Purifi SPK5 Speaker Review (Prototype)

[Ilkless]

You know what tweeter would mate really well with it? A small midrange and a 40 dollar dome. I really do think the small form factor 3 way is an interesting and viable approach.

SEAS has a very cool small 22mm tweeter that's a perfect candidate for crossing to a small midrange actually. It's halfway between a ring radiator and conventional dome because it has a massive surround around a small alum/mag dome. Been out for a decade+, but has a distortion profile that can compete with a Bliesma >3kHz, slightly higher H2 (~-45dB) but stupendously low (-70dB broadband) H3 and above. Very flat as well, with dome breakup at a very high frequency. The only thing that betrays it's age and price is that it doesn't have the fancy variable thickness dome that gives Bliesma very wide controlled dispersion for the diameter and it can't extend as low or cross as low. $43 only on Madisound. Honestly doesn't get as much attention as it deserved even early on, I only know a few obscure DIY designs with it. I reckon better off playing with a dome like this than messing with mediocre AMTs and ribbons of dubious tolerances.

 

[BostonJack]

If built to the plan, the front baffle calls for MDF and there is a rather major diagonal brace in the center of the (plywood) cabinet. I tend to build with MDF but have had good results with quality plywood. I suspect the problems are more related to the shipping abuse (and maybe not gluing the back panel). Have limited experience with UK shipping, but have seen some pretty beat up packages domestically too!

Slightly off-topic question: Do you find a significant difference between MDF and Baltic birch plywood (3/4" for both) in small speakers?

I'm asking as I am starting a DXT-MON build in the 8L cabinet and prefer working with Baltic birch, but have some concern that the MDF is acoustically better. (Cabinet has 2 layers of Al-butyl rubber on the interior to increase damping). Thx.

 

[Wolf]

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.

I also concur there are problems with the box and or port seal, and I would not be surprised if a magnet slipped somewhere and made the tweeter not perform to spec. A hard fall is a hard fall.

I also agree with Duke, that there should be a zip-tie and/or adhesive for every part on that board.

By comparison, I think the 4" Purifi and the new AMT from SB might make a slick combo...

 

[JustIntonation]

The Purifi driver itself is the best there is for this size.
But this demonstration speaker was quickly put together in the early days of releasing their driver. Didn't expect it to be any good personally.
I think in time they'll come out with a much better DIY demonstration speaker. I know they've been researching different tweeters (among which BlieSMa tweeters) and have since then also released a matching passive radiator for the PTT6.5.

 

[Wolf]

$43 only on Madisound. Honestly doesn't get as much attention as it deserved even early on, I only know a few obscure DIY designs with it.

dlneubec's 'Blades'
Rory Buszka's 'Neutrinos'

There are others, but those immediately come to mind.

 

[Ilkless]

I wonder why they haven't used their (matching?) passive radiator? That would have avoided the high frequency port resonances.

https://purifi-audio.com/transducers/ptt6-5pr-01/

This is just a proof-of-concept design that shows the Purifi as part of a functioning loudspeaker for manufactures to evaluate. Several designers have also remarked a PR (ideally dual PRs) is almost mandatory for the Purifi, but imagine trying to sell a driver that needs dual PRs to reach it's potential to manufacturers. Where other drivers mostly can work well enough ported, a dual PR is going to make it look incredibly finicky and raises the BOM cost to an even more prohibitive level, likely driving away manufacturers.

 

[Ilkless]

dlneubec's 'Blades'
Rory Buszka's 'Neutrinos'

There are others, but those immediately come to mind.

Troels has one pairing it to the classic CA paper cone SEAS. But, yeah not a driver one sees a lot beyond one-offs, compared to something like a 27TDFC, XT25 or SB29. The distortion profile is uncannily similar to the Bliesma's at an eighth the price.

 

[amirm]

The port in the specs is pretty convoluted (trying to fit within the cabinet) and likely to close too the back of the tweeter...

That's what it looked like inside including the brace. The port space is indeed very limited and I had to reassemble it blind as I put the back on.

 

[GimeDsp]

Fr

I wonder why they haven't used their (matching?) passive radiator? That would have avoided the high frequency port resonances.

https://purifi-audio.com/transducers/ptt6-5pr-01/

" Long Stroke Passive Radiator with Ultra Low Distortion "

DO PRs create distortion
Have the distortion profiles of other PR's ever been measured?

 

[andreasmaaan]

Fr

" Long Stroke Passive Radiator with Ultra Low Distortion "

DO PRs create distortion
Have the distortion profiles of other PR's ever been measured?

Yes, they absolutely do produce distortion, mostly as a result of nonlinearities in their suspension. However, this tends to be less objectionable than distortion produced by the woofer itself, for a couple of reasons:

• Although any PR's suspension (like any woofer's) must be nonlinear, the PR does not have a motor. In other words, one of the major and most objectionable sources of nonlinearity in a woofer is avoided in a PR.
• The PR's bandwidth is very limited compared to that of the woofer. So any distortion it generates will be confined to a narrow band of low frequencies, where they will be far less audible.
• Although PRs do produce some distortion of their own, by limiting the woofer's displacement around the tuning frequency, they reduce the stress on the woofer, which (all else equal) will produce more distortion (as it has a motor) than a PR per displacement (NB: ports do this too, ofc).

Also worth mentioning that ports themselves produce distortion as a result of nonlinearity in the flow of air through the port. So the natural alternative to a PR is not distortion-free either.

As to whether PR distortion has ever been rigorously measured/studied - not that I know of - sorry!

 

[AnalogSteph]

You know what tweeter would mate really well with it? A small midrange and a 40 dollar dome. I really do think the small form factor 3 way is an interesting and viable approach.

While it would be a shame not to run the Purifi up to ~1 kHz at least, I might give the TEBM46C20N-4B BMR a good look as a midrange (not sure whether that's the same as in the BMR Philharmonitor?)... seems like sensitivity should be a good match with the PTT6.5W08, both around 86 dB.

A 2-way would probably require a 1" or even 1-1/4" tweeter with a fairly big waveguide and highish-order crossover so you can cross no higher than 2...2.5 kHz. Also seems doable. A 3-way could have wider dispersion though.

 

[Lorenzo74]

With steep crossovers no problem. KH80 DSP? Ez. My Event Opal? Ez².
As said, there so point in crossing that low that high with this midwoofer. A combination with Seas' DXT would be worth a shot.

that’s why B. Putzeys used DXT in kii three.
let’s wait Kii “two” with Purifi drivers.
pls note purifi developed 4” and 6.5” as in the kii three.

 

[ROOSKIE]

Slightly off-topic question: Do you find a significant difference between MDF and Baltic birch plywood (3/4" for both) in small speakers?

I'm asking as I am starting a DXT-MON build in the 8L cabinet and prefer working with Baltic birch, but have some concern that the MDF is acoustically better. (Cabinet has 2 layers of Al-butyl rubber on the interior to increase damping). Thx.

The general consensus based on my research and some limited experimentation is that mixed materials are better than any 1.
Example 1/2 MDf + 1/2Birch Ply for example. Add some cork or Black Hole or butyl rubber.
You can also try adding in some layers of HDF (hardboard - often only found in 1/8 and 1/4" sizing.

When it comes to MDF realize is it is very inexpensive on the industry scale, it can easily be shaped and is lighter in weight than Birch Ply.
I think that is why it is more common.
Good plywood is much stronger than MDF and due to the multiple layers some say when properly used it is the better choice acoustically.

 

[sgoldwin]

The port in the specs is pretty convoluted (trying to fit within the cabinet) and likely to close too the back of the tweeter...

View attachment 95585
Did the test speaker have something else?

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.

 

[GimeDsp]

Yes, they absolutely do produce distortion, mostly as a result of nonlinearities in their suspension. However, this tends to be less objectionable than distortion produced by the woofer itself, for a couple of reasons:

• Although any PR's suspension (like any woofer's) must be nonlinear, the PR does not have a motor. In other words, one of the major and most objectionable sources of nonlinearity in a woofer is avoided in a PR.
• The PR's bandwidth is very limited compared to that of the woofer. So any distortion it generates will be confined to a narrow band of low frequencies, where they will be far less audible.
• Although PRs do produce some distortion of their own, by limiting the woofer's displacement around the tuning frequency, they reduce the stress on the woofer, which (all else equal) will produce more distortion (as it has a motor) than a PR per displacement (NB: ports do this too, ofc).

Also worth mentioning that ports themselves produce distortion as a result of nonlinearity in the flow of air through the port. So the natural alternative to a PR is not distortion-free either.

As to whether PR distortion has ever been rigorously measured/studied - not that I know of - sorry!

Thanks for sharring the info. PR seems like the best solution for a 2way if money is no issue?

Golden ears makes a 2 way with AMT (?) and a PR on both sides.
GoldenEar Technology | A Passion for Sonic Perfection - Aon Series | GoldenEar Technology | A Passion for Sonic Perfection

 

[andreasmaaan]

Thanks for sharring the info. PR seems like the best solution for a 2way if money is no issue?

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).

 

[Lorenzo74]

The crossover is the SPK5 Crossover Kit ordered from Purifi and assembled by me.

Hi you’re saying you are the crossover maker.
what’s your opinion about the results?
Seems not so good compare to expectation.
shall someone send a new example to amir for confirmation?

 

[mrmoizy]

Late to the party, not going to read 7 pages to make sure this comment isn't redundant, so forgive me for what is - but I had 3 thoughts:

1. Purifi seems to be very scientific in their approach, always using measurements to back up their theories (their whitepapers are interesting). It seems contradictory, then, to include expensive crossover components. The Jantzen Cross Cap capacitors aren't too expensive (only US distributor that sells them). But that copper-foil-in-wax inductor is costly, especially if it's a thicker gauge, probably costing $35-60, maybe more? I know Purifi eschews iron-core inductors due to claims of hysteresis distortion, but copper wire air-core inductors of similar gauge are usually less than half the price of the copper foil inductors. @amirm Purifi sells this crossover to consumers - perhaps that explains the attractive but concealing black silk screen look that seems above and beyond for a development board? Looks expensive, and prevents people from just deriving the crossover layout from following traces. Just guessing. The crossover here retails from Purifi for $299. And that's their cheap option - why the expensive crossovers that don't provide any measurable contribution?
2. Interesting that Purifi makes a matching 6.5" passive radiator, but it wasn't implemented with this build. Lately in reviews on here it seems that ports tend to contribute some deleterious resonance in the mid-bass region (like we see here), while I've seen some nice, smooth passive radiator implementations in the past. Plus, it sounds like implementing this port inside of this bookshelf box seemed to require some geometric gymnastics, while implementing a passive radiator, if you get the counter-weighting correct, seems much simpler. Why didn't they utilize their own passive radiator?
3. Again, they like measurements, so why did they utilize that Mundorf ribbon tweeter? Ribbon tweeters, while having some strengths, are known to struggle in the mid range (where this one crosses over) and also have directivity issues (Interesting article testing similar ribbons). And these Mundorf ones are expensive!! More than Purifi's own woofers! I think this is that exact tweeter model. For less cost, Purifi could have implemented a better performing Berylium tweeter with a waveguide, achieved outstanding midrange performance in the crossover region, and had much broader and much more uniform directivity. Why this tweeter? Is it just for appearances? To sell the part and match the brand, "elite performance from a well-engineered European design"?

I'm an amateur speaker designer with little experience. I haven't spent the time nor do I have the equipment to be an excellent designer. But these points seemed like issues to even my level of experience that could have been rectified, producing a better performing product for much less cost.

 

[mrmoizy]

Late to the party, not going to read 7 pages to make sure this comment isn't redundant, so forgive me for what is - but I had 3 thoughts:

1. ...

I'm an amateur speaker designer with little experience. I haven't spent the time nor do I have the equipment to be an excellent designer. But these points seemed like issues to even my level of experience that could have been rectified, producing a better performing product for much less cost.

Don't want to come across as a Purifi hater - I love their amp and I like this woofer. Just had high expectations and am disapointed in the mediocre performance from something so expensive.

 

[617]

Don't want to come across as a Purifi hater - I love their amp and I like this woofer. Just had high expectations and am disapointed in the mediocre performance from something so expensive.

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.