The proposed Aus GB (proposed today in I was modelling the woofer and PR with Jeff Bagby's Woofer Box Model and Circuit Designer, and it looks like you would need two PR's per box?
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I think it is generally not a good idea to add resistive elements (on purpose) in the path of a woofer. It reduces sensitivity and that is what we are paying for. We are already losing about -5dB due to baffle step so an 88dB woofer is really 83dB. The 2ohms will take that to maybe 80dB at 2.83v. People use ultra high damping factor amps (low impedance outputs in the millOhm range), 12 gauge cables from the amp to the speaker, and then to add a 2 ohm resistor would spoil all that hardware and negate some of its key touted features.
If you are going to use a 25L box, maybe a well-designed tapered TL can achieve lower tuning and keep the higher sensitivity, and smooth out the impedance peaks.
If you are going to use a 25L box, maybe a well-designed tapered TL can achieve lower tuning and keep the higher sensitivity, and smooth out the impedance peaks.
I understand what you say.
Why I feel the resistor approach interesting or superior is, it allows you to tune the speaker system much lower if you are after "ruler flat" BR box.
For example, with very high damping factor, you get ruler flat bass for 10L tuned at 42hz, with a group delay of ~10ms@50hz and barely makes use of the "ultra long throw" feature of the driver.
On the other hand, with 2 Ohm resistor, you could tune the box ruler flat with 25L/26hz, with lower group delay >35hz(better transient), much more bandwidth, better use of the port velocity, better utilization of the available throw of the driver, and simple construction.
Arguably the only thing lost is sensitivity, which might be an ok trade off for some.
Best,
These are $70 from Wavecor. Available at PE. Haven’t tried modeling them yet but specs are here. They seem well made. Although that is only nominally less than the Purifi ones.
PR178WA01
There are Dayton aluminum ones for $15ea here:
Dayton Audio DSA175-PR 6-1/2" Designer Series Aluminum Cone Passive Radiator
PR178WA01
There are Dayton aluminum ones for $15ea here:
Dayton Audio DSA175-PR 6-1/2" Designer Series Aluminum Cone Passive Radiator
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DaveFred asked “For people ordering PR's to go with the woofers, I take it you are ordering four PR's per pair of woofers?” Actually out of the 16 individuals who signed up for the Purifi group buy only 3 of us are adding the PTT6.5PR-01A passive radiators. Of the three trying Purifi PRs two are getting 4 PRs and one 2 PRs. In the group buy early adopters 80% are going simple vented designs or non-Purifi passive radiators.
Reading this thread’s recent posts it may appear everyone trying the PTT6.5W is going with a quad of passive radiators (PRs). Some of us are, most are not. I plan to try both, but then I am chronic in that regard. The focus on PRs I observe is partly from their proponents and those more experienced than I and is most welcome. Also once we have the software running sims in CAD only costs our time. The other discussion driver is how much fun it is to spend other peoples’ money for them on the internet. The reality is getting a pair of these woofers to your workbench will cost over $500, add a quad of PRs and cost jumps to $900. Step back to two woofers and two PRs from Purifi and the moving parts cost ‘only’ goes to circa $700.
I think those costs speak to why in both this group and in commercial speaker designs ports are much more common compared to PRs. But talking dollars is no fun, let’s get back to geeking out on design tradeoffs.
When the Purifi PTT6.5W04-01A woofer initially caught my attention I was disappointed its Thiele-Small parameters do not work for a sealed box. My last designs have been sealed box because I like that well damped no abrupt phase shift bass. Also that they do not unload below a vent tuning frequency. So it goes, I like vented also if the ports are big enough to avoid compression effects. Later when considering the PTT6.5PR-01A PR I was initially puzzled that its Fs is 17 Hz. Usually a 6.5” PR will be tuned to something like 30 Hz and if one wants lower Fs mass is added to the cone. Eventually it occurred to me what I believe Purifi intends making a PR with Fs at 17 Hz. That low tuning yields extended bass shelf enclosure alignments that like a sealed box keep the woofer loaded well into the very bottom octave.
Now onto the question for speaker systems that use one each PTT6.5W04-01A woofer plus PTT6.5PR-01A passive radiator(s) in a 15 to 25 liter enclosure is a single PTT6.5PR-01A sufficient? Of course one listener’s ‘more than sufficient’ is another listener’s ‘completely inadequate’ especially when we are talking bass, or Bass, or BASSSS. So I will rephrase the question. Is a speaker with one PTT6.5W04-01A woofer plus one PTT6.5PR-01A passive radiator a desirable design compromise that will show a large number of listeners Purifi has ‘cracked the long stroke code’? Spoiler alert, I will make the case of it’s a matter of picking your design’s tradeoffs.
I explored this running sims using the UniBox Excel based speaker design tool. As a base case for a vented solution to compare against I used Purifi’s SPK5 simple vented example design as a guide, its 14 liter box tuned to 30 Hz delivers F3 (the –3 dB frequency) 44 Hz and Fb (-6 dB frequency) 30 Hz yielding 100 dB+ outputs from 200 watts and driver excursion not exceeded above 25 Hz. I count that as cracking the long stroke code. Writers who have heard this design report amazement at the sound and especially depth and power of bass along with very clean midrange. When I look at the SPK5 design on paper and in speaker CAD software I judge the port diameter is too small, but in the real world that compromise does not seem to lower the WOW factor.
Turning to the PR equipped designs I compared PTTW6.5W + PTT6.5PR to PTTW6.5W + two PTT6.5PR. With that low Fs I do not find with PRs a max flat alignment, settled on 25 liters enclosure yielding a drooping response (often referred to as extended bass shelf) with F3 at 73 Hz but intriguingly Fb 24 Hz all above 100 dB with 200 watts input. However comparing Peak Cone Excursion a single passive radiator will be overdriven between 20-30 Hz with dual PRs just touching a 30 mm peak cone excursion. Those numbers simulate 200 watts input with dual PRs solution yielding 104(!!) dB at 30 Hz in a 25 liter (0.9 cu ft) box, cracking then smashing the long stroke code.
For a more real world living room simulation returning to the PTTW6.5W + single PTT6.5PR in 25 liter box 20 watts of input power now brings PR peak cone excursions below 20 mm peak while still yielding 94 dB of output between 25 to 30 Hz. I think a great many people would be thrilled with that capability and resulting sound. To me the unknown is what happens when the PRs maximum peak cone excursions are exceeded? It may make unmusical noises clanking against its frame. However that will be at levels over 94 dB in the deep bass, maybe 97 dB if we include room gain. Out of a not quite one cubic foot box! For every speaker there comes a time we find that’s all she’s got, turn it down a bit.
All this theory has yet to consider what the box has to be and how we want it to look. Personally I find the vision of a compact stand mount 1 cu ft box with woofer and tweeter on the front and one PR on the back sporting an elegant finish on the sides that can go below 30 Hz above 94 dB very attractive. Put two PRs on the side of that box it looks less elegant IMHO but more technical. And gains all kinds of power handling and output. Then I consider a slim floor standing tower with tweeter, woofer, and two PRs again with so much power handling and output capability.
Now I just ramble, because it is as the saying goes ‘swings and roundabouts’. Or as I like to say good design is the art of balancing compromises. As in high performance cars speed costs dollars, how fast can we afford to go? For any conceivable real world street use 350 hp is more than enough, and that is the vented or one PR solution. But it is fun to lust after the 550 hp motor I do not need (but internet car pundits will always choose), that pair of PRs are the supercharger that delivers the extra 200 hp.
And there's another of my verbose posts. Sorry if I went full nerd and further confused the issue. Feel free to ask for clarifications. Alas definitive answers are some weeks away when the drivers arrive and our systems start to make music in the real world.
Happy Listening & Designing
Reading this thread’s recent posts it may appear everyone trying the PTT6.5W is going with a quad of passive radiators (PRs). Some of us are, most are not. I plan to try both, but then I am chronic in that regard. The focus on PRs I observe is partly from their proponents and those more experienced than I and is most welcome. Also once we have the software running sims in CAD only costs our time. The other discussion driver is how much fun it is to spend other peoples’ money for them on the internet. The reality is getting a pair of these woofers to your workbench will cost over $500, add a quad of PRs and cost jumps to $900. Step back to two woofers and two PRs from Purifi and the moving parts cost ‘only’ goes to circa $700.
I think those costs speak to why in both this group and in commercial speaker designs ports are much more common compared to PRs. But talking dollars is no fun, let’s get back to geeking out on design tradeoffs.
When the Purifi PTT6.5W04-01A woofer initially caught my attention I was disappointed its Thiele-Small parameters do not work for a sealed box. My last designs have been sealed box because I like that well damped no abrupt phase shift bass. Also that they do not unload below a vent tuning frequency. So it goes, I like vented also if the ports are big enough to avoid compression effects. Later when considering the PTT6.5PR-01A PR I was initially puzzled that its Fs is 17 Hz. Usually a 6.5” PR will be tuned to something like 30 Hz and if one wants lower Fs mass is added to the cone. Eventually it occurred to me what I believe Purifi intends making a PR with Fs at 17 Hz. That low tuning yields extended bass shelf enclosure alignments that like a sealed box keep the woofer loaded well into the very bottom octave.
Now onto the question for speaker systems that use one each PTT6.5W04-01A woofer plus PTT6.5PR-01A passive radiator(s) in a 15 to 25 liter enclosure is a single PTT6.5PR-01A sufficient? Of course one listener’s ‘more than sufficient’ is another listener’s ‘completely inadequate’ especially when we are talking bass, or Bass, or BASSSS. So I will rephrase the question. Is a speaker with one PTT6.5W04-01A woofer plus one PTT6.5PR-01A passive radiator a desirable design compromise that will show a large number of listeners Purifi has ‘cracked the long stroke code’? Spoiler alert, I will make the case of it’s a matter of picking your design’s tradeoffs.
I explored this running sims using the UniBox Excel based speaker design tool. As a base case for a vented solution to compare against I used Purifi’s SPK5 simple vented example design as a guide, its 14 liter box tuned to 30 Hz delivers F3 (the –3 dB frequency) 44 Hz and Fb (-6 dB frequency) 30 Hz yielding 100 dB+ outputs from 200 watts and driver excursion not exceeded above 25 Hz. I count that as cracking the long stroke code. Writers who have heard this design report amazement at the sound and especially depth and power of bass along with very clean midrange. When I look at the SPK5 design on paper and in speaker CAD software I judge the port diameter is too small, but in the real world that compromise does not seem to lower the WOW factor.
Turning to the PR equipped designs I compared PTTW6.5W + PTT6.5PR to PTTW6.5W + two PTT6.5PR. With that low Fs I do not find with PRs a max flat alignment, settled on 25 liters enclosure yielding a drooping response (often referred to as extended bass shelf) with F3 at 73 Hz but intriguingly Fb 24 Hz all above 100 dB with 200 watts input. However comparing Peak Cone Excursion a single passive radiator will be overdriven between 20-30 Hz with dual PRs just touching a 30 mm peak cone excursion. Those numbers simulate 200 watts input with dual PRs solution yielding 104(!!) dB at 30 Hz in a 25 liter (0.9 cu ft) box, cracking then smashing the long stroke code.
For a more real world living room simulation returning to the PTTW6.5W + single PTT6.5PR in 25 liter box 20 watts of input power now brings PR peak cone excursions below 20 mm peak while still yielding 94 dB of output between 25 to 30 Hz. I think a great many people would be thrilled with that capability and resulting sound. To me the unknown is what happens when the PRs maximum peak cone excursions are exceeded? It may make unmusical noises clanking against its frame. However that will be at levels over 94 dB in the deep bass, maybe 97 dB if we include room gain. Out of a not quite one cubic foot box! For every speaker there comes a time we find that’s all she’s got, turn it down a bit.
All this theory has yet to consider what the box has to be and how we want it to look. Personally I find the vision of a compact stand mount 1 cu ft box with woofer and tweeter on the front and one PR on the back sporting an elegant finish on the sides that can go below 30 Hz above 94 dB very attractive. Put two PRs on the side of that box it looks less elegant IMHO but more technical. And gains all kinds of power handling and output. Then I consider a slim floor standing tower with tweeter, woofer, and two PRs again with so much power handling and output capability.
Now I just ramble, because it is as the saying goes ‘swings and roundabouts’. Or as I like to say good design is the art of balancing compromises. As in high performance cars speed costs dollars, how fast can we afford to go? For any conceivable real world street use 350 hp is more than enough, and that is the vented or one PR solution. But it is fun to lust after the 550 hp motor I do not need (but internet car pundits will always choose), that pair of PRs are the supercharger that delivers the extra 200 hp.
And there's another of my verbose posts. Sorry if I went full nerd and further confused the issue. Feel free to ask for clarifications. Alas definitive answers are some weeks away when the drivers arrive and our systems start to make music in the real world.
Happy Listening & Designing
Do not work how? They only have an sealed F3 of around 70 Hz. Is that what you mean?
I think they work well in sealed + resistors.
QTS is just too low without resistors. With 2ohm(and probably extra capacitor loading), however, works well in 12.5Liter sealed with F3 = 50hz.
And I believe this system still has higher 2.83v sensitivity than YG acoustics Carmel 2. Correct me if I'm wrong, winisd told me 87+db with 2.83v@100hz.
QTS is just too low without resistors. With 2ohm(and probably extra capacitor loading), however, works well in 12.5Liter sealed with F3 = 50hz.
And I believe this system still has higher 2.83v sensitivity than YG acoustics Carmel 2. Correct me if I'm wrong, winisd told me 87+db with 2.83v@100hz.
Hi Norman , Thank you!! for all the info and simulations! hmmmmmm as a guy that took a 1,800 pound 914 Porsche, then put a very cool after market fiberglass body on it and then dropped a 575 horse power , balanced and blue printed Chevy V-8 in it - - - - - - Can I settle for less than State Of The Art after paying for one of the Best drivers available -- 
--
Sooo maybe Two passive radiators, the $15.00 ones Xrd mentioned from parts express , one on either side ... But under nice grill covers, so they don't look ugly, then if i understood right -- I saw a Single driver tuned in a bandpass down to almost 20 hz .. so maybe underneath the monitor part of the speaker we add a slim base using it to divide the box and add that bandpass second 6.5 inch and end up with a very slim full range floor speaker that rocks ( If needed) down to 20 hz with a little EQ on the amp for that second woofer ...... It is real opportunity to maybe have something Special --
Best Regards,
Dean
----------------------- or maybe that's overkill ...... LOL
-- Sooo maybe Two passive radiators, the $15.00 ones Xrd mentioned from parts express , one on either side ... But under nice grill covers, so they don't look ugly, then if i understood right -- I saw a Single driver tuned in a bandpass down to almost 20 hz .. so maybe underneath the monitor part of the speaker we add a slim base using it to divide the box and add that bandpass second 6.5 inch and end up with a very slim full range floor speaker that rocks ( If needed) down to 20 hz with a little EQ on the amp for that second woofer ...... It is real opportunity to maybe have something Special --
Best Regards,
Dean
----------------------- or maybe that's overkill ...... LOL
The group buy status is 13 of the 15 GB participants have confirmed their order with contact information allowing shipping costs to be determined. I have just sent a third and final reminder to those who have gone silent stating:
If I have not heard from you by 10 AM CST February 7 I will assume you have decided not to join this GB and I will remove you from the list as we proceed.
I do have confirmations from johngore; mordikai; xrk971; racingpht; cpdk; ramenconnoisseur; a chap who wishes to remain anonymous; jmpsmash; Paul Ebert; ani101; jsy; DaveFred; and myself. A couple of folks who were tentatively interested have confirmed they will not be ordering. Thanks to all who promptly replied yea or nay this week.
Tomorrow 2-7-2020 once the stragglers speak up or are left behind I will get a firm shipping quote from Purifi, estimate costs to individual participants and communicate those costs privately via email.
Speaking of email, the diyaudio PM (personal message) system is not really designed for the message volume a GB with 15 participants generates. Last night I had to download as text and delete off diyaudio all your messages as I was about to hit the max of 100 messages we are allowed to retain on diyaudio. Participants please keep an eye on the Inbox and Spam folders for the email address you provided me for GB related emails. I will also continue to post general updates to this thread.
If I have not heard from you by 10 AM CST February 7 I will assume you have decided not to join this GB and I will remove you from the list as we proceed.
I do have confirmations from johngore; mordikai; xrk971; racingpht; cpdk; ramenconnoisseur; a chap who wishes to remain anonymous; jmpsmash; Paul Ebert; ani101; jsy; DaveFred; and myself. A couple of folks who were tentatively interested have confirmed they will not be ordering. Thanks to all who promptly replied yea or nay this week.
Tomorrow 2-7-2020 once the stragglers speak up or are left behind I will get a firm shipping quote from Purifi, estimate costs to individual participants and communicate those costs privately via email.
Speaking of email, the diyaudio PM (personal message) system is not really designed for the message volume a GB with 15 participants generates. Last night I had to download as text and delete off diyaudio all your messages as I was about to hit the max of 100 messages we are allowed to retain on diyaudio. Participants please keep an eye on the Inbox and Spam folders for the email address you provided me for GB related emails. I will also continue to post general updates to this thread.
I guess my question is, what impact will a sealed application have on the performance (especially sound) other than a higher F3?
I intend to use my PTT6.5s as midranges, so the lowest bass extension isn't a high priority.