My New PA Setup w/ ServODrive

[FairfaxStu]

Originally Posted by JMFahey

Very interesting, I'm tempted to cook my own, just to see (hear) what happens.
Upper frequency limit looks too good to be true, but experimenting is king.
Thanks for the idea

Not to burst your buble, but the engineering that went into this thing is scary impressive. Tom Danley designed it and I must say he did an amazing job. Trying to replicate the actual ServODrive with bass module and cabinet will be quite challenging. From what I can tell, you would have to be both a master cabinet maker and a very skilled machinest.

-Stu

[JMFahey]

My only doubt lies in the low-mass-rotor motor; the cabinet is .... a cabinet .... , cones/frames/suspensions are piece of cake , in fact I'll start experimenting with an epoxy impregnated cone but if steel is really necessary, that's easy too.
Now if it were Titanium or something like that, well, *that* will be impossible.
But worst case I'd trust more some carbon fiber composite ... and that's well within reach.
Thanks anyway and if you have any suggestion, you're most welcome.


PS: to qualify things: to *exactly* duplicate it, would be difficult; if any because of the absolute lack of useful data (motor specs, drive electronics, exact composition and properties of the rotary-to-linear transfer strip, etc.) but a reasonable approach can be estimated from the pictures, but as an experiment for fun, it's interesting.

EDIT: some specs can already be deduced from the pictures:
1) X_damage is around 40/45mm tops; meaning it can be used , say, up to +/-25mm excursion.
And electronics need to calculate instantaneous cone position very accurately, or it will "bottom out" (or its equivalent) in a catastrophic way.
Or it needs to have some kind of "excursion limit switch" (which may very well be optical) to achieve the same end.
2) the horn where it's mounted is not *that* large, specially if used singly; I recognize that used in quads as suggested it will reach quite lower.

[Speedskater]

The ServODrive was designed has those big compute tape drives were going obsolete. The tape drives had a perfect motor for this application and then were available dirt cheap. Now all the surplus motor sources have dried up.

[wg_ski]

When originally designed, conventional voice coil drivers which had enough motor strength and x-max at the same time simply weren't available. They are now.

[JMFahey]

Good to know, thanks.
In my city there's a big surplus (junk? ) dealer, you know the type, a half block open air yard with (mostly military obsolete stuff) piled 20 Ft high, no kidding.
He also has tons of old IBM junk; when I was an empty pockets kid (some 45 years ago) I used to buy "IBM cards" and emptied them by the "burn and slap" method : melting solder with a propane torch and slapping the component side against a table, instant crop of transistors, resistors, caps, diodes, etc.
Also bough the incredible Rotron and Papst coolers.
So he *should* have some old tape transport lying around.
Or so I hope.

[Speedskater]

If you are truly interested in the ServoDrive, you might join the diyspeakers forum:

The DIYspeakers Forum • Index page

Then search the archive for ServoDrive (members only)

This rather inactive forum is the remnant of the BASS e-mail list of long ago.

Most of the earlier threads have been lost with time.

[imix500]

Amazing subwoofer. I remember concerts with rows of ServoDrives across the front of the stage.

Did you happen to get a spare set of belts with the module? They are among the most coveted spare parts for these subs.

[JMFahey]

Thanks a lot.
Interesting speakers, I'm amazed I had never even heard about them.
Will join the Speaker Forum and search it.

[FairfaxStu]

Originally Posted by imix500

Amazing subwoofer. I remember concerts with rows of ServoDrives across the front of the stage.

Did you happen to get a spare set of belts with the module? They are among the most coveted spare parts for these subs.

Actually, I was able to get in touch with the company that is now supporting these beasts. All of the rubber components are still in good condition as of now. However, I can always hit them up for spare parts.

-Stu

[FairfaxStu]

Originally Posted by JMFahey

My only doubt lies in the low-mass-rotor motor; the cabinet is .... a cabinet .... , cones/frames/suspensions are piece of cake , in fact I'll start experimenting with an epoxy impregnated cone but if steel is really necessary, that's easy too.
Now if it were Titanium or something like that, well, *that* will be impossible.
But worst case I'd trust more some carbon fiber composite ... and that's well within reach.
Thanks anyway and if you have any suggestion, you're most welcome.


PS: to qualify things: to *exactly* duplicate it, would be difficult; if any because of the absolute lack of useful data (motor specs, drive electronics, exact composition and properties of the rotary-to-linear transfer strip, etc.) but a reasonable approach can be estimated from the pictures, but as an experiment for fun, it's interesting.

EDIT: some specs can already be deduced from the pictures:
1) X_damage is around 40/45mm tops; meaning it can be used , say, up to +/-25mm excursion.
And electronics need to calculate instantaneous cone position very accurately, or it will "bottom out" (or its equivalent) in a catastrophic way.
Or it needs to have some kind of "excursion limit switch" (which may very well be optical) to achieve the same end.
2) the horn where it's mounted is not *that* large, specially if used singly; I recognize that used in quads as suggested it will reach quite lower.

Couple of thoughts here:
Your estimation of xmax is about right. However, there are no sophistacated electronics in the mix. It is just a large blue servo motor that drives 2 15" woofers in harmony. One thing that you could not see, is the cooling fan which sits under the module in the orientation you can see it in the pic. It is a 120 VAC fan and gets its power from the sub amp. Also, on the back of the panel in the rear are some really interesting components. Namely, a full wave bridge rectifer, a couple of inductors, and a cap as I recall. I still have not figured out why they are using a bridge rectifier to drive an AC fan, but it works.