it might mean that there is a passive drum(woofer) in the elcosure, as well as an active one. The passive one will reflect the active woofer in the cabinet. On the -ve half the active drum compresses the air inside the cabinet causing the passive drum to extend (+ve), thus reflect the active woofer.
RobPhill: Are you talking about a Passive Radiator, (Drone Cone), system? This is where an undriven speaker-without magnet or voice coil-is used to tune the box instead of a vent or port.
If it is not that, then may I ask you describe or give a link to describe what you are talking about? I am unfamiliar with it.
If it is not that, then may I ask you describe or give a link to describe what you are talking about? I am unfamiliar with it.
If it is a Passive Radiator, (Drone Cone), then here is a link to someone who is adding one to his Peerless XLS enclosure. It is customary to have the area of the Passive Radiator be twice the area of the driven speaker-the driven speaker is the one that is hooked up to the amplifier. The Passive Radiator, of course, is not.
If the Passive Radiator should be twice the area of the driven speaker, or if it is the same size, there should be two Passive Radiators.
http://www.diyaudio.com/forums/showthread.php?threadid=9608&highlight=Peerless+passive
If the Passive Radiator should be twice the area of the driven speaker, or if it is the same size, there should be two Passive Radiators.
http://www.diyaudio.com/forums/showthread.php?threadid=9608&highlight=Peerless+passive
Rob: I figured that is what you meant. I haven't seen it explained quite that way, though.
Here is a link that will explaing to Takashi the difference between a Ported or Vented box, and a Passive Radiator box. In fact, if Takashi scrolls up and down the page, a great variey of loudspeaker boxes will be explained, with links for further exploration.
http://www.snippets.org/ldsg/boxes.php3#PORTED
Here is a link that will explaing to Takashi the difference between a Ported or Vented box, and a Passive Radiator box. In fact, if Takashi scrolls up and down the page, a great variey of loudspeaker boxes will be explained, with links for further exploration.
http://www.snippets.org/ldsg/boxes.php3#PORTED
Well, you went into it with a lot more detail than I ever imagined. I think you described the action, stroke-by-stroke, of the Passive Radiator versus the driven speaker. That was what I had trouble following.
Basically, I have always just followed the practical advice. That there are two ways to tune a box-vent (port), or Passive Radiator. That what tunes the box is the mass of air in the port, or the mass, (weight) on the Passive Radiator diaphragm.
The only other thing I know is that unlike a port, a Passive Radiator has a resonance frequency itself, and this resonance frequency has a tendency to take the edge off the bass of the Passive Radiator. While a vented enclosure will drop at the rate of 24 dB/octave, the Passive Radiator enclosure, with the same speaker in the same box, will drop 30 dB/octave. This will result in a slightly higher F3 as well, as provide a bass sound that is slightly flabbier, less distinct.
That is why Passive Radiators are generally not used unless the size of the port in the box will be too large-like taking up 30% of the box volume. Since the volume of the air in the port must be subtracted from the volume of air in the enclosure, that means you have to build your box 30% or more larger-or use a Passive Radiator.
With speakers like the Peerless XLS line providing deep bass in a relatively small box, Passive Radiators seem to have been re-discovered. They were kind of "on the shelf" for awhile, because up to now, any speaker that went down really low needed a bigger box, and the bigger the box, the smaller the vent length needed to tune it low. There was no problem with vent length. Now the boxes are smaller, so the vent lengths are getting impractical, and the Passive Radiator has been put back into use.
Basically, I have always just followed the practical advice. That there are two ways to tune a box-vent (port), or Passive Radiator. That what tunes the box is the mass of air in the port, or the mass, (weight) on the Passive Radiator diaphragm.
The only other thing I know is that unlike a port, a Passive Radiator has a resonance frequency itself, and this resonance frequency has a tendency to take the edge off the bass of the Passive Radiator. While a vented enclosure will drop at the rate of 24 dB/octave, the Passive Radiator enclosure, with the same speaker in the same box, will drop 30 dB/octave. This will result in a slightly higher F3 as well, as provide a bass sound that is slightly flabbier, less distinct.
That is why Passive Radiators are generally not used unless the size of the port in the box will be too large-like taking up 30% of the box volume. Since the volume of the air in the port must be subtracted from the volume of air in the enclosure, that means you have to build your box 30% or more larger-or use a Passive Radiator.
With speakers like the Peerless XLS line providing deep bass in a relatively small box, Passive Radiators seem to have been re-discovered. They were kind of "on the shelf" for awhile, because up to now, any speaker that went down really low needed a bigger box, and the bigger the box, the smaller the vent length needed to tune it low. There was no problem with vent length. Now the boxes are smaller, so the vent lengths are getting impractical, and the Passive Radiator has been put back into use.
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