1) According to my bookish knowledge the average adult human hearing capability is from 20Hz to 20 KHz. Most loudspeakers give an output of highs much higher than mentioned above so highs are not an issue. But how important is it for the loudspeaker to produce levels as close to 20hz? I know that the subwoofers do this.
without any distortion, I honestly can not even hear below around 24hz. My sub is very low distortion. It's only when distortion products (known as doubling) are formed can I hear tones that low, and technically what i'm hearing is double the frequency - IE 48hz. HOWEVER we most certainly "feel" and experience infrasonic bass. It's a unique experience, and some movies definitely dig at least as low as 12hz or so, and some movies go even lower into the 7hz type ranges. Many commercial subwoofers will cut this out of the signal before it reaches the amplifier, in order to protect the driver from overexcursion. If you've got enough "air moving ability". you don't need to protect the driver in that capacity, because there's so many drivers contributing to output that the full signal is converted to acoustic energy without breaking any subwoofers.
An added, although not necessarily audible advantage of not using a high pass filter, is that the driver experiences less phase shift / lower group delay.
As for high frequencies, they're mostly inconsequential, but there might be slight differences in some HF sounds based on the transfer function of the speaker. Berylium tweeters as well as Ribbon Tweeters extend well beyond the audible limtis of our ears, whereas other materials might be about 1 or 2db down by 20hz - but how it sounds is a function of distortion at audible frequencies, not extension to inaudible frequencies.
THe thing ot note is that at high frequencies, the balance between off axis and on axis response is what determines "realistic reproduction". IN some rooms, flat response is a bad idea up high because reflections tilt the power response upwards. As a general rule, don't put too much stock into specifications above 10khz. I can only even hear up to around 14.5khz, personally.
2) JBL synthesis does not have dedicated center speakers. So does this mean the audio signal intended for the center speaker otherwise would be in fact coming out of the loudspeakers. So won’t this hamper the sound quality.?
No, it would just mean the center speaker is identical to the left/right speakers, which is optimal. You NEED acoustically transparent screen material.
3) TAD reference one gives the best range of frequency responses amongst all. But then how do I use them in a 7 ch home theater. they have no other speakers like the center or sub or surround?
There is no matching sub, and if there was, I suspect it would be overpriced.
What you would do is three of TAD Reference Ones, up front.
Mated to four TAD Reference Ones or Compact References, or Pioneer S-2EX on the sides and back.
4) All speakers except the subwoofers I guess require less than 1000W of output amplifier power (RMS). So will it be a good idea to keep the 2000W amplifier for every speaker or use that for 2 speakers combined.?
2000W is a lot of power. Enough to blow even the most robust midrange driver with the right signal. Quite frankly you don't need this sort of power - this is the territory of LARGE professional venues like Cinemas and Stadiums.
In a home, even 250w into 4 ohms is often the most power you'll ever use. I use an amp rated at about 575w into 8 ohm/750w into 4 ohm/1400w into 2 ohm and I can not say decisively if I've yet used any more unclipped power than my 100 watt into 8 ohm receiver. For subs however, limitless headroom is a great idea, because the LFE section of movies is 10db higher in maximum level.
Also bear in mind that the load presented by the speaker is a big determining factor in how much power you need, along with your distance. My speakers are about 88db, nominal 6 ohm with some dips near 4 ohm. About an average load and my 100w receiver drove them fine. If I were using Apogee Scintillas, I bet my high power amp would make a big difference compared to the receiver. If I were using Gedlee Abbeys, I could probably get away with a 50 watt amp with no current reserves and it would probably give me the same dynamics.
