Well...as it goes out of phase it is also dropping SPL quickly, so it's not really contributing any sound energy at all. No more than the box walls anyway.
The other thing with passive radiator is that it's not as good of a sound insulator as say mdf. So it will radiate negative air pressure of midrange frequencies. At least it seem logical to think this way
So how much of not really best to be measured. Good to see some measurements. Just curious.
why do people keep ignoring things that happen outside of the area of interest since the early 80's i've not understood why people can't come to grips with what's going on at higher frequencies with bass reflex designs...
such as based on size these things behave as horns at higher frequencies...do your own homework...
not diks. just posers who don't understand what they are talking about. so they say "do you homework". " i am surprised you are so ignorant". classic replies of incompetent and unknowledgeable. it's more important for them to look cool and smart in the crowd as opposed to actually know the matter. kindergarten basically
it's all written in here https://en.wikipedia.org/wiki/Bass_reflex
(spoiler: the two emissions are in phase! 😏)
(spoiler: the two emissions are in phase! 😏)
we already agreed about the phase question . its in phase only at that little window of resonance frequency. but the "limitations" paragraph in wikipedia pretty much sums up all my commonsensical suspicions about passive radiators
Richard you should consider sealed w/ EQ. There is also the option of using a large cap in the woofer crossover to create a 3rd order rolloff but with adjustable "boost" just above the knee.
Seems like I'm only one here to join the club of BR/PR haters. Simple logic IMO... My first hifi speakers were sealed 3-way in ´70s. Then I tried to live with big and mid-size BR speakers during 80s-10s. Then diy was possible again and my latest builds have been sealed 3-ways with dsp. No going back to BR!
The problem is to make definitive measurements to show the problems with phase mismatch. I have only a USB-mic, so no way to keep timing/phase angle fixed. But for sure the PR or port do radiate lots of "noise" from the box, and with phase difference to direct sound, because of different pathlength.
Best place for the port/PB is the backside of the cabinet, because then sound well above tuning resonance will get attenuated most, and gets even more time delay.
Nearfield measurements of the driver and the port can be done, but summed response must be measured further away which will show also diffractions and even room modes if done indoors. Low frequencies need long gating...
Best measurements to show port/PR problems are those done with Klippel NFS at ASR or Erin's Audio corner
Here my measurements of my poor 10"+passive 10" sub (from my museum). Drivers are side by side as per instructions... Spl of gp measurement is not with same amp gain. 500ms and 20ms gating.
Nearfield of each unit and groundplane at 60cm, all indoor. We can see summation below 25Hz and at 50-60Hz, then a deep notch at 65Hz, low notch at 85Hz, peak at 105Hz etc.
The problem is to make definitive measurements to show the problems with phase mismatch. I have only a USB-mic, so no way to keep timing/phase angle fixed. But for sure the PR or port do radiate lots of "noise" from the box, and with phase difference to direct sound, because of different pathlength.
Best place for the port/PB is the backside of the cabinet, because then sound well above tuning resonance will get attenuated most, and gets even more time delay.
Nearfield measurements of the driver and the port can be done, but summed response must be measured further away which will show also diffractions and even room modes if done indoors. Low frequencies need long gating...
Best measurements to show port/PR problems are those done with Klippel NFS at ASR or Erin's Audio corner
Here my measurements of my poor 10"+passive 10" sub (from my museum). Drivers are side by side as per instructions... Spl of gp measurement is not with same amp gain. 500ms and 20ms gating.
Nearfield of each unit and groundplane at 60cm, all indoor. We can see summation below 25Hz and at 50-60Hz, then a deep notch at 65Hz, low notch at 85Hz, peak at 105Hz etc.
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OK, but to fully understand the action of a port requires knowledge of the physics of the Helmholtz radiator.
https://newt.phys.unsw.edu.au/jw/Helmholtz.html
The attached diagram shows the internal force acting on the compliance and mass of the air within the port.
At frequencies higher than resonance, the mass hardly moves and the internal force works mainly against the spring or compliance of the air in the port. Acoustically, the applied force is 90° behind the air flow into the port.
As the frequency decreases towards resonance, the spring and mass begin to move together as a single mass and the acoustic impedance increases. Acoustically, the applied force is 90° ahead of the acoustic flow into the port.
Attachments
Do you know of a paper that has measured step responses of various ported/PR speaker systems?
That would be interesting.
Juhazi posted interesting measurements. So would be good to see more of similar. And especially outside the sweet spot of resonance of passive radiators
And again just to learn the issue
Not to prove that ports and passive radiators are bad in general. So far it seems they are not so great in audiohile set up..maybe great for small portable Bluetooth speakers
So those "hardly moves" spots and radiation of midrange through the dish of passive radiator. Since radiator is like a patch paper/aluminum foil over the box
Maybe in a full range speaker midrange radiation is far worse than in a subwoofer
And again just to learn the issue
Not to prove that ports and passive radiators are bad in general. So far it seems they are not so great in audiohile set up..maybe great for small portable Bluetooth speakers
So those "hardly moves" spots and radiation of midrange through the dish of passive radiator. Since radiator is like a patch paper/aluminum foil over the box
Maybe in a full range speaker midrange radiation is far worse than in a subwoofer
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Me neither. Actually I can't find published nearfield measurements of subwoofers with PR. Only simulations....
Galu, this thread is not only about resonance maximum, but wide band noise from port or PR. And it happens! Phasematch is another more difficult topic here. Noise is not a big problem for subwoofers or 3-ways, but an awful disaster for 2-ways...
Here are measurements with Klippel NFS and nearfield, of a speaker project with PR.
https://www.audiosciencereview.com/...sponse-open-source-purifi-speaker-png.157078/
And a good case of BR port on the backside, woofer 8"
https://www.audiosciencereview.com/...onitor-audio-silver-100-review-speaker.29190/
Typical bad example of a slotted frontside BR port leakage
https://www.audiosciencereview.com/forum/index.php?threads/jbl-4309-review-speaker.27255/
https://www.audiosciencereview.com/forum/index.php?threads/jbl-4309-review-speaker.27255/
Would a double chamber, triple ported ( or triple PR? ) speaker have the same phase characteristics as a conventional single chamber, single port?
I guess you could use a simple rule, PR best for really small ( Bluetooth speakers ), ported best for small ( bookshelf/stand mount ) sealed for medium, double chamber with aperiodic vent between for large speakers.
I guess you could use a simple rule, PR best for really small ( Bluetooth speakers ), ported best for small ( bookshelf/stand mount ) sealed for medium, double chamber with aperiodic vent between for large speakers.