Google Groups no longer supports new Usenet posts or subscriptions. Historical content remains viewable.
Dismiss

What is Yamaha's Active Servo Technology

1,253 views
Skip to first unread message

Joseph M. Reagle Jr.

unread,
Oct 31, 1996, 3:00:00 AM10/31/96
to

Is it just a fancy name for their version of bass-reflex?

--
Regards, | GON OUT |
| BACKSON |
Joseph M. Reagle Jr. | BISY |
rea...@mit.edu | BACKSON | http://farnsworth.mit.edu/~reagle/home.html

Neil Koomen

unread,
Nov 1, 1996, 3:00:00 AM11/1/96
to

As I inderstand it, it's an active electronic device that measures distortion at the
driver and attempts to correct the distortion by sending a signal to the amplifier so
that the amplifier's output can reduce the distortion and better control the driver.

Similar designs are used in Infinity and Velodyne subs, I believe. It's said to be quite
effective.

Here's a definition of a servo from "Newton's Telephony Dictionary" (8th ed., 1994, pg.
924) that may be useful:

Servo
"Short for servomechanism. Devices which constantly detect a variable, and adjust a
mechanism to respond to changes. A servo might monitor optical signal strength bouncing
back from a disc's surface and adjust the position of the head to compensate."

While the example cited above isn't ideal for the purpose of understanding the servo
concept in subwoofers, I think you'll get the general idea of the advantages of servos.

Maybe somebody could explain it technically in the context of subwoofers?


Neil Koomen

unread,
Nov 1, 1996, 3:00:00 AM11/1/96
to

Minor correction (maybe I need a servo to monitor and correct my own
mistakes!):

The correct title of the book:

"Newton's Telecom Dictionary"


Thorsten Loesch

unread,
Nov 4, 1996, 3:00:00 AM11/4/96
to


Joseph M. Reagle Jr.

> Is it just a fancy name for their version of bass-reflex?

No. It is essentially motional feedback (well it really is negative output
impedance).
This uses the back-emf from the Speakers Voice-coil to get the "Signal" for
the Servo.
The circuit is fairly simple, It has also been widly documented. To make it
simple,
to the Amp is added another Circuit that makes the Amp's output a negative
impedance
of the Value of the Speakers Voicecoil DC-Resistance (eg. Speaker - 5.4 --
Amp -5.4 Ohm).
The biggest problem is however that the Speakers Voicecoil Changes it's DC
Resistance
with changing temperature. Yamaha seem's to have cracked a working
temperature
compensation, but don't ask me how.

It does work, it is better than anordinary Amp-Speaker combination, but
Yamaha
usually uses it to get by using smaller drivers and so on, which
essentially negates
any possibile Sound Advantages.

Regards Thorsten.

0 new messages