Commercial motional feedback woofer available sort of - diyAudio
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Old 2nd March 2013, 05:27 PM   #1
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Default Commercial motional feedback woofer available sort of

Sony SA-W2500, saw it at Walmart for $100 but Sony says it is discontinued. This is a small box, presumably sealed, with a 10 inch "mica reinforced" cone and "motion feedback" with a 100-watt amp. Nobody seems to bother to mention basic specs like input, cross-over, controls.... and basic necessary information like that.

It seems to have the kind of voice-coil bobbin sensor coil (tactically massaged) that I believe is best way to get feedback signal. Seems to fulfill one of the oldest target goals of motional feedback R&D (going back to JAES 1954): making a smallish box do remarkable woofing.

I haven't yet found a meaningful review. But the Amazon review crowd is quite ga-ga as to value.

Anybody know about this woofer or Sony's efforts along those lines?

Ben
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Last edited by bentoronto; 2nd March 2013 at 05:30 PM.
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Old 2nd March 2013, 05:44 PM   #2
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It's definitely ported. I've never been impressed by any Sony audio product and this thing just looks like it sounds bad. Boomy mass-market junk.
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Old 2nd March 2013, 05:58 PM   #3
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So am I understanding correctly that this is some form of a servo "corrected" woofer?

What's to stop someone from redesigning the cabinet if it is a one note wonder; to achieve a more reasonable f/r?
That is a good deal for a not so simple circuit to implement well as DIY.
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Old 2nd March 2013, 06:30 PM   #4
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Quote:
Originally Posted by theAnonymous1 View Post
It's definitely ported. I've never been impressed by any Sony audio product and this thing just looks like it sounds bad. Boomy mass-market junk.
I haven't asked Walmart to open the box to let me check it out. But a ported box with motional feedback is an oxymoron. Of course, theAnonymous1's post does seem to have an authoritative and definitive ring to it, so who am I to doubt him or her.

Just doesn't make much sense from the theory. Of course, doesn't mean some really dumb company wouldn't do it.

About Sony, they have sometimes produced HiFi gear of the first order (a famous turntable, for example). But maybe not any mass-produced speakers... for $79 on Amazon.

I wonder if motional feedback has as little enthusiasm on this forum as I sense it does, because it demands skills both in mechanical and electronic fields.

Ben
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Last edited by bentoronto; 2nd March 2013 at 06:35 PM.
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Old 2nd March 2013, 06:38 PM   #5
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I don't see anything about motion feedback. Where are you getting that?
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Old 2nd March 2013, 06:43 PM   #6
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Originally Posted by Svendingo View Post
So am I understanding correctly that this is some form of a servo "corrected" woofer?

What's to stop someone from redesigning the cabinet if it is a one note wonder; to achieve a more reasonable f/r?
That is a good deal for a not so simple circuit to implement well as DIY.
Right. A prime function of motional feedback is to "eat" the resonance.

Ordinarily, there are few frequency-correcting tricks in MF to worry about changing the box. In theory they are not needed. So putting the little driver into a big box ought to achieve a lot.

However, a crucial element of MF is the substantial frequency correction for radiation resistance (which is miraculously achieved by other drivers kind of automatically if accidentally, on a good day). MF deprives a driver of this automatic accidental correction so it has to supply it back using electronic correction.

But a 10 inch driver is under the thumb of decreasing radiation resistance at ALL frequencies of interest. So any correction in the Sony amp is already appropriate for it in any box.

Ben
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Old 2nd March 2013, 08:30 PM   #7
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Quote:
Originally Posted by bentoronto View Post
I haven't asked Walmart to open the box to let me check it out. But a ported box with motional feedback is an oxymoron. Of course, theAnonymous1's post does seem to have an authoritative and definitive ring to it, so who am I to doubt him or her.
My apologies, what I though was a port must just be a Canadian cup holder.

Click the image to open in full size.
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Old 2nd March 2013, 08:41 PM   #8
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bentoronto,
What you may be missing is that in a real motional feedback speaker system is that the speaker itself is part of the electrical circuit usually. It can have a second voicecoil that is sensed or it can be reading the back emf output to derive the correction circuit. I doubt that if you opened this speaker up you would find any of that. It is more than likely just a marketing catch phrase for the dollar amount you are talking about. And yes Sony has been known for some very good sounding gear, but it is as I know under the Sony "ES" branded label only. Check those out if you like that brand, the normal Sony consumer product is nothing special that I have ever seen.
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Old 2nd March 2013, 09:20 PM   #9
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Hi bentoronto,

Post #1: "...It seems to have the kind of voice-coil bobbin sensor coil (tactically massaged) that I believe is best way to get feedback signal...."

It looks like the "feedback signal" is a voltage from a small value resistor in the ground line of the speaker drive (also, it seems to be a vented design). I found the schematic here: SA-W2500 Sub blowing fuse . I'll attach a detailed view:

Regards,
Attached Images
File Type: jpg FB_Tap_SA_W2500_annotated.jpg (55.9 KB, 294 views)
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Old 2nd March 2013, 09:46 PM   #10
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So they are in fact measuring the back emf output and using that signal for correction. If that is the case you should be able to substitute any speaker into the equation but that is counting on there not being any other specific correction filter for this exact speaker in that box.
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