Home |
Search |
Today's Posts |
#1
|
|||
|
|||
Voice coil inductance
I have been reading older posts in this group regarding the inductance
of the voice coil, and I realize that the inductance is far from ideal, that its inductance drops with frequency (in one way of looking at it). I also read an article by Marshall Leach (JAES no 6 2002, p 442-) which describes this phenomenon quite nicely and presents a model that I have succeded in fitting very well to a small number of real speakers I have had at hand. I actually carved the cone and coil away from one element and measured the impedance curve again, and indeed the impedance was quite different. Apart from the obvoius (the peak corresponding to the mechanical resonance disappeared) the inductance now looked like an inductance normally would, ie with a 90 degree phase shift and a +6dB/oct slope above some frequency (for the disected loudspeaker, nb). This brings up the question what the manufacturers say in their data sheets. They mostly specify an inductance. They rarely specify the "lossiness" (the n value in the article above) of this inductance or the frequency at which the inductance was measured. So, what does the "voice coil inductance" figure that the manufacturers supply us with mean, really? |
#2
|
|||
|
|||
Voice coil inductance
|
#4
|
|||
|
|||
Voice coil inductance
(Dick Pierce) wrote in message ...
(Svante) wrote in message news:hO3db.435049$Oz4.241458@rwcrnsc54... First of all, your data is inconsistant with Leach's and also with Lip****z and Vanderkooy's, as well as my own, where it is the mechanism of lossy eddy current generation in the pole piece and other moederatey conductive parts in proximity to the voice coil that is responsible for the non-ideal behavior of the inductance. The phenomenon we observe is that as we go higher in frequency, we see an increase in eddy current coupling in the metal parts, which have a fairly high ohmic loss. The result is a decrease in inductance and an increase in resistance that pretty reliably follows a 1/sqrt(f) for inductance and sqrt(f) for resistance. Pardon me for responding twice, but I thought you may be interested in seeing the actual curves. The curves are available at http://www.tolvan.com/disected_lsp.jpg As I said I observe the same as you do, the red line is from the disected loudspeaker, without any iron or magnet present, the black curve is the impedance of a normal element of the same brand and model, and the green dashed line is modelled data with a "n" value of 0.67. The model also includes the mechanical resonance, as you may see. I think we agree that there is a huge difference between the black and the red curves. The model fitting was done manually by adjusting the parameters of the model until the curve fitted well. I think the match between the green and the black line is is pretty good. (Don't look to carefully at the phase towards high frequencies, my sound card makes the phase values a bit too low there) |
#5
|
|||
|
|||
Voice coil inductance
(Svante) wrote in message news:n3Idb.619108$uu5.100398@sccrnsc04...
(Dick Pierce) wrote in message ... (Svante) wrote in message news:hO3db.435049$Oz4.241458@rwcrnsc54... First of all, your data is inconsistant with Leach's and also with Lip****z and Vanderkooy's, as well as my own, where it is the mechanism of lossy eddy current generation in the pole piece and other moederatey conductive parts in proximity to the voice coil that is responsible for the non-ideal behavior of the inductance. The phenomenon we observe is that as we go higher in frequency, we see an increase in eddy current coupling in the metal parts, which have a fairly high ohmic loss. The result is a decrease in inductance and an increase in resistance that pretty reliably follows a 1/sqrt(f) for inductance and sqrt(f) for resistance. Pardon me for responding twice, but I thought you may be interested in seeing the actual curves. The curves are available at http://www.tolvan.com/disected_lsp.jpg As I said I observe the same as you do, the red line is from the disected loudspeaker, without any iron or magnet present, the black curve is the impedance of a normal element of the same brand and model, and the green dashed line is modelled data with a "n" value of 0.67. The model also includes the mechanical resonance, as you may see. I think we agree that there is a huge difference between the black and the red curves. The model fitting was done manually by adjusting the parameters of the model until the curve fitted well. I think the match between the green and the black line is is pretty good. (Don't look to carefully at the phase towards high frequencies, my sound card makes the phase values a bit too low there) I must confess as to having misread your first post. For some reason, in a quick reading that was interrupted by my ISP going south for a week I somehow thought you were saying that removing the cone gave the data, when you said removing the cone and coil from the magnet gave the data (the "data" being the near-ideal LR behavior). Now that I have read it more carefully, your data is entirely consistent with the current knowledge of the behavior, including my own measurements and models. |
#6
|
|||
|
|||
Voice coil inductance
(Dick Pierce) wrote in message ...
(Svante) wrote in message news:n3Idb.619108$uu5.100398@sccrnsc04... (Dick Pierce) wrote in message ... (Svante) wrote in message news:hO3db.435049$Oz4.241458@rwcrnsc54... The phenomenon we observe is that as we go higher in frequency, we see an increase in eddy current coupling in the metal parts, which have a fairly high ohmic loss. The result is a decrease in inductance and an increase in resistance that pretty reliably follows a 1/sqrt(f) for inductance and sqrt(f) for resistance. Pardon me for responding twice, but I thought you may be interested in seeing the actual curves. The curves are available at http://www.tolvan.com/disected_lsp.jpg As I said I observe the same as you do, the red line is from the disected loudspeaker, without any iron or magnet present, the black curve is the impedance of a normal element of the same brand and model, and the green dashed line is modelled data with a "n" value of 0.67. The model also includes the mechanical resonance, as you may see. I think we agree that there is a huge difference between the black and the red curves. Now that I have read it more carefully, your data is entirely consistent with the current knowledge of the behavior, including my own measurements and models. So, what about the 1 kHz? Have you actually seen in datasheets that manufacturers specify that they use this frequency when they measure the inductance? What about tweeters, shouldn't there be be a great interference from the mechanical resonance at 1kHz? The reason that I ask is that I am writing a simulation software, and I would like to use the inductance figure that one can find in the datasheets. This is why its usefulness is of interest for me. |
Reply |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Forum | |||
Wiring 2 ohm DVC sub, 2 channel or Bridged | Car Audio | |||
Replacement voice coil for Dynaudio tweeter?? | Car Audio | |||
Question about Dual Voice Coil Subwoofer | General | |||
connect dual voice coil to 2 channels | Car Audio | |||
Only use one voice coil in a DVC sub? | Car Audio |