Low freq. from small drivers? Is it possible

Sean...The original (sealed) Bose speakers are the only ones that I ever thought sounded good. All speakers generate output below the driver resonance, and many use equalization, but designers usually try to get resonance down as much as possible so as to minimize operation below resonance. The Bose idea was to deliberately push the resonance up, and equalize the hell out of the signal. I think that the speakers we are talking about here take somewhat the same approach, but not in such an extreme way as Bose.

Again I note that Bose's objective was not bass extension, but rather smoothness of the response curve because of the inherent smoothness of the drivers response when operating below resonance. LF roll off was taken care of by the drastic LF boost.

I had original 1st series 901's back in the 1970's. Harry Pearson stated that the 901's are the only speaker that has gotten worse with each new generation. I guess that means that he thinks that the 1st were the best. I would tend to agree.

As a side note, i've still got all of the drivers from those 901's. Those used nine 8 ohm drivers wired in a series-parallel circuit to achieve a nominal 8 ohm impedance. To be specific, they used 3 parallel banks of 3 drivers wired in series. The second series and up used nine 1 ohm drivers all wired in series. If you blew a driver with the first series, you could still use the speakers. If you blow a driver with any 901 after that, one driver takes the whole speaker down, kind of like old style Christmas tree lights. Sean
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Sean,

Sorry, I was unclear about the "loss" of 10dB at the speaker. I should have said "reduction" instead. In other words, the average music SPL that the speaker is able to deliver is almost 10dB less when used with the BOMB. This is, of course, due to the extra excursion needed with the boost. In other words, you cannot turn the volume knob up as high with the BOMBs in the system, because the drivers are now excursion-limited to a greater degree than previously. This naturally has the effect of simultaneously limiting the (average) allowable power input to the speaker from the amp. So while the spectral distribution of power is shifted, its maximum allowable value is not significantly increased overall, and may even be reduced depending on the program material. Of course, the overall system efficiency is reduced also, again depending on the program material. Hope this makes sense.

I mean no offense by my use of the term "sane". Trust me, I've always been a bit crazy myself, and have been known to dial the volume to 11 on more than a few occasions. I was only trying to make the point that not many people listen at 90dB average SPL. Most of them don't even own SPL meters, so wouldn't even know. I trust that you have one and have used it on a variety of program material, and so know what levels you listen at. (If you truly exceed 90dB average regularly, the physician in me would advise you to turn it down a little, for your ears' sake. This means you are likely running peaks in excess of 110dB, and there's no question about the long-term effects of that practice. Again, no insult intended, merely caution.)

I would also guess that if you took a wide sample of audiophiles, the vast majority of them would show a continuous average SPL at the chair of 80 +/-5 dB. I certainly don't know many folks who exceed this regularly.

Sheesh, being compared to Bose 901's. Now that really hurts.

Best Regards,
Karl Schuemann
AudioMachina

Thanks for your very up-front response Karl. As fine of a speaker as you have been able to produce, your comments varify what i and several others have stated. That is, obtaining extreme low bass out of a smaller driver comes at the expense of some other area of operation. I applaud your honesty and integrity, both in your responses here and in the design attributes of your product.

As a side note, neither Mr Dartford or myself were actually making an "apples to apples" comparison between your speaker and the 901's as much as we were discussing the various manners that technology can be applied and how it is actually used in various products.

I do have one question for you though. Have you ever tried running these actively crossed? I'm curious as to what your thoughts / experiences were in this regards IF you tried that.

Other than that, i do remember you posting positively about sealed box designs in the past and contributing some excellent information / comments in various threads. I knew that i always respected your opinions and now i know why. That is, we basically agree. At least on this specific issue : ) Sean
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Sean,

When you ask if I've tried them actively crossed over, I assume you mean to a sub on the low end. The answer is that I haven't. It is my opinion, having played with this stuff for a long time, that putting any crossover on the low side of the midrange drivers, anywhere but in the low bass, causes more problems than it solves. The transition from woofer to midrange is always audible.

Many people (and I would guess that you would be in this camp) would rather run subs with active crossovers on both high and low sides, primarily for the reason we have been discussing: limiting excursion in the midrange drivers. But there is another way that is superior, in my opinion.

First of all, I will state that a subwoofer should be crossed over as low as humanly possible, for all kinds of reasons. 100Hz is way too high, and 80Hz is pushing it. Given that this is the case (and I would be very surprised to hear anyone disagree with this, if they've had experience in this area and have good ears), then it makes far more sense to let the speaker itself provide the high-pass function. In the case of the UM, its natural rolloff is essentially equivalent to a 12 dB/octave Butterworth at just under 70 Hz. Of course, this only works with a sealed-box monitor, which is self-limiting in the deep bass, but of course that is exactly what I intended from the start.

This approach is exactly equivalent to an electrical solution, but with the advantage of no added electronics and their inevitable colorations. It allows perfect compatibility with the RELs and other similar subs which are designed for exactly this approach. In my experience, this is the only way of connecting a subwoofer that actually achieves the goals of making the transition sonically invisible and causing no sonic degradation to the main monitors.

Best Regards,
Karl Schuemann
AudioMachina