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So what exactly was so special about the Intersonic Servodrive?

C

CheshireCatFun

Mar 9, 2013
162
2
#1
I know Billy Sheehan used to use one, and it probably had something to do with his subwoofing pickup set deep into the neck, but what was so special about it? It ostensibly had a more powerful sound, definition, and presence due to the cones being driven by a servo drive vs. magnetic coils, but how did that play out in reality?

C.
 
#3
Here is a nice blurb from one of the pro audio blogs that kind of summarizes other stuff I've read about these. Basically, it explains why it disappeared and is not longer needed. Not sure about the exact 'mechanical motor' deal used to produce the sound, but these days, the powerful subwoofer drivers available seem superior.


'Tom Danley's Intersonic servodrive subwoofers had an Xmax of 12.5 to 16 mm depending on the unit.

At a time when most woofers had an Xmax of around 4mm, the advantages where huge, and with four units of the BT7 having a sensitivity of 110 dB 1 watt one meter, half space, 28- 125 Hz, they were as efficient as cone speakers. There simply were no cone speakers with the BL product or Xmax anywhere near what the servodrive units had at the time.'
 
#5
KJung said:
Here is a nice blurb from one of the pro audio blogs that kind of summarizes other stuff I've read about these. Basically, it explains why it disappeared and is not longer needed. Not sure about the exact 'mechanical motor' deal used to produce the sound, but these days, the powerful subwoofer drivers available seem superior.


'Tom Danley's Intersonic servodrive subwoofers had an Xmax of 12.5 to 16 mm depending on the unit.

At a time when most woofers had an Xmax of around 4mm, the advantages where huge, and with four units of the BT7 having a sensitivity of 110 dB 1 watt one meter, half space, 28- 125 Hz, they were as efficient as cone speakers. There simply were no cone speakers with the BL product or Xmax anywhere near what the servodrive units had at the time.'
Click to expand...

Whereas, today . . . .? (I'm still very new to all this.)

C.
 
#8
alexclaber said:
Look at what Tom Danley now makes:

http://www.danleysoundlabs.com/

The Tapped Horn subs beat the ServoDrive ones on all fronts. Wouldn't want any of them in backline though!
Click to expand...

KJung said:
Today there are neo drivers (i.e., standard heavy duty speakers) that have incredible specs for subwoofer systems. I'm just an interesting layman that reads about this stuff. Maybe Alex can chime in, since he posted above.
Click to expand...

What is the term for the attribute of a horn path doubling back and forth within the enclosure?

So, whatever that attribute is, the Intersonic had it, and a number of subwoofer cabs today have it, but the thing that made the Servodrive different was the motor driven cone vs. a magnet driven cone, but now there are magnet driven cones that are much stronger than the motor driven cone was, ergo, it's become absolute. Is that correct?

In what setting would a Servodrive or one of it's betters work best? A massive arena or outdoor concert, like these massive rock festivals? I assume while playing in a small club setting, or modest venue, one of these subwoofing behemoths wouldn't be necessary?

Also . . .

Downunderwonder said:
Probably played hell with the PA subs.
Click to expand...

Do tell.

C.
 
#9
Servodrive was a way of getting high sensitivity and high excursion from a subwoofer driver, although with very limited upper bandwidth. With modern neodymium magnet motors you can achieve similar results. Then do something clever liked the tapped horn (which makes a driver appear to change parameters by driving the higher low frequencies with both sides of the cone in phase and then the lower low frequencies with just one side of the cone) to fully leverage a huge excursion, huge voice coil, high moving mass driver.
 
#10
alexclaber said:
Servodrive was a way of getting high sensitivity and high excursion from a subwoofer driver, although with very limited upper bandwidth. With modern neodymium magnet motors you can achieve similar results. Then do something clever liked the tapped horn (which makes a driver appear to change parameters by driving the higher low frequencies with both sides of the cone in phase and then the lower low frequencies with just one side of the cone) to fully leverage a huge excursion, huge voice coil, high moving mass driver.
Click to expand...

This has piqued my interest. "Tapped" horn? Do tell.

C.
 
#12
Balog said:
Invalid Link Removed
Click to expand...

Very compelling! . . . . what am I looking at? :confused:

attachment.png


It seems that the cones are projecting into the cab, not out, so do they project into an internal chamber, and then the horn paths finds their way out thru the center? Am I close?

C.
 

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#15
I've seen Billy perform years before he used the Intersonics, as well as the year or 18 months he actually used one, and the many years after he stopped using them. He didn't sound remarkably better when he had them. They were designed and conceptualized to amplify sub-lows. They did that well but most of what they excelled at isn't of optimum usefulness for bass guitar. If they were, Billy and most everybody else would be using them still, and they aren't.
 
#18
fdeck said:
I don't know about how the horn works, but one reason for pointing the speaker "backwards" is to suppress direct radiation from the dust cap.
Click to expand...
The reason the speakers are backwards is that there isn't any rear chamber, so they wouldn't fit facing the other direction.
A tapped horn is a resonant air column effectively using both sides of the speaker cone, which can result in an output around 6 dB more than the same speaker (of the proper parameters) used in a bass reflex cabinet.
Click to expand...
That's not right. A tapped horn and a bass reflex both use both sides of the cone. A tapped horn is more efficient than a bass reflex because it's a horn. There's nothing about a tapped horn that's magical, it's a simple variation of a rear loaded horn that's been around since the 1950s. It's only advantage over a regular horn is that it's smaller, because it doesn't have a big rear chamber for the speaker. It's disadvantage is that it needs a longer excursion higher power speaker than a regular horn, so they cost more.
 
#19
https://en.wikipedia.org/wiki/Subwoofer

"Servo subwoofers

Some active subwoofers use a servo feedback mechanism based on cone movement which modifies the signal sent to the voice coil. The servo feedback signal is derived from a comparison of the input signal to the amplifier versus the actual motion of the cone. The usual source of the feedback signal is a few turns of voice coil attached to the cone or a microchip-based accelerometer placed on the cone itself.[29][30] An advantage of a well-implemented servo subwoofer design is reduced distortion making smaller enclosure sizes possible.[31] The primary disadvantages are cost and complexity.[32]

Servo controlled subwoofers are not the same as Servodrive subwoofers whose primary mechanism of sound reproduction avoids the normal voice coil and magnet combination in favor of a high-speed belt-driven servomotor. The Servodrive design increases output power, reduces harmonic distortion and virtually eliminates the loss of loudspeaker output that results from an increase in voice coil impedance due to overheating of the voice coil (called power compression.) This feature allows high power operation for extended periods of time.[33][34][35] Intersonics was nominated for a TEC Award for its Servo Drive Loudspeaker (SDL) design in 1986 and for the Bass Tech 7 model in 1990.[36][37]"
 

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