OK. My searching has only caused me to be even more confused. One article indicates that putting a resistor across one VC would cause a drop in Qts while another says a rise. One says it changes Qes another says it changes Qms. Nobody seems to define a starting point either.
So what is the story. Say I get a DVC sub with a Qts of 0.4 with both VCs driven in parallel. What happens when I
1) drive only one with the other open
2) drive only one with the other shorted
Can I raise it to say .6 with an appropriately chosen resistor? How would I calculate this.
mike
So what is the story. Say I get a DVC sub with a Qts of 0.4 with both VCs driven in parallel. What happens when I
1) drive only one with the other open
2) drive only one with the other shorted
Can I raise it to say .6 with an appropriately chosen resistor? How would I calculate this.
mike
(JPK) This may be more detailed than you want, but Eqs 24 and 25 show how to relate Qts to the values of Qes and Qms to the value of the resistor connected across the second voice coil. In Eq 24 Qes and Qms are the values for a single voice coild conection, with the second VC open. Qms is the same regardless of now the VCs are connected. Qes for the single VC connection is twice the values quoted when both VCs are connected in either parallel or series.
http://www.geocities.com/kreskovs/Dual-VC.html
http://www.geocities.com/kreskovs/Dual-VC.html
http://www.mhsoft.nl/spk_calc.asp
See new Qts with series DCR of inductor
Hi,
Is another way of manipulating Q (and wasting amplifier power).
For an active bass system you can make amplifiers with virtual output
resistances that do not waste power and set Q to what you like.
/sreten.
See new Qts with series DCR of inductor
Hi,
Is another way of manipulating Q (and wasting amplifier power).
For an active bass system you can make amplifiers with virtual output
resistances that do not waste power and set Q to what you like.
/sreten.
Ron E said:
(JPK) I would choose to disagree. Ultimately the impedance is derived from Vs/I where Vs is the source voltage and I is the current flowing through the amplifier loop. For the dual VC woofer with one VC loaded by and external resistor this is given by my Eq 6. So Z = (Vs Re)/(Vs-BL X'). The question then becomes how X' (cone velocity) is expressed in terms of the damping of the system. The damping can be considered to be composed of any number of sources; electromagnetic damping associated with the VC back emf generated in the amplifier loop, mechanical damping, fluid damping, and in this case additional electromagnetic damping external to the amplifier loop. Thus in the present case there are the 3 Q's: Qes, Qms and Qds. All of them combine to form the system Qts (Eq 19) which is what will determine the behavior of X'. If you want to combine Qds and Qms into a single Q so the system is described by 2 Q's that is fine, but I would prefer to think along the lines that these are Qes associated with the amplifier loop electromagnetic damping and a second parameter, Qext, which represents the effective damping due to all other sources of damping outside the amplifier current loop. The impedance expression as given by Small would then be expressed in terms of Qext as opposed to Qms. The Q in Small's impedance function needs to represent all external damping. I would personally rather look at it this way since Small never considered sources of external damping other than mechanical resistance and the additional damping due to the resistive loading of the second VC just isn't mechanical. Of course, it is also possible to write the impedance expression in terms of Qts and avoid the argument of what gets modified and how.
john k... said:Nothing good ever comes easy.
Cute. Putting yourself on a pedestal? A ford tempo with a $1000 paint job don't go any faster, but it might make you proud to own it
Your ODE model might be useful in a nonlinear simulation, but concepts like Qms would then have no meaning...
Besides, it's incomplete, there is no acoustical stuff in there....Put it in a lumped (or T/S) model and what happens to "Qds"? It gets lumped...
Good is a value judgement, and just yours at that.
Ron E said:
A ford tempo with a $1000 paint job don't go any faster, but it might make you proud to own it
Ron, you know I drive a Ferrari!
Your ODE model might be useful in a nonlinear simulation, but concepts like Qms would then have no meaning...
Put it in a lumped (or T/S) model and what happens to "Qds"? It gets lumped...
Oh poppy ****. In a lumped prameter model everthing gets lumped. Qtc is all you need to deterimine the system response. But the more you lump together the less you know about the actualy system. Anyway, where do you think all those lumped parameters came from in the first place? The problem with extracting the T/S parameters from the impedance curve is that it is incomplete for the dual VC case. Besided you can't actually extract Qms from the impedance anyway. What you get Qes associated with the amplifier loop and a parameter, typically referred to as Qms, that represents all additional damping in the system. That is, Qms, as extracted from the impedance curve does not allow you to then calcualte Rms, given Fs and Mms unless the only additional damping comes from Rms. What is extracted is, as you put it, a lumped Q, call it Q1, but not Qms if we accept the common definition of Qms = Fs x Sqrt(Mms/Rms). Now if you take two impedance measurements, one with the the second VC opened and then one with the second VC loaded by a resistor the second measurement will allow extraction of another lumped Q, Q2. And from the two lumped Q's it would be possible to extract what I called Qds, and another Q which would be Qms if there were no other damping mechanisms present.But why bother with any of this since all that really matters is the final lumped prarmater, Qts (or Qtc).
Lastly, my model isn't any good for nonlinear distortion, nor is Small's, since they are linear moddels. But they can be extended to include nonlinear Bl, nonlinear compliance, etc.
This is great, I'm actually learning how to use smiles and stuff.
john k... said:Ron, you know I drive a Ferrari!
And a miata! I'm not a fan of 308's. Maybe a 246?
Right, so un-lumping it is adding unnecessary complexity - which may make you feel as if you "discovered" something, but since anyone capable of doing that analysis knows where the damping comes from anyway, it is a moot point. Why analyse a bunch of parallel resistors when you can work on the equivalent...
Right and IMO that is the only good reason to use an ODE model, but you would have to extend yours to use nonlinear fundamental parameters rather than T/S to make it useful. This is why I likened it to a painted tempo. Then you would have to measure those nonlinear parameters to characterize the driver, another challenge.
Ron E said:
I think we are looking at this from different points of view. If all that is cared about is the final result then we can just write:
(24) Qts = Qms Qes / (Qes + c Qms)
where
(25) c = 1 + Re /(Re + Rl)
and it would look to all the world that the result is just a modification to Qms, which is one way to express the result. But I am, and I believe there are others who might be, interested in how that result is obtained. Even if they are capable of doing the analysis themselves that doesn’t mean they have nor have the desire to do so. It’s just information for those who are interested, to be ignored by those who aren’t.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.