I am considering a small two way speaker, which will be heavily inspired by the SPK5 kit, I even consider using the same x-over for my build. I can see that a lot of your great builds are using passive radiators instead of the original reflex design. What are the advantages and disadvantages with this method? And can you recommend alternatives to the passive Purifi radiator and the one from SB?
I must say that the transmission line design looks amazing too.
I must say that the transmission line design looks amazing too.
Colakurt,
Another passive radiator design for your consideration:
Purezza Kit — Selah Audio
Measurements and review:
Selah Audio Purezza Bookshelf Speaker Review
Another passive radiator design for your consideration:
Purezza Kit — Selah Audio
Measurements and review:
Selah Audio Purezza Bookshelf Speaker Review
Colakurt asked:
“I can see that a lot of your great builds are using passive radiators instead of the original reflex design. What are the advantages and disadvantages with this method?”
Let’s see if I can summarize the tradeoffs.
Port Advantages
Port Disadvantages
Passive Radiator Advantages
Passive Radiator Disadvantages
“I can see that a lot of your great builds are using passive radiators instead of the original reflex design. What are the advantages and disadvantages with this method?”
Let’s see if I can summarize the tradeoffs.
Port Advantages
- Low cost.
- Proven familiar technology.
- Output roll off below tuning frequency not as steep as passive radiators (but steeper vs sealed systems).
Port Disadvantages
- Tuned to low frequencies they can become rather large consuming significant volume forcing a larger enclosure.
- Tradeoff between port area vs higher frequency distortion vs whistling. It is one of those engineering tradeoffs where we have to pick two criteria to benefit while a third suffers. Large area ports reduce whistling air noise but can add distortions due to organ pipe resonances arising because they get so long. Small area ports may suffer from whistling air noise but create fewer distortions due to organ pipe resonances arising because they are shorter for a given tuning frequency.
- If the enclosure has standing waves or other higher frequency noise/distortions the port is literally an open hole through which these can leak into the room
Passive Radiator Advantages
- Consumes minimal enclosure volume even when tuned to quite low frequencies.
- Typically easy to adjust tuning frequency lower by adding mass. Not the case with Pirifi’s which without mass added are tuned to 19 Hz.
- Cannot suffer whistling air noises.
- Attenuates standing waves or other higher frequency noise/distortions occurring in the enclosure.
- Adds to perceived value i.e. two-way speakers look like they have extra ‘woofers’.
Passive Radiator Disadvantages
- Cost, always more than a plastic or cardboard tube.
- Cost again because the good ones that are linear can cost 2/3 the price of the woofers they partner.
- Cost yet again because they operate at resonance = big excursion the PRs ideally need approximately 2x the area x displacement of the woofer(s) they serve. Gaining this extra area is why oval PRs or larger diameter PRs than the woofer are popular.
- When under sized or of insufficient quality PRs can add distortion or limiting into the system.
- Below tuning frequency roll off faster that ported systems.
I think you did a pretty good job summing up the pro's and cons of ported vs pr vs sealed.
There are 2 things you forgot that are relevant. Resononators increase the roll off slope. Sure you get slightly deeper bass, but below the resonance frequency of the port/pr there is less bass!
Secondly, resonators resonate ( who wouldve thought!). They ring like a bell and take some time to get going. Sealed doesnt have this problem and has much better transient response.
There are 2 things you forgot that are relevant. Resononators increase the roll off slope. Sure you get slightly deeper bass, but below the resonance frequency of the port/pr there is less bass!
Secondly, resonators resonate ( who wouldve thought!). They ring like a bell and take some time to get going. Sealed doesnt have this problem and has much better transient response.
Thank you Norman for the fulfilling explanation.
I would like to do a high-end build but have also realized that the Purifi radiators will be out of my budget. And I would fear that a cheaper radiator might induce distortion to the system, especially since the Purifi drivers offer such a high Xmax that they actually manage to outperform most radiators so I would need more than two radiators to satisfy the normal 2 x area and same Xmax ratio to the driver.
I would like to do a high-end build but have also realized that the Purifi radiators will be out of my budget. And I would fear that a cheaper radiator might induce distortion to the system, especially since the Purifi drivers offer such a high Xmax that they actually manage to outperform most radiators so I would need more than two radiators to satisfy the normal 2 x area and same Xmax ratio to the driver.
I found only two PM's which could be use instead of Purifi PM, all others are too large for a 15-20 L Speaker or resonance FS will not match.
- one Dayton DS215-PR,
Dayton Audio - DS215-PR 8" Designer Series Passive Radiator
or
- two Wavecore PR176WA01 in a 15 L box,
PR178WA01
- one Dayton DS215-PR,
Dayton Audio - DS215-PR 8" Designer Series Passive Radiator
or
- two Wavecore PR176WA01 in a 15 L box,
PR178WA01
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Thats a very unique coil. Perhaps to make the BL integration more linear vs cone travel.
The SB acoustics racetrack passive radiator looks like a good fit.
5″ x 8″ SB15SFCR-00 / Paper – Sbacoustics
Interestingly there is a counterpart with a real motor that is only slightly more costly
https://sbacoustics.com/product/5x8-sb15sfcr39-4-paper/
The sonus faber extrema speaker uses a woofer tied to a variable number of resistors:
"The Extrema adds a neat twist to the tale: here the B139 is not just a diaphragm but the complete bass driver complete with motor coil and magnet. While careful schemes could be devised for bass damping using acoustically resistive apertures, Sonus Faber has exploited electromagnetic damping. They place a desired resistor across the auxiliary woofer's motor coil; damping energy appears in the moving-coil and is dissipated in the resistor.
Sonus Faber has gone even farther in their exploitation of this principle, providing user-variable bass damping in the ABR range, effective over an octave centered on 50Hz. No less than five switch-selected positions are available. This is only too easy to accomplish once the working principle has been adopted. The step resolution is fair enough at 1.5dB once the ABR output is integrated into the main response. A mass-loading cylinder has been applied to the B139's diaphragm to lower the resonant frequency."
(from Sonus Faber Extrema loudspeaker Page 2 | Stereophile.com )
Not sure how that actually works ?
5″ x 8″ SB15SFCR-00 / Paper – Sbacoustics
Interestingly there is a counterpart with a real motor that is only slightly more costly
https://sbacoustics.com/product/5x8-sb15sfcr39-4-paper/
The sonus faber extrema speaker uses a woofer tied to a variable number of resistors:
"The Extrema adds a neat twist to the tale: here the B139 is not just a diaphragm but the complete bass driver complete with motor coil and magnet. While careful schemes could be devised for bass damping using acoustically resistive apertures, Sonus Faber has exploited electromagnetic damping. They place a desired resistor across the auxiliary woofer's motor coil; damping energy appears in the moving-coil and is dissipated in the resistor.
Sonus Faber has gone even farther in their exploitation of this principle, providing user-variable bass damping in the ABR range, effective over an octave centered on 50Hz. No less than five switch-selected positions are available. This is only too easy to accomplish once the working principle has been adopted. The step resolution is fair enough at 1.5dB once the ABR output is integrated into the main response. A mass-loading cylinder has been applied to the B139's diaphragm to lower the resonant frequency."
(from Sonus Faber Extrema loudspeaker Page 2 | Stereophile.com )
Not sure how that actually works ?
I agree with hidjedewitje that in the general case:
“Resononators increase the roll off slope. Sure you get slightly deeper bass, but below the resonance frequency of the port/pr there is less bass!”
Actually the previous two serious systems I built before diving head first into the PTT6.5 rabbit hole were sealed using in one case a Accuton 8” and in the other a clone of the 6.5” paper woofer used in the Yamaha NS10. I was sold on the better transit response and more gradual roll off below Fs of those sealed designs.
However……until….along comes Purifi……
When compared to the Purifi PTT6.5 it is not so much comparing apples to oranges as apples to hand grenades. The bass is so much deeper and output capabilities so much higher what happens below Fs is really only an issue with movie low frequency effects. In music everything is covered.
It’s interesting juxtaposing hidjedewitje’s comment “resonators resonate (who would’ve thought!). They ring like a bell and take some time to get going” (as do ports I will note) with cph2000 bringing up the Sonus Faber’s Extrema adjustable damping PR. They actually made both the classic Extrema and a few years ago an homage to it called the ex3ma that also includes the adjustable damping PR. I attach some pics of those details on the the ex3ma.
Note the knob labeled ‘Brake’ on the rear panel. On the shot of the disassembled rear panel we see the voice coil of the PR connected to that knob (selector switch) and three anodized gold power resistors. When the brake knob is set to ‘0’ the resistors are disconnected and no added damping is added to the PR. As hidjedewitje notes it will ring, I would prefer the word resonate, to the maximum extent it’s mass and suspension compliance allows. As the Brake knob is advanced 1, 2, 3 more electrical resistance is placed in series with the PR’s magnet and voice coil. Now the voltage generated as the PR vibrates is dissipated across those resistors. This will resist movement of the PR. As a result lower bass will be reduced and more damped. I would guess the audible effect is depending on room acoustics and your personal taste you can adjust the bass to be rich, dry, or very dry. I judge it as a very cool complication, admittedly expensive but I tend to discount costs that implement a clever idea.
“Resononators increase the roll off slope. Sure you get slightly deeper bass, but below the resonance frequency of the port/pr there is less bass!”
Actually the previous two serious systems I built before diving head first into the PTT6.5 rabbit hole were sealed using in one case a Accuton 8” and in the other a clone of the 6.5” paper woofer used in the Yamaha NS10. I was sold on the better transit response and more gradual roll off below Fs of those sealed designs.
However……until….along comes Purifi……
When compared to the Purifi PTT6.5 it is not so much comparing apples to oranges as apples to hand grenades. The bass is so much deeper and output capabilities so much higher what happens below Fs is really only an issue with movie low frequency effects. In music everything is covered.
It’s interesting juxtaposing hidjedewitje’s comment “resonators resonate (who would’ve thought!). They ring like a bell and take some time to get going” (as do ports I will note) with cph2000 bringing up the Sonus Faber’s Extrema adjustable damping PR. They actually made both the classic Extrema and a few years ago an homage to it called the ex3ma that also includes the adjustable damping PR. I attach some pics of those details on the the ex3ma.
Note the knob labeled ‘Brake’ on the rear panel. On the shot of the disassembled rear panel we see the voice coil of the PR connected to that knob (selector switch) and three anodized gold power resistors. When the brake knob is set to ‘0’ the resistors are disconnected and no added damping is added to the PR. As hidjedewitje notes it will ring, I would prefer the word resonate, to the maximum extent it’s mass and suspension compliance allows. As the Brake knob is advanced 1, 2, 3 more electrical resistance is placed in series with the PR’s magnet and voice coil. Now the voltage generated as the PR vibrates is dissipated across those resistors. This will resist movement of the PR. As a result lower bass will be reduced and more damped. I would guess the audible effect is depending on room acoustics and your personal taste you can adjust the bass to be rich, dry, or very dry. I judge it as a very cool complication, admittedly expensive but I tend to discount costs that implement a clever idea.
Attachments
The sb acoustics race track passive radiator is used in both the Buchardt and the selah speakers. The device without a magnet is 30 eur while the speaker version is 39 eur so virtually no extra cost. The drawback as I see it with the speaker device is that it will be a bit more involved to add mass to the cone.
Note that with the extrema approach the rear firing speaker with attached variable “brake” is not wired to the cross over, only the resistors are wired to the terminals.
Note that with the extrema approach the rear firing speaker with attached variable “brake” is not wired to the cross over, only the resistors are wired to the terminals.
A newbies thoughts/question on how to make a super compact speaker with these drivers.
From my understanding the Purifi drivers are "best" implemented with dual passive radiators. I saw Hifi Compass "Pure Bliss" speaker and first thought was, why not put radiators in rear panel to benefit from some force cancellation?
If the Purifi drivers are that good in low+mid range, they move so much air that a looong port or big passive radiators is needed... Could they be implemented in a similar design to Devialets Phantom with success?
Dual opposite Purifi drivers (2x PTT4.0W04-01A) front+rear
Wave guided tweeter on top (SB Acoustics SB26STWGC-4)
or use the 6,5 woofers and Satori TW29BNWG-8
It would be a super easy build with layered HDF (with help from force cancellation). And sooo compact!
Am I being stupid or is it a viable design?
From my understanding the Purifi drivers are "best" implemented with dual passive radiators. I saw Hifi Compass "Pure Bliss" speaker and first thought was, why not put radiators in rear panel to benefit from some force cancellation?
If the Purifi drivers are that good in low+mid range, they move so much air that a looong port or big passive radiators is needed... Could they be implemented in a similar design to Devialets Phantom with success?
Dual opposite Purifi drivers (2x PTT4.0W04-01A) front+rear
Wave guided tweeter on top (SB Acoustics SB26STWGC-4)
or use the 6,5 woofers and Satori TW29BNWG-8
It would be a super easy build with layered HDF (with help from force cancellation). And sooo compact!
Am I being stupid or is it a viable design?
Sorry let me rephrase that. Not “some force cancellation” but “some force reduction” at least? (What Troy said
)Any thoughts on the Phantom design?
Something I never really understood. If you are gonna build a small speaker.... you put it on a stand to raise the tweeter and midrange to ear level. But why not use that volume under the small speaker, to give the driver some space and let it breath.... instead of pushing the sensitivity down to make the driver able to play deep bass in a smaller enclosure?
I'm all for new technology and smarter design. But is it really that difficult to build a good 3 way and use a smaller midrange, that would integrate easier with a lot of tweeters, so that we could save some money. I mean.... the purifi is rather expensive.... so what is the argument. The Kii3 is a small top-notch - kinda 3 way - with nice cheap drivers. It performs great.... so why the fuzz?
I know it might sound like a provocation.... but I find many good sounding speakers, that do not use expensive drivers... as a rule.
I'm all for new technology and smarter design. But is it really that difficult to build a good 3 way and use a smaller midrange, that would integrate easier with a lot of tweeters, so that we could save some money. I mean.... the purifi is rather expensive.... so what is the argument. The Kii3 is a small top-notch - kinda 3 way - with nice cheap drivers. It performs great.... so why the fuzz?
I know it might sound like a provocation.... but I find many good sounding speakers, that do not use expensive drivers... as a rule.
This has restarted a fun, interesting, informative discussion.
Thanks cph2000 for stating explicitly what I inferred that the extrema approach using a woofer magnet and voice coil as a passive radiator that the thus created variable “brake” is not wired as part of the cross over. Mentioning Buchardt also reminds me to point out a couple of points.
First the SB Acoustics oval PR 5″ x 8″ SB15SFCR-00 has an Sd area of 178 sq. cm vs. the PTT6.5 133 sq. cm. The rule is twice the Sd (driver cone area) on the PR vs woofer to not limit output. So ideally one uses two for the SB15SFCR-00, that’s still only circa $75usd with SB vs $354usd per speaker with Purifi, or ~$500 if one buys 4 pieces to do a pair of speakers direct from Purifi.
Second is Buchardt is an example that in commercial offerings we often see compromise in the twice the Sd on the PR vs woofer ‘rule’. Their lauded S400 has a 6” woofer with the 5″ x 8″ PR like the Selah Audio Purezza Purifi equipped design referenced above. In contrast GoldenEar Technology is a company they seems more dedicated to generous Sd on their PRs.
Regarding his “sooo compact!” proposals emilkoz asks “Am I being stupid or is it a viable design?” I vote not stupid, viable. It is interesting when you invoke Devialet’s Phantom. Let’s save that discussion to include with the Kii3.
In his post above digitalthor mentions tradeoffs including enclosure size, 2-way vs. 3-way, and driver costs concluding: “The Kii3 is a small top-notch - kinda 3 way - with nice cheap drivers. It performs great.... so why the fuzz? I know it might sound like a provocation.... but I find many good sounding speakers, that do not use expensive drivers... as a rule.”
OK, one of the controversies around the Kii3 is when the ‘net pundits cost its “nice cheap drivers” at a few hundred bucks and then complain about that vs the $15,000 a pair retail price. Devialet’s Phantom come in at $2,000 to $7,000 a pair depending on model. In both cases that extra cost is covering self-powered bi-tri-amped multi-way DSPed up the wazoo, and multi input options capabilities. Some say “all I care about is sound quality”. It is also my first priority (although I do spend an inordinate amount of time on styling and finishing details). What DSP brings to Kii, Devialet, and other’s game is the ability to force deep bass out of smaller that ‘maximally flat’ enclosure volumes as defined by classic Thiele/Small parameter theory. With modern DSP horsepower they can look at the spectral content of the music being played and in real time compare that to a model of the driver/enclosure then EQ out the bass loss from the small enclosure right up the point the driver(s) run out of Xmax and then softly limit. Without that EQ plus limiting capability when one tries to “use that (added) volume under the small speaker, to give the driver some space and let it breath.... instead of pushing the sensitivity down to make the driver able to play deep bass in a smaller enclosure” physics rears her head and she’s in a bitchy mood. Adding enclosure volume above the ‘maximally flat’ enclosure volume Thiele/Small parameter theory dictates yields what is often referred to as EBS (Extended Bass Shelf) responses. EBS does have a couple more dBs of bass below the driver’s Fs, but the tradeoffs include less bass just above Fs and reduced power handling. And not flat bass added, just bass not rolling off as fast. In the case of the PTT6.5 EBS gives a bit more output at 30 Hz paid for as a roll off starting earlier in the 40-80 Hz range. Given most of us listen to rock, jazz, pop where 90% of the bass content is in that 40-80 Hz range that is a questionable tradeoff in my experience. “Questionable” is too strong a word. Rather let me advise you that taking a given driver from a maximally flat enclosure to an EBS enclosure without DSP tricks expect the difference to be subtle.
Finally I agree “many good sounding speakers, that do not use expensive drivers... as a rule” exist. Offerings in the $200 to $1500 a pair in retail speakers are in a golden age, as are drive units available for DIYers. However this thread is about Purifi drivers. Sum together their breakthroughs in force factor modulation linearization, reduction of surround radiation distortion, reduction of magnetic hysteresis distortion, linearization of long stroke performance, and reduction of cone edge ringing and they are presently ahead of everyone else by a significant margin. The only way in my experience to outperform Purifi is resorting to very large radiating area solutions like the Volti Audio Vittora horns or GR Research NX-Treme line sources to mention a couple I heard at LSAF 2019.
Thanks cph2000 for stating explicitly what I inferred that the extrema approach using a woofer magnet and voice coil as a passive radiator that the thus created variable “brake” is not wired as part of the cross over. Mentioning Buchardt also reminds me to point out a couple of points.
First the SB Acoustics oval PR 5″ x 8″ SB15SFCR-00 has an Sd area of 178 sq. cm vs. the PTT6.5 133 sq. cm. The rule is twice the Sd (driver cone area) on the PR vs woofer to not limit output. So ideally one uses two for the SB15SFCR-00, that’s still only circa $75usd with SB vs $354usd per speaker with Purifi, or ~$500 if one buys 4 pieces to do a pair of speakers direct from Purifi.
Second is Buchardt is an example that in commercial offerings we often see compromise in the twice the Sd on the PR vs woofer ‘rule’. Their lauded S400 has a 6” woofer with the 5″ x 8″ PR like the Selah Audio Purezza Purifi equipped design referenced above. In contrast GoldenEar Technology is a company they seems more dedicated to generous Sd on their PRs.
Regarding his “sooo compact!” proposals emilkoz asks “Am I being stupid or is it a viable design?” I vote not stupid, viable. It is interesting when you invoke Devialet’s Phantom. Let’s save that discussion to include with the Kii3.
In his post above digitalthor mentions tradeoffs including enclosure size, 2-way vs. 3-way, and driver costs concluding: “The Kii3 is a small top-notch - kinda 3 way - with nice cheap drivers. It performs great.... so why the fuzz? I know it might sound like a provocation.... but I find many good sounding speakers, that do not use expensive drivers... as a rule.”
OK, one of the controversies around the Kii3 is when the ‘net pundits cost its “nice cheap drivers” at a few hundred bucks and then complain about that vs the $15,000 a pair retail price. Devialet’s Phantom come in at $2,000 to $7,000 a pair depending on model. In both cases that extra cost is covering self-powered bi-tri-amped multi-way DSPed up the wazoo, and multi input options capabilities. Some say “all I care about is sound quality”. It is also my first priority (although I do spend an inordinate amount of time on styling and finishing details). What DSP brings to Kii, Devialet, and other’s game is the ability to force deep bass out of smaller that ‘maximally flat’ enclosure volumes as defined by classic Thiele/Small parameter theory. With modern DSP horsepower they can look at the spectral content of the music being played and in real time compare that to a model of the driver/enclosure then EQ out the bass loss from the small enclosure right up the point the driver(s) run out of Xmax and then softly limit. Without that EQ plus limiting capability when one tries to “use that (added) volume under the small speaker, to give the driver some space and let it breath.... instead of pushing the sensitivity down to make the driver able to play deep bass in a smaller enclosure” physics rears her head and she’s in a bitchy mood. Adding enclosure volume above the ‘maximally flat’ enclosure volume Thiele/Small parameter theory dictates yields what is often referred to as EBS (Extended Bass Shelf) responses. EBS does have a couple more dBs of bass below the driver’s Fs, but the tradeoffs include less bass just above Fs and reduced power handling. And not flat bass added, just bass not rolling off as fast. In the case of the PTT6.5 EBS gives a bit more output at 30 Hz paid for as a roll off starting earlier in the 40-80 Hz range. Given most of us listen to rock, jazz, pop where 90% of the bass content is in that 40-80 Hz range that is a questionable tradeoff in my experience. “Questionable” is too strong a word. Rather let me advise you that taking a given driver from a maximally flat enclosure to an EBS enclosure without DSP tricks expect the difference to be subtle.
Finally I agree “many good sounding speakers, that do not use expensive drivers... as a rule” exist. Offerings in the $200 to $1500 a pair in retail speakers are in a golden age, as are drive units available for DIYers. However this thread is about Purifi drivers. Sum together their breakthroughs in force factor modulation linearization, reduction of surround radiation distortion, reduction of magnetic hysteresis distortion, linearization of long stroke performance, and reduction of cone edge ringing and they are presently ahead of everyone else by a significant margin. The only way in my experience to outperform Purifi is resorting to very large radiating area solutions like the Volti Audio Vittora horns or GR Research NX-Treme line sources to mention a couple I heard at LSAF 2019.
Good luck putting together a UK group buy. Be advised that to qualify for the listed price breaks Purifi insists a single payment and that all drivers ship to one address. So keep your time, funds transfer, and shipping costs dispersing drivers to group members in mind while planning.
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@Studley: I want a pair but not this year!
@Digitalthor: interesting question, but possibly wrong thread for it. I understand that IF you have the space for multiple drivers or an 8" then you can get similar performance in a larger box for less money, BUT if a 6.5" in a 20litre box is your limit and you want the performance possible the Purify is there.
For everyone else. I keep wondering about the 4" as that is a form factor I am used to coming from the world of mini monitors. But the ripple between 1 and 2kHz just looks horrible to deal with. Anyone looked closely at what could be done with that?
@Digitalthor: interesting question, but possibly wrong thread for it. I understand that IF you have the space for multiple drivers or an 8" then you can get similar performance in a larger box for less money, BUT if a 6.5" in a 20litre box is your limit and you want the performance possible the Purify is there.
For everyone else. I keep wondering about the 4" as that is a form factor I am used to coming from the world of mini monitors. But the ripple between 1 and 2kHz just looks horrible to deal with. Anyone looked closely at what could be done with that?