Wish Updated Speaker Impedance Control

York Audio

Fractal Fanatic
Vendor
Since I deal with real speaker cabs every day, I always measure the speaker impedance. It's rare that an 8 ohm speaker reads exactly at 8 ohms or a 16 ohm speaker reads at 16 ohms. The current parameter can offset the actual impedance, but it would be great for the parameter to read in ohms rather than the current 0.250 - 4.00 range. For instance, I just measured a 16 ohm 4x12 cab that read at 14.5 ohms. If the default impedance was set at 8 ohms, I could raise the value to 14.5 ohms and get a more accurate impedance interaction rather than guessing where 14.5 ohms would be on the 0.250 - 4.00 scale.

It would also make it easier to accurately match models with cabs. A Mesa 4x12 is an 8 ohm cab. So choose your amp model and set the Speaker Impedance control to 8 ohms with a Mesa IR and you have a closer match to the real world amp/cab interaction.
 
With this said, I'd like to have a way to save my configured curve and use it as default for every amp model.
It would definitely be awesome if the Impedance curve and Speaker Impedance stayed the same while flipping through models, kinda like how the Input drive doesn’t change as you try different models. It would let you keep your cab while you swap out heads.
 
One thing to note Justin is that Impedance is a combination of Resistance and Inductance, and inductance varies with the frequency being measured. Your multimeter is only measuring Resistance (the fixed part that doesn't vary with frequency, since it's using a voltage with no frequency content to measure). That means invariably it will measure below the rated impedance on a multimeter. But doesn't doesn't mean the speaker itself isn't really at 16 Ohms impedance.

Conversely, it also doesn't mean the real speaker is at 16 Ohms impedance. But the resistance number alone isn't necessarily going to get you a more accurate result than the default. Impedance also varies with frequency, so a 16 Ohm impedance speaker will only be 16 Ohms at a single specific frequency they measure with. All of this is stuff that is probably handled in the speaker impedance curve and it's corresponding modelling.

So I'm not sure being able to set the DC resistance value for a speaker directly is going to do what you want, or that the field you're hoping to enter it in corresponds with that.
 
I was thinking on how this could be implemented the easiest way and came up with user stories :smiley:

Story 1:
As a user of the FM3 if I add an AMP block, I want the impedance curve to be set to "default", so that the most fitting curve is paired with the amp model in a single amp block channel.

Story 2:
As a user of the FM3, if I change the impedance curve to a different than "default" I want all my changes in the speaker page to be persistent across amp model changes in a single amp block channel.

My rough estimate 8 Story Points :cool:

.... sorry, I had a long working day and was still in story writing as a product owner :tearsofjoy:
 
I was thinking on how this could be implemented the easiest way and came up with user stories :smiley:

Story 1:
As a user of the FM3 if I add an AMP block, I want the impedance curve to be set to "default", so that the most fitting curve is paired with the amp model in a single amp block channel.

Story 2:
As a user of the FM3, if I change the impedance curve to a different than "default" I want all my changes in the speaker page to be persistent across amp model changes in a single amp block channel.

My rough estimate 8 Story Points :cool:

.... sorry, I had a long working day and was still in story writing as a product owner :tearsofjoy:
I don't think Fractal is an Agile development environment but I could be wrong ;)
 
I don't think Fractal is an Agile development environment but I could be wrong ;)
To nitpick: I don't Fractal is doing Agile©®™(Scrum©) the way people Certified in Agile are, but those people are so divorced from what agile software development means that it's a joke (They aren't following agile, they're just selling a process developed by a team that was following agile. And just blinding following the process coincidentally contradicts the very first rule of agile). But Fractal, or at least Cliff, is definitely using an agile approach.

Individuals over process ✔ (He's not worried about following the progression of betas or release schedules strictly, he's worried about people doing good work that's safe to release)
Working Software Over Comprehensive Documentation ✔ (I'm fairly certain Cliff isn't writing detailed specification documentation on Cygnus algorithm before implementing it, etc)
Customer Collaboration Over Contract Negotiation ✔ (Cliff isn't making a big plan based on user asks, disappearing for 3 years, then delivering a whole new Axe FX with it. He's actively collaborating with user feedback in real time.)
Responding to Change Over Following a Plan ✔ (Cliff isn't mapping out 2 years of updates and strictly following it, he's responding to customer feedback, needs, ideas, suggestions, and working on what seems highest priority at a given time).

So yeah, by the 4 core values of agile software development he's definitely in alignment. Other competing companies very much don't align with one or more of these.

Frequent delivery of working software on short iteration cycles is also a really common trait of agile approaches, which again Cliff is the bar all competing products should be measured against.
 
Since I deal with real speaker cabs every day, I always measure the speaker impedance. It's rare that an 8 ohm speaker reads exactly at 8 ohms or a 16 ohm speaker reads at 16 ohms. The current parameter can offset the actual impedance, but it would be great for the parameter to read in ohms rather than the current 0.250 - 4.00 range. For instance, I just measured a 16 ohm 4x12 cab that read at 14.5 ohms. If the default impedance was set at 8 ohms, I could raise the value to 14.5 ohms and get a more accurate impedance interaction rather than guessing where 14.5 ohms would be on the 0.250 - 4.00 scale.
How are you measuring them? If you are taking a DC ohm reading, then you will typically get a low reading, as the AC portion of the impedance is not accounted for in a DC ohms reading.
 
The impedance of the cab is only half the equation. The current range of values reflects the match between the speaker's impedance and the expected load from the amp side. For example, you can take an 8 ohm cab and connect it into the 4, 8, or 16 ohm taps of a tube amp's power transformer. That same cab impedance could then give you possible impedance match values of 2, 1, and 0.5 respectively.

Put another way, Impedance Match is a ratio of the expected impedance value to the actual impedance value. 0.25 means the amp is driving 1/4th the impedance it is expecting, like plugging a 4 ohm cab into the 16 ohm output. On the other side of the range, 4.0 would mean the amp is driving 4 times the impedance it's expecting, like plugging a 16 ohm cab into the 4 ohm output. Instead of modeling discrete impedance values, the Impedance Match control lets you pick any ratio of cab impedance to transformer tap you want between those two extremes.

If you're trying to replicate the ratio of a real amp and cab, then take the actual impedance of the cab and divide it by the output value of the speaker jack you have it connected to. So if you have a cab with an actual impedance of 14.5 ohms and you have it connected to the 8 ohm output of the amp, then 14.5 / 8 = 1.8125. That's your impedance match value to use in the Axe FX.
 
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I’m measuring them with DATS, which sends a sweep through the cab and gives the ohms, low frequency resonance, and the impedance curve.
Ok, so a proper measurement, then. The older common spec for British/Euro amps was 15 ohms rather than 16, so maybe it is made to the 15 ohm spec, which would make 14.5 a bit closer to the expected impedance. Also, instead of 8 ohms, you often see 7.5, and 3.75 instead of 4 on the old transformers....
 
The impedance of the cab is only half the equation. The current range of values reflects the match between the speaker's impedance and the expected load from the amp side. For example, you can take an 8 ohm cab and connect it into the 4, 8, or 16 ohm taps of a tube amp's power transformer. That same cab impedance could then give you possible impedance match values of 2, 1, and 0.5 respectively.

Put another way, Impedance Match is a ratio of the expected impedance value to the actual impedance value. 0.25 means the amp is driving 1/4th the impedance it is expecting, like plugging a 4 ohm cab into the 16 ohm output. On the other side of the range, 4.0 would mean the amp is driving 4 times the impedance it's expecting, like plugging a 16 ohm cab into the 4 ohm output. Instead of modeling discrete impedance values, the Impedance Match control lets you pick any ratio of cab impedance to transformer tap you want between those two extremes.

If you're trying to replicate the ratio of a real amp and cab, then take the actual impedance of the cab and divide it by the output value of the speaker jack you have it connected to. So if you have a cab with an actual impedance of 14.5 ohms and you have it connected to the 8 ohm output of the amp, then 14.5 / 8 = 1.8125. That's your impedance match value to use in the Axe FX.
Not quite.

The Speaker Impedance Curves include the D.C.R. If you select, for example, the 4x12 Basketweave, its D.C.R. is 14.0 ohms. So if you have a cab with an actual D.C.R. of 14.5 the Speaker Impedance value would be 14.5 / 14.0 = 1.036.
 
Ah, Gotcha. I forgot about the selectable impedance curves. That makes sense.

Would that also assume you'd be plugging the real world cab into a closely matched output? What if you are trying to recreate a particular purposeful mismatch?
 
Just had a flickering lightbulb moment. I believe I've been thinking of the Transformer Match parameter, not the Speaker Impedance parameter.

@FractalAudio would I be correct in thinking that Transformer Match parameter would be more for replicating a purposeful impedance mismatch like running a 16 ohm cab on the 8 ohm tap, while the Speaker Impedance parameter would be for compensating for differences between the selected Impedance Curve cab and the actual impedance of the reference cab you're trying to recreate?

Or is Transformer Match more for the primary side of the OT?
 
Just had a flickering lightbulb moment. I believe I've been thinking of the Transformer Match parameter, not the Speaker Impedance parameter.

@FractalAudio would I be correct in thinking that Transformer Match parameter would be more for replicating a purposeful impedance mismatch like running a 16 ohm cab on the 8 ohm tap, while the Speaker Impedance parameter would be for compensating for differences between the selected Impedance Curve cab and the actual impedance of the reference cab you're trying to recreate?

Or is Transformer Match more for the primary side of the OT?
If you want to simulate a speaker impedance mismatch you use Speaker Impedance. If you want to adjust the transformer impedance ratio you use Transformer Match.
 
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