can you buy preassembled servo feedback systems for subwoofers?

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No. It must be custom designed and purpose built for the specific driver, cabinet, and amp

You might be better served fixating on something else. There's a reason why only a few companies use this technology........

The distortion isn't all that high in current high-end subwoofers. If it were a major issue, don't you think everyone would be jumping on the Servo bandwagon?
"There's a reason why only a few companies use this technology........"

some famous subwoofer companies use this technology

I have rarely seen simple high end subwoofers that are only composed of a box, a driver, a amp, and a filter.

"You might be better served fixating on something else."

What else can i fixate on?
An externally hosted image should be here but it was not working when we last tested it.

so do you just figure out the values of the components in this circuit by using the spreadsheet supplied in the esp website and then i can just get someone to construct the circuit...right?

im all this the right circuit? I am bridging the amp so more power is extracted, this power will run the sub.

[Edited by pkgum on 12-09-2001 at 05:01 AM]
Using simulation software i figured out that all the circuit does in my sealed BP 1503 subwoofer is to flatten the response
Without the linkwitz circuit the response in the upper bass frequencies are louder but the SPL in the low 20Hz - 40Hz frequency response is the same

So in conclusion theres no piont using a linkwitz transform circuit when trying to create more SPL in the lower frequencies in sealed enclosures.

anyone disagree?
pkgum nothing will get you higher spl in the lower frequencies except adding more drivers or using bigger ones and using a box that is the right size for the drivers..... the servo wont buy you more spl at lower frequencies because the driver simply cant move enough air without exceeding Xmax. If you want lower bass without adding more drivers or passive radiators and still want a flat response in a sealed box then all the circuits work the same as each other ....... and you lose efficiency in the higher frequencies.

[Edited by AudioFreak on 12-09-2001 at 07:13 AM]
the linkwitz transform circuit is there to give you a flat response down to a lower -3dB frequency but at the expense of spl. Nothing and i mean NOTHING can get you higher spl at low frequency except by displacing more air which means increasing cone area or increasing excursion and excursion is already at its limit at the lower spl figure. If you would like to know more read

[Edited by AudioFreak on 12-09-2001 at 07:49 AM]
What else can i fixate on???? I can't construct linkwitz transform 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.

"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.
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.
diyAudio Moderator Emeritus
Joined 2001

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.

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.
"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.
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.

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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