DizRotus Posted July 9, 2005 Share Posted July 9, 2005 I seem to recall a system (perhaps Speakerlab) many years ago that used two dynamic drivers, but one was not powered. Instead, it had a resistor across the contacts. When the motion of the active driver caused the passive dynamic driver to move, the current it generated was sent through the resistor. Wouldnt it be possible to get more elaborate than a simple resistor, e.g., an L-pad or something even more sophisticated to tune the passive dynamic driver? Intuitively, it seems the first penalty would be inefficiency. Quote Link to comment Share on other sites More sharing options...
sfogg Posted July 9, 2005 Share Posted July 9, 2005 Usually passive radiators have no voice coil at all. They are tuneable though, by adjusting the mass of the radiator itself is how they are typically tuned. For example the 'cone' on the passive radiators in my ContraBass subwoofer are actually baltic birch discs which are attached to the surrounds and to a spider. The weight of the discs are what determines the tuning of the PRs. Shawn Quote Link to comment Share on other sites More sharing options...
DizRotus Posted July 9, 2005 Author Share Posted July 9, 2005 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. Quote Link to comment Share on other sites More sharing options...
johnyholiday Posted July 9, 2005 Share Posted July 9, 2005 just my 2 cents, i would think the counter EMF would be the highest with no resistance, an lowered by resistance Quote Link to comment Share on other sites More sharing options...
WMcD Posted July 9, 2005 Share Posted July 9, 2005 The resonant frequency Fs is set by the compliance (spring) of the surround and spider and by the mass. So the resonant frequency can be tuned by the mass. I've read about screw on weights. There is little to be done about the compliance. The Qms (mechanical system) or peakyness of the system is set by the mechanical resistance in the surrond and spider. It is usually fairly low. This is why woofers have high Qms compared to Qes (electrical system). The overall resistance could be adjusted by the voice coil load as you point out. But I think the Fs is the thing most designers would like to fool with. It is not going to be changed by the electrical load. Gil Quote Link to comment Share on other sites More sharing options...
DizRotus Posted July 9, 2005 Author Share Posted July 9, 2005 ---------------- On 7/9/2005 10:33:50 PM johnyholiday wrote: just my 2 cents, i would think the counter EMF would be the highest with no resistance, an lowered by resistance ---------------- I believe you have that backward. If the voice coil on the "passive" radiator were open it would not generate an "EMF." With a load, it would be forced to do work. Try turning a generator (dynamo) with no load; it's easy. Now put a large wattage bulb in the circuit and it gets hard to turn. Quote Link to comment Share on other sites More sharing options...
johnyholiday Posted July 9, 2005 Share Posted July 9, 2005 well i'm 2 cents waiting for change ,is this a trick ? like perpetual motion machine Quote Link to comment Share on other sites More sharing options...
DizRotus Posted July 9, 2005 Author Share Posted July 9, 2005 ---------------- On 7/9/2005 10:41:12 PM William F. Gil McDermott wrote: The resonant frequency Fs is set by the compliance (spring) of the surround and spider and by the mass. So the resonant frequency can be tuned by the mass. I've read about screw on weights. There is little to be done about the compliance. The Qms (mechanical system) or peakyness of the system is set by the mechanical resistance in the surrond and spider. It is usually fairly low. This is why woofers have high Qms compared to Qes (electrical system). The overall resistance could be adjusted by the voice coil load as you point out. But I think the Fs is the thing most designers would like to fool with. It is not going to be changed by the electrical load. Gil ---------------- Either I'm totally off base, or failing to make myself clear, or both. It seems to me that putting an adjustable load (independent of the signal going to the "active" driver) across the voice coil of the "passive" driver would alter the compliance of the unit, just like adding mass, decreasing enclosurure volume, etc, i.e., the Fs would change as the increasing load across the voice coil caused the passive driver to increasingly resist being moved by the change in pressure inside the enclosure. There would be no direct electrical connection of the passive driver to the other driver or the amplifier. EDIT: Gil, I think I now understand why the Fs would not be changed by a load across the voice coil of the passive driver. The Fs is determined in free air, is it not? Quote Link to comment Share on other sites More sharing options...
djk Posted July 10, 2005 Share Posted July 10, 2005 This is probably what you are referring to. "All Nestorovic loudspeakers feature a woofer design which uses both active and passive components in a patented configuration, allowing you to hear frequencies as low as 25 Hz from the full-range models. 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." http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=/netahtml/srchnum.htm&r=1&f=G&l=50&s1=3,984,635.WKU.&OS=PN/3,984,635&RS=PN/3,984,635 Images require a free TIFF viewer. "Low range loudspeaker system Abstract An audio speaker system that provides enhanced fidelity of sound reproduction in the bass acoustic frequency range, by comprising a usual driven primary radiator, a pair of conductors for connecting the primary radiator to its energy source, a driven auxiliary radiator connected to that pair of conductors via a reactive network, both radiators being acoustically coupled by being housed in a closed cabinet common to both of them except for the respective separate diaphragm openings for each of said radiators, and the respective function and value of the individual component elements of said network relative to one another and the volume of the cabinet are such as to have the system operate on the bass-reflex principle." Quote Link to comment Share on other sites More sharing options...
DizRotus Posted July 10, 2005 Author Share Posted July 10, 2005 I guess I was recalling the Nestorovic design. Speakerlab sold a version. It was that concept that caused me to wonder about doing something similar on a simpler scale, such as a variable load across the voice coil of a passive active radiator. By variable, I mean adjustable, not constantly variable during use. Quote Link to comment Share on other sites More sharing options...
sfogg Posted July 10, 2005 Share Posted July 10, 2005 I think Adire Audio has some information on doing something like this with a dual voice coil woofer. You drive one coil and feed the other coil into a resistor to adjust its tuning somewhat. Shawn Quote Link to comment Share on other sites More sharing options...
michael hurd Posted July 10, 2005 Share Posted July 10, 2005 What Djk posted sounds like a 2.5 way crossover like the Klipsch center channels that have dual woofers. Quote Link to comment Share on other sites More sharing options...
djk Posted July 10, 2005 Share Posted July 10, 2005 Its quite a bit different. In a 2.5 way only one woofer works up to the crossover point, and both work down low. In this patent both drivers work up to the crossover point, and only the smaller driver works down low. The larger driver has a resistor in series with it, removing power and making it a not quite passive radiator. Quote Link to comment Share on other sites More sharing options...
michael hurd Posted July 11, 2005 Share Posted July 11, 2005 I stand duly corrected, I did not read the patent information, just read the brief description. Quote Link to comment Share on other sites More sharing options...
djk Posted July 11, 2005 Share Posted July 11, 2005 Its really a quite interesting patent, I'd like to leard more about the T/S parameters required for the drivers. The auxiliary radiator is driven through a 25 ohm resistor (this could be made variable) bypassed with a 500µF cap. The auxiliary radiator has an Fs about half of the main woofer. From Jeff Joseph (JSE speakers with infinite slope crossovers) I learned that Mile Nestorovic recently suffered a stroke, I hope he makes a good recovery. Mile Nestorovic and Richard Modafferi (the other name on this patent) both worked for McIntosh. Nestorovic was best known for the creation of the MC3500 (Mac's biggest tube amp). Quote Link to comment Share on other sites More sharing options...
Klipschguy Posted July 11, 2005 Share Posted July 11, 2005 I built a sealed sub using a dual voice coil driver. One voice coil is amplified the other voice coil has a resistor across it to act as an "inductively coupled" brake. The damping resistor value was precisely calculated to tune my driver to the box where Q=.707. The results are excellent. Maybe the passive radiator Neil was talking about was tuned by similar resistive damping? Andy 1 Quote Link to comment Share on other sites More sharing options...
michael hurd Posted July 11, 2005 Share Posted July 11, 2005 Klipschguy, this is exactly what sfogg was talking about, plans at the Adire audio website. Quote Link to comment Share on other sites More sharing options...
Klipschguy Posted July 11, 2005 Share Posted July 11, 2005 Michael, sorry I missed Shawn's post - that's what I get for skimming too quickly. Anyway, the technique works well, especially if you are trying to precisely tune a woofer to an existing exclosure. Quote Link to comment Share on other sites More sharing options...
D-MAN Posted July 11, 2005 Share Posted July 11, 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. ---------------- I see what you're thinking, adjust the output of the active driver to control the output of the active driver to subsequently control the passive. A resistor across the active VC is not going to alter frequency (hence no tuning), only overall loudness (limits current), but seems a waste of energy and is at cross-purposes, IMO. The passive would be tuned by the overall enclosure volume to a degree. Also a tuned cavity could be put behind and coupled to the passive to tune the resonance. But aside from that, it seems to me that the passive is intimately coupled to the active driver by the shared air space in the back chamber, and the resonance of that is determined by overall volume and the active driver's parameters. DM Quote Link to comment Share on other sites More sharing options...
Marvel Posted July 11, 2005 Share Posted July 11, 2005 ---------------- On 7/11/2005 12:59:52 PM D-MAN 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. ---------------- I see what you're thinking, adjust the output of the active driver to control the output of the active driver to subsequently control the passive. A resistor across the active VC is not going to alter frequency (hence no tuning), only overall loudness (limits current), but seems a waste of energy and is at cross-purposes, IMO. The passive would be tuned by the overall enclosure volume to a degree. Also a tuned cavity could be put behind and coupled to the passive to tune the resonance. But aside from that, it seems to me that the passive is intimately coupled to the active driver by the shared air space in the back chamber, and the resonance of that is determined by overall volume and the active driver's parameters. DM ---------------- D-Man -- Let's try to be clearer with this: Driver A connects to the amp. Driver B is a speaker with a VC as well, but connected to a variable resistance. Driver B acts like a passive radiator, the compliance (and therefore, tuning) of which can be adjusted by varying the resistance across the VC. More resistance would put a greater load on the EMF generated by the VC, causing a stiffer compliance. Is this what we are talking about? 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. Bruce Quote Link to comment Share on other sites More sharing options...
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