can you buy preassembled servo feedback systems for subwoofers? - Page 3 - diyAudio
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Old 10th December 2001, 07:39 AM   #21
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there is no reason why an electronicly assisted sub should sound bad so long as you dont exceed Xmax or the power rating of the driver and you dont expect it to produce frequencies below Fs or drive the amp into clipping. if none of this is the case and the sound is bad then the driver or amp or both are of poor quality or the enclosure is poorly designed. Most of the commercially available subs that are electronicly assisted use drivers with big Sd and huge Xmax and Power ratings. Having said that, these subs are not SPL monsters.

[Edited by AudioFreak on 12-10-2001 at 03:05 AM]
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Old 10th December 2001, 10:32 AM   #22
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I was thinking more along the lines of, a sealed box for the 50-100Hz range, and a ported box tuned for the 49Hz and below range. This would produce the best of both worlds, in terms of sound quality, bass extension and SPL. + a LTC may even extend the range of the ported box, without a loss of overall bass volume.

If you wished, the whole setup could probably be built as a long cabinet, and adding some rubber feet and a flat extended top to produce an isolated surface, a TV set could be placed on it, serving a functional use as well.

For example, the ported box could easily use a 12"-15" inch driver that has high excursion, and decent quality for HT effects, compared to a more expensive 12" driver for the sealed box which would produce most of the bass notes, where sound quality is more important. + if you leave the drivers uncovered, it would make a great conversation piece.

[Edited by downhere on 12-10-2001 at 05:36 AM]
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Old 10th December 2001, 10:06 PM   #23
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Downhere:

I am not sure how much increase in accuracy is to be had by dividing the bass up into two speakers: 20 Hz-50 Hz range, (ported), and 50 Hz-100 Hz range, (sealed), over a single ported system covering the entire 20 Hz-100 Hz range.

The port only has output for one octave. If the port is tuned to 20 Hz, then at 40 Hz, there is no more port output and the speaker from 40 Hz up should be identical to a sealed system.

As for intermodualtion distortion caused by the speaker carrying a low bass note while trying to play a higher note, the cone excursion of a ported speaker is the same as for a sealed system with a 12 dB/octave high pass filter set at the octave above Fb. In our case, the ported system will act like a sealed system from 100 Hz down to 40 Hz, and then act as if it is crossing over to a subwoofer. The "subwoofer" it is crossing over to is the port output. From what I can see, there is little to be gained by having a sealed system play from 100 Hz down to 50 Hz, then crossing over to a ported system.
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Old 21st December 2001, 12:20 AM   #24
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Default A Using an Accelerometer to Make an Active Subwoofer

Here is a link to Analog Devices web-site on a project done there.

http://www.analog.com/technology/mem...woof.html#prob

If you cannot get directly to this page, type subwoofer into the search box and it should bring this page up.

Maybe this will be helpful

Surf, Sun & Sound
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Old 21st December 2001, 01:06 AM   #25
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The fly in the ointment here is the price of the accelerometer. I looked into this several years ago when I was planning my current subs, and nearly had a heart attack. The ones they used for that project are about $40-50. That's for one chip. Ugh. I was able to find some cheaper ones (don't remember the part number) at about $20 each. For me, it was a deal-killer. You also have to modify the driver itself, something I would prefer to avoid, if possible. Then there's the issue of the added mass. Generally, you'll hear people say that the servo will compensate for its own mass, and to an extent it's true, but not fully. The lightest add-on sensor I'm aware of is a piezo element, but then you're into the whole phase shift thing.
For someone who was only buying one or two (or was able to finagle them for free) it would be a lot more practical.
I'm still trying to fiddle the optical thing into reality, but have been working on other projects (like the Aleph PCB stuff) instead. I'll get there one of these centuries.

Grey
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Old 21st December 2001, 02:00 AM   #26
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Default Accelerometers

Grey,

I have no interest in the project as such, I just happened across the web-page and remembered the thread here. I did not remember if this site was mentioned or not. Just thought if not, maybe this would be a helpful input.

I am currently enarmored with the probably flawed single driver idea. I know that is always a "fly in the ointment", but I was amazed at what a cheap "full range driver" can sound like.

Surf, Sun & Sound
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Old 21st December 2001, 02:33 AM   #27
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Sx3,
I'd probably be more interested in the accelerometer idea if the blasted things weren't so expensive. I imagine that the price will come down with time--possibly wishful thinking on my part. Pity that you can't buy off the shelf drivers with something of that nature already incorporated into the driver.
Any time you can get an all-in-one driver going, you automatically get rid of the crossover. This is a large part of the magic of electrostats. Despite the obvious limitations, they do manage to sound as though they're "cut from the same cloth" from top to bottom. Not to mention the incredible transient response from having such a light diaphragm.

Grey
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