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Speaker Time Constant...

Wolfenstein98k

Power User
As introduced in Quantum 9.

What does it do, exactly? If you had to summarise its effects with words? Why would you turn it to 20ms, or 500ms?
 

FractalAudio

Administrator
Fractal Audio Systems
Moderator
It adjusts the thermal time constant of the virtual voice coil. Lower values cause the voice coil to heat and cool faster and vice-versa.
 

edo

Power User
It adjusts the thermal time constant of the virtual voice coil. Lower values cause the voice coil to heat and cool faster and vice-versa.
Do you know what the accurate values for a celestion blue would be? (Or is there any way to figure it out?)
 
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Hubi

Experienced
In early days Cliff recommended higher values for british (200msec), lower for the americans.
 

edo

Power User
In early days Cliff recommended higher values for britisch (200msec), lower for the americans.
Yeah, I remember, iirc it was 200ms time constant and 6 for speaker comp, does this guideline still apply after the recent epiphanies?
 

guitarnerdswe

Power User
In early days Cliff recommended higher values for britisch (200msec), lower for the americans.
Can you find this quote? I remember it being about higher motor drive settings for British speakers, not the time constant. After using the search function, all I could find was what I stated. Around 3 dB compression for American speakers and about 6 dB for British.
 

edo

Power User
Can you find this quote? I remember it being about higher motor drive settings for British speakers, not the time constant. After using the search function, all I could find was what I stated. Around 3 dB compression for American speakers and about 6 dB for British.
You might be right, because on fw 7 time constant defaulted to 200ms, so it could just have to do with speaker comp
 

Tahoebrian5

Fractal Fanatic
I'm having a hard time hearing/feeling what this does regardless of the technical description. It definitely changes something but it's hard to quantify since I'm not really sure what to listen for.
 

NMG

Experienced
I guess the next question should be, What are the audible effects of a hot or cold voice coil?
 

crg123

Experienced
If you liked 8.02 you'll love 9.01. There is no need to reset anything. Just adjust the Speaker Compression and Speaker Time Constant to taste (default values are 3.00 and 100 ms respectively).
According to the man himself the default values should be Speaker Compression - 3.00 and Speaker Time Constant - 100 ms.
 

edo

Power User
Yeah, I know the default settings, but as far as I can tell this should be different depending on the virtual speaker type one is using
 

Wolfenstein98k

Power User
I thought the "50ms American, 200ms English" thing was got an unrelated parameter. Wasn't "speaker time constant" only introduced in Q9?
 

VegaBaby

Fractal Fanatic
you guys are confusing speaker time constant with Motor Drive introduced in 7.02. there it was stated that American speakers roughly compress around 3dB and British around 6dB. no specifics have been stated on time constant so far.
 

Rex

Legend!
I guess the next question should be, What are the audible effects of a hot or cold voice coil?
@Hubertus nailed the first half of the answer:
When the voice coil heats up the speaker sensitivity decreases --> compression
At low values of Speaker Time Constant, the voice coil heating effect is quick. Pluck a note, the voice coil heats up. Release the note, it cools off quickly. Compression ramps up and down as each note begins and ends.

At high values, it takes longer for the voice coil to heat up. Pluck a note and let it ring out: the voice coil heats more slowly, and compression comes in more slowly. Release the note, and compression rolls off more slowly. A fast run of notes might have a cumulative effect on temperature and compression.


In other words, as @DLC86 said, it's pretty much the same as attack and release on a compressor.
 

Smittefar

Fractal Fanatic
Yeah, I know the default settings, but as far as I can tell this should be different depending on the virtual speaker type one is using
I don't know the exact number, but my feeling is that a Celestion Blue (my favourite speaker in the world) has a fairly long time constant that really lets the notes bloom and develop over time. I would definitely try values that are higher then default. Off the top of my head, a guess could be as much 500 ms, as I think the Blue does a lot of the same things to single notes as an LA2A compressor would do.
 

ETOLKIEN

Experienced
you guys are confusing speaker time constant with Motor Drive introduced in 7.02. there it was stated that American speakers roughly compress around 3dB and British around 6dB. no specifics have been stated on time constant so far.
Yeah VegaBaby is right, the American/British thing was about Motor Drive, I have some links for the quote lovers as I am:
"Gain monitoring of the Motor Drive is available on the MIX page of the Cabinet Block and the PWR DYN page of the Amp block. In the case of the Amp block the monitoring is available when the Motor Drive parameter is selected. Note that typical guitar speakers have around 3-6 dB of compression when driven hard with American speakers being on the low end of that range and British speakers being on the high end. Some speakers can exhibit even more compression than this with compression amounts of 8 dB or more depending upon the magnetic materials used and the construction of the speaker motor."
https://forum.fractalaudio.com/threads/axe-fx-ii-quantum-rev-7-02-firmware-release.125625/#post-1494622

The time constant parameter was introduced in Q7.02 beta and the initial value was 500ms fixed:
https://forum.fractalaudio.com/threads/axe-fx-ii-quantum-rev-7-02-firmware-release.125625/page-10#post-1495821

For Q7.02 final version Cliff made the parameter adjustable:
"Finally I've made the time constant adjustable. I did some more calculations and measurements and found that a typical guitar speaker is actually lower than what I had previously calculated because thinner wire is used than I was assuming. Regardless you can now set the thermal time constant to get whatever response rate feels best."
https://forum.fractalaudio.com/threads/speaker-drive-vs-motor-drive.125541/#post-1494518

...with 200ms default value:
"200 ms is based on a typical theta of 1 degree C/W and a mass of 10g. I don't really feel like destroying all my nice vintage speakers to measure the voice coil mass."
https://forum.fractalaudio.com/threads/axe-fx-ii-quantum-rev-7-02-firmware-release.125625/page-10#post-1495722

As an evolving product I would take the last advice as a starting point (Speaker Compression 3.00 and Speaker Time Constant 100 ms):
https://forum.fractalaudio.com/threads/axe-fx-ii-quantum-rev-9-01-beta.131857/page-4#post-1561059
 
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