garyrc Posted February 22, 2011 Share Posted February 22, 2011 It seems to me that someone should be challenging these statements but maybe its due to lack of information as was noted previously. Thanks, Nic Go ahead and get the sub first. As to amplifiers (or receivers), here is the wattage I once figured was needed for each separate speaker, with all channels operating (some people allow you to cut the power needs in half to feed to each of two channels, or 1/4 for 4 channels, etc., but what if a very loud sound is way off to one side, and uses mainly just one channel?) with a speaker of typical efficiency [90 dB @ 1watt (2.73v into 8 Ohms) @ 1M). You can convert these figures to match any speakers, remembering that a 3 dB change is like doubling or halving the wattage, depending on which way you are going (I don't happen to know the sensitivity of your speakers). The typical 90 dB @ 1 w @ 1M in an anechoic chamber is increased to about 93 dB by "room gain" in a 3,000 cu. ft. room (see ahead), then reduced by 3 dB for every doubling of distance (INSIDE ... it would be 6 dB for every doubling of distance OUTSIDE). So at about 13 feet away (two doublings) we lose 6 dB, lowering our previously raised figure down to 87 dB @ 1 watt. Keep in mind that all rooms are a bit different, and there will be high and low bass pressure zones in the room. Moving on up in sound pressure level (almost equivalent to "loudness"), we need 2 watts at 90 dB, 16 watts at 99 dB (pretty loud), but 128 watts at the 108dB level THX often measures in theaters (e.g., in tests while running The Empire Strikes Back -- in the deep bass, they got 110 dB, but you will have a powered sub for most or all of that range). When I've measured this very loud level in a listening room or a theater, it has been a "broad" peak, staying at 108 dB or so for anywhere from 1/2 second to 3 seconds, so I think one's amp should have a rated power of at least that 128 watt level, when using speakers of typical efficiency. To get the 115 dB peaks Paul Klipsch advocated, you would need about 341 watts for just an instant into the typical speaker (but only 63 watts into his beloved Klipschorn). Some approx 130 watt amps can squeeze out that 341, or so, if the duration is short enough. How long is an instant? Maybe 1/2 second? That's the way it looks on my meter. According to Don Keele (a former chief engineer at Klipsch) some amps can produce, without clipping, a peak of 10 dB over their rated power (by coincidence, about 10 times the wattage). He is probably talking in terms of a few milleseconds, though, and was writing back when good amp companies didn't use specs as misleading as many manufacturers of Home Theater and Car Audio do now. This would mean that an excelent 130 watt amp might produce 1,300 watts for that tiny slice of time, which into the typical speaker we are talking about, would produce about 121 dB for a split second, if the speaker didn't burn out. Keele's table lists Heritage speakers only, which are much more efficient (6 to 14 dB) than the typical speaker, but if you want to look at it, it is in Dope from Hope Vol 16, No. 1, January 1977. To be safe -- to avoid clipping that can take out your tweeters -- a more powerful amp might be a good investment, perhaps one that is rated at 300 watts or more. Quote Link to comment Share on other sites More sharing options...
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