Low Impedance & Frequency (Hz)

[Mr. RF62]

If a low impedance dip of a speaker is something like 3.84 ohms at 500Hz, but the speaker is nominal at 8 ohms(don't know if it matters), does the amount of resistance(in ohms) change if you boost or cut that 500Hz band???

Thanks

[Guest " "]

this is a tricky question which a lot off folks will have to stop and think about. normally, the answer is no......but...the unknown factors are the quality of the crossover componets and if, we are talking low pass, hi pass, or band pass filters. The specific issue is inductor saturation which occurs in low quality componets which could increase bandpass or lopass impedeance as the inductor becomes saturated.

[Mr. RF62]

Thanks for the quick response speakerfritz, I understand what your saying. Great.

Good to see you posting.

[Quiet_Hollow]

Riddle me this...How can impedance be 8 Ohms nominal but dip to 3.84?? The only time that a deviation that large could still be considered "nominal" is if something is operating outside of it's passband. What have you got going on over there?

[StephenM]

Riddle me this...How can impedance be 8 Ohms nominal but dip to 3.84??

You would have to ask the manufacturers I suppose. Take the Klipsch RF-83 for example.

http://www.klipsch.com/rf-83

Per the spec sheet: NOMINAL IMPEDANCE:
8 ohms compatible

http://www.hometheater.com/content/klipsch-reference-rf-83-speaker-system-ht-labs-measures

Impedance reaches a minimum of 3.60 ohms at 179 Hz and a phase angle of –56.86 degrees at 74 Hz.

[Guest " "]

Riddle me this...How can impedance be 8 Ohms nominal but dip to 3.84?? The only time that a deviation that large could still be considered "nominal" is if something is operating outside of it's passband. What have you got going on over there?

you know how manufactures do impedeance math.....they measure impedeance at every octave, add the numbers together and then divide by the events......so if you have 1 ohm at 20hz, 1 ohm at 60hz, 1 ohm at 240hz, 1 ohm at 480hz, 1 ohm at 960hz, 1 ohm at 1920hz, 1 ohm at 3670hz, 1 ohm at 7340hz, and 64 ohms at 14680hz the nominal impedeance is 8 ohms ((8+64)=72))/9=8

[Guest " "]

Riddle me this...How can impedance be 8 Ohms nominal but dip to 3.84?? The only time that a deviation that large could still be considered "nominal" is if something is operating outside of it's passband. What have you got going on over there?

you know how manufactures do impedeance math.....they measure impedeance at every octave, add the numbers together and then divide by the events......so if you have 1 ohm at 20hz, 1 ohm at 60hz, 1 ohm at 240hz, 1 ohm at 480hz, 1 ohm at 960hz, 1 ohm at 1920hz, 1 ohm at 3670hz, 1 ohm at 7340hz, and 64 ohms at 14680hz the nominal impedeance is 8 ohms ((8+64)=72))/9=8

[Quiet_Hollow]

I've never run across such a disparity between a nominal value and lowest value. 1-2 ohms maybe, but 4.16? He's not mixing up DCR (Re) and impedance (Z) is he? Was just curious about the application.

[garyrc]

Riddle me this...How can impedance be 8 Ohms nominal but dip to 3.84?? The only time that a deviation that large could still be considered "nominal" is if something is operating outside of it's passband. What have you got going on over there?

you know how manufactures do impedeance math.....they measure impedeance at every octave, add the numbers together and then divide by the events......so if you have 1 ohm at 20hz, 1 ohm at 60hz, 1 ohm at 240hz, 1 ohm at 480hz, 1 ohm at 960hz, 1 ohm at 1920hz, 1 ohm at 3670hz, 1 ohm at 7340hz, and 64 ohms at 14680hz the nominal impedeance is 8 ohms ((8+64)=72))/9=8

So you're saying that "nominal" is in name only? Sorry, just had to say it.

[StephenM]

I've never run across such a disparity between a nominal value and lowest value. 1-2 ohms maybe, but 4.16? He's not mixing up DCR (Re) and impedance (Z) is he? Was just curious about the application.

Here's another example:

http://www.stereophile.com/content/klipsch-rb-15-loudspeaker-measurements

Again, the RB-15 is rated as "8 ohm compatible" under nominal impedance, but if you look at the impedance trace, between the 200-300Hz mark, it does dip slightly below 4 ohms.

[Quiet_Hollow]

Ah, I see. Nice how they throw the word "compatable" in there to cover for that. Given that case, and if that's what the OP's dealing with, then:

normally, the answer is no..

+1

[WMcD]

There seems to be two questions. And I'll add to them.

1) How come a manufacturer can say a speaker is 8 ohms nominal yet a plot of impedance versus freq shows that it drops to 4 ohms or less? Answer. The impedence of any speaker varies quite a bit and apparently an industry standard allows for them to state what is pretty much an average for "nominal.".

2) Resistance of a load is the ratio of voltage applied to current resulting. R=V/I. We will not go into a.c. impedance here Nonetheless. if you apply 1 volt to an 8 ohm load there is 1/8th amp. If you apply 1 volt to a 4 ohm load, there is 1/4th amp resulting. Or twice as much current. All this scales because of Ohm's law. and at the lower impedance number, more power is drawn.

3) Take this with a grain of salt. I only have old amps with no protection circuits. Still. It looks like many modern amps have protection circuits which will shut down the amp if there is too much current demanded. And therefore, if the speaker impedance actually drops in some freq range, and you applying voltage (loud music) the amp;s protection circuits may very well shut down.

4) We've had reports of AV receivers shutting down when Klipsch speaker are attached. I can only think that this is because of the dips to low impedance which demand current. It looks to me that Klipsch has long been using low impedance in woofers to draw current (power) out of amps in th name of reported speaker efficency or sensitivity, by the numbers..

But by this, owners find they have have amps which shut down at high levels. No, it is not a matter of cables or wires touching in a bad hook-up. Rather, I suspect, the amp manufacturer has set protection circuits so that 4 ohm loads and resulting current trip out the cirucit protection.

5) To address the initial question. If you have a speaker which dips to 4 ohms or less (this is measured at the input to the box), at a particular point in the freq response, and for some reason you have an equalizer, and you goose up the applied voltage in that point, what is the result? Does the impedance/resistance of the speaker change? Answer: No. What does happen is that with more voltage applied, current increases.

WMcD

[Mr. RF62]

Nicely put William, and thanks for replying. Your last point is the answer I was looking for. Begs another question.

You said " If you have a speaker which dips to 4 ohms or less (this is measured at the input to the box), at a particular point in the freq response, and for some reason you have an equalizer, and you goose up the applied voltage in that point, what is the result? What does happen is that with more voltage applied, current increases.

Pardon me if I seem dumb here, but if goosing up the applied voltage in that point with the equilizer, am I correct in thinking that the current is increasing anyway without turning the amp up? In that case is the amp(if not suited to handle low impedance) not having to work as hard to deal with that impedance at the particlar section of frequency/ies?

For all intents and purposes, this is for learning and applying for anyone if curious.

Thank you to all.

[StephenM]

Pardon me if I seem dumb here, but if goosing up the applied voltage in that point with the equilizer, am I correct in thinking that the current is increasing anyway without turning the amp up? In that case is the amp(if not suited to handle low impedance) not
having to work as hard to deal with that impedance at the particlar
section of frequency/ies?

By giving an EQ boost at a certain frequency, you are in essence "turning up the amp" at that particular frequency, and your amplifier will have to work harder for any given master volume level. The EQ isn't actually adding any juice to the mix.

[Mr. RF62]

Thank you Stephen, THAT is what I was looking for.

[Trey Cannon]

FYI: we hate the word 'nominal" as it applies to Z. That is why we add "compatible" to the words.