Michael: I simply posted comments in agreement with others that had taken the time to share both their personal points of view and / or scientific data pertaining to the situation at hand. Sorry if that offends you.
Karl: Thanks for taking the time to post a response. As i mentioned, it is quite obvious to me that a lot of love and thought went into this product. I hope that this was abundantly clear in my original post.
1) I am aware that they've made great advances in terms of reducing distortion byproducts as excursion increases, but as a general rule, longer excursion still equals more distortion. Some designs are obviously better at this than others. The laws of physics still apply and we can't yet get something for nothing. As you mentioned, there are trade-offs involved in every aspect of speaker design. The end product becomes a balancing act based on what the engineer was willing to sacrifice in order to achieve their desired goals.
2) "I pointed out that while there is a 10dB boost at the amplifier, there is also nearly a 10dB loss in maximum output at the speaker".
What do the losses at the speaker involve? From what i know about such designs, the losses are incurred due to inefficiencies in power transfer below the point of resonance. The end result is a high percentage of power being dissipated as heat. As you stated, the end result might sum to a neutral response, but at the expense of much higher thermal stress.
3) According to your post here, anybody that listens above 90 dB's is "insane". Call me and dozens of other audiophiles that i know "crazy" then. Especially if you are talking about 90 dB's at 1 meter. As far as i'm concerned, spl levels should be taken and compared at the listening position, not at 1 meter. Readings taken at 1 meter are only handy for sake of sensitivity or efficiency ratings, and even then, they don't tell the whole story due to differences in dispersion patterns.
El: The original and second series 901's were a sealed design. The curve for those EQ's is different than that for the series III and all those after that.
Bose obviously had to run the drivers below resonance as the drivers were run full range. Karl is doing the same thing in principle but limiting the top end of the drivers being EQ'd and using a fancier circuit. Due to the fact that the 901 drivers resonated higher in frequency, and they were applying X amount of db's to compensate for the roll-off per octave, the total boost figure for the 901's would be much higher than Karl's design. In the long run, the use of equalization below the point of resonance is nothing new. The end result is that one can increase bass extension by appr half an octave at the expense of increased power requirements, increased power dissipation in the drivers and a lower maximum spl for the same percentage of distortion. It is really a tough balancing act to do correctly and requires very close production tolerances, both in the speaker itself and the correction circuitry being used.
As a side note, Bag End makes use of bass extension technology via a calibrated EQ curve in their subs. They chose drivers that resonated above the intended band of use and then EQ it for flat response below that point. This is a very lossy method and quite out of the ordinary, but has many advantages. Woofers and sub-woofers especially are the only drivers in most speakers were "resonance" or "break up" are considered normal and acceptable, yet most engineers / designers try to avoid that circumstance like the plague with mids and tweeters. Bag End took the high road, but in this case, the efficiency and power requirements of the system was what they were willing to sacrifice to achieve their desired goals. Sean
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