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Author Topic: What Is the Real Lowest Audible Frequency & Best Subs to Achieve It?  (Read 20096 times)

Art Welter

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Re: Suddenly it's slower
« Reply #20 on: January 30, 2011, 02:26:30 pm »

Mac Kerr wrote on Sat, 29 January 2011 14:17

Art Welter wrote on Sat, 29 January 2011 15:18

100 "changes" a second is not sudden?
Of course, that 100 changes would be only the upper fundamental frequency, when a woofer is responding to a musical signal, there are multiple frequencies involved, the "changes" it needs to respond to are in the thousands.

When are changes sudden, at 1000, 10,000 Hz ?

How does transient response apply to one set of frequencies and not to another?


Yes, the changes it needs to respond to are in the thousands, but all of them are below about 100Hz. In a sub, maybe an impulse with a 2.5ms 1/4 wave rise time or greater can be called "transient". What often gets mentioned in discussions about sub "transient response" in subs is the first snap of the beater on the bass drum. It you compare the rise time of that first impulse as heard by the mic to the signal as heard by the sub, the signal at the sub won't look so much like a "transient". If the "snap" of a bass drum is around 4kHz it has a rise time 1/40th of that of 100Hz, or 0.0625ms.

If "transient response" is the ability of the output to track the input, there is no lower limit to what a transient is, it is defined by the mechanical system's ability to track the input. If a "transient event" is defined by the frequency content of the original full range source, what happens at the sub is slow motion.

Mac

Exactly, accurate transient response is the ability of the output to track the input, particularly in respect to time, rather than frequency response.

If a "transient event" is defined by the frequency content of the original full range source, the ability of a sub to accurately reproduce the low frequency portion of the original "transient event" source related to time constitutes good transient response.
Lagging on the initial portion of the signal or "ringing" after would be poor transient response.

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John Halliburton

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Don Gspann wrote on Wed, 26 January 2011 07:49

... but I do have 2 ContraBass subs in my living room.  I'm sure the transient response is much better on the new subs, but for the size and weight and the sheer wall/floor shaking, knick-nak knocking off shelves enjoyment, I'm not giving them up anytime soon!  A Telarc/DTS disc that has a recording of a space shuttle launch is too much fun to play for people.  At first, all your you hear is the windows rattling, and feel the house shaking!  Love them!


Transient response of a Contrabass is actually some of the best you'll ever come across, even impressive if it didn't have a -3db point at 16hz.  The design is very, very good, and nothing that small has that kind of ELF output either.
I've had mine out of pro "retirement" for the last couple of events I've done, and one was a movie presentation in a small gym of Toy Story 3.  Nice fx from Disney/Pixar, the Contrabasses worked like a charm.

Best regards,

John
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drewgandy

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Re: Suddenly it's slower
« Reply #22 on: February 03, 2011, 01:53:43 pm »

How about this?  'If a moving coil dynamic loudspeaker has a hard time "stopping" then it also has a hard time "starting"?'

drew
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Bob Somers

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Re: Suddenly it's slower
« Reply #23 on: February 03, 2011, 02:22:42 pm »

I have not given the issue of transient response a lot of thought, so I'm just going to throw out some ideas. Tell me what you think of them.

The question will be if an ideal speaker system, including a subwoofer, is fed a 100Hz tone that starts at time t=0 and is a cosine wave (so that at t=0, it starts out at max value which means it has an infinitely fast rise time) and it lasts for 1 second and then abruptly stops with an infinitely fast fall time, what should be the response of a perfect subwoofer?

Per Fourier analysis, all signals can be matched by a sum of sine waves. I also assume the subwoofer is fed by a perfect crossover set to pass everything at or below 100Hz and nothing above it. Possibly, this crossover is an active digital crossover. I'm rusty on some of my theory and so if implementing such a perfect filter is not possible, then the filter used will be assumed to be the best that can be realized and will be set so that nothing above 100Hz is passed to the sub even if that means also attenuating some frequencies at or below 100Hz.

This is now fed through a perfect (or near perfect) crossover to a subwoofer.

All the sub has to do therefore is reproduce frequencies at or below 100Hz. Therefore, nothing in the signal being sent to the sub can move fast. In fact, any sharp rise or fall times in the signal will actually be reproduced by the tweeter and/or midrange, not the woofer!

The fastest possible changes the sub must reproduce would be those of a 100Hz sine wave at the maximum amplitude the sub can handle with acceptably low audio distortion. Any frequency/amplitude combination below that changes even slower, so can be ignored.

If a sub can't "track" a 100Hz sine wave it max amplitude, isn't that simply a measure of distortion??? Stated another way, if a woofer can't reproduce some part of a 100Hz signal when the signal stops or starts, it won't be able to properly reproduce any cycles of that signal, not just the ones that start up the signal or stop it. If the start and stop of a signal can't be composed of anything higher than 100Hz, then there is no difference between that part of the signal and the "steady state" part that might be in between the start and stop. Therefore, the woofer will have distortion on all parts of the signal, not just the start and stop of it.

It seems to me there is no such thing as transient response and that what is incorrectly called transient response is really included within the definition of distortion.

Please give me your thoughts about my views on this.

Thanks,
Audioresearch
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Art Welter

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Re: Suddenly it's slower
« Reply #24 on: February 03, 2011, 08:42:03 pm »

Bob Somers wrote on Thu, 03 February 2011 12:22



It seems to me there is no such thing as transient response and that what is incorrectly called transient response is really included within the definition of distortion.

Please give me your thoughts about my views on this.

Thanks,
Audioresearch


I think you are trying to change the definition of transient response.

Any variation of a signal by the driver under test could be considered distortion, but transient distortion is different from harmonic, intermodulation or phase distortion.

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Don Gspann

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Re: Suddenly it's slower
« Reply #25 on: February 03, 2011, 08:54:03 pm »

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.
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Don Gspann

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Re: Suddenly it's slower
« Reply #26 on: February 03, 2011, 09:00:42 pm »

   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
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jeff harrell

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Re: Suddenly it's slower
« Reply #27 on: February 10, 2011, 06:58:55 pm »

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 !!!
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Bob Somers

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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?
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Art Welter

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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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