short story: a PR works the same way as a port: it is a piston worh a mass exactly lile a port is a position where the air column is the mass load.
Differences: a PR has a suspension that has a compliance and the PR has a free field resonance frequency. At this frequency, the PR acts as an opening to infinite space and the output of the PR and driver cancels out. A PR system has a 5th order response with a deep null at the PR free field resonance frequency. This is in contrast to a ported system here the response is a 4th order high pass. The null of a PR eats away some bass extension.
both a PR and port leaks midrange. they are both mass loaded pistons and leak essentially the same if they are tuned to the same frequency.
the big difference though is that a port has multiple pipe resonances that cause resonant peaks in he port output. The port output can in fact cancel the sound from the driver at these resonances.
And that is all I have to say about port vs PR
cheers and happy Xmax,
Lars@PURIFi
Differences: a PR has a suspension that has a compliance and the PR has a free field resonance frequency. At this frequency, the PR acts as an opening to infinite space and the output of the PR and driver cancels out. A PR system has a 5th order response with a deep null at the PR free field resonance frequency. This is in contrast to a ported system here the response is a 4th order high pass. The null of a PR eats away some bass extension.
both a PR and port leaks midrange. they are both mass loaded pistons and leak essentially the same if they are tuned to the same frequency.
the big difference though is that a port has multiple pipe resonances that cause resonant peaks in he port output. The port output can in fact cancel the sound from the driver at these resonances.
And that is all I have to say about port vs PR
cheers and happy Xmax,
Lars@PURIFi
It is run by a d1ck,what else do you expect?
A few free samples:
I see you are really qualified to fight and insult others:
JMfahey you writing syphilitic fiction under an influence of something. Nothing of scientific value in your posts. Please save your passionate catharsis of personal attacks for elsewhere. You are wasting internet bandwidth and polluting this other wise informative thread, plus attempting to hijack a thread and turn it into a dumpster. How different are you from people throwing trash on the streets.
AR only was able to describe the second order filter that eventually was found to be a special case of a ported box with the port closed. The AR 1 preceeded the 2 and 3. I had a 4s until the foam turned to power. Still have one box with a RS full range in it.
Because they behave exactly like any other alignment? Where it is at is phase through the crossover region. At least for me. Protecting the tweeter from harmonics to prevent IM.
PRs are best suited when the math defines an impractical port. It depends on the driver. The Purify drivers work out to be insane ports, so PRs. I tried a BP sub and it calculated for a 32 foot port. I went sealed instead. A PR is just a port. No magic. No simple rules. Math.
A simple rule can be to look at the Mms/Sd ratio for a driver. If high then a port will be long and a PR might be better. in addition a high Mms/Sd means that the box can be small. A low Mms/Sd works better in a larger box and the port will be shorter (and hopefully the pipe resonance is above the working range
I sort of agree with you, but they do have a following, particularly the 104 aB, which go for £250-350 on well known auction site. And it isn't for their looks or WAF.
Well, they must represent a nearly transparent window for midrange sound to escape - more so than a port. Even a B139, with its thick composite diaphragm will have this problem.
I'm seeing a lot of strange ideas here how passive radiators work and the effects on phase. Passive radiators are NOT 180 degrees out of phase, they are a full 360 degree cycle out of phase or one full cycle, identical to fourth order crossover. As far as active driver movement, if done correctly, the closer to the system resonance, the more the passive radiator moves and the less the active driver moves. Passive radiators work over a wider range than a port. A perfect example that I have 30 years experience using, Polk RTA 12C. The system is tuned at 15hz. A 12" passive radiator is driven by two 6.5" midwoofers with one of the two rolling off early leaving only one to handle the midrange. The lower the frequency the more the passive moves and the less the two 6.5" midwoofers move. That is the benefit of tuning to a low frequency, the lower the note, the more the passive moves. I think this is where people's understanding lacks as it seems to be implied that the active and passive move the same or the passive slightly less, not in the bass! For the system to behave like many here think it would, it would have to be the poorest designed PR system ever since it was invented in the 1930s. Because it is a passive radiator system as far as tuning, the system Q is on the tight side, in the 0.6 range so bass is very tight. Polk was famous for that before he got big, erroring on the tight side rather than flabby like those deliberately high q sub designs for cars driven by the less sophisticated listeners. The designers know it's wrong but some people want it wrong so they give them wrong and they drive off happily. My RTA 12C is not an expensive system by any means, 1000 a pair in 1983. Still one of the best imaging systems I have heard to date but not without it;s problems. It sounds great up to moderately loud but they fall apart when really pushing, the low cost 6.5" drivers are a lot of the reason for this. Really loud is where a dedicated midrange shines anyway. The pair are asymmetrical, on each side, only the inside midwoofer does midrange, if you reverse them, the image is diffuse rather than pinpoint like taking the stage and cutting it up and having some performers far right and others far left with not much life in the middle. I experimented, they knew what they were doing when they marked one cabinet left and one cabnet right but I digress.
I see other things mentioned like midrange leak, the passive radiator is too heavy for that to occur in any meaningful way and the resonance can be lowered further with weights. Midrange is so far above the resonance of the passive and the cone is too big to really reproduce much if any midrange. I like that not only can a passive operate over a wider range of bass frequencies than a port, it can do so in a much smaller cabinet. The worst possibility of midrange leaking even though much will be absorbed by the fill in the cabinet, is having the port directly behind the driver as many systems do which I scratch my head over, a front port is really optimum for this. Passive radiators are not very picky as to where they are mounted.
The rule of thumb is that the passive should have twice the area as the active driver(s) driving it. If the passive is the same size, it's Xmax must be much longer than the active driver because it needs it. Basically double the displacement. For example, two 8" woofers would ideally drive a single 15" passive radiator. I personally do not like ports nearly as much as I like passive radiator systems. For me the order is 1) Large sealed system with big enough bass drivers, 2) Passive radiator system in a smallish box, or 3) a transmission line. If I'm going to have a big box, it's going to be sealed with all active drivers which is the most phase correct way to do it rather than have a big box for a ported system to work properly.
I've also got other systems, some using the Nestorovic woofer system where the larger bass driver goes through a high pass filter still in the bass and it becomes more passive as the frequency lowers and one can change the damping just by changing a resistor and it already has three position switches that change the damping by each position using their own resistor value. It would be known as an active bass reflex rather than passive. The other system I have uses a 10" bass driver and a 12" driver with a 40 ohm voice coil which was the closest one could get without violating Nestorovic's patent. Dave Graebner designed this as he had only a year to come up with a Nestorovic Replacement. This was done when Mila Nestorovic took his patent and left Speakerlab. Richard Modafferi also of McIntosh Fame like Mila Nestorovic and also helped with the Nestorovic woofer system, came up with another system that he felt was better and worked in the opposite manner. Both the smaller driver and bigger one in the bass operate together at low bass in a sealed system and the larger woofer cuts out in the higher bass notes and is passive up higher and more active way down. Vandersteen did something similar but just weighted the larger driver so it will cut off higher naturally. Both Mila Nestorovic and Richard Modafferi's patents have expired by now. Richard is still alive and recently taking existing systems and employing his bass alignment as well as using his infinite slope crossovers that he originally came up with for Joseph Audio and making them sound of a magnitude better than their original design. It was in an issue of AudioXpress not long ago so there are active variations of passive radiation used.
I see other things mentioned like midrange leak, the passive radiator is too heavy for that to occur in any meaningful way and the resonance can be lowered further with weights. Midrange is so far above the resonance of the passive and the cone is too big to really reproduce much if any midrange. I like that not only can a passive operate over a wider range of bass frequencies than a port, it can do so in a much smaller cabinet. The worst possibility of midrange leaking even though much will be absorbed by the fill in the cabinet, is having the port directly behind the driver as many systems do which I scratch my head over, a front port is really optimum for this. Passive radiators are not very picky as to where they are mounted.
The rule of thumb is that the passive should have twice the area as the active driver(s) driving it. If the passive is the same size, it's Xmax must be much longer than the active driver because it needs it. Basically double the displacement. For example, two 8" woofers would ideally drive a single 15" passive radiator. I personally do not like ports nearly as much as I like passive radiator systems. For me the order is 1) Large sealed system with big enough bass drivers, 2) Passive radiator system in a smallish box, or 3) a transmission line. If I'm going to have a big box, it's going to be sealed with all active drivers which is the most phase correct way to do it rather than have a big box for a ported system to work properly.
I've also got other systems, some using the Nestorovic woofer system where the larger bass driver goes through a high pass filter still in the bass and it becomes more passive as the frequency lowers and one can change the damping just by changing a resistor and it already has three position switches that change the damping by each position using their own resistor value. It would be known as an active bass reflex rather than passive. The other system I have uses a 10" bass driver and a 12" driver with a 40 ohm voice coil which was the closest one could get without violating Nestorovic's patent. Dave Graebner designed this as he had only a year to come up with a Nestorovic Replacement. This was done when Mila Nestorovic took his patent and left Speakerlab. Richard Modafferi also of McIntosh Fame like Mila Nestorovic and also helped with the Nestorovic woofer system, came up with another system that he felt was better and worked in the opposite manner. Both the smaller driver and bigger one in the bass operate together at low bass in a sealed system and the larger woofer cuts out in the higher bass notes and is passive up higher and more active way down. Vandersteen did something similar but just weighted the larger driver so it will cut off higher naturally. Both Mila Nestorovic and Richard Modafferi's patents have expired by now. Richard is still alive and recently taking existing systems and employing his bass alignment as well as using his infinite slope crossovers that he originally came up with for Joseph Audio and making them sound of a magnitude better than their original design. It was in an issue of AudioXpress not long ago so there are active variations of passive radiation used.
Lemme drop in 2 magical words : APR - Reflex!
LspCAD pro has even a module in it for simulation!
Look for AES and Dave Clark or David Clarke for original techpaper
Special PR construction - two PRs of different sizes connected and two chambers
No Dip below tuning and not out of phase!
1/3rd octave deeper cutoff frequency with same sensitivity
who says speaker building isn't a challenge and boring 🙂
LspCAD pro has even a module in it for simulation!
Look for AES and Dave Clark or David Clarke for original techpaper
Special PR construction - two PRs of different sizes connected and two chambers
No Dip below tuning and not out of phase!
1/3rd octave deeper cutoff frequency with same sensitivity
who says speaker building isn't a challenge and boring 🙂
PR vs port: very similar way of operation and similar response: both a port and a PR makes out a resonator more in combination with the box volume. At this box tuning frequency the Port or PR is making almost all the radiated sound.
Ports and PRs transmit about the same amount of midrange (frequencies well above the box tuning frequency) when tuned to the same frequency (both are essentially mass loses pistons).
Differences: ports have pesky pipe resonances absent on PRs. PRs have a free air resonance and this causes a deep notch in the system response and this causes the bass to roll off faster than for a ported system (which causes more phase lag).
that’s the short story
Ports and PRs transmit about the same amount of midrange (frequencies well above the box tuning frequency) when tuned to the same frequency (both are essentially mass loses pistons).
Differences: ports have pesky pipe resonances absent on PRs. PRs have a free air resonance and this causes a deep notch in the system response and this causes the bass to roll off faster than for a ported system (which causes more phase lag).
that’s the short story
David Clarke had his hands in many areas. As a 30+ year avionics tech working on aircraft, David Clarke headphones were our set of choice. I'll look for the tech paper, this sounds interesting to me. Sadly he passed about four years ago. My thinking is in line with his and he disproved a lot of Snake Oil and Flooby Dust marketing which is just replacing knowledge with mysticism and wishful thinking which humans are very good at. I think he is one of the reasons why AES used to be so good as an article had to endure tough peer review. I was sad to just now find out. His wife was very cool about equipment strewn through the house and also was reported to make great home cooked meals and many say that marrying her was the best thing he ever did but I digress.
Thanks for the lspCAD tip. Even though a perfect loudspeaker does not exist, some sure are good enough that they induce sleep deprivation because you want to try out your entire collection and next thing you know, it's getting light outside and the street lamps just turned off. Sure, blame the speakers for being too good and causing all this.😀