Placing DR250's based on vertical dispersion

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telecast
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Placing DR250's based on vertical dispersion

#1 Post by telecast » Fri Nov 10, 2006 2:33 pm

Am I doing this correctly?

The plans for the 250 state the vertical dispersion is about -6dB @ 10 deg. off-axis. A 10 deg. slope equates to about 8" in a 4' run.

If you place the cabinets on poles and leave the bottom of the tweeters about 5' off the floor, the 10 deg. slope is roughly 42" high about 8' from the cabinet. This seems to be a reasonable height for seated listeners.

If the cabinet is 6' off the floor, the slope reaches 42" at about 14'.

The 42" height is about 5' from the speaker if it's set at 4.5' high.

The questions: in closely seated rooms where the nearest audience is within 5-6' feet of a speaker, is it better to ride them low, or are they going to blast them out of the room?

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#2 Post by Bill Fitzmaurice » Fri Nov 10, 2006 3:18 pm

Vertical dispersion varies with frequency, and with a vertical array of either tweeters or cabinets it varies a lot . The -6dB at 10 degrees off-axis figure is above where the tweeter array is at least 3 wavelengths high, or about 2.3kHz. Below that it widens, to omni-directonal below 400 Hz or so. Place the center of the box somewhat above the ear level of the audience or it will be too much for those close in to handle. The seated audience further back won't have a problem hearing them.

When you go to two cabs high the potential minimum dispersion angle drops to about 1.2kHz, while the frequency where the array is directional drops to about 200 Hz. The more cabs you add the lower those two frequencies go. If you have enough boxes the array becomes so directional in the vertical plane that you have to aim the lower boxes downward at the near audience, while the upper boxes aim to the back of the soundfeld. This a 'J' array. The best thing about vertical arrays is that no matter how many boxes you go high the horizontal dispersion is the same as with a single cab.

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