Brian Oppegaard wrote on Mon, 14 February 2011 14:50 |
Could someone please point me to or send me the impedance curve of the lab sub? Thanks |
Art Welter wrote on Mon, 14 February 2011 17:21 | ||
I think Silas Pradetto posted an impedance curve not too long ago, check his posts. To be safe, assume a 3 ohm load for a parallel wired LabSub, though most portions of the curve would be high enough to consider it a nominal 4 ohm load. |
Quote: |
Here's the impedance of the two I just shipped today. Green and purple are the individuals, blue is both in parallel. |
Brian Oppegaard wrote on Wed, 16 February 2011 13:42 |
Thanks for the replies. The voice coil resistance of Gen II woofer 4.29 ohms is low compared to the nominal 8 ohm impedance of the driver. And I see now that the actual cabinet impedance dips to almost that resistance. I am trying to determine which version of my subwoofer amplifier to recommend for this speaker. Normally I would say the 2400W/4 ohm capable model, but with this low impedance perhaps the 4000W/2 ohm model could be justified. |
Silas Pradetto wrote on Wed, 16 February 2011 18:52 [b |
What are you actually doing, and why do you need this plot?[/b] |
Brian Oppegaard wrote on Wed, 16 February 2011 22:14 | ||
Thanks for the info Silas. See the web site in my signature. I have been manufacturing plate amplifiers for OEM customers since 2003. But I am considering a new line of amps to be sold direct to DIYers. The LAB sub is a popular project and I need information to be able to see which amps might work. |
Art Welter wrote on Thu, 17 February 2011 15:44 | ||||
Brian, As an amp manufacturer, you should be concerned with your amp's performance at the lowest impedance likely to be presented to it. Although every type of box the speaker is placed in will present a different curve, you would be well advised to simply use the voice coil DC resistance (Re of 4.29 for a single Lab 12) as a "worst case" scenario. Most designs will present dips in the impedance response that approach the DC resistance, and music may end up being concentrated at those points. If the amp cant handle those minima without current limiting, it is not a good choice for the load. The plots below compare Silas charts with two and four Lab 12 in parallel with single Lab 12 in various size ported boxes with different tunings. As you can see, The Lab sub has various points that show impedance minima equal the the VC DCR, 2.145 ohms for the parallel load. It is of interest that the ported impedance graphs appear to be higher than Silas' graphs, the old saw that "horns make the impedance higher than nominal" is very frequency and horn dependent. Lab 12s are frequently used in tapped horns and a variety of bass reflex alignments, I'd guess that the use in the specific LabSub alignment actually is only a fraction of their use. Could you provide me information on the duty cycle (and pricing) of your amp line ? Art Welter |
Brian Oppegaard wrote on Thu, 17 February 2011 21:51 |
I agree that knowledge of the load is vital to selecting the right amp. Usually the DCR is all you need to know if there are impedance minimums in the passband. High mechanical losses might keep it from reaching the DCR if I remember my theory correctly, but that is clearly not the case here. A sealed direct radiating sub may be an exception as it could have high impedance throughout the passband due to the single large resonance peak. But that is another forum. Current limiting can be no worse than voltage clipping if it is clean and/or eliminated by reducing level on a short term basis. The days of VI current limiting snapping and carving out odd chunks of the waveform are gone in modern designs. What sort of duty cycle specs would you like to see? And to keep on topic, what sort of numbers would the LABsub require in your opinion? |