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Re: A More Realistic Presentation...

If you are actually going to engineer a high fidelity loudspeaker system rather than merely throw one together from parts (as most probably are) one problem you ought to consider is how you are going to deal with room reflections. Currently, a popular approach (although not an exclusive one) seems to be to reduce them to a minimum. This entails designing speakers to be located away from walls and restricting their radiation pattern as much as possible. This approach IMO has several major disadvantages. For one thing, it is very difficult to restrict low frequency dispersion as the diameter of the woofer is much smaller than the wavelength of the frequencies in its range, it has a natural tendency to be nearly omnidirectional. As you go up in frequency, the dispersion can be rather irregular depending on the size of the midrange driver. At high frequencies, it is relatively easy to restrict dispersion and most modern dome tweeters do. You can see this by the fact that they invariably have a small groove around the perimeter of the dome which semi-horn loads it increasing efficiency at the expense of dispersion. Some domes even sit in a small well. Most are down a good 5 to 10 db just 30% off axis at 15 khz. This includes the ScanSpeak 9900 Revelator, one of the most expensive dome tweeters available. Contrast this with the other extreme, the AR3a tweeter being the widest dispersion dome tweeter I know of. It's 3/4" not 1" or 1 1/4" which improves dispersion and there is no such groove. This tweeter is down only 5 db 60 degrees off axis at 15 khz compared to its on axis response. Even so, to create a speaker system with even wider dispersion, AR developed the LST (cloned by Cello) which incorporated 4 AR3a tweeters, two on panels angled 45 degrees to either side of the front. The restrictive HF dispersion of most speaker systems reduces the optimal location in the room for listening, the so called sweet spot and as soon as you move away from it, FR changes very rapidly with HF response falling off at a steep rate. Placement becomes critical too. Read the Stereophile review of Wilson Sophia II and you will see the manufacturer adjusts the location of the speaker by moving it 1/4 inch at a time to tune it to the room. Another disadvantage is that you don't get bass reinforcement which wall or corner placement offers. This often requires an additional subwoofer but if you only use one, it will be located a sufficient distance from at least one of the main speakers to have a significant interference pattern around the crossover freqeuncy with at least one of them resulting in an irregular FR in that region. The only solution to this is a crossover network with a very steep slope such as a digital active network and bi or tri amplification or to buy two subwoofers and place each close to a main speaker. Bipolar flat panel systems and dynamic drivers systems with rear firing tweeters take an opposite approach but do not attempt to optimise the reflections by adjusting their radiation patterns and FR to compensate for the particular room or location they are installed in. In most situations, neither approach achieves both flat on axis FR and flat total power transfer simultaneously. They are also very dissimilar to the way most musical instruments radiate energy. Therefore it is hardly surprising that they don't sound like the musical instruments they are supposed to reproduce.

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