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Re: Ultimate realization of this technology

Hi Soundmind

Your talking about “work stuff”.
As the size of a room increases (all other things being the same) so does the difficulty in producing intelligibility at a distance.
The ratio of direct to reflected sound correlates to intelligibility of voices.
If you were in a very live gymnasium or Church etc, you can imagine this situation.
On a stool is a boom box playing conversations.
At a few feet you can understand perfectly well.
You step back doubling the distance and your sound level meter shows the sound level goes down –6dB, following the inverse square law.
As you double the distances you see the sound level stops falling at –6 dB and falls off less as the direct sound becomes closer in level to the reverberant field (the reflected sound bouncing around).
Far away, the sound level falls very slowly and your dominated by reverberant sound.
This far away, you hear a jumble of voice like sounds, but you can’t make anything out.
This has the same spectrum as the voices but is randomly correlated with the original.
With flat room absorption, the spectrum of the reverberant field is the same as the speaker’s acoustic power spectrum (which is not the same as on axis response but the total acoustic power).

Most people prefer (with music) to have the spectrum of the reverberant field roughly the same as the on axis response. This requires constant directivity with constant acoustic power if one also wants flat response on axis.
To maximize the distance which one transitions into the reverberant field (loosing intelligibility), one should confine the radiation angle to where the people are, or to maximize the distance before it hits the walls, floor or ceiling. This maximizes the direct field.

I design speakers to solve these problems in commercial spaces, some links about one that does it very well is below. To accomplish this requires a “different approach” which also solves several other problems.
A drawing and explanation is in the tapped horn paper. Fwiw, this speaker (unlike most hifi speakers) can reproduce a square wave from about 220Hz to about 2600Hz.
If you down load the CLF viewer and the SH-50 data file, you see most every aspect of it including the response at any angle off axis.

http://www.danleysoundlabs.com/knowledge baSE.htm

http://www.danleysoundlabs.com/pdf/danley_tapped.pdf

http://www.danleysoundlabs.com/pdf/Danley SH-50 - Pat Brown - Live Sound May-2006.pdf


http://www.danleysoundlabs.com/pdf/Danley SH-50 Spec Sheet_r2.pdf


In home stereo, one faces the same issues except they are not bad enough to prevent intelligibility of voices. Just like the first example, the reverberant sound “sounds like” the original signal but just like the other case, it competes /obscures the actual signal even if it “sounds like” the original.
With a dome /cone speaker in the speaker position in my living room, the measured response is altered by about + - 15 dB worse than 2M anechoic due to the reflections adding and canceling (which for the most part can’t be EQ’d either). A 30 dB spread in the peak to dip is 1000 to 1 in energy variation.
With the SH-50 in the same position, the response is only + - 4 dB worse than 2M anechoic.
This reduction in near field reflections (along with the time coherence) makes for a startlingly better stereo image than the dome /cone (when it is present in the recording)
Sadly, as much as I love hifi, as good as they sound, there are terribly few who could tolerate a speaker that large, so they are sold where what they do acoustically matters and where they aren’t that big.

Tom

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