Purifi SPK5 Speaker Review (Prototype)

[Dennis Murphy]

How about a beryllium tweeter. Good for distortion but pain with crossover and cabinet design.

Maybe you could elaborate a little. It seems to me that the Satori Be would be a perfect choice--low distortion, ruler flat response, and a cinch to cross over anywhere from 1900 Hz on up. Also, not that expensive compared with other Be's. I'm not aware of any cabinet design issues.

 

[GimeDsp]

I don't understand anything about this speaker.
Why the outside crossover?
Why speakon connectors?
What is the "look" supposed to be with them?
Is it supposed to be like a high end DIY type thing?

Can someone post pics of these actually set up in a listening room? thanks.

 

[w1000i]

I don't understand anything about this speaker.
Why the outside crossover?
Why speakon connectors?
What is the "look" supposed to be with them?
Is it supposed to be like a high end DIY type thing?

Can someone post pics of these actually set up in a listening room? thanks.

The idea to minimize hysteresis distortion by choosing specific part and design for the crossover, connectors, woofer magnet and their amplifer.

 

[amirm]

I don't understand anything about this speaker.
Why the outside crossover?
Why speakon connectors?
What is the "look" supposed to be with them?
Is it supposed to be like a high end DIY type thing?

Can someone post pics of these actually set up in a listening room? thanks.

This is a development platform from Purifi. It is designed for playing around with the crossover and such. Commercial implementations will have internal crossover and just normal speaker binding.

 

[Francis Vaughan]

I don't understand anything about this speaker.
Why the outside crossover?
Why speakon connectors?
What is the "look" supposed to be with them?
Is it supposed to be like a high end DIY type thing?

Can someone post pics of these actually set up in a listening room? thanks.

The speaker is a reference design from the designers of the bass driver - which comes from the same crowd as the Purifi amplifiers - so some pedigree, especially in DIY circles. As a reference design it isn't really supposed to be a commercial product. It is supposed to be built by potential clients so they can evaluate the driver. Nothing special about an external crossover etc, it does however allow for easy modification. Much like many reference designs in electronics. Otherwise it is supposed to be an easy build, with no special woodworking or effort needed. There is no expectation that anyone would be wandering into their local audio dealer and purchasing this exact design.
But the DIY community being what it is, a heap of them will be made. Many DIYers don't design, they wait for designs by others. So this fills that need. (IMHO badly.)

 

[Dogmeat88]

@sgoldwin
Purifi woofer have some interesting design solutions, but not this vented speaker kit.
Maybe Purifi can make a kit with passive radiator and amp from Purifi or Hypex included? That will be much more interesting, than a 2 way vented box - there are already lot of such kits out there. Active speaker with digital crossover can solve many problems with crossover performance, and use of passive radiator can make speaker less sensitive to the room placement, and still have good bass.

 

[Stretchneck]

Just to say to @amirm - thanks for your great work!

 

[Kuppenbender]

If you still want to have access, after you are sure the other seams are airtight, could use some wide masking tape to try to seal up the back panel.

Duct tape.

As the saying goes, you can fix anything with duct tape.
If you can’t fix something with duct tape,
you’re not using enough
....duct tape!

 

[Ilkless]

It does because the woofer is "state of the art" .
I am saying that $350 drive units are not impressive anymore. There are already so many good ones that one is better of taking advantage of other stars in the art.
And yes, if you send out a demo for a state of the art driver your demo unit ought to be impressive. If not I am going to think you are not a good engineer. This is a very exoensive driver paired with an expensive tweeter and very expensive caps and coils. You better believe I vote this better sound good.

The understanding I had was they pushed up the XO point because they couldn't find a tweeter with distortion levels at the low-end of its passband that matched Purifi's distortion at the high end, and that this speaker was purely about demonstrating the low distortion of the driver, with little regard for optimal tonal balance or directivity. Rick Craig, Hificompass, Alan and Joseph Crowe have come up with far better implementations that show the Purifis at their best while with good-to-excellent directivity. IMHO the Purifi strategy ought to have been give out drivers to respected, competent designers (like what Jantzen does with Troels) and publish whatever they come up with. It's also peculiar that their own reference doesn't use their PRs and their PRs have been shown to almost be mandatory in a standmount configuration by Hificompass and Dennis Murphy (as well as the other designers. Perhaps Purifi thought that having PRs would dilute the value proposition. We are talking Illuminator and Skaaning money (with none of the pedigree), even double Revelators, if one factors in the PRs. Going ported would push down the BOM cost they can present significantly, making it an easier sell to manufacturers.

 

[mSpot]

Can someone post pics of these actually set up in a listening room?

Pics here: https://audiophilestyle.com/ca/revi...and-1et400a-amplifier-technology-review-r866/

To expand on what others have said...
Purifi is an OEM driver manufacturer like Seas or Scanspeak that produces only the speaker drivers, not complete speakers. Their business model is to become a supplier of drivers to companies that build complete speakers. Purifi have created this design as an example of how their driver might be used in a complete speaker. It is to help speaker manufacturers evaluate the driver without having to start from scratch with their own design.

 

[witwald]

This is a driver that struggles to find a use case. The extraordinary excursion, one that is claimed to put it on par with drivers of significantly greater diameter is something of a significant handicap.

Yes, the driver has a ±10.5 mm linear excursion capability. That is quite impressive. However, other drivers in its size category can do ±6 mm, so the jump to ±10.5 mm isn't that great. In the end, it's still a small woofer, with all the inherent limitations (and benefits?) of a small woofer. Going up to the next woofer size with ±6 mm excursion essentially gets you the same results.

In order to build a viable bass reflex enclosure the port is forced to be extraordinarily large. So much so that it starts to dominate ones thoughts on design. Purify sell passive radiators, but these are just the same driver without a motor, and cost half the price of the full driver. Because of the nature of bass reflex, you need two. So suddenly you are looking at double the price in drivers, from what is already a pricey driver.

Indeed, those PRs are expensive. But in the total scheme of things, you buy a few worthwhile benefits: a) no port chuffing; b) no tube resonances from the port. One downside is that the design is a 5th-order system, with the attendant transient response trade-offs compared to a 4th-order system. However, there seems to be a large gain in low-frequency extension in what is really a very compact enclosure. If the speakers aren't pushed very hard, then they'll produce plenty of extended bass response at low distortion levels. The standard unmodified PRs seem to produce a bass shelf in the low-frequency response. This will probably help with siting the speakers closer to walls in a typical room environment.

 

[witwald]

Moving to the next region, that crossover region doesn't look right to me. We have that long and gradual slope for the woofer before dropping like a rock. Yet the tweeter has a sharper slope. Can't imagine those summing correctly. They do agree with the electrical measurements of the crossover as provided by Purifi though:
View attachment 95368
The red curve when applied to near flat response of the woofer by itself (as provided by Purifi) will result in what I have measured. So we are seeing the response as designed. Just doesn't sum well.

Looking at the acoustic filtered responses of the woofer and tweeter around the "crossover" region, and their sum, it appears that they sum reasonably well. At least well enough to get close to flat response through that region. It looks like the designers have opted for an in-phase crossover design, somewhat like Linkwitz-Riley designs. A bit more development work, and one or two extra crossover components, could potentially have resulted in much improved integration, with little increase in overall manufacturing cost.

 

[witwald]

Looks like something's wrong with port or enclosure seal (probably both). It's supposed to be tuned at ~32Hz:
View attachment 95390

From this impedance curve, the port tuning appears to be correct. The impedance minimum in the range from 20 Hz to 50 Hz seems to lie just a tad above 30 Hz. It seems quite close to 32 Hz, which indicates that the port is working as designed.

 

[mathman]

I'd rather use mdf for the cabinet instead of (thin) plywood.

 

[Helicopter]

Thanks for the review Amir. I like the speakon connector. I like working with plywood. I usually use 3/4 for everything. I have to wonder too if MDF would be a better choice for a high performance speaker though.

I have had similar experiences with shipping from the UK to the US. I think someone has a policy to toss everything down a giant flight of stairs or something. I don't know what the deal is. Romania, Russia, China, Taiwan, Hong Kong, France, Germany... no issues. Last time I got some LPs from the UK I laughed out loud when the package arrived because it was so rough and dirty and boot-marked, and that is what I have come to expect.

 

[ElNino]

This may be an institutional thing, because I have noticed a similar thing from SB Acoustics' factory kit designs (high xover freq + low order filters), maybe to show off the extended bandwidth of their flagship drivers.

This was my thought as well. The crossover design here and its issues (apart from the bass) are definitely reminiscent of the SB Acoustics Ara 2-way factory kit speaker. I find it strange that these premium manufacturers don't seem to place as much importance on smooth directivity as we do, but perhaps it is an institutional thing.

 

[AnalogSteph]

Yes, the driver has a ±10.5 mm linear excursion capability. That is quite impressive. However, other drivers in its size category can do ±6 mm, so the jump to ±10.5 mm isn't that great. In the end, it's still a small woofer, with all the inherent limitations (and benefits?) of a small woofer. Going up to the next woofer size with ±6 mm excursion essentially gets you the same results.

Well yes, but that would be selling this driver short. Its design is not just about long throw but rather peeling back the whole onion of distortion mechanisms that otherwise tends to go along with it. From their website:

• Low Force Factor Modulation
  • Prevents voice coil current from modulating Force Factor (Bl). The PURIFI motor completely avoids this classical Achilles’ heel of long stroke drivers. This translates into low intermodulation (IMD): clean, undistorted midrange even in the presence of a heavy bass.
  • Equates to low impedance modulation, meaning that drive current is not distorted by cone motion.
• Very Constant Force Factor over Excursion
  • Prevents voice coil position from modulating the force factor. This is the classical cause of “burbling” i.e. amplitude modulation of the midrange by large low-frequency cone excursions.
• Low Surround Radiation Distortion
  • The surround contributes to sound output. Conventional surrounds produce distortion as they deform. PURIFI’s Neutral Surround geometry avoids this mechanism without constraining motion. This reduces harmonic distortion as well as intermodulation distortion.
• Low Magnetic Hysteresis Distortion
  • Hysteresis means that magnetic domains in iron retain traces of previous magnetization / demagnetization cycles which cause distortion when magnetized or demagnetized again. This distortion masquerades as benign harmonic distortion when tested with a sine wave but takes on a crackling or noisy character with more complex signals.
  • Removing hysteresis distortion translates into a very “fluid” presentation with excellent front/back separation in the stereo image and a perfectly black background between instruments.
• Cleaner than large-cone short-stroke drivers
  • The combination of the above characteristics results in a compact long-stroke driver that delivers complex sound with a clarity and lack of effort that was previously the exclusive province of large-cone short-stroke drivers. Additionally, thanks to the small cone size, the driver has excellent midrange reproduction. It is highly suited for two-way systems.

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.

The one thing that it'll always have more of than a larger driver is Doppler distortion, but (a) that's not as audibly critical anyway and (b) its magnitude is determined only by geometry and levels which makes it easy to significantly reduce it by applying predistortion in DSP once you've got the frequency response straightened out.

 

[firedog]

https://audiophilestyle.com/ca/revi...and-1et400a-amplifier-technology-review-r866/
https://hificompass.com/en/reviews/purifi-audio-ptt65w04-01a-midwoofer

The reviews and measurements above give a very different picture. Maybe this speaker was still damaged when measured, or wasn't built correctly?

 

[ttimer]

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.

Doesn't that lead back to the critique by @Francis Vaughan ? If the small, low-distortion, long-throw driver requires a large cabinet, why chose it over a large low-distortion driver? Especially because the 6.5" mid-woofer size is already too large for truly form-factor constrained use cases under normal circumstances.

 

[gr-e]

From this impedance curve, the port tuning appears to be correct. The impedance minimum in the range from 20 Hz to 50 Hz seems to lie just a tad above 30 Hz. It seems quite close to 32 Hz, which indicates that the port is working as designed.

Yes, this is NRC's measurement, that's where I got the 32Hz figure from. Amir's impedance curve looks very different, which indicates a problem.