How to diagnose the need for room treatment?

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.

Only very high up (at 10 Khz and above), however,the 804S is a typical B&W with the "midrange scoop" - they run the excessively large midrange up to 4 Khz and the tweeter has no waveguide. This means you get beaming on the midrange and which causes the mids to lose energy between 1khz and 4Khz when in a room. Above 4Khz the energy returns as the tweeter takes over with its typical wide dispersion pattern in the absence of a waveguide.The power response would show a "scoop" in the midrange and a stereophile horizontal dispersion plot would show this hole at 60 degrees off axis. Perceptively this sounds laid back in the mids but with plenty of presence detail - it creates a very nice sound with emphasis on articulation that B&W is known for.

The only B&W's I know that do not exhibit this "midrange scoop" are the B&W silver signature, the B&W 805N (Nautilus and not the "S" version) and their top of the line 4 way Nautilus. It is actually not uncommon for most two ways with large 6 inch midranges and a tweeter crossed over high to sound this way.

The in room HF roll off is quite typical anyway - that would be completely normal for a room that size.

Here is a useful chart to explain how the speaker will sound. You can see why B&W would choose to voice it this particular way: bass string pluck, drum and guitar attack and vocal presence will all be increased- giving the impression of more detail compared to a flat power response.

Of course some people believe that measurements are like the zodiac and reading the position of planets ....i.e. "completely meaningless" ....just don't tell that to the engineers mixing/mastering your music. They use many rules of thumb based on measurements - a good engineer will know exactly what to do to create a desired effect and so will a speaker designer....

Shadorne -- Thanks for the good explanation and the good reference!

Regards,
-- Al

Shadrone/Almarg - Good point about beaming in HF and the effect of tinkering with toe-in. But with speakers 11 ft away, and with only a six ft spread, you really are not that far off axis to begin with.

Shadrone, "The bass response is superb...". Obviously I agree, but let me say that I never thought it was suspicious. It actually resembled my bass frequencies before I tweeked the set up a bit (without using any acoustic crutches, which I still do not need). For fun, and for illustration of the benefits of position tweaking for Lewinskih.

My set up is as follows, in a 13.5x19.5x9 ft room with the speakers 58" from the wall behind them, 9' apart and the listening spot (ear location) at either 52" or 36" from the back wall.

........52"....36"
1000 0db db0
200hz 0db 0 db
160 -1db 0 db
125 +2db +3db
100 +1db -2db
80 0db -2db
60 -2db -1db
50 -5db -4db
40 -4db -3db
32 +1db +4db

One might think that the bass response at 36 inches would be better because it is smoother and it has some beneficial (I think) boost at 32hz, like the poster. But to my ears, any linearity one might loose, the gain in imaging by moving the listening position forward 16 inches was huge.

Shadrone, I want to thank you for bringing to my attention something (some time ago in another post) about the creation of a null on the center line of the room. I've since moved my listening position and speakers off center line and it has helped in getting a more balanced frequency response whereas nulls had previously been a problem.

IMHO, of course, just a mid-day stream of (un)consciousness. :-)

Nice.

Newbee: thanks for sharing your experience in your room. Your freq response does resemble indeed the shape of mine!BTW, how far is the listening position from the speakers?

Al: the speakers are indeed facing straight ahead. I gather beaming refers to high freq, right? Shadorne's [very interesting] explanation seems to suggest beaming in the mids. I have no clue what the dispersion of the mids driver is. Anyway, as Newbee said, at 11 ft away it would seem dispersion would be wide enough, right?

Bottom line, what I'm taking away is:
a) frequency response looks "good enough". No need to get into bass traps, resonators, diffusors, etc.
b) imaging is likely to be improved by moving speakers further apart (will try it for fun)
c) playing with speaker location might improve things some, particularly if they are exciting a room mode

Are these fair takeaways?

Thank you!!