IMPEDANCE RISE?

[ambyrell1]

will someone please explain what this is, and how box size is a factor.

[BigPimpin91]

Impedance rise and box rise are used interchangeably but mean the same thing.

It has to do with electricity and magnetism.

When a wire moves through a magnetic field it creates electricity in that wire.

The amp sees this as additional resistance.

The way your woofer interacts with the surrounding air also changes the way the cone moves which changes the way the coil moves, thus, changing the interaction of the coil with your amplifier.

Hope this helps.

[ambyrell1]

so can this be pedicted before installation?

[Bunker]

Hard to do that impedance varies with frequency, same reason you see guys wiring down to .25 ohm at comps and burping the hell out of it. Need all you can get sometimes.

[andym85]

copied from ***,

what jacob from sundown has to say about impedence rise:

I know it is said a 100 times a day... "with impedance rise you are going to be over 1 ohm anyway" when talking about a half ohm load or lower on a daily system.

Sure... if you constantly played individual sine waves one at a time. But, is that what music is?

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http://www.audiograph.se/subpages/technica...odamplifier.htm

"The upper graph illustrates the conventional way of measuring the loudspeaker impedance.

The lower graph illustrates the dynamical approach.

We took a commercial ’off-the shelf’ loudspeaker and did a standard impedance plot for it. We swept the frequency from 20 Hz to 20 kHz, measured the input voltage and current, and calculated the impedance.

However, instead of using a sine wave input signal, we used a square wave. The reason for this is that square waves consist of a large amount of sine waves, as does music. The square wave is of course not an equivalent of music, but for this test it was an easy way of showing that a complex signal (not just a simple sine wave signal) may make the load, from the amplifier point of view, very low.

If you study the graph resulting from the test, you will probably agree that not only is it necessary to check the amplifier’s behavior for resistive, capacitive and inductive loads – the amplifier should also be checked for loads with lower impedance than the nominal impedance of the loudspeaker.

This proves to be very important, since a loudspeaker with a nominal impedance of 4 ohms will sometimes have an actual impedance of 1 ohm or less. The PowerCube helps you perform testing of an amplifier, taking all these load attributes into consideration. "

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Keep that in mind when you want to run your amplifier at a super low impedance "daily"

[Bunker]

so can this be pedicted before installation?

Going smaller helps, but remember to small can hurt you worse like being less efficient, and to much back pressure and then you will start folding cones. It's a battle, to honest you have to build a lot of boxes and keep testing.

[andym85]

QUESTION FROM "atsaubrey":

Since Sundowz brings up the issue, I would love to hear his take on low impedence loads period and how it effects things. Like, effciency, longevity, SQ, heat and electrical systems. I see it everyday on this forum, people asking can this or that amp run at .67 or .5 ohms although it is only rated at say 1ohm. Since the manufactuer stated the thread maybe people will listen. So Jake will you answer those questions? Jake at what impedence do you run your own personal gear at on a daily basis?

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MY ANSWER:

If you look at a data sheet you can see that as a transistor gets hot it has a lower current rating... running an amp at a lower impedance increases the current passing through the transistors, heating them up, and progressively lowering their ability to handle the current until something fails.

Dropping an amp to 1/2 ohm doubles the output current (up until the amp just can't put out more at least) and makes everything less efficient so the power supply in turn draws more current, often times inducing more voltage drop which calls for MORE current to maintain the same output level - again, turning into a cycle if it continues until something fails.

Many amps are robust enough to handle this pretty well - but the more you push the amp and the more clipping that goes on you get closer to realizing the impedance chart I posted above for a square wave which can drop down VERY low. That sort of thing can destroy even a very robust amplifier design when you are already running at 1/2 or less of the rated impedance load.

It all started with SPL competition... where you play ONE sine wave at a known impedance so you can get away with a really low nominal load. That is all well and good, but music is not a single sine wave - you do not know what the impedance curve can do and it CAN drop below the nominal load, unlike "common knowledge" on the forums may tell you.

[andym85]

so in conclusion...dont worry about impedence rise for a daily system..

[Bunker]

so in conclusion...dont worry about impedence rise for a daily system..

Exactly.

[ambyrell1]

so in conclusion...dont worry about impedence rise for a daily system..

THANKS!