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.
