How to diagnose the need for room treatment?

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?

My understanding is that a driver will tend to beam as its diameter approaches or exceeds the wavelength of the sound it is radiating. According to a quick calculation I did, the one inch diameter of your dome tweeter corresponds roughly to the wavelength of a 12 kHz note. So at or near that frequency, and higher, it could be expected that the tweeter's dispersion would narrow considerably, and progressively with higher frequency.

The speaker is spec'd for +/- 30 degrees dispersion, which your listening position clearly satisfies, but we have no way of knowing how rigorously that spec was defined, e.g., if it was intended to cover all frequencies up to 20kHz.

In principle, a similar concern could exist with respect to the mid-range driver, given its 6 inch diameter and 4kHz upper crossover frequency. But I would have higher confidence that the manufacturer's spec for dispersion would be accurate for the mid-range frequencies, than for say 15 to 20kHz which most people can't hear anyway.

So that is the background on why I raised the question, but I think that Shadorne's good response pretty much puts the issue to bed.

Regards,
-- Al

Al,

That is roughly correct but beaming starts a little earlier. If you look at figure 3 you will see that the prototypical 6" woofer and combined midrange should not really be used above 1.8 Khz - like was done in the famous Energy Pro 22 speaker.

So why do we see so many speakers with 6 inch woofer/mids and a tweeter with a crossover much higher than 2 Khz?

Cost is the answer - unfortunately few tweeters can handle SPL requirements at that low crossover point - not without distortion and risk of failure. However to avoid having to add another driver (increased cost/complexity) the designers make do with beaming in the midrange...odd really in what is ostensibly an audiophile design and given we have known about the physics of loudspeakers for donkeys years and considering this frequency region is where our hearing is the most acute and discerning.

Al, Shadorne,

Very informative answers. I wasn't aware of beaming.

Thanks all three for your input. If you don't mind checking back on Sunday, I will try to make time and play with all of the above and post back results. I trust your input will help me make sense of what I measure/hear.

Thanks again for all your valuable input.

Regards,
Horacio

I am in India. It looks like it is not possible to get fiberglass panels over here. Is it possible to use EGG TRAYS which are made of THICK paper to back and the side walls. Thickness of the egg tray could range from 1/10 in to 1/4 of an inch.

EGG TRAY is 1ft by 1ft in dimension has corrugations such that it can fit eggs. It am not sure it works as a absorber or diffuser.

Let me know your opinion.

Paper egg trays are, fundamentally, useless.

Kal