Low freq. from small drivers? Is it possible


Can you get really low freq. (lets say 30 and down) from a small driver (~6 inch? What is the relationship between driver size and frequency? Most speakers today have went away from a large base driver (10 inches or more). Have we really come that far or is it really a compermize?

Any recomendations for smaller floor standers with good bass?

Thanks,

Dr. Ken
drken
Karls...Thanks for the info. For your sake I hope there are enough people willing to spend $20K on speakers to make your effort worthwhile. If they go for multichannel you have it made.

You cite 10 dB as the boost. When Bose did it I seem to remember that the "inverse transfer function" (to use your technical jargon) was about 40 dB. Bose operated the drivers BELOW resonance because of the smoothness of the response in that range. I think he had driver resonance at about 200 Hz. Do you operate (mostly) below resonance?
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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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