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What Is the Real Lowest Audible Frequency & Best Subs to Achieve It?

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Don Gspann:
I'm with Art on this.  Just because the rise time is slow compared to higher frequencies doesn't mean that it doesn't experience a transient event. A transient doesn't have to have instantaneous acceleration.  It often does or comes close, but that doesn't mean the woofer isn't experiencing the fastest acceleration and deceleration of its world.  It's all relative.  Some woofers can accelerate and decelerate faster and better than others, so yes, transient response is appropriate  And a little time delay on the other speakers just makes things sound really nice.  

I'd like to add, that from my experience with them, and based on the use of the servo motor, they actually have an easier time going lower, rather than higher. Conventional cones still have a harder time the lower they go.

Don Gspann:
   2.   transient - (physics) a short-lived oscillation in a system caused by a sudden change of voltage or current or load
natural philosophy, physics - the science of matter and energy and their interactions; "his favorite subject was physics"
oscillation, vibration - (physics) a regular periodic variation in value about a mean

jeff harrell:
i started working on building an audiophile home speaker system back around 1986. i went with the Dynaudio 30W100 12" woofer that was said to go to 20HZ. my dad had a HP frequency generator and i ran it into my amp and even though i dont remember how loud it was it did go to 20 and i remember turining the dial to 1hz and watching the cone move but not hearing anything. i had put the woof in a "7 cu.ft." sealed box per dynaudios recomendation for a flat response to 20hz. the bass isnt punchy but its real detailed. eventually i was informed that i could use a 3.5 cu.ft. cabnet filled with polyester fiber fill and swithced to a smaller box. i have heard a many a time that you need a real big room to reproduce a 20hz note correctly. just for your info i use an ETON 7-380 hex mid , ACCUTON C-25-6-13 tweeter. x over points 125 & 1.2K. this system is not meant to be played loud cause the tweet is fragile. heres a pic of the 12" woof woof ........ tweet !!!

Bob Somers:
It just seems to my eye (just an educated guess not based on any measurements) from photos I've seen that the external servo motor Danley used is a much, much larger motor than what could fit into the "motor" portion of a conventional voice coil speaker and I would think that a cone driven properly by such an external motor would be likely to move a lot more air than a conventional voice coil driver with the same cone area because of what appears to be the much larger power that a big external motor could provide.

If I'm wrong about that, and I may be, which off the shelf woofers now available could equal or exceed or at least come very close to the displacement volume of the Danley-type external motor with attached cone that was used in, say, the Contrabass?

Art Welter:
Bob Somers wrote on Wed, 02 March 2011 15:48
It just seems to my eye (just an educated guess not based on any measurements) from photos I've seen that the external servo motor Danley used is a much, much larger motor than what could fit into the "motor" portion of a conventional voice coil speaker and I would think that a cone driven properly by such an external motor would be likely to move a lot more air than a conventional voice coil driver with the same cone area because of what appears to be the much larger power that a big external motor could provide.

If I'm wrong about that, and I may be, which off the shelf woofers now available could equal or exceed or at least come very close to the displacement volume of the Danley-type external motor with attached cone that was used in, say, the Contrabass?

The servomotors really were not that big (or heavy) compared to huge slab magnets used on big woofers, much smaller considering one motor drives two cones in some of the designs.
The Servodrive cones (depending on which brochure I look at)have 1" to 1.25 inch linear peak to peak excursion, an Xmax of 12.5 to 16 mm. That was a big deal in the 1980's when most 15-18" woofers had less than half that excursion. It takes about a 6 dB increase in power to double excursion.

The relatively inexpensive dual slab magnet Eminence Lab 12 has 13 mm Xmax.
The B&C BC18SW115 has 14-16mm Xmax.
A JBL 2256G has an Xmax of 20.3 mm.
Speakers with more Xmax potential, and higher Bl than Servodrives are increasingly common.
Small, powerful Neodymium magnets make it possible to concentrate high flux density over a longer gap with far less size and weight, and new coil winding schemes make it possible to get more linear response with long excursions.

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