So my previous understanding was that passive radiator and ported enclosures were very similar. I thought the diameter of the PR is the equivalent as the diameter of the port. The mass of the passive radiator is equivalent of the mass of air within the port. Therefore, changing the mass of the PR changes the tuning.
However, it turns out the tuning of the PR actually affected by the Fs of the driver and not just the Sd and Mms. Therefore, this means the tuning is affected by the Cms of the PR since Fs is determined by Cms and Mms.
So, there are 3 major things that determine the tuning of a ported enclosure: enclosure volume, port diameter, and port length. But it seems like there are 4 major things that determine the tuning of a passive radiator enclosure: enclosure volume, Sd, Mms, and Cms.
So what is the equivalent of Cms in a ported enclosure? Or is either port diameter or port length a combination of 2 passive radiator parameters?
However, it turns out the tuning of the PR actually affected by the Fs of the driver and not just the Sd and Mms. Therefore, this means the tuning is affected by the Cms of the PR since Fs is determined by Cms and Mms.
So, there are 3 major things that determine the tuning of a ported enclosure: enclosure volume, port diameter, and port length. But it seems like there are 4 major things that determine the tuning of a passive radiator enclosure: enclosure volume, Sd, Mms, and Cms.
So what is the equivalent of Cms in a ported enclosure? Or is either port diameter or port length a combination of 2 passive radiator parameters?
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I use use at least twice the cone area of the woof as the only measure. It's always work for me. I just built a pair od small speakers with a 5" driver and used two 5" PRs. It sounds great.
General Links on Passive Radiators.
Hi bcodemz,
Post #1: "...my previous understanding was that passive radiator and ported enclosures were very similar. I thought the diameter of the PR is the equivalent as the diameter of the port. The mass of the passive radiator is equivalent of the mass of air within the port. Therefore, changing the mass of the PR changes the tuning."
That is basically correct. I'll re-post the link I posted in your other thread, maybe you didn't see it:
AE Speakers --- Superb Quality, Unforgettable Performance, Definitely.
Also, at PE's website you can find that PR specifications include Fs/Vas/Cms/Mms/Rms/Sd. These are the raw specifications prior to adding tuning mass, e.g.:
Peerless by Tymphany 830878 3-1/2" Passive Radiator
Brian Steele has a nice write-up on his
Subwoofer DIY Page (with further links):
The Subwoofer DIY Page - Passive Radiator Systems
Hope this helps,
Regards,
Hi bcodemz,
Post #1: "...my previous understanding was that passive radiator and ported enclosures were very similar. I thought the diameter of the PR is the equivalent as the diameter of the port. The mass of the passive radiator is equivalent of the mass of air within the port. Therefore, changing the mass of the PR changes the tuning."
That is basically correct. I'll re-post the link I posted in your other thread, maybe you didn't see it:
AE Speakers --- Superb Quality, Unforgettable Performance, Definitely.
Also, at PE's website you can find that PR specifications include Fs/Vas/Cms/Mms/Rms/Sd. These are the raw specifications prior to adding tuning mass, e.g.:
Peerless by Tymphany 830878 3-1/2" Passive Radiator
Brian Steele has a nice write-up on his
Subwoofer DIY Page (with further links):
The Subwoofer DIY Page - Passive Radiator Systems
Hope this helps,
Regards,
A PR has its own inherent springiness. When you put it into a cabinet, this lumps with the air compliance, to give a new resonance for the PR.
In a ported box, the air inside the box is the only spring acting.
Chris
In a ported box, the air inside the box is the only spring acting.
Chris
They are similar in the principle on which they work:
In both cases the bass driver is coupled to a mass via the internal air within the box.
Tuned correctly both will resonate in sympathy with the bass driver.
The main difference is that with a port the mass in question is a few grams while with a PR it is a few hundred grams. Tight bass is not a PRs strength.
In both cases the bass driver is coupled to a mass via the internal air within the box.
Tuned correctly both will resonate in sympathy with the bass driver.
The main difference is that with a port the mass in question is a few grams while with a PR it is a few hundred grams. Tight bass is not a PRs strength.
When you ignore the suspension compliance and losses (of the PR), PR and ported are identical. Therefore bass tightness is also identical, even tough a PR has a mass of a few hundred grams.
but we can get rid of port rezonance.
in exchange we get more cone rezonance errors, and as the PR moves we have a less linear spring load on the woofer.
bracing is yet a nother problem for some cases, as the passive radiators take away space needed for bracing. accoustic coupling between the woofer and a port may be better in some cases, we can choose the port exit loaction better in many cases than the passive radiator, summing of the 2 might happen better with ports.
i don't dislike PR sound, and it does have advantages in a few areas, but for me the drawbacks outweight the gains.
in exchange we get more cone rezonance errors, and as the PR moves we have a less linear spring load on the woofer.
bracing is yet a nother problem for some cases, as the passive radiators take away space needed for bracing. accoustic coupling between the woofer and a port may be better in some cases, we can choose the port exit loaction better in many cases than the passive radiator, summing of the 2 might happen better with ports.
i don't dislike PR sound, and it does have advantages in a few areas, but for me the drawbacks outweight the gains.
You seem to confuse your terminology here. You say that PR tuning depends on the Fs of the driver - that is false.
Here is a picture of a 12" driver in a 150Lbox tuned to 20Hz, ported and with a loose and stiff 15" PR. The loose PR has a Vap of 2200L, the stiff one 225L.
Total mass is 434grams for the 15" diameter port (for comparison), 464 grams for the loose PR and 723g for the stiff PR.
You can see the loose PR has a response very similar to the ported box. I actually changed the leakage losses so you could see it better near cutoff. The main effect of PR compliance is to make a null at the PR's free air resonance frequency. Basically you want to keep the PR resonance as far away from the passband as possible.
Woofers don't make good PR's generally because their compliance is too low and the resultant notch will mess up your curves....
Ports don't have a compliance...it's a really funny question 😉
Attachments
Thank you for the insightful post.
Haha yeah I was really confused because I couldn't imagine ports having compliance.
What program are you using to get those models? WinISD is not accurate for PR modelling and Jeff Bagby's excel sheet does not account for parameters that cause PR losses. I'd be very interested to work with a program like that.
Even in your example, the stiff PR needed almost twice the mass to achieve the same tuning. Wouldn't that imply that it's not just mass and surface area that determine's a passive radiator's tuning?
I agree most woofers don't make good PRs for the reason. Unfortunately the number of 5.25'' passive radiators on the market is exactly one, not exactly a lot of choices, hence my attempts at making a DIY PR.
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Hi bcodemz,
Post #10: "...Jeff Bagby's excel sheet does not account for parameters that cause PR losses..."
Could you, please, list the parameters that Jeff's spreadsheet does not account for?
For a PR you are shooting for an installed Fsp (w/ added weight) as low as possible to keep the resultant notch below the enclosure passband. For a given radiator Fsp changes because of changes in Mms, while Cms stays the same (as long as the radiator is driven in its linear range).
If the installed Fsp is very low (high Cms and high Mms) the mass of an equivalent air duct w/ the same area will be close to the adjusted mass of the PR.
In Ron E's example Post #9 the stiff example PR has too low a Cms for the application resulting in an Fsp that is too high, and "...the resultant notch will mess up your curves...".
It would help me, if you could list the parameters that are not accounted for in Jeff's spreadsheet.
Regards,
Post #10: "...Jeff Bagby's excel sheet does not account for parameters that cause PR losses..."
Could you, please, list the parameters that Jeff's spreadsheet does not account for?
For a PR you are shooting for an installed Fsp (w/ added weight) as low as possible to keep the resultant notch below the enclosure passband. For a given radiator Fsp changes because of changes in Mms, while Cms stays the same (as long as the radiator is driven in its linear range).
If the installed Fsp is very low (high Cms and high Mms) the mass of an equivalent air duct w/ the same area will be close to the adjusted mass of the PR.
In Ron E's example Post #9 the stiff example PR has too low a Cms for the application resulting in an Fsp that is too high, and "...the resultant notch will mess up your curves...".
It would help me, if you could list the parameters that are not accounted for in Jeff's spreadsheet.
Regards,
It's a Benson-inspired spreadsheet I wrote myself 18+ years ago. I don't distribute it.
FYI, LspCad.........
GM
+++++++++++++++++++
LspCAD 6 manual © Ingemar Johansson, IJData, Luleå, Sweden
50
9.3.4 Passive radiator component
A passive radiator or auxiliary bass radiator (ABR), has all the
properties of an ordinary TS driver unit except for the absence of a
magnet structure. Also, if a box is referenced (like is the case for the
port component) it is possible to see the resonance of the ABR – box
system (fb).
The properties that can be set are:
Rmp: Loss resistance of suspension
Mmp: Moving mass
Cmp: Compliance of suspension.
Sd: Effective radiating area.
Vap: Equivalent volume.
Qmp: Loss factor.
fp: Resonance frequency of passive radiator in free air.
fb: Resonance of passive radiator in box.
# units: Number of identical units.
Of the above properties Rmp, Mmp and Cmp can be optimized.
Nonlinear modeling : Model nonlinearities
GM
+++++++++++++++++++
LspCAD 6 manual © Ingemar Johansson, IJData, Luleå, Sweden
50
9.3.4 Passive radiator component
A passive radiator or auxiliary bass radiator (ABR), has all the
properties of an ordinary TS driver unit except for the absence of a
magnet structure. Also, if a box is referenced (like is the case for the
port component) it is possible to see the resonance of the ABR – box
system (fb).
The properties that can be set are:
Rmp: Loss resistance of suspension
Mmp: Moving mass
Cmp: Compliance of suspension.
Sd: Effective radiating area.
Vap: Equivalent volume.
Qmp: Loss factor.
fp: Resonance frequency of passive radiator in free air.
fb: Resonance of passive radiator in box.
# units: Number of identical units.
Of the above properties Rmp, Mmp and Cmp can be optimized.
Nonlinear modeling : Model nonlinearities
Hi bcodemz,
Post #14: "Vas and Qms are not accounted for in Jeff's spreadsheet."
The driver's Vas and Qms are listed under Woofer Parameters, and the PR's parameters are listed under Passive Radiator Parameters:
Vasp and Qmp
these parameters are then recalculated, and listed under Calculated Radiator Parameters:
Vasp' and Qmp'
Maybe time to take another look at Jeff's spreadsheet? :=) I still find it the easiest free tool for designing PR enclosures, and the associated electronic filtering.
Regards,
Post #14: "Vas and Qms are not accounted for in Jeff's spreadsheet."
The driver's Vas and Qms are listed under Woofer Parameters, and the PR's parameters are listed under Passive Radiator Parameters:
Vasp and Qmp
these parameters are then recalculated, and listed under Calculated Radiator Parameters:
Vasp' and Qmp'
Maybe time to take another look at Jeff's spreadsheet? :=) I still find it the easiest free tool for designing PR enclosures, and the associated electronic filtering.
Regards,
It doesn't seem to make any significant difference when I change the values. The response curve is within 0.2dB compared to the vented curve. There should be much bigger differences than that, shown in Ron E's curve, since the PR I'm modelling isn't exactly close to ideal.
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PR Qmp is fairly subtle unless it is very low, like 3. It also increases with added mass.
If you share your design then I / others can model it and see what it looks like. I mean posting all the particulars, no links to data sheets, etc. I have limited time.
If you share your design then I / others can model it and see what it looks like. I mean posting all the particulars, no links to data sheets, etc. I have limited time.
I will simplify the design to just the woofer section.
This speaker's goal is to produce as much bass to 40Hz as possible in a box with 5L of internal airspace. I plan on using a pair of Wavecor WF152BD05 and a pair of 5.25'' passive radiators tuned to 42Hz. The extremely limited enclosure size means only 2 PR's can fit. Even if more can be fit, mass requirements for 42Hz tuning becomes far too high. Each woofer gets up to 125W from a single ICEpower 125ASX2 with one woofer per channel. Realistic max input power is 75W per woofer. The specs for the Wavecor woofers are below.
Originally the plan is to convert 2 Tang Band W5-1138SMF to passive radiators because the Peerless 5.25'' has only 6mm Xmax when I need up to 11mm of PR excursion.
Tang Band W5-1138SMF specs
Peerless 5.25'' passive radiator specs
The concern with the modified Tang Band PR is too much added mass needed due to low compliance and the suspension may not hold 100+ grams of mass for a 42Hz tuning. The Vas and Qms are also low.
The concern with the Peerless 5.25'' PR is not enough excursion at only 6mm Xmax. However, excursion demand is reduced due to thermal compression (but transients are still a concern). PR losses will also reduce excursion demand.
If you're curious about the whole speaker design, you can read about it here. I'd value your feedback.
http://www.diyaudio.com/forums/multi-way/295160-ultimate-small-speaker-final-design-feedback.html
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Attached is a sim, alignment1 is a woofer and a single tangband as a PR,
alignment2 is a woofer and 2x peerless PR.
Excursion is as driven by a +/- 21.91V peak sine wave - that is what gives 75 watts into 3.2 ohms. Excursion is directly proportional to voltage. So the boxes have roughly 7mm peak excursion to get that to 4.5 you multiply volts by 4.5/7 the design will handle ~+/-10VRMS P=10*10/3.2 ~=30Watts at the excursion max above tuning, which is what you see on page 6.
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