size of the driver

A driver is not characterized just by its size. Some 12 and 15 inch drivers have monster magnets and coils, and have a motor strength-to-cone-mass ratio as good as smaller drivers.

Long cone excursion leads to non-linear spring effect, and distortion. The less excursion the better, which leads to multiple large cone drivers, or, better yet, planars.

04-29-12: Johnnyb53
>04-29-12: Tamule1
>real bass comes from moving a large surface area gently -not a small surface violently . 6.5" is not a woofer size IMO

"Violent" isn't a problem until you reach the linear or physical limits which geometry dictates you do when using such small drivers.

>And you base this opinion on what?

I draw upon personal experience with speakers including transmission lines built with similarly small drivers (I've heard various examples and owned Definitive BP8s when I was young, naive, and less proficient with power tools ) and identify the underlying physics which cause such issues. They get strained at moderate listening levels when the source material contains bass, where that's low bass you get doubling where you hear tones at twice the fundamental frequency due to distortion which although inaccurate isn't too bad, and the IM distortion happening to midrange frequencies is offensive.

These are some of the same reasons "audiophile" speaker demos are done with female vocalists and not orchestral music.

>What then shall we call all those 5.25" and 6.5" drivers that provide real bass extension down to 25-30 Hz?

Having more measurable bass extension at low to moderate listening levels than stand mounted monitors with similar drivers, good marketing, or fiction depending on your perspective.

>You also left out the part about how the back wave is managed, which accounts for why the Atlantic Technology AT-1 extends usable bass to 29 Hz from a pair of 5-1/4" woofers.

Assuming the 88cm^2 Sd and 3.5mm xmax of the 5.25" drivers I used in my example with driver output attenuated per the Stereophile measurements they'd reach their linear limits with program material calling for 94dB 1 meter from the speaker at 60Hz (one driver will net 83dB, two 89db, and the Stereophile nearfield measurement has the drivers -5dB down with the remainder coming from the port/transmission line hybriddrivers and 89dB (one will net 71dB, two 77, and they're 12dB down) at 30Hz.

As stated I like my jazz at a moderate less-than-live 85dBC SPL average which can yield peaks 105-107dB 3 feet from a speaker.

Pulling _Take Five_ from _Time Out_ off the CD and feeding the two channels through second order IIR Butterworth low-pass filters at 60Hz using GNU Octave I find right channel peaks at -10dB below the full-range peaks; or 95-97dB SPL.

The arithmetic explains why such speakers don't work well - up to 9dB shy is off by a factor of 8.

This is also an optimistic simplification. Distortion product SPL is more a function of total driver displacement although the fundamental output is dropping for a given excursion at lower frequencies so you might find only half the total linear excursion is clean.

>Next thing we'll need a disclaimer:
"No violence was committed in the generation of these low frequencies."

I'd like something quantitative such as output levels and distortion numbers for given input frequency + level combinations like independent testers are starting to do with sub-woofers plus a practical frame of reference: In our small and large listening rooms, we could average xx and yy dBC SPL with Sir Solti conducting the Chicago Symphony playing Beethoven 9. Elevator music averages xxdB, the typical middle aged male gets to yydB when his spouse is home, and the average audiophile prefers zzdB in a darkened room with a tumbler of single malt.

My PMC Fb1i Signature speakers have a 6.5" driver and go down to 28 hz. I wouldn't have believed it before got them, but they have a transmission line design and really do go that low. IMHO, it's all about the design.

I currently own - and will continue to into the forseeable future - a pair of Polish built speakers with a 12" woofer/midrange and 12" waveguide(Geddes-based) "fed" by a compression driver. The 12" units supposedly extend to ~1.5kHz, but I can honestly and wholeheartedly say that I've never heard more (or even as much) cohesive sounding speakers as these(save perhaps the Quad's..), nor are the central mids marred by any signs of "beaming" now that we've entered and passed the above mentioned critical 1100Hz. Moreover, there's just something completely beguiling about the way a 12"(or 15"+) woofer produces bass that's simply not equalled by smaller units, be they one their own(per channel) or multiples. The history of these sonic impressions of mine - i.e. the evidence of my stance, if you will - are based on and generalized by a long list of "representatives" on both sides(speakers with either smaller or larger bass/mid units).

That is to say: many of the con's against larger cones (as well as the pro's directed at smaller units) seems to be founded predominantly in theory, no doubt led on in some instances by marketing efforts, and this goes both with regard to the larger cones qualities into bass reproduction as well as their abilities as midrange units. Whenever these discussions break out it's noteworthy how little is said of actually perceived differences that would in some way, or not, confirm the variety of theories on this - a matter I believe of utmost importance; what I find interesting about the theorizing, or least its attempts on this issue, are trying to come about reasons for the reporting on perceived advantages (or disadvantages, for that matter) of larger units, at least with regard to bass reproduction, instead of seeing the theoretical advantages of smaller units not called into (perceived) question.

Based on what I've actually heard, my foremost area of attention, I can only say that larger bass/mid drivers(12-15"), as well as 18"+ sub-only bass drivers, not only merely "does the job," but in many combinations does so with a clear advantage compared to speakers based on smaller bass/mid drivers. It would require a much longer message to come about the different aspects in which I see these advantages - perhaps another time.

"Hoffman's Iron Law". First formulated back in the early 1960's by Anthony Hoffman (the H in KLH), Hoffman's Iron Law is a mathematical formula that was later refined by Thiele and Small, whose work now forms the basis of all modern loudspeaker design.
Hoffman's Iron Law states that the efficiency of a woofer system is directly proportional to its cabinet volume and the cube of its cutoff frequency (the lowest frequency it can usefully reproduce). The obvious implication is that to reduce the cutoff frequency by a factor of two, e.g. from 40 Hz to 20 Hz, while still retaining the same system efficiency, you need to increase the enclosure volume by 23=8 times! In other words, to reproduce ever lower frequencies at the same output level you need an extremely large box! This is why we see so many subwoofers or low eff multidriver towers. Using 5-7 in drivers. Larger woofers are better woofers, larger cabinets are more efficient and produce deeper bass with less thermo compression and Superior transient response. If one compromises size efficiency or range one can make a smaller design.