Please review the site Rules, Terms of Service, and Privacy Policy at your convenience. Rules, TOS, Privacy
Get familiar with the reaction system: Introducing the Reaction System

ported vs passive radiator designs- thoughts

lots of links, but lots of miscues...

I've just recently been playing around with PR's, and would like to get your inputs.  
Especially regarding experience relative to quality of low frequency reproduction,
and integration (of PR's output) with woofer's output above fs / fb.

thx
(and if I've missed previous discussions at MAC/DIY, sorry, and plz provide link)

Comments

  • edited February 10
    When designed correctly, passive radiators are superior to ports. The frequency response may look the same on paper, but its a scale of volume displacement, a large surface area moving a small distance, vs a small area moving a large distance. With absolutely no wind/chuffing noise, a PR is simply a better experience.

    Here's some more technical stuff:

    For big theatre speakers, IMO tuning below 30Hz can become problematic, of needing an unreasonably large port to get the tuning without air noise, and then the huge port then has a resonance within the passband. Below we have a theatre PR setup with a 20Hz tuning, the cleanest low frequency sound I've heard!




    My opinions are 100% factual
  • thanks for the link, and interesting comment about the scales of volume displacement
    looks like you've paired 2+ to 1, what drivers are you using here- thx
  • @tajanes
    I've designed and built many ported speakers.
    Lately, mostly because Jeff Bagby's been "preaching" about PRs, I've built some PR designs.
    The biggest difference for me is the low bass.
    I'm sure you know that ported systems "unload" below Fb. What this means to me is that even
    if a ported speaker does not exceed xmax when very low bass is present, the overall sound
    will sound like some kind of flabby bass - it's there, but sort of unfocused and blurred.
    I hear much better control on very low bass sounds when using a PR.
    BTW, I hear the same thing, even better when using a TL design, but that usually requires a much
    larger box (IME).
    Hope  this helps.
    Don, Donno, or "Hey you" all work for me, But never "Mr Johnson"
  • tajanes said:
    thanks for the link, and interesting comment about the scales of volume displacement
    looks like you've paired 2+ to 1, what drivers are you using here- thx
    Volume displacement is the most important thing to understand when designing subwoofers. Surface area * xmax to determine how much air you can move. Greater surface tends to sound more effortless to me, whether we are talking about the port cross section or the driver surface area.

    That's an Adire Tumult, 15", 34mm xmax, 1600W, 55lbs.



    Silver1omo
    My opinions are 100% factual
  • that pic just puts a smile on one's face...
    (guessing your UPS person has you help pull it in from the truck...)

  • FYI

    Just came across this, Pat McGinty /  Meadowlark Speakers

    Back in biz, but not with TL’s this time around

    A quick look at the changes in bass systems.

    The TL, like the VB, adds an additional resonant system to the simplest alignment, the CB. The CB resonates due to the fundamental resonance of the driver combined with that of the trapped air volume. The VB tags on the additional resonance of a tuned port and the TL attempts to damp that resonance by resistive techniques that can be quite varied and interesting.

    Both VB and TL are attempts to lower F3 by causing the system to resonate at a lower F. Of course there's no free lunch; one buys extension with wobble. A little wobble can be quite pleasant because what is actually a lack of signal tracking can be perceived as warmth and body. It's a delicate design issue that consumed much of my attention. You've all heard systems that attempted to buy TOO much extension with TOO much resonance because they manifest 'fat blat', one note bass or boominess. (aside: seems like kids' automotive LF systems are intentionally misaligned to exacerbate these problems)

    The take away is that, to achieve pleasant bass with decent extension one had to blend in a certain amount of deviation from accurate signal tracking. The alternative was to go with a critically damped CB and put up with a lack of extension. Invariably these systems sound dry and tight and unwilling, so few entered the market.

    Today we can tear up those old rules. I simply align each CB LF system for optimal signal tracking then make up for the lost extension in the processor. No added resonances required. And the happy thing is that I can dial in that little bit of warmth I prefer in the PEQ. And, even better: you can do as you like once you have your hands on that PEQ. 

    Now that the infernally awful passive low pass filter is out of the way, the amp has a much better grip on cone motion. In our systems there's nothing but a short bit of wire between amp and driver. So we're hearing more texture in the bass; there's a real sense of speed and detail. More 'open' at the bottom end.

    Improvements that are at least this compelling are also happening in the midrange.  

    Woof! Ain't life grand?
  • @tajanes
    I'd suggest taking McGinty's post as 1/2 marketing.
    Some VERY respected designers and commercial speakers use TLs, and no one has noted that those sound
    flabby or "slow". McGinty also conflates "teenager auto subs" (probably 6th order bandpass one note bass) with standard VB or TL designs. His designs probably sound good, but he is trying some voodoo marketing.
    Don, Donno, or "Hey you" all work for me, But never "Mr Johnson"
  • I'd agree, evidenced by many great reviews of McGinty's older TL designed speakers...

    Q: So what are your thoughts, of possibly an aperiodic vented TL loaded ( AVTL ) system in combo with a DSP based amp?  With the DSP one can a) put in a very narrow and deep notch to address the fs of a speaker / box system ( I did for my open backed speaker system and workes well), b) get the advantage of reducing imped rise @ fs (as with aperiodic vented systems) and c) atteunate the closed box coloration (reflective waves) via both the TL line and the restrictive vent?  
  • Are there bad speaker reviews?
    tajanes said:
     With the DSP one can a) put in a very narrow and deep notch to address the fs of a speaker / box system ( I did for my open backed speaker system and workes well)
    Huh?
    My opinions are 100% factual
  • edited February 11
    with an open back / open baffel to offset the low freq cancellation you can use the DSP with a 3 or 6dB low shelf, and then a notch to moderate this lift where the woofer(s) fs gets loose / distortion
  • edited February 11
    re speaker reviews, yes unfortunately they tend to often correlate with cost of speaker / value of advertising
    or reflective of the author's personal preference / bias

  • Using DSP to combat the diffraction and low frequency response of an open baffle system is fine, but it has nothing at all to do with the driver Fs.
    My opinions are 100% factual
  • edited February 11
    It does directly exacerbate the effects (distortion, lack of control..) of a driver at / near its Fs  (where you are boosting the lows to offset the diffraction), but of course does not change the driver's Fs.  
  • Let's be a little more clear here...

    You cannot compensate the Fs either with DSP. DSP is like a series attenuator or parametric EQ if you look at it right, where everything is approximated as a series-wired boost or cut. There is no method of using DSP to compensate anomalies that usually require shunting circuits in passive networks. If you are placing an EQ dip at Fs, then your (mid)bass response will suffer for it.

  • edited February 11

    ...Sure
    Sorry guys - for any confusion; I did not / do not suggest compensating, but attenuating effects of add'l boost... (to a woofer around its Fs)

    i.e. with W with Fs in low 20's or so, and a notch Q of up to 50 (may be too narrow- however possible with DSP - but for this point of clarification... so as to not affect (mid)bass) and with a nominal negative gain, i.e. cut in view of the low shelf's add'l boost >  this will help address the issue(s) of a low-shelf which is put in relative to baffel step diffraction characteristics (when used with an open back / open baffle system).

    This in combo with a HP around the Fs biz a low-shelf continues 'south' unlike a peak Eq setting w/o trying to push a speaker below its range, providing for a rational low-end roll off.  Whereas a passive system may be subject to just flapping in the wind (unloaded below and specifically around Fs)  
  • I remember a discussion where Jeff Bagby said a passive radiator will always have more losses and be less ideal than a properly designed port.  He said a PR was just a way around an excessively long port in a small enclosure.  I'm too lazy to go searching for it but it stuck in my head because I remember thinking to myself "That's great because a port tube is chump $$$ compared to those nice PR's.  Maybe he changed his mind recently but I do remember that being his stance a few years ago.  FWIW I have never designed a woofer/PR system.

  • As Roseanne Roseannadanna said 'its always something'   (SNL)

    And balancing / managing tradeoffs are in the details.... but for me this is what makes going to the DIY shows sooo interesting >  to see many different ways people deal with designing around the inexact science / art of speaker building  
  • PWRRYD said:
    I remember a discussion where Jeff Bagby said a passive radiator will always have more losses and be less ideal than a properly designed port.  He said a PR was just a way around an excessively long port in a small enclosure.  I'm too lazy to go searching for it but it stuck in my head because I remember thinking to myself "That's great because a port tube is chump $$$ compared to those nice PR's.  Maybe he changed his mind recently but I do remember that being his stance a few years ago.  FWIW I have never designed a woofer/PR system.
    I remember that, and agree with you 100%
    Recently on FB, Jeff Bagby posted a long(ish) piece stating that PRs were better than ports.

    Don, Donno, or "Hey you" all work for me, But never "Mr Johnson"

  • rjj45 said:
    Recently on FB, Jeff Bagby posted a long(ish) piece stating that PRs were better than ports.

    If it's the post I'm thinking of, it wasn't too recent, and was just a re-post of the article he wrote for Salk sound several years back. You can find the link in the first reply to this thread.
    My opinions are 100% factual
  • Found it on FB. July 2018. IMHO, not nearly the same as the Salk article.
    This goes into quite of bit of technical detail about PRs and overall response.
    https://www.facebook.com/groups/DIYLoudspeakerProjecPad/search/?query=bagby passive radiator&epa=SEARCH_BOX
    Don, Donno, or "Hey you" all work for me, But never "Mr Johnson"
  • Thanks for posting that link, though I believe anyone clicking that will need to be a member of the "DIY Loudspeaker Project Pad".

    July 25 2018, posted a Salk Sound blog followed by some additional commentary.

    So there's this:

    This:

    And some FB commentary:
    Now to learn something that may be new to you about passive radiators. This will make you smarter than participants on other speaker building groups, which is part of our goal here on the Project Pad.

    Back on the old Madisound forum there were a lot of technical discussion with guys like Linkwitz, Kreskovsky, Verdone, Feyz, Ennenga, and more. But often these were loaded with complex mathematics. Not being an EE I still managed to work through the math OK, but this was not the case for many members. So, today I will make you smarter and do it without that pesky math stuff at the same time. If you are able to visualize the descriptions I give you, you will do just fine.

    Let's start with a woofer in a sealed box. As I mentioned in the article above, the air inside the sealed box is compressible. When it compresses due to the cone moving inward in the box, it push back. This behavior is like a spring and we call it the air compliance of the box. This air spring compliance helps a sealed box to control cone travel.

    Now, let's add a port to the box. This port must be tuned to the proper frequency to help extend bass performance. Actually, that's not exactly correct. The port is not really tuned, the box air compliance is tuned using the port. Here's how that works. As we mentioned, the air in the box acts like a spring. The air mass in the port acts like a weight attached to the spring. The greater the weight the slower, and lower in frequency the spring will oscillate. This is how the port is used to tune the box. Just hold on to that visual of a weight hanging on a spring.

    I am sure we have all heard that a passive radiator is like a vented speaker. This is true in the region of the box tuning frequency. The passive radiator acts like a mass hanging on the spring and can be used to tune the box compliance to the desired resonance frequency in much the same way as a port does.

    In both cases, port or passive radiator, the resonance creates a very high internal pressure in the box at this frequency. This pressure, if there were zero losses, would force cone travel to come to zero at this frequency as all output would come from the port or passive radiator at this frequency. However, there are some losses, so in reality we end up with a notch in the woofer's response at the tuned frequency (Fb) and most of the output does still come from the port / PR.

    Now, as we move below Fb the passive radiator begins to act very differently than a port. Here's why - You still have that image of a weight hanging a spring? Well, a passive radiator is a much more complex mechanical system than a simple port. It has its own moving suspension and it has its own resonance frequency ( which we will call Fsp). So in your image of the weight hanging from the spring, you need to attach another spring to the weight and add an additional weight hanging on it. So, now you have a weight on a spring hanging from a weight on a spring. Got that, right?

    In a vented system the port output and the cone output are in phase with each at the tuning frequency. Below that both are rolling off at 12 dB/oct. But, the port is moving out of phase with the cone as the frequency decreases. This is what causes vented systems to roll-off at 24 dB/oct. The same thing occurs with a passive radiator until we reach the frequency of Fsp.

    At this point (Fsp) the passive radiator output is out of phase with the output of the woofer cone and a notch in the summed response occurs. At this point the PR's phase "wraps" or flips, and below Fsp the PR's phase moves back in phase with the cone. This means that at very low frequencies the summed response, unlike the vented system, rolls-off at only 12 dB/oct, just like a sealed system. In fact, it is a sealed system below Fsp. This means we have the added benefit of the box no longer unloading at low frequencies like a vented box does. Excursions of the woofer cone are much better controlled at very low frequencies. With the Passive Radiator, you get the benefit of a vented box at the tuning frequency and the benefit of a sealed box at lower frequencies. You may have never heard this before, which is what makes this a smarter place to hang out.

    Here are a few graphs to demonstrate this phase and response relationship. These are based on the J.E. Benson Box Model, which is still considered one of the most accurate out there, and the one my software is based on. The first graph shows the response as I described. The second one shows the phase response of the cone, PR, and summed response. The third show response and phase together.


    Passive Radiators - part 3

    Just a few additional comments here. First of all, we need to keep in mind that for the vast majority of alignments, if we are merely considering bass extension, and a port of the correct size is able to fit in the enclosure, then it will be more efficient than a passive radiator. Ports have much fewer losses than PR's have and will be superior in most applications for bass reinforcement.

    Passive radiators have their greatest use with low tuned subwoofers in small enclosures, or to help limit excursion like I discussed yesterday.

    Third, a lot of people ask if old drivers can be converted in a passive radiator. They can, but they will usually be far from optimal in performance. Most of the time woofers make terrible passive radiators and most of the example of PR's made using existing drivers to match, they do not perform as well a PR's designed from the ground up.

    Optimally, you need a passive radiator to have as low of an Fsp and as high of a Qmp as possible. They also need to have very long linear mechanical travel. Most woofers have too high of an Fs and too low (lossy) of a Qm to do well. There are models from SB Acoustics, Scanspeak, and Peerless that do perform well. The key here is to model them in good software and see how they will do.

    The best radiators I have seen are the MDF radiators the Acoustic elegance made. These have an Fsp around 7 Hz and a Qmp of about 50. I had some custom made for me by another manufacturer and they had similar parameters. The CSS APR radiators, look like regular woofers, but they were designed by Dan Wiggins and perform very well.

    Parts Express has some new Reference series PR's made to match their Woofers. These are OK, but do not have quite the parameters I would prefer. I was asked to design a group of subwoofers using the Reference woofers and the matching PR. I found that in almost every case I really needed to use two PR's in order to lower Fsp enough and move enough air to make them work sufficiently as subwoofers. I bring this up because I know that PE advertises these to be used one for one, but that does not look adequate in my opinion. It should really take two, which gets a little costly, I know.





    rjj45
    My opinions are 100% factual
  • The best radiators I have seen are the MDF radiators the Acoustic elegance made.

    See photo of them above :)

    My opinions are 100% factual
  • thanks for posting this commentary
  • I have, like many others I'm sure, done extensive modeling. It is a rare PR that models worth a shit. Most commonly available simply tune too low out of the box to justify the cost over going sealed - and by the time you add a second of the same diameter as the driver... 

    Other benefits notwithstanding, until we see PR'S with lightweight cones that can also handle a lot of added mass we will not be seeing a lot of them in common use. Indeed, it seems only in the realm of ultra low tuned subwoofers are they worth tinkering with in DIY. YMMV.
    I have a signature.
  • edited February 12
    dcibel said:

    Passive Radiators - part 3



    "Just a few additional comments here. First of all, we need to keep in mind that for the vast majority of alignments, if we are merely considering bass extension, and a port of the correct size is able to fit in the enclosure, then it will be more efficient than a passive radiator. Ports have much fewer losses than PR's have and will be superior in most applications for bass reinforcement."


    Seems like Jeff hasn't really changed his stance at all.  Looks like he has found a small group of applications where a passive radiator is the better tool for the job.  Otherwise he wouldn't have made a point to add these comments with words like "vast majority" and "superior in most applications".



  • edited February 12
    I'm not interested in an argument, I am interested in learning best practices from experts. Here is what Jeff said in part 2 of the series of posts
    : Now, as we move below Fb the passive radiator begins to act very differently than a port. Here's why - You still have that image of a weight hanging a spring? Well, a passive radiator is a much more complex mechanical system than a simple port. It has its own moving suspension and it has its own resonance frequency ( which we will call Fsp). So in your image of the weight hanging from the spring, you need to attach another spring to the weight and add an additional weight hanging on it. So, now you have a weight on a spring hanging from a weight on a spring. Got that, right?

    In a vented system the port output and the cone output are in phase with each at the tuning frequency. Below that both are rolling off at 12 dB/oct. But, the port is moving out of phase with the cone as the frequency decreases. This is what causes vented systems to roll-off at 24 dB/oct. The same thing occurs with a passive radiator until we reach the frequency of Fsp.

    At this point (Fsp) the passive radiator output is out of phase with the output of the woofer cone and a notch in the summed response occurs. At this point the PR's phase "wraps" or flips, and below Fsp the PR's phase moves back in phase with the cone. This means that at very low frequencies the summed response, unlike the vented system, rolls-off at only 12 dB/oct, just like a sealed system. In fact, it is a sealed system below Fsp. 

    This means we have the added benefit of the box no longer unloading at low frequencies like a vented box does. Excursions of the woofer cone are much better controlled at very low frequencies. With the Passive Radiator, you get the benefit of a vented box at the tuning frequency and the benefit of a sealed box at lower frequencies.

    Don, Donno, or "Hey you" all work for me, But never "Mr Johnson"
  • edited February 13

    Ditto (on best practices)

    This last paragraph seems to provide some credence to PR’s being mated with full/broad range drivers, which often are a bit less robust in power handling and control, especially at lower frequencies (...potentially better suited than when mated with ports or even TLs).   

    One area I’m curious about is the integration (or lack thereof) of the PR’s vs. a port’s output with the woofer’s output above fs/fb (as it rolls off), i.e. which provides better integration and/or less destructive to the quality of sound reproduction.

    thx

     

  • edited February 13
    PWRRYD said:
    dcibel said:

    Passive Radiators - part 3



    "Just a few additional comments here. First of all, we need to keep in mind that for the vast majority of alignments, if we are merely considering bass extension, and a port of the correct size is able to fit in the enclosure, then it will be more efficient than a passive radiator. Ports have much fewer losses than PR's have and will be superior in most applications for bass reinforcement."


    Seems like Jeff hasn't really changed his stance at all.  Looks like he has found a small group of applications where a passive radiator is the better tool for the job.  Otherwise he wouldn't have made a point to add these comments with words like "vast majority" and "superior in most applications".



    I just wanted to put some context to the loss of efficiency when using a passive radiator. Recently I looked at using the new SB15 "racetrack" PR versus a port for a bookshelf design using Wavecor WF152. Since PRs generally need to have greater surface area than the driver, this racetrack design is great to provide that extra surface area without needing to make a wider speaker.

    Here I am using a 10L cabinet, tuned both systems to 40Hz. The grey line is a ported system, the black line is the SB15 PR. Less efficient, but still far more efficient than a sealed cabinet.

    Here's the excursion plot of the ported system:

    The excursion plot of the passive radiator system:

    I've never trusted the simulated excursion plots below tuning frequency for ported systems, and I don't think I'll trust them in passive radiator systems either. T/S parameters just don't give you the change in "spring force" as you reach the limits of the driver, which I think is important to make accurate comparisons here.


    My opinions are 100% factual
  • rjj45 said:

    This means we have the added benefit of the box no longer unloading at low frequencies like a vented box does. Excursions of the woofer cone are much better controlled at very low frequencies. With the Passive Radiator, you get the benefit of a vented box at the tuning frequency and the benefit of a sealed box at lower frequencies.

    Just to throw another wrench into the mix, if correcting for the driver unloading at low frequency is your goal, an active high pass circuit can be built for equal or less cost than most passive radiators. No cost at all if you already have a DSP in the mix, but a high pass circuit can be easily simulated at the cabinet design stage, and is just an op-amp and a couple resistors at the end of the day, only gets expensive if you need to put it into a box with a power supply, but the tech savvy can hack it onto a plate amp using the existing power available. You may end up with a slightly steeper low end rolloff, however.
    My opinions are 100% factual
  • edited February 13
    another wrench is another tool for consideration- thx 
    and, I appreciate the model outputs- interesting tools as well 


Sign In or Register to comment.