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Purifi SPK5 Speaker Review (Prototype)

Rick Sykora

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the test speaker had exactly this setup exactly as
In the SPK5 spec. But there is ample opportunity for leakage at the junction between the convoluted pipe and the exit flare that I am now investigating.
Hi, yes every aspect of that port needs to be airtight. Am not sure why they made the port tube so complex, but with the angled brace, appears they were trying to direct the airflow in a specific path. A standard bass reflex tuning for this size cabinet requires a almost 18 inch long port. Winding one around allows one to fit a longer tube along a shorter box wall, but the model has a f3 in the upper 60s and a comparable port resonance as a straighter tube has...

It would only have an f3 in the mid-50s, but you could flip the back panel upside down and run with a 2 inch diameter port tube at about 8 inches long. Just curious, how did you fabricate the "tapeworm"?
 
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mrmoizy

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The AMTs share little in common with ribbons other than the large radiator dimensions. In theory they should be a bit more robust down low, but in practice this is only true with larger units, and the larger units have narrow and uneven directivity issues.
Interesting - thanks. Too broad of a brush then to paint them as ribbons
 

Anthony T

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It looks like the box has come apart on the upper left seam on the picture of the back?
Indeed. The enclosure obviously isn’t sealed or even intact so measurements will be useless. Won’t they? Surely?

You can clearly see the damage on both the front and back images so one corner of the enclosure from front to back
is damaged badly enough that the panels are no longer touching.
You‘ve measured a obviously broken speaker that was damaged during shipping or you unfortunately damaged it taking the back off? Naughty boy.
Unfortunately I believe that this was a wasted exercise.
 

restorer-john

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You‘ve measured a obviously broken speaker that was damaged during shipping or you unfortunately damaged it taking the back off? Naughty boy.
Unfortunately I believe that this was a wasted exercise.
You need to consider @amirm is perfectly capable of determining the integrity of the cabinet and components before running hours' worth of tests. He's already stated he made whatever running repairs he needed prior to measurement. As for people suggesting tweeter magnets have moved, that is extremely unlikely unless they were poorly manufactured in the first place. Magnet shifts or chassis deformation from impacts is easy to hear - it's not subtle.

Speakers get damaged all the time in shipping and it takes an awful lot of cabinet/internal/driver damage to render a speaker untestable.

There's a bunch of Purifi loyalists here making excuses or denying what is a disappointing set of results. (kind of reminds me of certain election outcomes) But as more and more speakers using these drivers start rolling in, a pattern will emerge of how good (or not) they really are.
 

Doodski

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You need to consider @amirm is perfectly capable of determining the integrity of the cabinet and components before running hours' worth of tests. He's already stated he made whatever running repairs he needed prior to measurement. As for people suggesting tweeter magnets have moved, that is extremely unlikely unless they were poorly manufactured in the first place. Magnet shifts or chassis deformation from impacts is easy to hear - it's not subtle.

Speakers get damaged all the time in shipping and it takes an awful lot of cabinet/internal/driver damage to render a speaker untestable.

There's a bunch of Purifi loyalists here making excuses or denying what is a disappointing set of results. (kind of reminds me of certain election outcomes) But as more and more speakers using these drivers start rolling in, a pattern will emerge of how good (or not) they really are.
You're reminding me of Baghdad Bob. :facepalm: hehe
 

Mudjock

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You need to consider @amirm is perfectly capable of determining the integrity of the cabinet and components before running hours' worth of tests. He's already stated he made whatever running repairs he needed prior to measurement. As for people suggesting tweeter magnets have moved, that is extremely unlikely unless they were poorly manufactured in the first place. Magnet shifts or chassis deformation from impacts is easy to hear - it's not subtle.

Speakers get damaged all the time in shipping and it takes an awful lot of cabinet/internal/driver damage to render a speaker untestable.

There's a bunch of Purifi loyalists here making excuses or denying what is a disappointing set of results. (kind of reminds me of certain election outcomes) But as more and more speakers using these drivers start rolling in, a pattern will emerge of how good (or not) they really are.
The key information is the impedance plot versus the manufacturer's spec. The locations and magnitudes of the impedance peaks (and the location of the saddle point between them that defines the tuning frequency) are very different. There really isn't a supportable argument that the speaker reviewed is performing to spec. The lower height impedance peaks are consistent with leakage. I'm not sure how easy it is to cause displacement of a magnet in an AMT tweeter - it's one of the few mistakes I haven't made yet. ;)
 
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Speaker has a damn tapeworm. PR should really be mandatory; no way to build a compact speaker with a big port. You need a big port for a driver with this kind of xmax.

Incidentally, I believe the anarchy woofers have similar xmax, although their distortion may be marginally greater and top end not as smooth.
...
The Anarchy 7 has a spec'ed 12mm XMax. The response however might be a bit rough—if the XOver is a two-way at 2500 Hz—with its 8-10 dB peak at 4 KHz.
 
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The capacitor parts used in this kit really are not boutique at all, and are made by Jantzen, not Jensen. The CrossCap is the cheapest offering from that brand name. More often than not, it runs neck and neck in price with the Audyn Q4 and Solen FC. I would say they are better than the Dayton and Bennic derivatives that likely cost a bit less, but those are not available in the EU. Other than the Wax-Foil coils, I would say the xovers are very frugal here.
Agreed. The Jantzen CrossCap series are a very good value metallized poly cap. Very affordable for any design.
 

Doodski

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The key information is the impedance plot versus the manufacturer's spec. The locations and magnitudes of the impedance peaks (and the location of the saddle point between them that defines the tuning frequency) are very different. There really isn't a supportable argument that the speaker reviewed is performing to spec. The lower height impedance peaks are consistent with leakage. I'm not sure how easy it is to cause displacement of a magnet in an AMT tweeter - it's one of the few mistakes I haven't made yet. ;)
Any magnet separation that I have seen had the magnet totally displaced or the basket was bent and twisted.
 

Francis Vaughan

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The effects are most obvious in IMD testing - e.g. see HiFiCompass article (very comprehensive) or observe the very low AM distortion (Lamd) when Erin does his 80 Hz + 200-6000 Hz IMD test (compare e.g. the Dynaudio MW172 8" and MW182 10" drivers - plus in multitone testing, the former is rather worse and the latter pulls ahead with limited bandwidth but falls behind when the deep bass tones come into play).

There may still be potential for improvement in this driver, but it's quite impressive for what it is already. It's just not terribly easy to tune a smallish cabinet for it.
That is pretty much my view as well. I feel they tried to do too much in one go. They trumpet the "breaking the extra-long throw code" as the premier feature of the driver. IMHO it is the chief handicap. Everything else is really good. But this headlong pursuit of a high x-max small driver seems to be a matter of throwing too many ideas into the mix too early. Especially as the driver has TS parameters chosen so that it is a difficult implementation. Had it been designed with a sealed alignment in mind it would have been more usable. But it seems they decided that the prime use case was small two-ways without use of a sub-woofer. For a company that prides itself on forward looking technical developments this seems just plain backwards. Perhaps they perceived that this was the market sweet spot. But the final BOM for a successful design using this particular driver along with its sibling PRs is probably not commercially viable. Designs with something like the SB PR may be much more successful. The price of the Purify PR is way out of line.

The question of distortion in PRs is interesting. The only possible distortion mechanism is suspension non-linearity. There is no motor, so all the difficult non-linearities that Purify have spent effort to remove are not present in the first place.
 

617

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You’ll get some extra bass extension with a ported enclosure, which could be a desirable trade-off in some cases. But generally speaking, yeh, a PR two-way is less likely to have issues than a ported two-way (not that the latter can’t be made to work well, too, ofc).
Andreas I wonder about the wisdom of PRs in small bookshelf sized enclosures with high power woofers? It seems to me that if any cabinet should be over-built and over-braced it would be for a woofer reproducing 30-3K with 12mm xmax being manufactured by a company that makes 300W amplifiers. The PR takes up a lot of cabinet space and bracing would seem to become more difficult.

I'm sure it can be done well but I would hope that if Purefi is serious about making a SOTA tiny speaker they spend a lot of time on enclosure testing; the KEF compliant bracing might be a good approach.

I know we had a speaker here, was it the Amphion or Buchardt with a PR and some cabinet issues. Still, probably better than port leakage.
 

Ericglo

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It seems to me that Purifi would have been better off just purchasing Rick's Purezza and using that as a demonstration piece.



By comparison, I think the 4" Purifi and the new AMT from SB might make a slick combo...
I think I mentioned it to Rick and I think he is already working on a design with the 4". The 4" could be an excellent midrange.
 

AnalogSteph

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I think I mentioned it to Rick and I think he is already working on a design with the 4". The 4" could be an excellent midrange.
Sensitivity arguably is a tad low for that (wouldn't matter in an active speaker), not to mention that it would be a shame not to be using it down to ~200 Hz at least. It would also seem to be beating the KH80 midwoofer by a country mile (not like the Neumann/Sennheiser folks would ever be using such an expensive part... maybe once the tech has trickled down to a more affordable realm).
 

FeddyLost

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Looks like bad implementation of techically advanced driver(s).
If something in exact speaker was done wrong, all the improvements are simply useless in fact.
Even bad chamfering of driver seating place or not good enough box damping will just bury all these low distortion numbers below vibration and reflections. And reflex tube ... is another sad story.
 
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Man, even as a prototype that thing looks gross.

Also, pardon my ignorance but what does "port cancellation" refer to?
In this design, the 300Hz dip is the port cancellation. Ports have harmonics that fester higher in the audible band unless damped, stubbed, or somehow treated. Usually, the higher the harmonic, the smaller the variance with the nominal output. Since it's at 300Hz here, and of large diameter and long dimension, it's out of phase magnitude at harmonic resonance causes the cancellation in the output of the woofer. The problem shifts lower with larger diameter ports, but too small and you get chuffing. This is the tradeoff.
 
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In this design, the 300Hz dip is the port cancellation. Ports have harmonics that fester higher in the audible band unless damped, stubbed, or somehow treated. Usually, the higher the harmonic, the smaller the variance with the nominal output. Since it's at 300Hz here, and of large diameter and long dimension, it's out of phase magnitude at harmonic resonance causes the cancellation in the output of the woofer. The problem shifts lower with larger diameter ports, but too small and you get chuffing. This is the tradeoff.
Ah, thanks. So the general phenomenon is just port resonance. Wonder why they didn't go with their own PR unit then, instead of a vent.
 
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