D-MAN Posted July 11, 2005 Share Posted July 11, 2005 Marvel, I am baffled. What are you guys talking about? The mechanical compliance of driver B is unalterable by electrical means. Are you implying that the reactance of the passive VC is used to modify the behavior of the active VC circuit of active driver A? In that case, maybe...but it would require an electrical circuit between the two. Now see why I'm confused? DM Quote Link to comment Share on other sites More sharing options...
Marvel Posted July 11, 2005 Share Posted July 11, 2005 This is awful, since it is making a lot of sense to me. I'll repeat and try to make clearer: No connection between Driver A and Driver B other than them being in the same box. A vibrates and makes B vibrate, generating voltage that is dropped across the resistor. Depending on the resistor, Driver B is stiffer, etc If you have a load across the VC of driver B, the counter emf will cause B to not vibrate as easily as 'no' load across the VC. As Neil said, it is like the load on a generator makes it harder to operate. In that sense, it would make driver B stiffer. Perhaps an iron core inductor would work better than a resistor, but you couldn't adjust it as easily. This would be something we should be able to test pretty easily. A speaker can work as a microphone, which generates a voltage swing. If there is counter emf from that, it would then influence how the speaker is moving. If this were in a box, changing how that speaker moves would change the tuning on the box. Clear as mud, right? Bruce Quote Link to comment Share on other sites More sharing options...
DrWho Posted July 11, 2005 Share Posted July 11, 2005 The concept is like those faraday rings...you put a copper ring around a tall cylindrical magnet and the current induced inside the copper ring from falling through the B-field actually causes the ring to produce a B-field which counteracts its motion...thus causing it to fall slower. Though the effects aren't identical, adding a resistor in series with the copper ring causes it to fall faster. The effect is mind-boggling to watch because it seems to defy all laws of physics until you start uncovering the complex situation. Now that I think about it...does it have to be a magnetized cylinder or does it only have to be able to conduct magnetism? Man it's been so long since I've seen the demo. I guess it doesn't matter for the sake of making an example though... So using this physics example, I see no reason why current induced in a voice coil couldn't alter the mechanical nature of the driver...it'd almost be the same thing as making the suspension stiffer (though it only gets stiffer the faster the cone is moving) That other design that electrically connects the two drivers seems to me like a way to make the passive radiator think it's in a larger box by electrically helping the passive to move (kinda like making the suspension less stiff, or countering the air pressure in the box). Quote Link to comment Share on other sites More sharing options...
DizRotus Posted July 11, 2005 Author Share Posted July 11, 2005 Bruce understands what I was trying to describe. His description accurately describes what I was suggesting. Drivers A and B are not connected to each other electrically. Driver A is conected to the amp, while driver B is not connected to the amp, but has its VC shorted by a resistor, which should cause driver B to resist being moved by the changing air pressure caused by the excursions of driver A. If Driver B had an open VC it would move more freely, similar to an unloaded generator. Quote Link to comment Share on other sites More sharing options...
DrWho Posted July 11, 2005 Share Posted July 11, 2005 http://www.adireaudio.com/Files/TechPapers/RDOOperation.pdf Kinda like this but on a passive radiator? Quote Link to comment Share on other sites More sharing options...
DizRotus Posted July 12, 2005 Author Share Posted July 12, 2005 ---------------- On 7/11/2005 10:40:12 PM DrWho wrote: http://www.adireaudio.com/Files/TechPapers/RDOOperation.pdf Kinda like this but on a passive radiator? ---------------- Not kinda, exactly! Assuming the author of the above tech paper is correct,, it's as I originally specualted; efficiency is one of the first casualties. Using a separate driver as the "passive" should eliminate the problems caused by the proximity of the VCs in a dual VC driver. I'm not planning on trying this, it just occurred to me that it might work and could create some interesting possibilities. Quote Link to comment Share on other sites More sharing options...
D-MAN Posted July 12, 2005 Share Posted July 12, 2005 The induced current in the passive VC is extremely low (that is EXTREMELY LOW). It has no great effect on the suspension compliance, or you could have a perpetual motion machine. It's an extremely weak generator. About equal to the output of an unpowered microphone. Now - hook up a microphone to your speaker and see if that alters the compliance in any way - NOT! DM Quote Link to comment Share on other sites More sharing options...
sfogg Posted July 12, 2005 Share Posted July 12, 2005 "The induced current in the passive VC is extremely low (that is EXTREMELY LOW)." You have measured it? "It's an extremely weak generator. About equal to the output of an unpowered microphone." Not really. Hook up a speaker directly to an o'scope or FFT. Make noise in the room... you will see it through the instruments. The voice coil acts like an altenator. The motion of the cone in this situation is dramatically lower then it would be for a passive radiator situation. "The induced current in the passive VC is extremely low (that is EXTREMELY LOW). It has no great effect on the suspension compliance, or you could have a perpetual motion machine." You sure about that? Ever heard the difference between the bass on an amp with high damping factor... and a low damping factor? (IE...One with a high output impedance....one with a low output impedance....) As far as the speaker is concerned what is the difference? The high output impedance changes how the voice coil/amp reacts to back EMF (signal generated by the speaker from its motion). It tends to resist letting the suspension of the speaker 'settle' the cone so you can get the sort of flabby/tubby/overly round bass high output impedance designs are known for. A low output impedance amp doesn't do that. Shawn Quote Link to comment Share on other sites More sharing options...
D-MAN Posted July 12, 2005 Share Posted July 12, 2005 The electrical output of the passive's VC is NON-USABLE to apply ANY control over its mechanical suspension, even at maximum acceleration and extension. Like I said, you can't get something for nothing, or you'd have a perpetual motion machine. I haven't seen one yet, regardless of how you measure it. DM Quote Link to comment Share on other sites More sharing options...
sfogg Posted July 12, 2005 Share Posted July 12, 2005 "The electrical output of the passive's VC is NON-USABLE to apply ANY control over its mechanical suspension, even at maximum acceleration and extension." You obviously have never played with a DC electric motor in your life. A very common setup... take any DC motor you like and leave its terminals unconnected. Put a crank handle on it and turn it quickly... it will turn very easily. Now connect a few light bulbs across the terminals of the motor and spin it again to the same speed. You will find it takes more force (usually considerably more) to spin the motor. Exact same principal is used for regenerative braking in electric cars. Same thing is being discussed here. "Like I said, you can't get something for nothing, or you'd have a perpetual motion machine. " You are physically moving the passive radiator through the pressure changes in the cabinet from the main drivers motion. That ain't nothing. Are you honestly claiming that moving a coil of wire in a magnetic field *ISN'T* going to produce a voltage? It of course will.... it also follows that the 'compliance' of that motor is going to change depending upon how much of a load it is connected to. Just like it is with the DC motor connected to a couple of light bulbs. Shawn Quote Link to comment Share on other sites More sharing options...
D-MAN Posted July 12, 2005 Share Posted July 12, 2005 Ok, hook up a driver and measure it using the motion of another driver to cause its cone to move, and post the VC induction results. I was an EW technician in the Navy, I know how motors work, thank you. DM Quote Link to comment Share on other sites More sharing options...
Marvel Posted July 12, 2005 Share Posted July 12, 2005 It doesn't have to have much effect on the compliance. Being able to vary it just a tiny bit would give you some tuning room. What might work better would be an inductor with an adjustable iron core. We don't need to get testy! Dana - my pc is shut down while we are having repair made to the house. I'll send an email as soon as I can. I still want to build one of those models I have plans for. Bruce Quote Link to comment Share on other sites More sharing options...
Blackmesa Posted July 12, 2005 Share Posted July 12, 2005 ---------------- On 7/9/2005 9:35:03 PM DizRotus wrote: I'm aware that most passive radiators have no voice coil. My question concerns the ability to use an active radiator as a passive radiator and tune it by varying the load across its voice coil. ---------------- yes, by changing the mass, you change the resonate frequency of the moving cone. Quote Link to comment Share on other sites More sharing options...
Shiva Posted July 25, 2005 Share Posted July 25, 2005 The way that VMPS audio tunes their passive radiators is that they apply something they call mortite damping compound to the passive radiators. By adding or removing some of it with your fingernail it is supposed to tune the passive. I was just reading about it in a review of one of their speakers. Quote Link to comment Share on other sites More sharing options...
dragonfyr Posted July 25, 2005 Share Posted July 25, 2005 ---------------- On 7/12/2005 10:53:09 PM Blackmesa wrote: ---------------- On 7/9/2005 9:35:03 PM DizRotus wrote: I'm aware that most passive radiators have no voice coil. My question concerns the ability to use an active radiator as a passive radiator and tune it by varying the load across its voice coil. ---------------- yes, by changing the mass, you change the resonate frequency of the moving cone. ---------------- Yes, and the passive radiator would exhibit a damped transient response measured in days or weeks!!!! Just what are we trying to do here????? I think the post has seriously veered off course! The audible contribution of this 'thing' (as i think we have created a monster!) has morphed into mush! Rather like an unbraced/undamped flexible cabinet wall! Perhaps you could simply dampen an MDF cabinet wall and achieve the same results - and tune it by virtue of the amount of water and resultant flexibility Quote Link to comment Share on other sites More sharing options...
sunnysal Posted July 25, 2005 Share Posted July 25, 2005 first: the weight of the cone has nothing to do with "transient response" second: a passive radiator works just like a port, in fact a cab with a passive radiator is just like a ported enclosure. instead of a port tube which allows for the manipulation of an air column to propagate into a space we manipulate a cone to do the same thing. when we vary the depth and width of the port tube (or slot) we are changing the mass of the air column as well as the surface areas, etc. the same thing is accomplished by varying the cone size and weight. third: there is no reason why a normal driver can not be expected to function as a passive radiator, it only needs to meet the criteria of mass, compliance and size that one needs when DESIGNING the passive radiator as part of the enclosure. the idea of using a resistor to set the compliance on a normal driver used as a passive radiator is an interesting approach and I see no reason why it would not work, it just seems like an expensive solution to a problem that can be handled via cone size, weight and surround compliance. regards, tony Quote Link to comment Share on other sites More sharing options...
dragonfyr Posted July 25, 2005 Share Posted July 25, 2005 ---------------- On 7/25/2005 9:17:34 AM sunnysal wrote: first: the weight of the cone has nothing to do with "transient response" second: a passive radiator works just like a port, in fact a cab with a passive radiator is just like a ported enclosure. instead of a port tube which allows for the manipulation of an air column to propagate into a space we manipulate a cone to do the same thing. when we vary the depth and width of the port tube (or slot) we are changing the mass of the air column as well as the surface areas, etc. the same thing is accomplished by varying the cone size and weight. third: there is no reason why a normal driver can not be expected to function as a passive radiator, it only needs to meet the criteria of mass, compliance and size that one needs when DESIGNING the passive radiator as part of the enclosure. the idea of using a resistor to set the compliance on a normal driver used as a passive radiator is an interesting approach and I see no reason why it would not work, it just seems like an expensive solution to a problem that can be handled via cone size, weight and surround compliance. regards, tony ---------------- First, I have NO desire to get caught in this tar baby. And unfortunately, as a radiator is a dynamic device, mass is a fundamental part of its compliance (either that or they added alot of extra material to that classical mechanics class - and since we aren't dealing with quantum mechanics, with its near massless objects travelling near the speed of light... We aren't dealing with near light speed response here are we???... ), then mass is a fundamental component in the dynamic model. As is the nature of air as a compressible medium which will naturally lag substantially behind the active dynamic driver response resulting in a very underdamped system - unlike a port with its near instantaneous response. And the very slow underdamped response would exert a back pressure radically out of sync with the dynamic driver's active response. The mechanical model where the PR response is delayed this substantially would present an amazingly complex mechanical model, and I would LOVE to see the incredibly complex non-linear model that would account for this system. Have fun! Quote Link to comment Share on other sites More sharing options...
Petrol Posted July 25, 2005 Share Posted July 25, 2005 hmmmm, that "..This is accomplished by crossing over to the two woofer drivers from the mid-range driver at 1 kHz and allowing the two woofer drivers to remain active down to 200 Hz, below which one of the drivers becomes passive.." sounds a bit like the Klipsch "Tapered Array" x-over used in the R series center channel speakers . . . except the woofer is never "passive" below 200 Hz, jsut by-passed, so to speak. Quote Link to comment Share on other sites More sharing options...
Petrol Posted July 25, 2005 Share Posted July 25, 2005 Oops! It appears that I should read the entire thread and associated links before displaying my ignorance . . . oh well, it was fun, LOL Quote Link to comment Share on other sites More sharing options...
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