That's an important characteristic to take note of. Many loudspeaker manufacturers use ferrite-cored inductors to help keep inductor DCR as low as possible.
As measured, the Thiele-Small parameters of a driver are based on the amplifier output impedance being Rg = 0 ohms, which also implies that inductor DCR, Ri, is zero ohms as well.
When trying to compute the enslosure tuning, the value of Qes needs to be adjusted for non-zero values of Rg and Ri. I think that the applicable formula is for the adjusted Qes value is simply: Qesa = Qes*(Re+Rg+Ri)/Re.
This results in Qesa>Qes, which means that the adjusted Qts value of the driver will also be greater than the Qts value specified in the driver data sheet. If they are large, changes in Qts will significantly affect the tuning required for a maximally flat low-frequency alignment.
The DCR value of the inductor also results in undesirable power dissipation in that circuit component, and an overall attenuation of the output from the loudspeaker.
The answer is > Every driver I have ever delt with - woofer or not.
Any woofer that has 4 ohms DC but 8 ohms AC 200Hz is an unusually highly inductive driver.
Mister Audio,
Good. Measurements are key to a good beginning!
A typical speaker system might be something like the following:
"8 Ohm" rated woofer may be 6 Ohms from 20 to 30Hz; and again 6 Ohms at woofer resonance in a ported cabinet (between the two typical 20 or 30 Ohm peaks); and 6 Ohms again at 200Hz.
For a closed box woofer, there is only one wooffer 20 to 30 Ohm peak, but the very low frequency is 6 Ohms, and again at 200Hz is 6 Ohms.
All Generalizations Have Exceptions.
I really miss the $50,000 Rohde & Schwarz Vector Network Analyzer, and $10,000 Calibration Kit I used to use.
I measured speakers, transformers, capacitors, inductors, amplifier frequency response and phase, etc.
This is the Tubes / Valves thread, where very few tube amplifiers have Zero Ohms output impedance.
Solid State, that is another thread area of this Forum.
However, if you read earlier posts, there was a poster who regularly talked about his tube amplifiers negative resistance output to make up for some less than ideal speaker woofer characteristics.
I worked in an engineering department of a T & M company, where together we developed 6 negative resistance circuits to drive 6 crystal resonators for the narrow resolution bandwidth filters of the worlds most capable spectrum analyzer.
That spectrum analyzer is un-obtanium now, but no other spectrum analyzer touched its sensitivity, low residual FM, Log dynamic range, low phase noise, and capability to measure 500GHz and more.
Good. Measurements are key to a good beginning!
A typical speaker system might be something like the following:
"8 Ohm" rated woofer may be 6 Ohms from 20 to 30Hz; and again 6 Ohms at woofer resonance in a ported cabinet (between the two typical 20 or 30 Ohm peaks); and 6 Ohms again at 200Hz.
For a closed box woofer, there is only one wooffer 20 to 30 Ohm peak, but the very low frequency is 6 Ohms, and again at 200Hz is 6 Ohms.
All Generalizations Have Exceptions.
I really miss the $50,000 Rohde & Schwarz Vector Network Analyzer, and $10,000 Calibration Kit I used to use.
I measured speakers, transformers, capacitors, inductors, amplifier frequency response and phase, etc.
This is the Tubes / Valves thread, where very few tube amplifiers have Zero Ohms output impedance.
Solid State, that is another thread area of this Forum.
However, if you read earlier posts, there was a poster who regularly talked about his tube amplifiers negative resistance output to make up for some less than ideal speaker woofer characteristics.
I worked in an engineering department of a T & M company, where together we developed 6 negative resistance circuits to drive 6 crystal resonators for the narrow resolution bandwidth filters of the worlds most capable spectrum analyzer.
That spectrum analyzer is un-obtanium now, but no other spectrum analyzer touched its sensitivity, low residual FM, Log dynamic range, low phase noise, and capability to measure 500GHz and more.
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Hey there 6A3sUMMER,
I wasn't debating or questioning an 8 ohm woofer measuring 6 ohms DC , I was questioning 4 ohms DC .
That equates to a 33% difference.
I wasn't debating or questioning an 8 ohm woofer measuring 6 ohms DC , I was questioning 4 ohms DC .
That equates to a 33% difference.
This is the Tubes / Valves thread, where very few tube amplifiers have Zero Ohms output impedance.
NO tube amplifiers have Zero Ohms output impedance !
NO tube amplifiers have Zero Ohms output impedance !
Mister Audio,
I have seen several reviews of speakers with an 8 Ohm rating, that dip down to 4 Ohms. I even remember a reviewer who reported a 3.5 Ohm minimum impedance of an '8' Ohm speaker.
You are correct!
Most tube and solid state amplifiers have an output impedance larger than zero.
But, there are amplifiers that have negative output resistance.
That means that as a speaker's impedance varies, higher impedance gets more current, and a lower impedance gets less current.
And in my book, negative resistance is less than zero resistance.
Strange, but true.
I have seen several reviews of speakers with an 8 Ohm rating, that dip down to 4 Ohms. I even remember a reviewer who reported a 3.5 Ohm minimum impedance of an '8' Ohm speaker.
You are correct!
Most tube and solid state amplifiers have an output impedance larger than zero.
But, there are amplifiers that have negative output resistance.
That means that as a speaker's impedance varies, higher impedance gets more current, and a lower impedance gets less current.
And in my book, negative resistance is less than zero resistance.
Strange, but true.
markbakk,
That was a good joke!
It might wake up some readers of Tubes / Valves
Some loudspeaker's Woofers sound really wooly if the damping factor is less than unity or less (DF = / < 1.0).
I have tried it, by the way.
And, loudspeaker impedance variations from 20Hz to 20kHz will cause the frequency response of the reproduced sound to vary accordingly, unless the loudspeaker was designed to work with a current source amplifier.
There are at least 2 excellent threads on Tubes / Valves that talk about Current Source Amplifiers.
Also, Wavebourn posted lots of good information about amplifiers with Negative Resistance outputs.
I miss Wavebourn since he stopped posting on Tubes / Valves.
Have fun researching all those posts!
That was a good joke!
It might wake up some readers of Tubes / Valves
Some loudspeaker's Woofers sound really wooly if the damping factor is less than unity or less (DF = / < 1.0).
I have tried it, by the way.
And, loudspeaker impedance variations from 20Hz to 20kHz will cause the frequency response of the reproduced sound to vary accordingly, unless the loudspeaker was designed to work with a current source amplifier.
There are at least 2 excellent threads on Tubes / Valves that talk about Current Source Amplifiers.
Also, Wavebourn posted lots of good information about amplifiers with Negative Resistance outputs.
I miss Wavebourn since he stopped posting on Tubes / Valves.
Have fun researching all those posts!
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