 🙂
 
#3,853
Joe Rasmussen said:
The key is to understand is that the difference between the two are entirely down to the back-EMF and this test can be done physically and also using a modeling program like SoundEasy. It reveals that only the voltage that appears across the Re of the driver's voice coil is part of the force that creates the final dB-SPL (F = Bl*i) and the two graphs shows the relative difference under current versus voltage drive. The back-EMF part of the impedance is not part of the force, but rather acts like a voltage source, an opposing force to the current. It impedes current and that is what makes it an impedance.
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Thanks for the clarification. You have said most of that before but never explained what the graph was, all you needed here was "the two graphs shows the relative difference under current versus voltage drive." Can you quantify the voltage at the speaker terminals and the current for those spot-check frequencies you highlighted?

Hope that helps, but I assure you this is no voodoo science, although the history of this thread tells me that... oh well. Negative comment is something I have come to expect.
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This thread has a long history of vigorous and constructive debate, often derailed by car talk and silliness. Your opinion of this thread appears to have changed. As for "negative comments" I think they usually start as questions after you write something in your eccentric way.
 
#3,855
Markw4 said:
Upper case can be DC, AC RMS. steady state, or sometimes average. Depends on the text. Lower case is instantaneous, usually. Not all texts respect the conventions, sometimes they are redefined chapter by chapter. Gets worse in some sub-areas of electronics.
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All of our experiences differ, but most of what I read is getting better about liberal use of subscripts to avoid these overloaded terms. It helps tremendously with clarity.

E.g. V_rms, V_pp, <V>, and so on.
 
#3,856
keantoken said:
With the motional feedback mod, the speaker has no damping and so it moves more freely with the air mass, experiencing less stresses.

I think I have calculated the output impedance of the motional feedback mod as 2.8R. Don't know if this is high enough to cause the change that is shown. Should I assume the measurements were taken at the same output levels at the given frequency?

Perhaps the motional feedback test had more damping in the box?
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The reflex box was not changed in any way. no extra damping inside the box and as said in figures... the same SPL (90db) at 3 feet was used. Only the amp mod was changed and not the speaker in any way between tests.



THx-RNMarsh
 
#3,857
simon7000 said:
Er not really V and I have no phase issues. The upper case letters refer to DC.
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As Mark said there are several conventions, some use italicized caps for vector quantities, there are others. I prefer amplitude and exponential notation because the trig identities are so much easier that way.

Talking speakers, DC has little use. Mr Doodie floats of course he's made of wood!
 
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