EV 12L spec sheet:
Thiele-Small Driver Parameters
fs (free-air resonance frequency): 55 Hz
Qes (electromagnetic Q at fs): 0.245
Qms (mechanical Q at fs): 4.37
Qts (total Q at fs: (Qes Qms) / (Qes + Qms): 0.232
I had a cab with 2 EV 12Ls. I measured the LFR by ear using the old trick*, resulting in 72Hz IIRC.
* "One way to find the SRF is to put a Filter block after the amp block. Set the type to Peaking, Q to 5 or so and Gain to 10 dB. Start with a Freq. of 50 Hz. Play some chugga-chugga and slowly adjust the Freq. until you hear and feel the cabinet resonate. Make a note of the frequency. Remove the filter block and set the amp block SRF to match."
With an FRFR system you want the resonant frequency of the speakers used in the IR you're using, not the resonant frequency of the FRFR cab.
A great write up as usual Cliff! One thought that cropped up and that might help Poweramp/Cab guys is the idea of a global Low Freq Resonance Setting. This would allow you to override the setting for all amps depending on what guitar cab you are using at the time. This would be useful if heading out to a fly show or a rehearsal space where you probably wouldn't take your own cabs. Otherwise you may have to tweak quite a number of patches which could be time consuming. As usual just a thought. Cheers Spence
It should be possible to extract at least the LF resonance frequency value out from an IR file! Almost every IR uses a simple "sine sweep" as reference signal, so it's possible to measure the phasing between the reference- and the response signal. There is a major phase change caused by the speaker resonance frequency. Maybe this could be a nice plus for a further data synchronisation between the cabinet- and the ampblock
You would have to have the exact test signal though correct? Not just an assumption and a generic sweep?
I'm not understanding this then compared to what defaults in the amps under the speaker page. For example, the Marshall plexi defaults at a LF of 114 Hz. Typical speaker cab attached to that would be a Marshall 4x12. G12M greenbacks are a very common speaker in those. Looking at the OH Marshall IRs, there are the M55 PRs with 55 representing (I believe) the LF. There are also M RI 75s where 75 represents (I believe) the LF. So if you assume the 10% cab enclosure method then you're talking about values of 61 and 83 respectively...way lower than the defaults. I've also read elsewhere that people have measured their Marshall cabs up around the 110-120 levels. Jay Mitchell states that's the average for a 4x12. Cliff noted in his post that trying to dial by feel (which I interpret as ear) is not a good way yet Scott P states that's the best way to find the right frequency. Color me confused...I'm just sticking with the stock values and if anything, adjusting down the LF if it's too boomy for my tastes. Just trying to educate myself...
I can tell you, it's a difference if the cabinet is closed or open back. Most resonance peaks on cabinets were between 80 - 110Hz, depends on the speaker size, speaker wiring (series, parallel) , size (TSP!!), open or closed back (or mixed! -> Cliff's favorite is a Mesa 4x12 cab from the late 80s, these cabinets were half open, half closed) or ported housing.......
Before you start turning on the advanced parameters, just make a new preset with a all fresh all new amp block and your prefered IR in a fresh new cabinet block (best is to choose a MIX-IR from the stock cabinets, you won't to choose a specific microphone and there is not much distraction from the proximity parameter, which also can pump up your LF feel)! Remember, the IR is one of the most important parts of your tone when working with a FRFR setup. After that, leave your Amp EQ at the default settings. If you want to learn how LF and HF resoance work, turn up the Master Volume on your patch, because this is most hearable with higher MV values. Note - don't push it too hard then, not too high pre amp gain values - otherwise your sound might get too flubby, it's just a "howto" for learning/understanding how these parameters will work, so you can make a slight (but right) change on your desired presets!