Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.1 6/24/83; site alice.UUCP Path: utzoo!watmath!clyde!burl!ulysses!allegra!alice!ark From: ark@alice.UUCP (Andrew Koenig) Newsgroups: net.audio Subject: Reply to Herb Chong (A/B CD, Bose 901) Message-ID: <3623@alice.UUCP> Date: Tue, 23-Apr-85 13:01:55 EST Article-I.D.: alice.3623 Posted: Tue Apr 23 13:01:55 1985 Date-Received: Wed, 24-Apr-85 03:40:45 EST Organization: Bell Labs, Murray Hill Lines: 109 Herb Chong made the following claim in a prior article: > The BOSE tends to be very forgiving of suboptimal sources, and might > lack the resolution to differentiate between the players. I asked him for evidence to support his claim. He responded by giving me arguments (not evidence) to support a completely different claim -- namely, that he thinks Bose 901's have significant design problems. Here's what he says, and here are my comments on his remarks. > for starters, by its very design, the Bose 901's are nonlinear phase > transducers. I'm not sure what this statement means. Is this somehow supposed to summarize what follows? > the primary sound is from the rear speakers which reflect > off of the walls and back into the listening area. great cancellations > occur between the back sound wave and the one from the front speaker. This is true of any loudspeaker in any room with partially reflecting walls, floor, or ceiling -- in other words, any room but an anechoic chamber. Believe me, having an anechoic chamber for a living room would be very uncomfortable indeed! It is far from obvious to me that these problems should be any more of a problem with 901's than anything else. > there are 8 drivers in the back. even if each were an ideal point > source, the combined is anything but, and after reflecting off of > uncontrolled wall surfaces with absorption curves that can be wildly > different between setups, flat freqency response can't be guaranteed > even with equalization. So far, you haven't said anything that isn't true of any loudspeaker. > which brings up another point, the supplied > equalizer. the drivers in the 901's are 5 inches nominal diameter. I think they're four inches. > equalization must be supplied to bring up the low end and the high end > to get flat response. this also means that the 5" drivers are being used > well above 10K. yes, plenty of boost will even allow a 10" woofer > to play a 15K tone decently, but how much power do you have to supply > when the natural roll-off of the driver is 6dB/octave above 5K? Answer: about 10 dB. No problem so far. Especially when you realize that almost none of the energy in music is above 5K. > so you put > high power voice-coils in, as Bose did, which increases mass, which > decreases the natural roll-off frequency. No, you ignore the problem, because it isn't a problem. > fortunately, he uses a sophisticated > ducting system to achieve decent low frequency response without equalization, > but then massive phase shifts are produced, and the air from the ducts > are such high velocity that you can sometimes hear them whistling (depends > upon how much other frequencies are being reproduced at the same time). And here I thought I had birds in the yard! :-) The surface area of nine 4-inch drivers is the same as the surface area of one 12-inch driver. Nine 4-inch drivers in a carefully-designed ported enclosure should therefore have about the same bass problems (or lack thereof) as a 12-inch woofer in a bass-reflex cabinet, something that we see all the time. > the direct/reflecting principle is very interesting and has some theoretical > advantages, but they are hardly ever realized in practice. Perhaps the biggest advantage is that it is much easier to design an active equalizer that goes ahead of the power amp than it is to design a passive crossover network that comes after the power amp. Yes, it is possible to use an active crossover network, with the attendant requirement for multiple power amplifiers, but that gets much more expensive. > the equalizer > removes some of the variables, but using electrostatic elements and > properly designed conventional woofer would have been better from the > point of view of reduced driver mass and little or no equalization > in the high frequencies. Evidence, please. > of course, electrostatic elements have a whole > set of problems of their own, but they are more appropriate for another > discussion. the type of drivers that Omar Bose should have used given > his design requirements were horrendously expensive back when he started > and notoriously unreliable. quads were about the only option. Every loudspeaker design has its problems. If there were a design with no problems, no one would build anything else! Therefore, even if your comments indicate serious problems with the Bose 901 design (which they do not), this information is only relevant if: 1. the problems actually affect the ability of people to hear differences between other components when using these speakers, and 2. other speakers do not generally have other problems that similarly prevent people from hearing differences between other components. By the way, you spelled Dr. Bose's given name wrong.