Damping Factor & impedance

[MrWizzard 10+ year member]

I know the Damping factor is the amps ability to control a speaker/sub, and i do know the sub and its enclosure certainly contributes to this.....

But, i seen somplace the damping facor is lower depening on the impedance... say the Zapco at like >1000 damping factor at @4ohms would be >500 @2ohms and >250 @ 1ohm? is this correct?

So, my main question is, does the impedance effect how well the amp can control the sub/speaker? or does the lower impedance mean it just dosent need as much damping factor to control it and would be the exact same at any impedance? like, would the amp have the same control of the sub at 4ohms as it would at 1 ohm with less the damping factor? or would it have less control?

I'm looking to understand this a little so i can pickup a nice SQ amp and run it for SQ.... I was looking at the Zapco C2K 6.0 to run my XXX 12" dual 4ohm at 2ohms with around 1300 watts, but now i'm wondering if would have more control of the sub at 4ohms rather than 2ohms so i could just get an amp that will push 400-500 rms into both coils seperately at 4ohms....

Thanks for any info regarding this...

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[thch 10+ year member]

damping factor -- often mispreceived.

1.) there is a maximum damping. a length of wire to the speaker quickly limits DF to about 100, especially with low impedance speakers.

2.) the majority of driver damping will be dictated by the box and woofer's motor and not the amp. the box models assume you use an amp with infinate DF, and thusly show that even with infinate DF, the amp cannot perfectly control the woofer.

3.) DF is given simply by Zsubwoofer / Zout. Zout is the output impedance of the amp, and is typically less then 0.1ohm. you are correct about the decrease in DF with lower impedance speakers.

4.) edited out -- a bit confusing and/or misleading.

in conclusion, i would not buy any additional equipment.

 

[JimJ 5,000+ posts]

a DF of 1 implies maximum power transfer (going with a higher or lower impedance speaker would result in less power).

It works this way in audio, as well? I'm seriously interested here...not trying to flame you or anything. I realize that's exactly how it's treated once you get beyond audio frequencies (in radio, it's called the VSWR - voltage standing wave ratio, where having an antenna/feedline system at the same impedance as the transmitter output stage results in no power being reflected back to heat the feedline, hence a VSWR of 1:1) but I wasn't sure if audio frequencies behaved the same way. It would make sense.

It's yet another reason why tubes reign supreme over the silly sand-and-silicon variety //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif

 

[thch 10+ year member]

It works this way in audio, as well? I'm seriously interested here...not trying to flame you or anything. I realize that's exactly how it's treated once you get beyond audio frequencies (in radio, it's called the VSWR - voltage standing wave ratio, where having an antenna/feedline system at the same impedance as the transmitter output stage results in no power being reflected back to heat the feedline, hence a VSWR of 1:1) but I wasn't sure if audio frequencies behaved the same way. It would make sense.
It's yet another reason why tubes reign supreme over the silly sand-and-silicon variety //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif

well, assuming resitive source and load of course!

V = Vs Rl / Rl+Rs

I = Vs / Rl+Rs

P = Vs^2 Rl / (Rl^2 + 2RsRl + Rs^2)

ok, to make things easier, Vs can be ignored (Vs is a common term) and we will minimize P^-1 (same as maximizing P)

P^-1 ~ Rl + 2Rs + Rs^2 / Rl

d(P^-1)/d(Rl) = 0 = 1 + 0 - Rs^2 / Rl^2

thus Rs^2 = Rl^2, thus Rs = Rl (for maximum power transfer).

of course at AF, you don't really have the same problems with reflections.

This wasn't meant to imply tubeamps are better or that a DF of 1 is important. it is the condition required for maximum power transfer, however 1000W at a DF of 100 is typically sufficiently powerful.

 

[maylar 10+ year member]

damping factor -- often mispreceived.
1.) there is a maximum damping. a length of wire to the speaker quickly limits DF to about 100, especially with low impedance speakers.

2.) the majority of driver damping will be dictated by the box and woofer's motor and not the amp. the box models assume you use an amp with infinate DF, and thusly show that even with infinate DF, the amp cannot perfectly control the woofer.

3.) DF is given simply by Zsubwoofer / Zout. Zout is the output impedance of the amp, and is typically less then 0.1ohm. you are correct about the decrease in DF with lower impedance speakers.

All true, with caveats...

1) Car audio is a bit unique.. 3 feet of 10 gage wire is not uncommon, and doesn't limit DF like long runs of speaker cable in a home system.

2) Ported enclosures and IB aplications are where DF can be significant. In a sealed box, acoustic damping has much more effect.

3) Some amps have output impedances in the milliohms. DF of 400 or more (Tru amps for example).

However, there's the issue of "specmanship". If the spec is calculated at 8 ohms, the DF figure would be twice the value of 4 ohms. It's a worthless spec unless the load impedance is also specified.

This wasn't meant to imply tubeamps are better or that a DF of 1 is important. it is the condition required for maximum power transfer, however 1000W at a DF of 100 is typically sufficiently powerful.

In car audio we're more concerned with efficiency than power transfer. Effieciency goes up as the load impedance goes up or the source impedance goes down. A 1:1 ratio gives 50% theoretical efficiency. OK in communications circuits, not OK in amps.

I agree with you that 100 is an acceptable number.

 

[thch 10+ year member]

its amazing. i made a basically "for information only" comment then realized it was confusing and a bit misleading in this context, so i removed it within 10 minutes. its been replied to a few times now.

* the fact is, DF = 1 gives max power transfer. this isn't really so much relevent with solid state amps or even tube amps (due to transformers). really, only RF apps need this condition due to reflections that occure otherwise.

* the comment was removed because it was misleading. i was making an interesting point and comparison to tube amps that i later realized would bring undue confusion and debate over points i wasn't trying to make, thus i removed the comment.

for solid-state audio amps, losses in this source impedance are typically much less then the other losses in the amp. even at 100A output current, it typically only attributes 1W of loss. and amp putting out 100A is gonna be rated much higher then 1W! possibly 2500W @ 1/4 ohm?

 

[maylar 10+ year member]

its amazing. i made a basically "for information only" comment then realized it was confusing and a bit misleading in this context, so i removed it within 10 minutes. its been replied to a few times now.

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I didn't get to read it. But transformer coupled amps usually have lousy DF, so I'll assume that was your point.

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* the fact is, DF = 1 gives max power transfer. this isn't really so much relevent with solid state amps or even tube amps (due to transformers). really, only RF apps need this condition due to reflections that occure otherwise.

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And telephone circuits, and pro audio, and... anywhere getting max power transfer is more important than efficiency.

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for solid-state audio amps, losses in this source impedance are typically much less then the other losses in the amp. even at 100A output current, it typically only attributes 1W of loss. and amp putting out 100A is gonna be rated much higher then 1W! possibly 2500W @ 1/4 ohm?

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Good point. My comment was only that the power losses of a Thevinen source get lower as the load impedance rises or source impedance goes down. But source impedance in a real amp is from the feedback loop and output devices, and doesn't represent the actual series losses. As you said, it's not meaningful.

Thanks for the banter. Hope the original poster isn't too confused.

 

[thch 10+ year member]

transformer coupled -- you change the 4ohm speaker to look like an 8ohm speaker, thus DF isn't as horrendously affected by changing speakers. of course neither is power.

my original post said something along the lines that tube amps typically have a low DF, and yet sound good to a lot of people. but i decided that was probably going to spark off a tube amp vs solid-state debate rather then focus on real issue of amplifier output imedance and its ability or lack thereof to control a speaker. i'm just waiting for the tube vs ss to start anyways...

i too like technical discussions.