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Author Topic: Lab Sub Impedance curve  (Read 7806 times)

Brian Oppegaard

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Lab Sub Impedance curve
« on: February 14, 2011, 04:50:05 pm »

Could someone please point me to or send me the impedance curve of the lab sub?

Thanks
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Brian Oppegaard
SpeakerPower Inc
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Art Welter

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Re: Lab Sub Impedance curve
« Reply #1 on: February 14, 2011, 05:21:52 pm »

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


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.
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Silas Pradetto

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Re: Lab Sub Impedance curve
« Reply #2 on: February 15, 2011, 08:26:02 pm »

Art Welter wrote on Mon, 14 February 2011 17:21

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


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.


And, at the same time, there are dips at certain frequencies that are at about 2 ohms.

The curve was in a For Sale post, so it won't be around forever.

Quote:


Here's the impedance of the two I just shipped today. Green and purple are the individuals, blue is both in parallel.
index.php/fa/34953/0/

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Brian Oppegaard

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Re: Lab Sub Impedance curve
« Reply #3 on: February 16, 2011, 01:42:26 pm »

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.
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Brian Oppegaard
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Silas Pradetto

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Re: Lab Sub Impedance curve
« Reply #4 on: February 16, 2011, 01:52:14 pm »

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.


Brian, let me clarify. First, the woofer nominal impedance has nothing to do with anything once it's in a horn.

The LAB12 woofer is actually nominally a 6-ohm driver, but a LAB sub has two drivers in parallel. This would make for a theoretical 3-ohm nominal impedance, but the horn adds to the impedance.

You will want an amplifier that is very good at driving reactive loads, as many amps can't handle the impedance varying so much.

It would be better to get a 2-ohm amp for a pair of LABs and a 4-ohm amp for a single LAB.

Also, there is no gen I woofer, it was the prototype and was never for sale.

Also again, DC resistance is useful for little more than confirming that the VC isn't open.

And another also, the impedance plot I posted is for TWO LAB12 woofers in the LAB sub box. Note that even thought hey have similar names, they are different things.

If you were to use the LAB12 woofers in any other box (sealed, ported, different horn, etc) then the impedance plot won't be even close to the same.

What are you actually doing, and why do you need this plot?
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Brian Oppegaard

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Re: Lab Sub Impedance curve
« Reply #5 on: February 17, 2011, 12:14:49 am »

Silas Pradetto wrote on Wed, 16 February 2011 18:52
[b

What are you actually doing, and why do you need this plot?[/b]


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.


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Brian Oppegaard
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Art Welter

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Re: Lab Sub Impedance curve
« Reply #6 on: February 17, 2011, 10:44:22 am »

Brian Oppegaard wrote on Wed, 16 February 2011 22:14

Silas Pradetto wrote on Wed, 16 February 2011 18:52
[b

What are you actually doing, and why do you need this plot?[/b]


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.



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.
index.php/fa/34954/0/

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
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Brian Oppegaard

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Re: Lab Sub Impedance curve
« Reply #7 on: February 17, 2011, 11:51:47 pm »

Art Welter wrote on Thu, 17 February 2011 15:44

Brian Oppegaard wrote on Wed, 16 February 2011 22:14

Silas Pradetto wrote on Wed, 16 February 2011 18:52
[b

What are you actually doing, and why do you need this plot?[/b]


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.



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


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?  


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Brian Oppegaard
SpeakerPower Inc
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Art Welter

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Re: Lab Sub Impedance curve
« Reply #8 on: February 18, 2011, 04:56:05 pm »

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?  



My experience is limited to the power I have used with Lab 12s in ported cabinets and a horn similar in layout, but much smaller than a Labsub. I no longer use the horn design, as more LF output per cubic foot of truck space can be achieved with the ported design.

In the ported cabinets I designed, the speakers will reach Xmax at slightly below double Pmax. I would consider an amp able to do about 1600 watts at 30 Hz into 3 ohms more than adequate.

If one wants to not exceed Xmax, my educated guess is the same power would do fine for the Labsub.
That said, the Lab 12 sounds pretty clean up to Xlim, so around 3200 watts peak would not be out of line, many users are using amps with that kind of power or more.

Dubstep, trance, among other types of music can have sustained, sine wave like tones for several seconds duration. Some amps are only able to provide full power for peaks of tens of milliseconds, OK for rock and roll kick drum, but not for sustained bass.

As far as duty cycle of your amps, I'd like to know how long they can sustain a sine wave of X power and frequency into X load before current limiting, going into thermal protection, or anything else that would prevent full power output.

PM me if you are interested in an evaluation of your amps for LF duty, I have been considering using built in power in some of my speaker designs.

Art Welter
Welter Systems, Inc.



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Brian Oppegaard

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Re: Lab Sub Impedance curve
« Reply #9 on: February 23, 2011, 06:20:23 pm »

PM sent
I looked around for a format to follow for specifying hold time but could not find any other manufacturer who does so. If anyone knows of one who does, please let me know.

My sub amp is set to run for about 3 seconds sine wave before limiting back to 1/2 to 1/3 power. This is into large 1000W/8 load resistors. Voice coils may heat up and increase resistance faster than they do so the amp runs longer. On the 4000W amp, the 20A breaker will open after 5-6 sec so that can be a limiting factor. I have never seen it open with music, but my collection of dubstep and trance is not what it should be. Thermal performance is very dependent on ambient conditions. But with efficency of 90-95% user's comments are that it barely gets warm.


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Brian Oppegaard
SpeakerPower Inc
www.speakerpower.net
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