Purifi SPK5 Speaker Review (Prototype)

[Anthony T]

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.

Well, I’m not one of them, haven’t owned any of their products either so that definitely counts me out. I have no idea what you are talking about wrt magnets.

Look, I’m not looking for a row, I think he’s doing too much already tbh.

Mistakes happen, everywhere, I’ve asked a valid question regarding a clear problem with the cabinet and you’ve jump out and replied like you’re his agent or something. Never mind, carry on.

 

[BDWoody]

By request, a bunch of posts were moved to the following thread.

https://www.audiosciencereview.com/...ker-review-prototype-from-other-thread.17973/

You can see how it was cleverly named with "from other thread" (referring to this one).

 

[Thomas savage]

Not read through all this but folks that think putting a performant driver in a box and hoping for the best is speaker design need to remove head from arse.

You can't just assemble performance parts with little else and expect a well engineered product.

Yes people do that, yes its kinda accepted but still being a expert in amplification or speaker engineering requires more than joe blogs assembler with half a clue and a web site.

 

[Francis Vaughan]

You can't just assemble performance parts with little else and expect a well engineered product.

Given this is a reference design from the manufacturer, with the specific intent of showing off the driver, we might assume it is a well engineered design. The crossover design and even PCB came from the manufacturer. That it may have some problems is the surprise.

Not read through all this

Do.

 

[Thomas savage]

Given this is a reference design from the manufacturer, with the specific intent of showing off the driver, we might assume it is a well engineered design. The crossover design and even PCB came from the manufacturer. That it may have some problems is the surprise.


Do.

I'd not assume that, maybe I have more respect for speaker design.

Also ' prototype ' .

 

[Francis Vaughan]

I'd not assume that, maybe I have more respect for speaker design.

Sure. But what are we to expect? If the manufacturer and designer of the driver are incapable of designing a speaker to go with their driver, what might we make of their general competence? Speaker design is not a matter of banging it in a box and hoping. A reference design is intended to be able to show off the driver with the intent of selling lots of drivers to speaker manufactures. The only conclusion we might draw is that the designers are not as smart as they think they are and that we might reasonably question their competence and hence the quality and design of the driver itself. If they are not able to design a speaker to show off the driver to best effect, we question whether the driver is actually any good.

This design is visible on the manufacturer's web site as the current reference design. Over a year from the driver's release. It is also not the first revision of a reference design. It isn't a prototype.

There are a lot of questions about the design. But also the question as to whether shipping damage is part of the problem. There are a lot of questionable aspects to the design, and those of us with at least some speaker design experience have questioned aspects of the design. It has some weird shortcomings. I agree, it really does look like a ham-fisted use of high price components with the hope that all will be good. It is a worry that Purifi have released this design. They must understand that inevitably any design they publish will end up becoming a common DIY build. Publishing a less than stellar, probably untested, design is poor behaviour.

 

[briskly]

I thought the driver was already analyzed in the Purifi woofer thread. The Purifi 6.5 woofer is a heavy, low-compliance driver with high motor strength (low Vas, moderate efficiency, low Qes), a "small subwoofer" type of driver. Small cavities with low tuning frequencies are more challenging to integrate with a wide vent than more typical drivers.
The reference design may be attempting to lower the port tune by placing the interior end closer to the wall; you need to be even more aggressive to chase lower tunings and shorter tubes. The existing cross-brace makes rearranging the tube difficult. A creative ventilation structure for the woofer goes beyond the scope of the test platform.

 

[AnalogSteph]

The Purifi 6.5 woofer is a heavy, low-compliance driver with high motor strength (low Vas, moderate efficiency, low Qes), a "small subwoofer" type of driver.

And actually it still is quite efficient considering its size and the low fs of 30 Hz. I guess the use of a shorting ring permitted throwing on a few more turns.

BTW, wouldn't that have to be high compliance? Given the same moving mass, higher compliance gives lower fs. Hence why high efficiency drivers tend to minimize moving mass and use stiff suspension to get fs up as far as possible, which in return reflects heavily in efficiency.

 

[watchnerd]

HiFiCompass measurements:
https://hificompass.com/en/speakers/measurements/mundorf/mundorf-amt21cm21


At ~$1000/pair, I have little clue why Purifi chose this AMT.

Price: Maybe to show that their woofers mate with tweeters that are even more expensive?
AMT: To show it mating with a driver type that commonly needs a high crossover.

So $1000/pair for the tweeter, $740/pair for the woofer, plus cabinet and crossover parts...

Shall we say the BOM is $2000?

Isn't the retail price of speakers often 3-4x of the BOM?

I know it's a POC and I realize there would be volume discounts for manufacturers, etc, but this this seems to fall well short of what you want in a bookshelf speaker with a retail price north of $5k.

 

[sgoldwin]

I’m the builder of this speaker. First off, the tweeters are NOT $1000 pr. they’re about a third of that.
Second, I’ve now done experiments with multiple versions of the SPK5 and I’m pretty sure that Amir reviewed a broken speaker in that I can duplicate the sound he describes by knocking the bass port out of its flare. The fix is simply silicone tape that you use for emergency plumbing repairs, wrapped tightly around both points where the bass port joins the flare. This makes an airtight seal and the sound snaps into place, seeming to affect the whole frequency range not just the bass. Voices are not recessed, treble seems smoother, less peaky. Bass, of course, is transformed.
I expect to finish up tomorrow and will send to @amirm immediately for his re-test. I hope this one makes it across the Atlantic without issue.

 

[Feyire]

I expect to finish up tomorrow and will send to @amirm immediately for his re-test. I hope this one makes it across the Atlantic without issue.

To be honest, I'm not sure why @amirm decided to give a "cannot recommended" rating to a prototype build that was partially destroyed in its transit across the Atlantic - In my opinion that was unnecessary on his part. I hope you are not discouraged by that and the subsequent comments that followed in the thread. I'm sure I'm not the only one feeling this way.

Thanks for your time and effort.

 

[Rick Sykora]

I’m the builder of this speaker. First off, the tweeters are NOT $1000 pr. they’re about a third of that.
Second, I’ve now done experiments with multiple versions of the SPK5 and I’m pretty sure that Amir reviewed a broken speaker in that I can duplicate the sound he describes by knocking the bass port out of its flare. The fix is simply silicone tape that you use for emergency plumbing repairs, wrapped tightly around both points where the bass port joins the flare. This makes an airtight seal and the sound snaps into place, seeming to affect the whole frequency range not just the bass. Voices are not recessed, treble seems smoother, less peaky. Bass, of course, is transformed.
I expect to finish up tomorrow and will send to @amirm immediately for his re-test. I hope this one makes it across the Atlantic without issue.

Appreciate your tenacity to get another speaker tested and hoping you saw this post: https://www.audiosciencereview.com/...g-speaker-s-for-asr-testing.17812/post-578576

Have only had some connectors shipped from UK. If bigger packages are problematic, you could ship to me and, if this next one is damaged, will fix before it goes to Amir.

 

[watchnerd]

Nothing against our UK builders, but wouldn't it be easier / less shipping to get the parts assembled in North America?

After all, its a POC / protoype, not a finished product.

 

[Rick Sykora]

Nothing against our UK builders, but wouldn't it be easier / less shipping to get the parts assembled in North America?

After all, its a POC / protoype, not a finished product.

Am pondering one but prob will not be as soon as @sgoldwin will get to Amir.

Am still sitting on a Bagby speaker to get tested yet too. Can only have so many around before my otherwise tolerant wife starts to complain.

 

[sgoldwin]

Appreciate your tenacity to get another speaker tested and hoping you saw this post: https://www.audiosciencereview.com/...g-speaker-s-for-asr-testing.17812/post-578576

Have only had some connectors shipped from UK. If bigger packages are problematic, you could ship to me and, if this next one is damaged, will fix before it goes to Amir. [
Rick, that is a very kind offer. Thanks. I also had not seen your helpful post on how to pack. Also, thanks!

 

[ZestClub]

Appreciate your tenacity to get another speaker tested and hoping you saw this post: https://www.audiosciencereview.com/...g-speaker-s-for-asr-testing.17812/post-578576

Have only had some connectors shipped from UK. If bigger packages are problematic, you could ship to me and, if this next one is damaged, will fix before it goes to Amir.

If its an important shipment that may get damaged - build a light weight wooded crate using thin plywood and strips of IPC treated wood.
That 1) protects the contents and 2) prevents staff from throwing the box because it takes 2 men or a pallet lifter to move it.
Costs a bit of time to make the box and a little more to ship BUT it gets there intact.

 

[watchnerd]

If its an important shipment that may get damaged - build a light weight wooded crate using thin plywood and strips of IPC treated wood.
That 1) protects the contents and 2) prevents staff from throwing the box because it takes 2 men or a pallet lifter to move it.
Costs a bit of time to make the box and a little more to ship BUT it gets there intact.

I had a reel-to-reel tape deck shipped to me from Amsterdam to Seattle using this.

 

[Rick Sykora]

If its an important shipment that may get damaged - build a light weight wooded crate using thin plywood and strips of IPC treated wood.
That 1) protects the contents and 2) prevents staff from throwing the box because it takes 2 men or a pallet lifter to move it.
Costs a bit of time to make the box and a little more to ship BUT it gets there intact.

Interesting as a bigger box is more expensive to ship, but maybe worth it if high value contents.

There are ways to mitigate with a smaller box but is why I posted how I package to ship speakers to Amir. Most of the time, I use ground shipping. Guessing international air shipping would be comparable, but perhaps the distance may increase handling too and more risk of damage.

 

[Yevhen]

This is a review of the Purifi SPK5 reference speaker design for their PTT6.5W04-01A 6.5 Inch Woofer. It was built and sent to me by the company, Celuaris (member @sgoldwin). The unit was shipped from UK and did not travel well. Just about everything that could come loose, did come loose. I had to take the back apart and reconnect everything and solder a few components in the Purifi crossover board. Final product from the company will not have these issues. Still, I think we can get a lot of valuable data from the design as is.

Celuaris has built the speaker to Purifi spec and visually it looks to be so:

View attachment 95357

The backside is butchered up by me opening it back together (screws were very stiff resulting in me stripping a bunch ).

View attachment 95358

The port is "S" shaped inside. There was barely enough room for it inside and since it was not glued together, it may not be in the optimal position as designed.

The crossover board is external and uses Purifi layout and build:

View attachment 95360

I did not appreciate the black silkscreen/solder mask one bit. It completely covered the traces making it very hard for me to figure out what went where. Why on earth a development board was taught to be better this way? Confusing the implementer can't be a good thing. I expect more from Purifi. Looks should be secondary to easy of use.

Note that the bent components is my fault. I had to flip it multiple times and they started to loose their straight orientation. Fortunately electrons don't care.

As you see, fancy capacitors and such are used throughout. Combined with high cost of the Purifi woofer ($365?), this would not be a cheap speaker if so dressed.

For my testing I had to put the crossover on top of the speaker separated by a 2 inch piece of foam. The Klippel NFS robotic scanner goes around the speaker and nothing can be separate from it or it will dangle. I don't think that made much of a difference in measurements but thought I mention it.

Note that this test is for experienced readers to analyze the design components here and less so about the finished speaker. Company plans to send me one of those later for proper review.

The measurements were made at about 61 degrees F which was comfortable to me but not if you are from a sunny place.

I used over 1000 measurement points which gave me less than 1% error for most of the spectrum with the exception of 2.5 to 8 kHz where the error crept up a bit more to around 2%.

Purifi SPK5 Measurements: Spinorama Frequency Response
As usual we start with anechoic response of the speaker plotted in multiple ways:

View attachment 95366

Well, this is not that good. Starting from left, we have a dip in upper bass frequencies. Things get better until we start to approach the crossover frequency and now we face a broad dip from 1.2 kHz to some 7 kHz! There was talk of Purifi adjusting the crossover region, pushing it up to 3.5 kHz. Don't know if that is the cause but what is there is definitely not optimal. We then hit a resonance around 8 kHz and a few more peaks with elevated response from the tweeter.

I researched other measurements and while there is some agreement with this data, they vary fair bit so I thought I dig in to see if what we have is correct. Let's start with near-field response of various radiating sources:

View attachment 95367

I had to adjust the port level so don't take that as absolute. What is strange about the port is that it does not augment the low frequency response of the woofer as we normally see. It simply reinforces what it can produce as is. I could be OK with it but not that sharp resonance that follows between 300 and 400 Hz. That corresponds with a dip in our frequency response so perhaps this is out of phase and sucks out the energy in that region.

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.

Next is the resonances in the tweeter. I looked up the specs for the Mundorf AMT AMT 21CM 2.1 tweeter and this is what they show:

View attachment 95369

A very large vertical scale of 80 dB (as opposed to standard 50 dB) helps to hide the same peaks we see in our measurements as marked. Was there not better choices here?

Purifi shows the following measurements which were sadly gated and in-room and hence, lack the resolution to see the port problems:

View attachment 95370

Notice that the tweeter ringing is there. What is different is that they show same ringing in the crossover region which hides the wide dip that I measured. Disappointing that a company like Purifi would not bother getting a proper anechoic measurement. If they had, these problems may have been fixable.

Anyway, going back to our regular programming, here is the early window reflections:

View attachment 95371

It seems to be more "correct" which helps tame the on-axis response issues when we look at the combined result:

View attachment 95372

Horizontal beam width shows decent response until the narrow width tweeter starts to beam toward the end (gets directional):

View attachment 95373

And the same as contour plot:

View attachment 95374

Vertical dispersion says you better stay at tweeter level or slightly below:

View attachment 95375

Purifi SPK5 Distortion Measurements
The main claim to fame of the Purifi woofer is lower distortion. So let's look at our standard measurements:

View attachment 95376

Ignoring the bass for a moment, I am not happy to see the rising distortion in lower treble. Anyone want to guess as to the source?

Here is our 96 dBSPL @1 meter graph:

View attachment 95377

Was hoping to see nothing above 50 dBSPL but we have fair bit. I leave it up to you all to dig up past measurements and compare to other speakers with similar sized woofer.

The distortion amount is much worse than what Purifi shows from my quick look. Looking at contributions to it, I see a lot more of it from the port than the woofer. My reassembly of the speaker may have something to do with this as well. Not sure.

Here is the impedance graph:

View attachment 95379

Our port issue/resonance is clearly apparent. Can't figure out the messiness around 30 to 40 Hz though. Anyone has a guess for that?

Since this is an ultra technical write up, I thought I include the waterfall/CSD plot as well:

View attachment 95380

I have not tried to adjust thresholds and such. But we can see some of the same issues we have seen in other measurements.

Purifi SPK5 Speaker Listening Tests
I placed the speaker in my usual stand in my listening room with the crossover separated from it (my poor Revel Salon 2 speaker acted as a crossover stand!). I always start with female music tracks to see if the highs are produced well without being too bright or recessed. Well, here they were clearly recessed and not that nice. So the EQ tool came right out resulting in this set after fair bit of experimentation:

View attachment 95381

The corrections follow the response errors. Lifting up the upper bass resulted in much needed bass energy as without it, there is just not a lot of it there. Broad EQ around 2500 Hz dealt with the crossover deficiency quite well, lifting the female vocals out and giving them the treatment they need: a bit brilliant and forward without it being too much. Actually, it was a too much at first without the higher frequency corrections. A PEQ dialed to lower the resonance at 8 kHz was very helpful as was the quick shelving filter above that.

At first I had the room mode dip active but as noted, there is not a lot of bass coming out of this speaker so I took it out. This helped and by this time, the response was very nice and high quality. Lots of detail without any bass notes becoming overbearing. It was a bit like getting rid of a room mode using EQ and the feeling of relief you get after that.

I played by "speaker killer tracks" and the SPK5 handled them quite well up to a point which was way ahead of what most small woofers can handle. It then followed with a bit of distortion. The woofer was going nuts as far as excursion by this time which would have really messed up the sound of other woofers. Push a bit more though and you are greeted with a static pop that implies the coil getting outside of the magnetic field.

There was a big miss though and that was any kind of physical bass response. Even at much elevated levels, you could barely feel the bass. You could hear it well and on techno tracks, celebrated it. But as a sensation which I crave, almost none was there. I wonder if this is due to the tuning of the poor which doesn't lower the response range.

Overall experience was a very light on its feet speaker that produced very satisfying sound with equalization. With out, it would not be my cup of tea.

Conclusions
Great to see innovations in woofer technology. Alas, the lesson of research in the last four decades was ignored in this development reference design: getting the tonality right. There could not be a more clear example here. I don't care how low the distortion is if you screw up the vocals. Or sound too bright. Fix these -- as I did with EQ -- and then the lower distortion of the bass (appears to ) come forward.

Thinking out loud, I wonder how much bass energy we loose by lowering distortion. Harmonics of low frequencies perceptually would raise the total energy in that region. I wonder if this, together with port issue, was behind lack of sufficient impact in bass response.

I am left thinking if a 6.5 inch driver is the right choice for this technology. Maybe an 8 inch driver would have been a better showcase so that we could have bass and low distortion. Alternatively maybe other designs would do better. I don't know. What I do know is that this was not a good attempt by Purifi to showcase their speaker.

Let's hope some issues here are due to difficulty I had in putting this speaker in working condition. I welcome detailed analysis from you all though on how it could be improved if the problems are real.

Overall I cannot recommend the Purifi SPK5 without equalization.

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As always, questions, comments, recommendations, etc. are welcome.

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Hi Amir,

I'm assembling the same speaker, just 8ohm version. It also sounded weird to me. But then I realized there is probably a mistake in the application note from Purifi. 2nd order filters in the crossover create close to 180 deg phase shift between LF and HF drivers. So the drivers should be connected in antiphase. But in the application note both outputs are marked as "+".
Could you please check if the drivers in your speaker were connected properly? Also the frequency response that you've measured with two notches at 2kHz and 3kHz is similar to what Purifi is showing in the test of crossover, when they charge polarity on purpose.

 

[amirm]

Could you please check if the drivers in your speaker were connected properly?

I really can't. The problem is that the builder used push on connectors for this sample and they are so ill fitting that the moment you take the back off, they get disconnected. He is building another sample so hopefully he follows the correct configuration.