About Matching Your Cabinet's Resonant Frequency

Moltenmetalburn said:
It's not based on, it's tied to the preamp sag parameter. Totally different .

The knob controls both functions, preamp and power amp sag simultaneously.
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Thanks for the new info. I read the release notes differently, thinking that preamp sag was calculated from power amp sag, which is a dynamic value that wouldn't be calculated if Sag were turned off.
 
Rex said:
Thanks for the new info. I read the release notes differently, thinking that preamp sag was calculated from power amp sag, which is a dynamic value that wouldn't be calculated if Sag were turned off.
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No problem. I never made it to the release notes, cliff answered me directly in the thread.
 
What if you are using a 2x12 cabinet that has 2 different speaker models that have different resonance frequencies? I have a 2x12 that has a G12H30 with a resonance frequency of 85Hz and a Vintage 30 with a resonance frequency of 75Hz. I can't find any impedance plots from Celestion, so I'll have to use one of the other methods to determine the impedance value.
 
I also have 2 different speakers in a closed 4x12 (et65 and retro 30). Any info on setting it on 2 separate speakers would be awesome.
Thanks.
 
FractalAudio said:
The only truly accurate way to set the simulated speaker is to measure the speaker being used with an impedance measuring device. These can be had relatively inexpensively in the form of the Woofer Tester 3 (from Dayton Audio IIRC). You can also make your own using a small value resistor (0.1 ohms or so) in series with you power amp and measure the voltage across the resistor.
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I can't find this woofer tester 3 anywhere for sale? Would be nice to have to measure my cabs...
 
Just stumbled on this pdf file online:
http://www.award-session.com/pdfs/Open Or Closed Back Cabs.pdf

Does this info appear to be fairly accurate?

It seems to be suggesting that for an EVM-12L in an open back cab the published free air low-resonance frequency of 55hz would not change much if at all when the speaker is in an open back cab.

I know I'm splitting hairs here, but would it be any better for me to use 55hz as the Amp Block's Low-Res Freq as opposed to the 65hz I'm using now?

Also his way of calculating the low-res-freq of a driver in a closed-back cabinet seems a bit different than Cliff's simple add 10% trick.
I don't know if there's a simple percentage you can apply to raise a given frequency up a Perfect 4th ("two and a half tones") but if there is, it'll be a bit more than the 10%.
 
I have difficulties with adjusting the correct frequency response...

I have a semi-open cab with a 12" Jensen Tornado in it.
I dialled in an AC30TB patch with everything at default. The default resonance frequency is 55 Hz.
The patch sounds really awesome.

But it can sound better - or can it?

Using Cliff's formula and Jensen's information regarding the frequency response behaviour of the Tornado I know that the resonance frequency is around 80 Hz (74.2 Hz + about 5% for the cab) and the Low Res Value is about 9.35.
When I dial these parameter in the sound deteriorates drastically.

Why is that? It is supposed to sound even better but it does not. What am I doing wrong?
 
mmh...the Low Res value seems pretty high to me.....

Other thing: A Vox AC30TB has a 16Ohm speaker out tap....your 12" semi-open cab with a Jensen Tornado has 8Ohms (regarding your fc of 72.4 (not 74.2!!)Hz). You now put a 8Ohm load with its specs onto a 16Ohm output tap of the "virtual AC30TB output transformer". To correct the speaker impedance transformer mismatch, turn down the Transformer Matching parameter to approx. 0.5 of value

cheers
Paco
 
I've got a similar problem with the Low Res. I can't find a value that seems right to me. I'm trying to match it my Celestion Century Vintage loaded cab. It either seems too low (lacking thump) or too high (boomy). Right now, I leave it at default therefore, although it appears to be a little too low. Celestion doesn't publish too much data which doesn't make it easier, either.
 
Lilarcor said:
I've got a similar problem with the Low Res. I can't find a value that seems right to me. I'm trying to match it my Celestion Century Vintage loaded cab. It either seems too low (lacking thump) or too high (boomy).
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Boom comes from the frequencies below 100 Hz. Thump comes from frequencies above 100. Try raising the low Res frequency.
 
PacoCasanovas said:
mmh...the Low Res value seems pretty high to me..... Other thing: A Vox AC30TB has a 16Ohm speaker out tap....your 12" semi-open cab with a Jensen Tornado has 8Ohms (regarding your fc of 72.4 (not 74.2!!)Hz). You now put a 8Ohm load with its specs onto a 16Ohm output tap of the "virtual AC30TB output transformer". To correct the speaker impedance transformer mismatch, turn down the Transformer Matching parameter to approx. 0.5 of value cheers Paco
Click to expand...

Turning down the transformer match did the trick! Thanks! I upped the hi res to about 6.4 too and it sounds killer now.

Now only one question remains - how are we to know what speaker load the individual models default to?
 
guitardoc said:
Now only one question remains - how are we to know what speaker load the individual models default to?
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Google? ;)

Some cab and amp combinations where a bit harder to find for sure (I know a few of them from personal experience, not all....). But maybe this could be a nice add to the axefx II wiki.....

cheers
Paco
 
PacoCasanovas said:
Google? ;) Some cab and amp combinations where a bit harder to find for sure (I know a few of them from personal experience, not all....). But maybe this could be a nice add to the axefx II wiki..... cheers Paco
Click to expand...

If there was an overview showing
- the actual cab the amp sim was modelled for (especially the SPKR tab)
- the impedance of the original cab
this would be mighty helpful.

E.g. Double Reverb - Double Reverb combo (cab #xyz), 16 Ohms.

This way when using 'real' guitar cabs the parameters of the SPKR tab and the Transformer Match parameter could be adjusted accordingly.

Moreover, different SPKR tabs and Transformer Match parameters for different routings would be killer... One routing with cab sims to FOH and one without cab sims to SS Power Amp + conventional guitar cab. This way the parameters could be individually adjusted to the cab sim and to the guitar cab.
Don't know if that can be done though since one amp would have to react differently depending on the cab sim and the guitar cab simultaneously. It is achievable by using two identical amps in individual rows though - even now.
 
Actually, it does matter with IRs as well.

The idea of the speaker resonance stuff being in the Amp Block is that you can get the amp sim to behave as if it's having the type of interplay a real tube amp would be having with whatever speaker is connected to it.

So if you're running your Axe through a power amp and an open back 1 X 12 guitar cab with an EVM-12L in it and you want the amp sim you're using to behave as if it was pushing an EVM-12L itself, you can set the parameters in the Amp Block's Speaker Page accordingly.
If you're running an FRFR rig instead and in the Cab Block you're using an IR of a an open back EVM-12L cab, then the Amp Block's Speaker Page parameters should probably use similar settings.

The Amp Block can't communicate with your external power amp and guitar cab.
Nor can it communicate with a Cab Block that follows it in the Layout.
But it CAN simulate the electrical interplay that the real amp being modelled would have if it were connected to various speaker cabinets with various reactive characteristics.

Please see Post #2 in this thread from Jay Mitchell:
http://forum.fractalaudio.com/ultra-std-discussion/27821-spkr-res-freq-intelligent-use.html
 
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