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In Reply to: RE: Some speakers sound good no matter where you sit posted by Frihed89 on December 16, 2009 at 19:17:58
Very interesting example you give!
The LS3/5a has very good power response, but at the expense of on-axis response. This is deliberate and in my opinion is the correct choice. You've no doubt heard of the "BBC Dip", a mild dip in the 3-4 kHz ballpark. This has been mis-understood to be a psychoacoustic compensation of some type. Instead, it corrects the power response by decreasing the tweeter's output in the region just above the crossover, where its radiation pattern is the widest.
What you heard when you walked around the LS3/5a was a combination of an unusually wide overall radiation pattern with unusually good power response.
Me being a dealer makes you leery?? It gets worse... I'm a manufacturer too.
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"What did the Romans ever do for us?"
Sound Power is a measure of the acoustic output of a device - in the case of a loudspeaker it is usually given relative to 1 Watt of broadband (pink noise) band limited to the specified pass band of the loudspeaker. This way a satellite speaker would not be penalized by its inability to produce the lowest frequencies. The units (confusingly) are also given in dB - but with a reference level of one picowatt (10E-12).
Since, at least for home use, listening rooms are mostly somewhat reverberant, and virtually all reflected energy occurs before 80msec, the sound power determines the "loudness" of the speaker. Unlike the pressure sensitive specification (xdB @ 1 meter @ 1 Watt), the sound power specification for sensitivity does not penalize dipole, omnis, and line arrays, while equalizing the effect of horns, phased arrays and waveguide loudspeakers.
The standard xdB @ 1 meter @ 1 Watt is a valid measurement for drivers (measured on an infinite baffle) and Professional (PA) loudspeakers because the important aspect of the performance is the the pressure they can create - at the listeners seat in a free field - no reflections.
Sometime once the ability to measure the sound power of a loudspeaker is more available - some mfg do this already - it may become a common specification. A 1% (fairly efficient) loudspeaker would be rated at 100dB, where a common 0.1% efficient loudspeaker would have a 90dB rating.
Note, this measurement is very difficult to make above 5KHz requiring thousands of points. There are some very trick techniques B&K have developed to make this measurement - none of them cheap.
The "power response" is the summed omnidirectional response of the loudspeaker; that is, the combined total of its output in all directions. The on-axis response is the speaker's output in one direction only.
Me being a dealer makes you leery?? It gets worse... I'm a manufacturer too.
Edits: 12/17/09 12/17/09
I always wondered about the "dip". Some people point to it scornfully, but I find this speaker to be very well-integrated, better than most, and I don't actually hear the dip. It seems smooth in the cross over region to my ears.
"What did the Romans ever do for us?"
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