Getting Your Gear Together Honolulu HI

You may believe that the rooms you design sound very good, but unless you consider all of the technical variables for your system, you will never know how much better they could sound.

Speakers & Subwoofers
Lets begin with choosing loudspeakers and work backwards up the signal path. Theres a lot here that you should have already figured out for yourself. Im talking about things like size, look, price, etc. There is also a list of technical criteria that many of you may not even know exists. It applies to both front and surround speakers, but with differing requirements.

First is directivity, which is the ratio of sound a speaker radiates on-axis vs. spherically. In short, directivity tells you how focused or spacious a speaker will sound, how clearly it will reproduce dialog, and how precisely it will image. Rarely will consumer manufacturers publish the directivity index (DI) of their speakers, so heres a chance to show your quality and aggressively pursue them until they do. Once you get the data, go with a DI of 7dB from 500 Hz to 10 kHz in medium-sized rooms and 9dB in larger rooms.

Second is the sound pressure level a speaker will produce. Start by looking for a sensitivity specification. Ideally, it will be given as a number of dB at 2.83 volts and 1 meter. You may find 1 watt/1 meter instead, but that only works if the speaker is 8 ohms. Subtract 7dB from the sensitivity to find out how loud the speaker will play at typical listening distances in a 3,000 ft.3 room. For twice the room volume, subtract 3dB more. For half the volume, subtract 3dB less, etc.

Unfortunately, sensitivity doesnt tell the whole tale. You also need to know a speakers power handling and maximum excursion. Power handling is a long-term average measurement, in watts, of the power a speaker will take before the voice coils melt. Speaker manufacturers are required to specify it for safety reasons and fairness to consumers. Excursion, on the other hand, is a measurement of maximum short-term output on brief dynamic peaks before a speaker goes into massive break-up. Manufacturers will likely not specify it and probably dont know it. Try asking them, and keep asking until you get results.

So how do you figure out if a speaker will play loud enough for your application? Say, for example, you want each main channel to produce a cinema reference level of 105dB. Take a 92dB/2.83 V/1 m speaker in a 3,000 ft.3 room, and subtract 7dB to reach 85dB at the seats. To get to 105dB, the speaker must handle 28 V, or 100 watts. A 6,000 Ft.3 room requires 3dB more, or 200 watts.

Third is sound quality. Much passion has gone into quantifying the sound quality of speakers, and many experts still disagree. There are some knowns, though. If a speakers axial frequency response, which is measured at one point directly in front of the speaker, looks like an accident, then throw that speaker out. Not all listeners are on-axis, though, so also consider the average response across 15...

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