Mike, I'm jealous that you have stalkers. Nobody gives a damn what I say. Except occasionally JonBuoy, but he's so polite about it that sometimes I don't realize he's calling me out.

Don't feel bad. Maybe the thing you actually don't know what you are talking about is the fact that you don't have any stalkers. It's the kind of thing we all hope we are clueless about I guess.

I'm reviving this topic because I decided to make a frequency response test with my audio monitors.
Several years ago I bought a cheap pair of audio monitors, Tapco S5, without great pretensions, just to have some reasonable speakers.
With the passing of time I began to realize the sound difference of my mixes when listening these monitors and listening in a good headphone.
I know it's a controversial subject, mixing with headphones, but what I'm saying here is about frequency response.
Amazingly, my headphones have a better frequency response that Tapco monitors, especially in deep bass.
And to measure more accurately, I used this excellent software to measure the frequency response, audioTester.
Basically I put my microphone in front of one of the speakers and used the "Sweep Measurement".
The result is the graph below:

As you can see, the response starts to get fairly flat only after 100hz.
This is terrible!
Now I wonder, should I throw these audio monitors in the trash?

bitflipper
Mike, I'm jealous that you have stalkers. Nobody gives a damn what I say. Except occasionally JonBuoy, but he's so polite about it that sometimes I don't realize he's calling me out.

Bit, I give a damn.   I give a damn about what Danny says too. 
 
I am still learning, but if you like math and are able to find a chart that tells you the length of waves at different frequencies, you can compare that to room size and find where the problems might be.  Ethan Winer's method is good too.  ARC can show you a whole lot of useful information too.  If you yake all the input, from all your knowledgeable sources, and synthesize it for your environment you can make a big difference in the quality of your produce.
 
basically, I have placed most of my sound reinforcement strategically.  Though my room is 20 x 12 x 7.5 (which is not very good), my mixing space is about  6x 6 x 6.  It is a tight little configuration.  My Monitors are in tight too, they are about equidistant from the walls, floors, and ceiling and the listening position, which follows the % rule, (I think it is 38%, but I cant remember.)
 
I have ARC 1, I used it for measuring the room.  It proved the math right, as there was a deep null at 200 right where I sat.  I don't mix much with it right now as I think I am figuring out when and where to boost and cut.  I do pull it out every now and then to verify my new techniques.
 
I can say my mixing has improved when I mix in my main room, and I always strive to get better, but when I travel and use a laptop and headphones it is a whole new ballgame.
 
Also, you should give a damn about what the knowledgeable people in this thread have shared, but you should probably nt give to much of a damn about what I say because I only know this, keep trying.
 
Also, I do have a stalker, and it is ME.  I can't get myself to leave myself alone and it drives me crazy, figuratively and literally.
 
Jesse Q. Screed
 
Also, avoid using to many effects and plugs and magic dust, this all messes with your music, get a good recording to start with.  If you slather your french fries with ketchup/catsup, are they still fries?

rogeriodec
Amazingly, my headphones have a better frequency response that Tapco monitors, especially in deep bass.
As you can see, the response starts to get fairly flat only after 100hz.
This is terrible!
Now I wonder, should I throw these audio monitors in the trash?

No, don't throw them out. It's not entirely your monitors' fault. 
 
Any speaker will have a minimum frequency that it can correctly reproduce. It's a physical limitation based on the natural resonant frequency of the speaker itself and the enclosure it's in. Low-frequency response can be aided somewhat by the enclosure design, e.g. porting, but ultimately it's a hard limit dictated by physics.
 
The room you're in is a critical part of the system, too, along with the speaker and its enclosure. Small rooms have the worst problems, but almost any room will be less than flat due to resonances. Even if you trashed the Tapcos and mortgaged your house to buy high-end mastering speakers, you would still not measure a flat frequency response because the room would still impose its own acoustical fingerprint.
 
And it gets worse...your room's frequency response isn't static, it changes over time. I don't mean years, but milliseconds. Some frequencies ring out longer than others, which makes it even harder to adjust your EQ, and smears the image. It's the reason "room EQ" solutions such as ARC only get you part way there. Get a copy of Room EQ Wizard and use it to create a waterfall graph, which is similar to the graph you made except it shows multiple measurements over time.
 
Adding acoustic absorbers will help flatten the room response, although getting them to solve low-frequency problems is expensive. A small investment will, however, smooth response in the mids and highs and help mitigate ringing. 
 
Absorption won't help the biggest problem revealed by your graph, though, which is simply lack of response below 70 Hz. There is no cure other than upgrading your speaker system. The cheapest and easiest solution would be to add a subwoofer for around $400. It's either that or replace your speakers, but that'll cost you $1500-2000 for a significant upgrade.
 

It reminds me of the time I was helping my son choose a pair of active speakers.  We were in a great shop that had many set up and operating and I had my trusty Steely Dan reference CD.
 
The same situation resulted comparing the Yamaha 5" model (HS5) to the 7" (HS7) and 8" (HS8) model.
No 5" speaker will give you thte bottom end period.  I think for a half reasonable home studio setup you need at least a 7" or 8" driver before you will even start to hear the bottom end properly.
 
The deep bottom end was just missing in all the 5" drivers we listened to.  OK for some reasonable playback for mix checking at low volumes but not great for any real bottom end hearing.  In the Yamaha range the deep bottom end came back big time with the 7" model and there was very little difference between the 7" and 8" models as well.
 
You can get most rooms even a smallish room to sound very good with little expense.  It can depend a lot on where and how things are placed in the room.  Some bass trapping to even out the bottom end, absorption in key areas on walls (flutter echo’s can easily be arrested) and also importantly above you, and even a little diffusion at the back can work wonders.
 
If you can get your speakers out from the walls and onto some quality stands as well a very real and decent sound can be had.  You don't need ARC to get a good sound either.  I prefer to get things sounding decent in the room and then maybe fiddle with ARC after.  With a good choice of speaker and a little effort with the room a very nice mixing environment can be had as well as a decent mastering one too.

It's perhaps worth remembering that most of the systems the "public" (for want of a better word) use to listen to music are pretty poor performers in the bass region. Mixing on a system that's a bit bass-light can actually result in a more transferable mix. If all your bass impact is down below 80Hz or thereabouts lots of reproduction systems just can't reproduce it accurately if at all.

Getting an accurate frequency plot from a monitor is a bit more complicated than putting a microphone in front of it as well. What matters is the frequency response at a reasonable listening distance because speakers don't transmit all frequncies in all directions. Higher frequencies principally come from the centre of the cone, so a close mic on the centre has less bass. Conversly a close mic at the speaker edge tends to have more bass, less of whatever the speaker's maximum treble frequencies happen to be. This is why guitar speakers can sound so radically different as you move a mic around them.

Then there's the issue of the tweeter vs the woofer. Tweeters tend to be searchlight-like in terms of dispersion so a mic too close to the woofer won't pick up much of their output at all. Assuming white noise as a test audio source, the frequency plot posted has a stunning drop-off in the treble for example - either there's something going on with the tweeter/cross-over design or the test mic wasn't picking it up either because of placement or maybe phasing effects between the speakers in the monitor. If that treble drop-off is genuine I'd be more concerned about that than the bass roll-off to be honest. A mix that compensates for it could be unpleasantly bright on other systems.

The closest thing to an "industry standard" measurement system is to place the speaker in either an anocheic chamber or a huge space so reflections from walls etc. aren't a factor then to take measurements using a specialist measurement mic that itself has a pretty flat - and known, so it can be compensated for - frequency response.

What matters is frequency response at the listening position in the room you're in. And even then "flat" may not be desirable. Human hearing isn't "flat response", hi-fi speakers and headphones aren't "flat response" and people don't live in echo-free empty spaces. And lots of consumer earbuds/headphones artificially boost bass up a lot anyway, so a slightly bass-light mix might even transfer better to those.

There's also an argument that a heightened mid response can be useful when mixing. The Yamaha NS10 was a very popular and successful near-field in its day, and it had an awful frequency response plot. No bass, not much top, shedloads of squawking mid. It just so happened that lots of people found them really good for making transferable mixes that sounded good to OK on pretty much any playback equipment - a lot of engineers and producers reckoned "If it sounds good on NS10s it'll sound good on anything".

If you're mixing/mastering anticipating playback through club PA systems, then yes, you do need to lnow what the sub-sub-bass might be doing. But then you'll also probably be mixing in mono and hoping the club PA is installed well enough not to create huge phasing issues.