How to diagnose the need for room treatment?

Nice work, freak!

The peaks @ 31.5hz & 80hz are probably the biggest concerns I see. In room high frequency plots tend to drop off steeply as you see, so not as surprising(at highest frequencies) as you might expect. However your overall picture of bass all + and treble all - doesn't seem like it would sound very natural. Do you get the sense that your "bass is turned up, and treble down?" Speaker placement & seating changes could affect this greatly. Since you are already far out from back wall, I'm guessing that current placement is exciting some room nodes. Experiment in small increments(i.e. 6in).
Lastly, not a big problem, but by definition, shouldn't 1000hz = 0? Cheers,
Spencer

SPL meter readings could be a LOT worse - a few observations.....

1)5db bump at 32 hz will add just a little sense of deep bottom end, not a bad thing actually for many.
2)3.5 db boots at 85db will add to the sense of bass, again not a bad thing, and the 2.0 db boost at 60hz will reinforce it. BUT...

3)Then you have a broad gently dip in the upper bass, lower midrange. Not a bad thing in itself, but might serve to over emphasize the appearance of the 'boosted' bass, and make it sound heavier than it actuall is.

4) After a normal 1 1/3d octave centering at 1000hz you have a broad and very audible dip in the mid/upper mid/highsrange which is going to make your speakers very 'forgiving', especially when using digital sources, but many might think the sound is dullish.

5)most speajers display the sharp roll off in the highs abouve 10K. I think mostly because you are comparing your 'in room specs' with anechoic measurements made by the manufacturer either 1 or 2 meters from the speakers.

I agree with Sbank about the effect of speaker placement, but what I think of when I see your comments about listening distance from speaker to speaker and speaker to listening chair, is not so much making a major correction to the SPL levels you mentioned because I don't see that so much a big deal. Some changes might be made in the bass, but the broad nature of the dips in the mids and highs suggest to me that the speakers are the cause, or the room surfaces are over damped.

What I do think you can do (if your wife and situation allows) is to get some space between your speakers. For example, I typically listen to dynamic speakers that are about one foot+/- closer together than they are apart. In your case that would be about 10 feet. If you thin that they are too close to the side walls you can simply try toeing the speaker in towards your seat, even substantially past it, to control 1st sidewall reflections. What you should get by doing this is getting a vastly improved since of sound stage in all dimensions.

FWIW.

SPL meter readings could be a LOT worse - a few observations.....

No kidding. The bass response is superb - almost to the point of being suspicious - hardly any room is ever that good without being treated.The broad dip in the midrange is probably just "midrange scoop" - most speakers are weak off axis in the upper midrange and your ears and SPL meter will sense this.

Since you have positioned your speakers in the middle of the room (15 feet out) they will not excite the room length mode nor its harmonics - as the speakers sit at a pressure null. I think this is the principal reason you are getting such good bass - as usual "acoustic physics" dictates how it will sound...

Good stuff!

Looking at the room dimensions and its modes I found f1 for length is 34 Hz and f0 for width is 36 Hz. Close enough to 31.5 Hz?
Also f3 for length is 69 Hz and f4 is 86 Hz, plus f1 for width is 72 Hz and f0 for height is 78 Hz. Might be a good shot at the 63 & 80 Hz bump?

Further comments following yur comments:
- room is not overdamped. If anything, it's underdamped. Hard stone floors with no rugs (for now). Brick walls. No drapes (for now).
- Cannot spread the speakers further apart. Room circulaion happens at the side of each speaker and it would be unpractical to change that (unless I change the whole setup, that is).
- I swear, no treatments are in place other than a bookcase and a sofa on the side first reflection points.
- to me it doesn't sound dull...but maybe it's me being used to it.

Will try playing around with positioning again next weekend.
Keep the good ideas flowing!

Cheers,
Horacio

most speakers display the sharp roll off in the highs above 10K. I think mostly because you are comparing your 'in room specs' with anechoic measurements made by the manufacturer either 1 or 2 meters from the speakers.

I wonder if treble beaming could be a factor as well, assuming the tweeters are pointed straight ahead. Should be easy enough to check, by toeing the speakers in a little, and re-measuring.

I had looked at the specs for the speakers, and they specify a horizontal dispersion covering a 60 degree arc (meaning +/- 30 degrees from straight ahead). Which would make toe-in especially important were they to be moved further apart.

It's unfortunate, though, that it's impractical to move them further apart; I agree with Newbee that it would be likely to improve imaging considerably.

Regards,
-- Al