Originally Posted by chewy4
The one thing that I have trouble with that is that I'm guessing on the +/- dB parts of the EQ. I don't really get how to interpret it, it says that some parts go as much as -16dB but that would obviously sound ridiculous if I had an EQ bumped up that much.
The headphones I have don't really rely on a seal or anything though, would a dummy head still be completely necessary?
Hmm... that sounds like the wrong problem to be having when you're about to embark on this kind of project.
Yes, for accurate measurements you need a dummy head, with outer and inner ear components. Otherwise, there's really no point. You also need to study up on why headphones should NOT have flat response. Until you have a good understanding in hand, this is probably not the project to undertake. But there's already good data, so you shouldn't need to measure anything to achieve your goal.
If you are finding the need to EQ your headphones in the first place, that shows a lack of satisfaction for how they sound now, and a desire to improve them.
Let's break the project down this way. Assuming the response of your headphones is somehow not ideal. There are two questions to be answered.
1. What is the response of your headphones?
2. What is the ideal response for any headphones?
3. What is the inverse EQ curve needed to compensate for your headphones variance from the ideal?
4. How can you apply that curve accurately?
Since your headphones always operate into the acoustic system of the ear, there is no point in measurements make without that acoustic system. All headphones of all designs always operate into the acoustic system of the outer ear and inner ear. No exceptions. So any measurements made without that system won't reflect their true performance. To answer the first question, you need good measurement data. If you can't take it yourself, you need to access that taken by someone else with the proper equipment. Hence, my suggestion of the graphs from headphone.com. You need to read them carefully, it's all there.
Answering the second question is much harder. Unless you can find something published from scientific research, all we have is the general idea that the ideal response contains a bass boost to make up for the lack of large sound waves striking the entire body, and a treble roll-off to compensate for the close proximity of the drivers to the ear. How much, though? One way to get a feel for what others seem to prefer is to take the response data from several high-end, top rated headphones and average them. You probably only need a data point every 1/3 octave, perhaps less, for a general trend. What you'd have then is an average response that some very learned designers have all agreed on. If you average enough good headphone data, that would make a fine target curve for some less than ideal headphones. In actual fact, averaging wouldn't be the best way to combine those measurements, but you can at least do it on a spreadsheet.
Now you have the response of your headphones, and the averaged response of "great" headphones of the world. If you subtract yours from theirs you'll have the difference that you need to correct for with your equalizer. Invert that curve and you'll have the target for your equalizer's response (not the total response, just that of the EQ needed to pull your headphones to the average target). The equalizer you'll need will be a multi-band full parametric, as you'll need to adjust gain, frequency and Q to hit the curve well. But the key is, you need a way to either plot or predict, exactly, the actual response of the equalizer. That's why a graphic wouldn't work, the curve you see represented by the controls isn't close enough to reality. Match the actual equalizer's response to the desired correction curve, and you'll be fairly close to the target curve you derived in question 2.
And...when you're done...you won't have headphones that sound exactly like the average high-end ones anyway because there are internal resonances that EQ will not address. EQ deals with response, and to a lesser extent, phase, but can't deal with ringing or resonances that carry on in time. The technique you'll use here is essentially time-blind. But probably as close as practical.