In my research and experience over the years, a tuned response curve similar to the one shown below in orange provides a very pleasing listening experience with heavily compressed recorded content and also works really well with live sound too.
What I'm going to do here is explain how to use the crossover filters instead of EQ to get us super close to the final response curve were looking for. It doesn't have to be spot on perfect. It seems even relatively close is often times fantastic on the first try. And you can always make changes and final EQ to suit your personal taste and ear. There are several strategies and methods in manipulating the signal, but here's how I like to do it.
Looking at the sub's response bandwidth in the chart above, it's essentially a straight line from about 45Hz to 125Hz, with 40-45Hz at +15db above 125Hz. To be honest, +15db is sometimes a little too much in the bottom and I end up pulling a little after listening. Anyway, back to it. If we then look at the response of the subwoofer, we can then start planning our strategy.
Since we don't have an actual response graph for the actual combination, a 30" wide T48 loaded with two 12's (
Fountek FW322 4ohm), let's just use something close. Below is the measured response of a 15" wide single loaded with a 3012LF, which I've added 6db to the trace to account for there being two to equal the cab in question. Simply adding 6dB doesn't accurately portray what actually occurs when doubling cab count. Typically the curve flattens and the corner frequency is pushed lower. And the difference in drivers will have slightly different overall response curve shape. But, for what we need, this should get us in the ballpark in leu of not having measurements of the actual cab combination.
I put some markers on the chart denoting what the sensitivity is at 40Hz and 125Hz, as well as where the desired response would be at 125Hz after tuning, in relation to the sensitivity at 40Hz.
At 40Hz we're looking at roughly 99.5dB. So, if we subtract 15dB from that number we get the desired 125Hz response level after tuning, 84.5db. If we subtract that figure from the native 125Hz response of 114dB, we know we want to attenuate the signal at 125Hz by about 29.5dB.
Every doubling of frequency is an octave. So, 40Hz to 80Hz is 1 octave and 80 to 160Hz would be another octave. But, we only need to get to 125Hz. So, to figure out how deeply into the second octave 125Hz is, simply subtract 80 from 125, giving us 45. 45 divided by the total bandwidth of the octave in question, 80, gives us 0.5625. So, from 40Hz to 125Hz is 1.5625 octaves.
The total desire attenuation at 125Hz (29.5dB) divided by the number of octaves (1.5625) will give us a slope... 18.88dB/octave.
That get's us a rough idea. We can fine tune it a little to get a little better result. Let's run the numbers for a 50Hz Butterworth filter which is down -3dB at it's specified cutoff frequency.
125 is 1.25 octaves above 50Hz. Subtract the 3db that the filter is already down at it's cutoff frequency from the total attenuation needed gives us 26.5dB. 26.5dB divided by 1.25octaves gives us a slope of 21.2db/Octave
Run the numbers for a 50Hz Linkwitz Riley filter which is down -6dB at the designated cutoff frequency gives us a slope of 18.8dB/Octave.
It looks like we may be able to use a 18dB/octave filter, set at about 50Hz to put the 40Hz-125Hz response just about perfect and achieve the majority of the needed "EQ" without much EQ at all.
I'd set your highpass 40Hz 24dB/Octave Butterworth and your lowpass at 50Hz 18dB/octave Linkwitz-Riley for the sub. Run a 125Hz 24dB/Octave highpass filter on the tops. Play a 125Hz sinewave through just the subwoofer and using your smartphone with a free SPL meter app, adjust your volume until it's say 90dB. The specific number isn't important, louder than ambient noise without being too loud. Make a written note of the specific volume reading. Do not change the volume. Disable/mute the subwoofer, enable the tops, and adjust the outptut gain in the DSP for the tops to get the SPL (measured from the exact same spot as before) to be as close to the same volume as the subwoofer was. Make a written note what the specific SPL is. Then, without adjusting the volume at all, enable the subwoofer and play the subwoofer and top together. If everything is perfect, the resulting SPL will be 6dB louder than either one played on it's own. The likelihood of it being perfect is low, so don't be worried if it's less than 6dB louder than each on their own. We'll iron that out later. But!, if the SPL goes down, the polarity needs to be inverted on one of them. Inverting the polarity can be as easy as swapping the wires on the amp. But, I'd personally just invert the signal in the DSP.
What this will accomplish is an "effective crossover point" of 125Hz, even though the low pass on the sub channel is set to 50Hz and the highpass of the mid/high channel is set to 125Hz. The point where they actually crossover is 125Hz. 125Hz should work well with the 6x9's you have and also work well with the DR200's.
From here, we can adjust delay to phase match the sub and top which should get the 125Hz SPL to be as close to a full 6dB summation, EQ the tops, and do a final system EQ.
Anyway, try it out and see how you like it. It may take a little adjusting slopes and cutoff frequency to get it to sound perfect, but it really shouldn't need much. This should put you really really close to sounding great.
I forgot to have you order an inexpensive "calibrated microphone" from PartsExpress when you put your tweeter order in. But, for your needs it's not entirely imperative. The microphone in your smart phone will get you close enough for government work. There are plenty of free audio apps you can use to measure and tune the system. I use "Audio Tool" by J.J. Bunn. I forget which one Bill uses, but there's a bunch and any one with a Spectrum Analyzer will likely do you just fine.
If any of you have a different way, questions/concerns about this method, or just wanna tell me I'm wrong and/or call me a big jerk, please feel free to do so. I certainly don't know everything and I'm more than happy to learn how you would do it.
