From the LDSG Speaker Selection Guide on Passive Radiators: "Sometimes, the rear spiders are also omitted, but PR's with spiders are highly preferred."
http://www.snippets.org/ldsg/boxes.php3#PORTED
Why? What is wrong with a piece of material of the proper weight and a rubber or foam surround?
I am assuming that the Passive Radiator is at least twice the cone area.
Anybody with advice on how to make your own Drone Cones, (Passive Radiators) is extremely welcome to post. Yes, I know about the surrounds at Parts Express and Madisound, but let's see if we can get cheaper. I am thinkng several Passive Radiators for a total area several times the speaker's cone.
http://www.snippets.org/ldsg/boxes.php3#PORTED
Why? What is wrong with a piece of material of the proper weight and a rubber or foam surround?
I am assuming that the Passive Radiator is at least twice the cone area.
Anybody with advice on how to make your own Drone Cones, (Passive Radiators) is extremely welcome to post. Yes, I know about the surrounds at Parts Express and Madisound, but let's see if we can get cheaper. I am thinkng several Passive Radiators for a total area several times the speaker's cone.
kelticwizard:
Rather than using a passive radiator, I prefer to use standard woofers, complete with motor. I can apply weights to the diaphragm to alter the f0, but I can also place networks across the electrical terminal to affect the damping behavior. Variable resistors, capacitors, R-C networks etc. are all worth trying, and give you much more freedom to adjust the sound than a straight passive radiator.
hth, jonathan carr
Rather than using a passive radiator, I prefer to use standard woofers, complete with motor. I can apply weights to the diaphragm to alter the f0, but I can also place networks across the electrical terminal to affect the damping behavior. Variable resistors, capacitors, R-C networks etc. are all worth trying, and give you much more freedom to adjust the sound than a straight passive radiator.
hth, jonathan carr
JCarr:
Thank you for this reply. I had only just become aware of this phenomenon a few months ago from the following discussion:
http://www.diyaudio.com/forums/showthread.php?threadid=7165
Tuning the box with a second speaker does have some disadvantages, mostly cost. One thing though, I could think could make it worthwhile.
If you take a speaker and build an appropriately sized and tuned vented box and a Passive Radiator box of equal volume, the vented box will roll off at 24 dB/octave after the tuning frequency is reached. The Passive Radiator will roll off at 30 dB/octave.
Can you tune a full speaker, one you are not hooking up to an amp, to change that situation? Have you heard of a network you can attach to the voice coil wires of the second (passive) speaker that will restore that order of rolloff to the system?
I am thinking of perhaps adding weight to the cone of the passive speaker to tune it too low, then adding a network to the voice coil that would tune the passive speaker higher.
Just a thought.
Thank you for this reply. I had only just become aware of this phenomenon a few months ago from the following discussion:
http://www.diyaudio.com/forums/showthread.php?threadid=7165
Tuning the box with a second speaker does have some disadvantages, mostly cost. One thing though, I could think could make it worthwhile.
If you take a speaker and build an appropriately sized and tuned vented box and a Passive Radiator box of equal volume, the vented box will roll off at 24 dB/octave after the tuning frequency is reached. The Passive Radiator will roll off at 30 dB/octave.
Can you tune a full speaker, one you are not hooking up to an amp, to change that situation? Have you heard of a network you can attach to the voice coil wires of the second (passive) speaker that will restore that order of rolloff to the system?
I am thinking of perhaps adding weight to the cone of the passive speaker to tune it too low, then adding a network to the voice coil that would tune the passive speaker higher.
Just a thought.
Thank you for pointing out an informative thread.
The speaker that I had directly in mind was the current AudioPhysic Brilon loudspeaker (it was created at our request, and we provided some design input). However, I believe that its goals and your goals may differ.
The Brilon is a compact speaker designed for high-quality sound in a small room (it can be considered to be the "head" section of the current AudioPhysic Virgo, sans bass section). The bass and mids in the Brilon are handled by an approximately 5-inch driver, which in concert with the compact cabinet, is inadequate to produce much bass on its own. Hence the desire for some sort of of bass augmentation system. However, room acoustics are a big variable, especially in small rooms. The bass response from woofers, passive radiators and vents changes substantially according to the proximity to room surface(s). We felt that some sort of tuneable bass augmentation system was the appropriate choice, and this led to the choice of an unpowered woofer operated as a passive radiator, and with the voice-coil leads brought out to a separate pair of electrical terminals for bass tuning purposes.
As you can see, the reasons for why the Brilon uses a tuneable passive radiator system are different from what you had in mind. I imagine that some sort of complex impedance compensation network may get you in the ballpark of where you want to be. However, the passive radiator impedance should be measured mounted in the cabinet, and the stiffness of the air in the cabinet will change as you alter the damping. This will affect the bass response and impedance curve of the main unit in addition to those of the passive radiator. Definitely sounds like a situation where trial-and-error and multiple iterations are called for.
regards, jonathan carr
The speaker that I had directly in mind was the current AudioPhysic Brilon loudspeaker (it was created at our request, and we provided some design input). However, I believe that its goals and your goals may differ.
The Brilon is a compact speaker designed for high-quality sound in a small room (it can be considered to be the "head" section of the current AudioPhysic Virgo, sans bass section). The bass and mids in the Brilon are handled by an approximately 5-inch driver, which in concert with the compact cabinet, is inadequate to produce much bass on its own. Hence the desire for some sort of of bass augmentation system. However, room acoustics are a big variable, especially in small rooms. The bass response from woofers, passive radiators and vents changes substantially according to the proximity to room surface(s). We felt that some sort of tuneable bass augmentation system was the appropriate choice, and this led to the choice of an unpowered woofer operated as a passive radiator, and with the voice-coil leads brought out to a separate pair of electrical terminals for bass tuning purposes.
As you can see, the reasons for why the Brilon uses a tuneable passive radiator system are different from what you had in mind. I imagine that some sort of complex impedance compensation network may get you in the ballpark of where you want to be. However, the passive radiator impedance should be measured mounted in the cabinet, and the stiffness of the air in the cabinet will change as you alter the damping. This will affect the bass response and impedance curve of the main unit in addition to those of the passive radiator. Definitely sounds like a situation where trial-and-error and multiple iterations are called for.
regards, jonathan carr
Hi Kelticwizard
I did once make a passive radiator without a spider exactly as you suggested - a piece of material of the proper weight and a rubber or foam surround.
Disaster! Instead of moving backwards and forwards like a piston, the thing wobbled all over the place and sounded awful. I did think that perhaps I could cure this with another piece of material with another surround, connected to the first a little distance away. The passive radiator would then be a cylinder.
Never tried it though. Sustituted the passive cone for a tuned port and, finally, dumped the whole design and started again.
One can stumble many times on the road to Audio Nirvana.
Good luck with yours
Steve
I did once make a passive radiator without a spider exactly as you suggested - a piece of material of the proper weight and a rubber or foam surround.
Disaster! Instead of moving backwards and forwards like a piston, the thing wobbled all over the place and sounded awful. I did think that perhaps I could cure this with another piece of material with another surround, connected to the first a little distance away. The passive radiator would then be a cylinder.
Never tried it though. Sustituted the passive cone for a tuned port and, finally, dumped the whole design and started again.
One can stumble many times on the road to Audio Nirvana.
Good luck with yours
Steve
Side back and front.
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Not so odd really, Keltic. That's exactly what I was attempting to describe (badly) by saying: "I could cure this with another piece of material with another surround, connected to the first a little distance away. The passive radiator would then be a cylinder".
The purpose is to keep the radiator straight and stop it wobbling as it goes backwards and forwards. The cylinder must have some depth - the deeper it is, the more stable.
I hadn't seen this Celestian passive when I came up with my cylinder proposal - honest!
As for the vent, I don't know. If the foam plug on the inside is attached to both the back and front of the radiator, it should do nothing at all.
The purpose is to keep the radiator straight and stop it wobbling as it goes backwards and forwards. The cylinder must have some depth - the deeper it is, the more stable.
I hadn't seen this Celestian passive when I came up with my cylinder proposal - honest!
As for the vent, I don't know. If the foam plug on the inside is attached to both the back and front of the radiator, it should do nothing at all.
Spiders
Yeah, using a spider also absorbs some of the acoustic load from the woofer. That is, the passive radiator doesn't just flop all over the place outside of its proper vertical alighnment, and higher masses can be used. I have some crappy passive radiators made by Pioneer that only had one surround, and they flopped around terribly. Definitive Tech uses a passive radiator that is 8" and has a surround on each side of the membrane, rather than just one surround. This does a better job of symmetrically supporting the weight.
I remember reading a web page about this somewhere real recently.
What someone needs to do is build an 18" passive radiator with a Blueprint 1803's basket and surround and dual spiders and a flat diaphragm for an ultra-excursion passive radiator to work with the Tumult.
Yeah, using a spider also absorbs some of the acoustic load from the woofer. That is, the passive radiator doesn't just flop all over the place outside of its proper vertical alighnment, and higher masses can be used. I have some crappy passive radiators made by Pioneer that only had one surround, and they flopped around terribly. Definitive Tech uses a passive radiator that is 8" and has a surround on each side of the membrane, rather than just one surround. This does a better job of symmetrically supporting the weight.
I remember reading a web page about this somewhere real recently.
What someone needs to do is build an 18" passive radiator with a Blueprint 1803's basket and surround and dual spiders and a flat diaphragm for an ultra-excursion passive radiator to work with the Tumult.
The following might be of interest.
<a href="http://www.danmarx.org/audioinnovation/flatpassives.html">Flat Passive Radiators ~ Tricks & Methods</a>
<a href="http://www.earthquakesound.com/slaps.htm">SLAPS12 & SLAPS15</a>
and the patent is here
<a href="http://164.195.100.11/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=/netahtml/srchnum.htm&r=1&f=G&l=50&s1=6044925.WKU.&OS=PN/6044925&RS=PN/6044925">US Patent 6,044,925 Sahyoun April 4, 2000 Passive speaker </a>
Regards
James
<a href="http://www.danmarx.org/audioinnovation/flatpassives.html">Flat Passive Radiators ~ Tricks & Methods</a>
<a href="http://www.earthquakesound.com/slaps.htm">SLAPS12 & SLAPS15</a>
and the patent is here
<a href="http://164.195.100.11/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=/netahtml/srchnum.htm&r=1&f=G&l=50&s1=6044925.WKU.&OS=PN/6044925&RS=PN/6044925">US Patent 6,044,925 Sahyoun April 4, 2000 Passive speaker </a>
Regards
James
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