Diffraction be gone

Interesting.

Do you have ASLT or 20-2?

Do you listen with the grill off? (grill should definitely be ON for the towers to avoid those sharp baffle edges)

How close are the speakers to side walls? (4 feet or more away is best)

FWIW: I found a significant improvement in clarity, definition and jaw dropping imaging - all by simply soffit mounting my ATC's - similar to what they do in studios for the mains (it was an expensive project however that nearly cost more than the speakers). With teh saoffit mount my observations were that cymbals sounded more open and natural and vocal/instrument locations tightened in the soundstage. I also found mid bass or male vocals improved their articulation, as well as a more tangible bass. Some GIK tri-traps helped with lower midbass definition/clarity too - although they had little effect on soundstage. (downside is that room modes became more of an issue with the soffit mount - so treating the wall behind the listener becomes important too - and more expense).

My very old Energy Pro 22's (I love these speakers too) had a circular foam surround around the "hyperdome" tweeter (it was about 2 inches wide but fairly thin - 1/4 of an inch of foam) - these speakers imaged like there was no tomorrow - so diffraction be gone is surely on to something! (The hyperdome was great but it was not that reliable unless you fed it really clean music - perhaps this is why Energy no longer make it - sending out replacement tweeters to keep customers happy must have been costly)

One word of caution, however, by adding this pad you will change the dispersion of the tweeter and reduce some of the baffle reinforcement (3 db boost). At the crossover of 3800 Hz, where the tweeter kicks in, wavelengths are around 4 inches - so anything within 2 inches of the center of the tweeter is likely to affect the primary sound too and not just the off axis/diffraction stuff. Above about 6 Khz the pad is probably doing what you want it to (reduce edge diffraction issues coming off the sides of the speakers box). Frankly, I'd check with ATC and see what they say - they consult for pro clients regularly - so I'm sure they have come across this and have an opinion. In essence, a 3db drop in the 4 to 6 Khz range may make the speaker sound less harsh or forward - and you might even like this too, however, you could also do this with an EQ if you wanted.

Here is a picture of the Dual Hyperdome Tweeter - so you get the idea. The faceplate was recessed so that the foam "gasket" sat flush with the baffle. When you consider that a tweeter generally costs a mere $25 in most speakers and that foam can be dented/scratched and will all to easily shows finger marks or will discolor with age - then you can understand why these extra details might be rare in commercially available designs.

a smoothing of peaks and valleys from 2k to 5kHz can be seen from 1 to 3db resulting in a much flatter response curve.

That would be expected. linkwitz lab diffraction measurements show that anything that reduces edge diffraction (smaller baffle, square instead of circular shape, and an off-center tweeter mount) will result in a flatter response.

It is not clear if these slight frequency variations are actually audible. It seems accepted, however, that it somehow confuses the ear/brain as to the precise direction for the source of the sound and hence the "imaging" accuracy. In essence, a point source will image very well but anything reflected within 5 to 10 msec can be detrimental. (Our brain does a careful analysis of the difference in high frequencies arriving in each ear, which is how we are able to tell direction of a sound.)

The science suggests there are three options for great imaging.

1) Tweeter mounted with almost no baffle and away from any possible sharp edges. B&W tweeter on top designs achieve this 2/3 of the way round the tweeter - but undoubtedly will suffer from diffraction off the baffle box below the tweeter but this is very close to the tweeter and may not affect imaging much. Other designs with a small triangular baffle also try to keep the diffractions close to the tweeter. This means that the diffraction signals detected by our ears are very close to the point source of the tweeter and therefore one can still locate the origin of the source fairly precisely.

2) Tweeter mounted in an infinite baffle such as mounting the speaker flush in a wall. In this case, with a smooth transition from the speaker baffle edge to the smooth wall, there is no diffraction at all, PERIOD. Imaging will be as absolutely precise as the recording will allow.

3) Felt or absorptive foam surround around the tweeter. If you can reduce the strength of the diffraction by 10 db then it may become so small that the ear/brain will not detect it from the primary signal and therefore it will no longer confuse the brain as to the precise source of the sound.

In practice either 1 alone or a combination of 1 and 3 will work best. As a rule of thumb, anything that reflects the primary signal with about 7 msec can affect the image (so keeping speakers well away from sharp objects or walls is a good thing id you want a precise image). The brain ignores later arrivals in its quest to assign a location to the source of the sound. In practice there is a big improvement by placing the speakers 3 feet or more away from a wall or an object - after this you still get improvements up to 5 feet away, however, it is diminishing returns after about 3 feet. Speakers that are in a cluttered position and next to sharp corners of furniture or close to a wall will never image properly.

In practice either 1 alone or a combination of 1 and 3 will work best.

Oops I meant to say "In practice either 2 alone or a combination of 1 and 3 will work best."

I did not mention the trade offs but when you have no baffle at all around the tweeter then you lose LF extension. This may not see important but remember that 6" woofers tend to beam above 1Khz and tweeters distort at rather modest SPL's if driven anywhere close to that low....so often there are several conflicting compromises involved in the design choices. B&W top of the speaker mounted tweeters (which lack any baffle boost) are often crossed over quite high say at around 4 Khz - no doubt they would probably distort at all too modest SPL's if driven much lower - so this often means that the 6 inch woofer is already beaming significantly (limited off axis response) by the time the tweeter kicks in (in a sense a smoother off axis frequency response has been traded for precise imaging of a baffle-less tweeter) The huge success of B&W indicates this small compromise is well worth it to many audiophiles because of the precise imaging that it attains.