Re: Speaker frequency responce charts and graph eq pedals???
The problem I have with manufacturer-supplied charts is the lack of details on how that chart was constructed, i.e. whether it was completely theoretical or if it was measured in reality.
If it was measured in reality, what are the specs of the cabinet it was mounted in?
What amp with what settings, and what variances will that model of amp itself have?
What guitar?
What pickups?
Who played the guitar, a man or a machine?
If a machine struck the string that eventually came out of the speaker as sound, at what level of force was the string struck? Open or fretted? If fretted, what with, and with what frets on what fretboard? What value and brand of pots in the guitar?
On the other hand, if the signal was generated by an electronic tone generator, what model? And what is its tolerance? Had the unit been calibrated to ensure a 1kHz tone was not 1024 or 980Hz?
If it was purely theoretical based on the components and build spec, what's the allowable variance of those components and the build spec? Is the voice coil wound by hand or machine? Is the starting point of the coil winding identical on every speaker or will some speakers have more or less winds than others?
What about the magnet used for the sample speaker? Best-quality that doesn't get used in full production or "we picked one off the line at random"? What's the variance in gauss?
What about the dust cover and surround? What material variance is there?
These are the questions I encountered a few years back when I went on a similar journey: I was dead-set on getting a fully programmable EQ so I could model various amps based on their graph charts for direct recording purposes. After looking up various EQ charts, and multiple layerings of EQ tweaks with both parametric (with Q control) and full-range graphic to notch specific frequencies, and generating output graphs in Adobe Audition and comparing them to the printed graphs, these questions started coming up.
The fact that you can buy an AxeFX or a Kemper as well as several other up-and-coming "true-to-life" modelers is astounding, and once you start delving into the process like I did, and run across those same questions, you begin to understand why those units are so expensive.
As for trying to approximate a given speaker, you have to know not only the target speaker's specs, but the current specs of your amp and cabinet and how they interact with your guitars and pickups. What frequencies are the amp and current speaker and cabinet accentuating, or cancelling out, and to what degree? Is that hump at a given frequency a harmonic aberration caused by the speaker? The cabinet? The amp? The pickup? The guitar? Your personal tone? The pots? The cables? The pedals? The room? The listening angle?
All of these are factors in the sound you perceive coming from the amp. I don't think a GE-7 is going to be wide enough to do that. You're going to need a 20+ band graphic, because a parametric EQ will usually only be 3 bands, with High and Low Shelving on 5-band models. Even with a Q knob, it's still only going to let you zero-in on 3 primary EQ frequencies, and the Q control is going to either squash or enhance frequencies on either side like a blanket. A graphic EQ will be more precise, assuming it is also voiced identically to the amp it's being run through, where the "Mid" control may or may not be on 1kHz. If you cut or boost the 1kHz with an external unit, and the amp and/or speaker favors the 975Hz notch, you'll have some degree of phasing.
I know you're not trying to make speaker A sound like speaker B, but you must realize you're only going to get so close this way, and that it may not be close enough to justify the expense.
Personally, I'd get the EQ pedal (or a rack with a fuller range) and use it for tone-sculpting rather than merely tone-tweaking.
