can you buy preassembled servo feedback systems for subwoofers? - Page 2 - diyAudio
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Old 9th December 2001, 02:20 PM   #11
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What else can i fixate on???? I can't construct linkwitz transform circuits...my only hope is that i find a company that can make me one according to my needs.
You could fixate on getting KNOWLEDGE. That's gained by education, learning what's real and what's not real. It's gained by going to school, studing physics, acoustics, engineering. It's not gained from mfgr's websites, mgfr's literature, magazine reviews, or posting on internet forums.

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"how did the bob carver sunfire subwoofer(as well as many other high spl tiny box subs) produce its usable 16Hz bass out of a small sealed box tuned to a very high resonant frequency?"
Carver tries to do it with TONS of EQ, very high power. But the Carver/Sunfire subs sound like crap. There is tremendous distortion and pathetic transient response. The bass has a one note sound. The old so called 'white paper' that was posted on the Sunfire site was nothing but pseudoscientific nonsense (aka BS and advertising hype).

Do you believe everything you read on a mfgr's website regarding the performance of a product?. Websites are SALES tools for the companies, not a substitute for an education.

The only thing gained by the use of a LT circuit is being able to electronically change the Qtc. This means that the bass will be 'tighter', not louder or have less distortion. The LT circuit also means that higher amplifier power will be needed.

There are laws of physics that control what and how things can be done in the world of audio. And no one yet has built a sub that is able to defy these laws. So unless you understand the principles of speaker design, you'll spend lots of time being blindly lead around by the nose as a result of slick marketing.
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Old 9th December 2001, 02:43 PM   #12
Super is offline Super  United States
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Another thing you may take into consideration is the reason that some manufacturers include servos: to compensate for poor quality drivers, several of which have low xmax figures. In my opinion, using multiple lesser quality drivers without servo will produce louder, tighter, and cleaner bass than one of those same drivers with servo. The need for servo can be compensated for by using quality drivers to begin with.
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Old 9th December 2001, 07:42 PM   #13
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Gum:

Just so that you get an appreciation of what is involved with a servo system, here is a project done by a whole class of college students at Brigham Young University. Remember, these people are only a year away from being electrical engineers. When completed, the project was judged to give only minimal advantage over the same system without servo control.
http://www.et.byu.edu/~danmarx/dpmaudio/servosub.html

On the other hand, I have seen response plots for the Velodyne where the system produced extremely low distorion figures, which the reviewer ascribed to the servo system.

Suffice it to say that I do not think that a servo system is going to make the difference between a successful project and an unsuccessful one. Get yourself a good driver, install it in a box according to tried-and-true methods, and you will have a hell of a subwoofer.

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Old 9th December 2001, 10:23 PM   #14
jduncan is offline jduncan  United States
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"why would anyone want a flatter response as a trade off for SPL? "

I thought this was kindof obvious but for most people around here the purpose of a speaker is to reproduce sound as naturally as possible and that, by definition, involves a flat frequency response. Large peaks etc completely destroy the reproduction of the music. We can deal with a lower SPL as if its really too low it can be compensated for by using higher powered amps as discussed.
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Old 10th December 2001, 12:15 AM   #15
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trouble is jduncan you usually cant pump more power into the sub when using a lt circuit cause it will then exceed Xmax at the lower frequencies and if you dont exceed Xmax you will exceed the power rating of the driver.
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Old 10th December 2001, 01:14 AM   #16
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has anyone built seperate subs with boxes tuned to different frequencies? With enough boxes, + a decent crossover, it may sound pretty good.

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Old 10th December 2001, 02:21 AM   #17
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Downhere:

The purpose of the separate boxes being to take advantage of the cone excursion notch which is greatest near the box tuning frequency?
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Old 10th December 2001, 05:03 AM   #18
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I believe that downhere refers to multiple boxes as in multiple drivers simply to get more SPL while keeping Qtc 0.707.... extra boxes are not neccessary just increase the size of the box for as many drivers as are required...

[Edited by AudioFreak on 12-10-2001 at 12:07 AM]
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Old 10th December 2001, 06:14 AM   #19
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Seems like it wouldn't be impossible to design a universal add on subwoofer servo box. Sure it wouldn't be optimal, cheap, have broad appeal, simple to implement, etc. But it could be done.

The students that did the servo project got some good results for a first stab at this problem. Considering their test equipment, it was really impressive.

pkgum,
Do you have access to an oscilloscope, accelerometer, and signal generator needed to do a servo project? There is a wide range for the tradeoff on complexity vs. performace for servo systems. A simple (read: low performance) servo system could be pulled off by anyone that can design simple op amp filters. They can get absurdly complex quickly, but don't have to.
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Old 10th December 2001, 07:06 AM   #20
pkgum is offline pkgum  Australia
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thomas w,
i do not believe advertising
but i do believe what i see in magazine reviews

the sunfire sounds crap? you are the first person l've heard who has critized this sub. A few ppl had provided positive feedback about this sub
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