A Type of Amplifer

[Bassick]

This question is for experts only. What if there existed an amplifier that was made to power a Passive Radiator System. Let me explain what I mean. In a standard PR configuration there exist a Subwoofer and a Passive Subwoofer. Is it possible to have a amplifier design that allows for two distinct channels, one channel for the Subwoofer with normal output, and one channel for the Passive Subwoofer with a weaker signal that has been modified in such that it provides the PR just enough resistive force to counter act the pressures inside the enclosure.

I know, I know, why not just use another subwoofer and a port, sense you have to use current to power the PR. But think about it.

The amp want be using as nearly as much power with the PR that it would be with the regular Sub.

The main focus behind this idea is to utilize the back wave at all frequencies.

Understanding how a PR works. PR's use the back wave to reinforce the front wave the same way as a Port does. Just like a port a PR can only do this at a given range. And to achieve this range, ports and PR have to be tuned. With a port cross section and length comes into play. With a PR, its all in the mass of the cone. If you had a theoretical port that could adjust its cross sectional area (changing its mass) fast enough to keep up with the electrical signal. You would in theory, be using the back wave to reinforce the front wave at all frequencies (frequencies that the sub produces). But such a port does not exist. Now, the PR on the other hand, can change its mass mechanically by adding mass to the cone assembly.

Now what I'm proposing is to utilize a sub not a real PR. Using a subwoofer with the magnet (motor structure) still attached as a PR. With this Subwoofer as a PR, applying a signal with just enough current will simulate the adding and removal of mass, through resistance (of course the theoretical amp would have to have a variable timing delay knob).

I hope I have been clear in what I am asking. Only serious feedback is accepted. Keep in mind this is just something to ponder.

I am in no way saying that this will work. Its just an idea.

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[Side Show 10+ year member]

i'd say if both are being fed a signal and pwr in the same box, the two subs will compeate with each other for the airspace causeing the sub getting less pwr to fail/overheat the coil and would just sound bad.

very interesting idea tho... if you have the means and the money... try it and let us no how it goes

 

[So Low iT Hz]

Would you be mad if knew the answer but didn't tell you? I'll give you a hint. You don't need an amplifier you produce an electrical signal. All you need is physical motion of conducting wires in a magnetic gap.

 

[So Low iT Hz]

Ok I was going to try and spare you some serious math headaches, and I can't even show you how to calculate the resulting tuning in an enclosure without use of Maple or MathCAD but here's a start. You may or may not be familiar with RDO speaker operation, which is essentially utilizing one undriven voice coil of a speaker connected through a potentiometer to introduce back EMF in the coil to change the q alignment of the speaker. Change the value of the potentiometer, change the q. It works great for a few notable dual vc drivers, JL W6, the ol' Atlas, and a few Dayton HT woofers as well. It's a lot of fun, just play music and turn the dial and fine tune the sound. Here's a quick background of that:

Again, for those who don't know, resistively damped operation (RDO) involves changing Qms of a dual voice coil woofer by connecting a resistor across the terminations of a first one of the two coils of the woofer and running signal current through the second coil only. Here is an equation that I derived for calculating modified Qms or Qms' by RDO:

Qms' = Rt*Qms*Qes/(Re*Qms + Rt*Qes)

where

Rt =Re + Rx

Re = DC resistance of a single voice coil

Rx= resistance of the resistor connected across the terminations of the first coil

Qms = mechanical Q of the woofer

Qes = electrical Q of the DVC woofer with the terminations of one of the woofer's coils open and unconnected.

The above equation for Qms' I derived from an equation for Qms' by Ron Ennenga (formulated eons ago) that is calculated with the fundamental mechanical parameters,

Qms' =2*pi*Fs*Mt/Rmt

where

Fs= free air resonance frequency

Mt= total moving mass of driver

Rmt = total mechanical resistance

Rmt = Rms + Rms'

Rms = mechanical resistance of driver

Rms' = Bl^2 / Re + Rx

Bl = motor strength

Re = DC resistance of a single voice coil

Rx = resistance of resistor across terminations of one of the voice coils

My equation for Qms' of course makes it much easier to calculate the required resistance of Rx to change Qms and thereby also Qts of the woofer as it is formulated with the Thiele/ Small parameters.

Being that for passive radiator usage there can be multiple coils in RDO (quad coil woofers yeah?) you can compound this calculation significantly to determine the effective radiator efficiency given certain values in either fixed resistors, or my personal preference potentiometers. Before attempting to calculate this effect, I would say that given all the time and effort you are going through to maximize a single drivers efficiency along with the expense of investing in a perfectly good woofer with a high BL to use as a passive radiator you are much better served by just using a dual woofer configuration and calling it a day.

That being said, that's how pu$$ies roll. I've done an install of two W6s in separate chambers in RDO with a pair of undriven voice coils connected in series through a potentiometer and wow what an experience that was. The fun of changing Q on the fly is certainly something that any hardcore audihile would enjoy a lot but it is not easy to do to say the least.

But have fun!

 

[bbeljefe]

As was touched on above, it could be done with a drone cone that had coils but the circuitry required to integrate the signal processing into an amplifier would be akin to designing a highly computerized mouse trap. Would it work? Yes. But it would not be cost effective. That might be different if standard mouse traps simply did not catch mice. But they do.... so why spend the money to increase efficiency by, say, .5-1%?

 

[So Low iT Hz]

^^^like he said. Is it going to worth your time? Depends how valuable you consider your time!

But will it be the greatest acoustic achievement you've ever accomplished? No. But I won't tell you not to try it out if you insist