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In Reply to: Re: Ahh the legend in his own mind TINKERER is back ... posted by kentaja@yahoo.com on August 13, 2006 at 16:33:57:
" All the ills are supposedly tamed with massive amounts of EQ. ""Good designs do not start with bad ideas full of 'fixes' to get the thing to perform. "
RIAA equalization which makes microgroove long playing phonograph records possible 20-20khz....40 db equalization (that's a factor of 10,000:1)
NAB eqalization which makes analog high fidelity magnetic tape recordings possible, 20-20 khz....also about 40 db of equalization.
FM pre-emphesis/de-emphesis which makes high fidelity FM broadcasts possible 75 microseconds, you figure out how many db of equalization that comes out to from 50 hz to 15 khz.
US National Color Television Standards....IF bandpass amplifier section must have properly equalized response required for reception and decoding of the colorburst subcarrier signal while maintianing adjacent channel interference rejection.
Equalization is a valid and long established part of electronics signal processing. Most phonograph records made since the 1950s used considerable equalization tweaking during mixdown. The German term for mixing engineer "Tonmeister" pretty much says it all.
Equalization of the Bose 901 was not a fix of a bad idea, it was an integral part of a very ingenious one where the inventor observed that below the bass resonant frequency, response fell off linearly and could be compensated for with a precision equalizer. Proof that it worked was evidenced during the early 1970s when Bose 901 was among the world champions for producing low frequencies from a commercial loudspeaker for consumer use beating out AR3a and JBL Paragon D44000. The small box was an integral part of the design pushing the system resonance frequeny up to 180 hz where Bose claimed the associatd phase shift was no longer audible. The pentagonal shape of the cabinet reduced internal standing waves. The use of multiple closely coupled drivers eliminated secondary resonances characteristic of individual drivers leaving only the resonances characteristic of the basic driver design to deal with. The similar Bose 802 was widely used by professional installers and engineers who could just as easily have bought other systems like JBL, Altec or EV.
As I said, the overall response was not flat and the speaker could not reproduce the highest octave of sound because the inertal mass of the drivers was too great even with an equalizer. This does not negate the advantages and innovations of the 901. As for its unique radiating properties, it is much closer to the way musical instruments radiate sound into space than conventional speakers and it is uniform as a function of frequency which is also much like the way most musical instruments work. The radiating pattern of the overwhelming majority of high fidelity loudspeakers on the market stinks with virtually all of their high frequency radiation beamed over a very narrow solid angle straight forward. The problem is made even worse by use of 1" domes which are horn loaded as seen by the slight recess around their perimeter. You would be hard pressed to find one which is not off at least 10 to 12 db at 15 khz around 45 degrees off axis. compare that to woofers which are nearly omnidirectional off less than 10 be 180 degrees off axis.
The design offered many unique advantages but it had not been perfected in the embodiment offered to the market and it was decided to cheapen it in the mid 1970s by making it more efficient which allowed it to be marketed to a wider customer base. Undoubtedly this generated far more profits for Bose than had he further refined it into a product designed to compete at the audiophile level. Unfortunately, to do this, the bottom octave had to be sacrificed. Bose began making his own drivers and abandoned wood cabinets for an injection molded plastic one. Given the special shape he needed for his unusual ported design, this was a good choice.
Try to be more objective about the realities of products on the market. If you are an engineer, it is not wise to become emotionally involved with what are only machines. Every one of them has their limitations. It is valuable to learn from both success and failures and there is much knowlegde this professor of Electrical Engineering and Acoustics at MIT brought to this innovative idea.
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- Re: Ahh the legend in his own mind TINKERER is back ... - Soundmind 08/13/0618:56:45 08/13/06 (0)
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