if you put any resistor in series with the loudspeaker and just measure the voltage over this (= current) plus measure the output voltage just coming out from the power amplifier, the results will have an offset of that resistance (0.1 ohm in this example).
There are definitely ways to compensate for this, but putting such a small resistance just between the output of the amplifier and the feedback loop of the amplifier is much easier.
An error of 0.1ohm is small, but it's one nevertheless
Yeah that is also doable, actually pretty handy and a great idea!
Gives you much better control about what is going on and you can just keep the gain of the audio interface fixed basically.
For a balanced input it's best to also make this balanced as well.
I showed this in another topic, but will just copy-paste it here as well
This is with a bridged amplifier, but a single-ended amplifier (= negative to ground) will work the same.
If you just want to use it for loudspeaker measurements, I would recommend putting some capacitors in parallel as well.
With a f3 around 40-50kHz or so.
There are those 2 pole 6 throw (2P6T) rotary switches, that are perfect for this!
Just leave the zeners out btw (originally in ARTA's manual), they just introduce quite a bit of additional distortion in some cases.
Any modern audio interface will tell you when you're near clipping.
The impedance network for a bridged amplifier can also work this way.
That being said, the series resistor attenuator method isn't the best, but unfortunately the only thing that programs like ARTA (LIMP) support.
The 0.1ohm method that AP is using is already better.
I gave this a thought. It likely is true if you want the impedance on a voltage source. But why do we measure impedance? Quite often because we want to cross passive and use inductive and capacitive networks that also bring a real part of impedance in series with the speaker. So maybe the method is quite fit for that application. What do y‘all think?
The problem with the series resistor attenuator method, is that the voltage isn't constant.
Especially with the recommended values of around 27 ohm.
For just a simple measurements at a low voltage for a (passive) crossover design, this will be fine.
But if you want to get more data, especially on a poor man's Klippel LSI way, this won't work well anymore.
Being able to measure this way can be helpful with troubleshooting, see my earlier post before.
All that being said, as I mentioned before, most software programs like ARTA (LIMP), work with a fixed formula to calculate the impedance. Which cannot be changed by the user. (Which is extremely unfortunate)
So unfortunately we are a bit stuck with the things we can do.
Although there are some tricks we can come up with.
Or alternative ways to get the same information.
Unfortunately in most cases the y-axis is fixed to decibels instead of a linear scale.
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Yes but it does account for this making it accurate, doesn't it? The problem with more common choices like 400 or 1k is SNR.
That's pretty nice way to measure BL. How reproducible were the readings between individual measurements? And how did the measured BL values compare to the numbers from the spec sheets?
I think you mean more simple?
SNR is better, you're correct.
I guess you indirectly bring up a good point, that for low voltages we can use the attenuator method and switch to small resistor for higher levels.
Since a decent and simple audio interface does a SNR of about 90-100dB (or better), I am gonna calculate how low we can actually go.
Otherwise some additional circuitry is needed or the inside feedback loop method.
Measuring loudspeakers horizontally (facing the ceiling) will introduce quite an offset unfortunately.
Since this is a DC offset, that already happens at low voltages.
The most elegant method I have seen, is one from Novak.
Which doesn't involve adding mass not volume, but we need to measure cone excursion to be able to measure the "acoustic" impedance. (Mechanical rather)
Using a current sensing resistor does not cause an error. The operator (or the software) will of course take into account the voltage drop. That's part of the measurement principle.
@b_force please stop claiming stuff without knowing the technical background and context (also in other threads). Thank you.
No idea what you're talking about?
Just please explain things, instead of ignoring or yelling to everyone that they don't know anything.
Without even trying to explain a single thing yourself.
It's not only extremely rude, but most importantly not helpful for the conversation and discussion,thank you.
If you disagree with something, simply come up with arguments, evidence and explanation.
That's how a mature conversation goes.
Up till now, you only ever yell that people are wrong with zero evidence or explanation yourself.
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That totally depends how the voltage is being measured.
But as you can read in the same post, it can be compensated for.
I ignored your comment because it is incorrect. The offset of the cone position in horizontal position is cancelled out because the current is adjusted to bring the cone back to it's initial position before adding the test mass.
Edit: you just made it to my ignore list (see also discussions in the Klippel thread etc.)
A real grown up and professional man I see.
Just ignore people so you don't have to explain things anymore 👍
This circuit can show the Voltage across the driver as well as the current running through it, as long as the resistor value is known. Am I missing something.. how is that anything but accurate?
Have you ever heard of misreading or miscommunication?
Instead of just jumping right into conclusions? Talking about being rude, jeez.
Anyway, I guess that could work.
Although I wonder how this will effect the parameters in general, since you put a constant strain onto things?
Also heating up the voice coil.
Which will shift Re.
@Kravchenko_Audio , what are your thoughts about that?
I think we are talking about two different things here probably.
The circuit you're showing is the attenuator circuit we have been talking about.
I am talking about how the voltage (and current) changes with an higher output voltage from the amplifier with such a circuit.
This can easily be moddeled and calculated.
A long time ago I even went as far as putting this into some error analysis.
But not the accuracy of the input of the soundcard etc.