Purifi Audio SPK5 Measurements | SoundStage/NRC

[Deleted member 14468]

Yeh, look, I realise I'm applying quite high standards in my criticisms of this speaker

I'm wondering if you've seen the actual speaker. It's a rather rudimentary plywood box. There are some chamfered edges on the front baffle, but it's far from ideally shaped. We're not talking Vivid Audio cabinetry here. It's to demonstrate the woofer.

Doug

 

[napilopez]

Yeh, look, I realise I'm applying quite high standards in my criticisms of this speaker. Essentially, my rationale is that this speaker is supposedly (or at least is likely to be assumed to be) a reference 2-way design using a woofer that is (not without some basis) touted by its manufacturer to be the best woofer of its class on the market. Moreover, the speaker is being promoted by said manufacturer on its website (I'm not sure if Purifi is also responsible for actually designing the speaker, but that question seems neither here nor there).

So I'm not suggesting this is a bad speaker in absolute terms. I'm just contending that it is a mediocre speaker whose design is somewhat primitive relative to other examples, and that it fails to be the equal of the potential sum of its parts

Fair enough, I suppose that's a reasonable perspective given expectations and standards here, and knowing the woofer's potential. I was talking more from the perspective of this speaker being an option against other passive speakers. Perhaps it's not the most optimal implementation of the driver, but where else in a passive design will you get extension this low and clean? Considering nothing else is terribly broken, I could see myself recommending this if it were a design intended for the wider market.

I also forgot the speaker is asymmetrical. I wonder what the other side measurements like and if is perhaps less peaky.

 

[andreasmaaan]

I just want to make sure no one gets the wrong idea. Our measurements are done at 1/24th octave. There is no smoothing that some people might miscontrue, but the Listening Window is "averaged," which doesn't smooth, per se, but gives equal weighting to five measurement axis. That might've been what you meant, but I just wanted to make sure others knew.

Absolutely clear. I should have put "smooth" in inverted commas so that that wasn't ambiguous.

I'm wondering if you've seen the actual speaker. It's a rather rudimentary plywood box. There are some chamfered edges on the front baffle, but it's far from ideally shaped. We're not talking Vivid Audio cabinetry here. It's to demonstrate the woofer.

Fair enough. Point taken.

I think what's happening here at my end is that I'm struggling to understand why a merely rudimentary design the was chosen to demonstrate what is apparently a SOTA component. It seems the woofer, if anything, is being done a mild injustice here.

Just my 2c

 

[AudioJester]

Guys bear with me - at the limits of my knowledge...

But what is the contribution of the passive crossover to the low sensitivity??
In the other thread I was wondering the merits of ditching the external passive crossover and switching to a miniDSP 2x4 with 4 channel amplification.

 

[HooStat]

I tend to agree with @andreasmaaan that, since the DIY market is something they support, it would be nice to provide a reference implementation of some kind. Perhaps they might do something new to show off the passive radiator in combination with their woofer.

And we have @Selah Audio who has developed a very nice implementation, reviewed by @hardisj with measurements.

 

[andreasmaaan]

Guys bear with me - at the limits of my knowledge...

But what is the contribution of the passive crossover to the low sensitivity??
In the other thread I was wondering the merits of ditching the external passive crossover and switching to a miniDSP 2x4 with 4 channel amplification.

In a 2-way like this, a passive crossover is unlikely to significantly reduce sensitivity.

In this case specifically, the woofer's half-space sensitivity is about 88dB, and in this design we have a full-space sensitivity of about 82dB. So the passive XO has eaten up no more than 1dB (probably less) of sensitivity here.

 

[MZKM]

In a 2-way like this, a passive crossover is unlikely to significantly reduce sensitivity.

In this case specifically, the woofer's half-space sensitivity is about 88dB, and in this design we have a full-space sensitivity of about 82dB. So the passive XO has eaten up no more than 1dB (probably less) of sensitivity here.

Yeah; you are gonna lose a bit for baffle step compensation; and if you want to increase base extension, that can also be achieved by reducing the sensitivity above where it rolls off.

 

[Massimo]

I tend to agree with @andreasmaaan that, since the DIY market is something they support, it would be nice to provide a reference implementation of some kind. Perhaps they might do something new to show off the passive radiator in combination with their woofer.

And we have @Selah Audio who has developed a very nice implementation, reviewed by @hardisj with measurements.

I don't see anything any more sophisticated in the design of the Selah implementation which is also just a box.

 

[Massimo]

I'm wondering if you've seen the actual speaker. It's a rather rudimentary plywood box. There are some chamfered edges on the front baffle, but it's far from ideally shaped. We're not talking Vivid Audio cabinetry here. It's to demonstrate the woofer. Doug

Personally, I don't see any issue with the design. This looks like 90% of bookshelf speakers on the market, many very expensive. Rectangular in design, with edges being typically chamfered, square, or rounded.

 

[andreasmaaan]

When I called the design somewhat “primitive” and “rudimentary”, this was not directed primarily at the shape of the box (FWIW, my view on box shape is that by the time you’ve built any kind of rudimentary box that is sufficiently bevelled at the edges of the baffle and is adequately stiff and damped, the law of diminishing returns has already kicked in).

Rather, the elements of this design I find unbefitting of a demonstration design for a woofer of this class are primarily:

• Use of a low-order XO frequency, resulting in a wide band of vertical off-axis cancellation.
• Placement of the XO at a frequency of wavelength significantly longer than the drivers’ centre-to-centre distance (which - especially in conjunction with the previous point - will lead to a particularly poor vertical dispersion characteristic).
• Failure to address resonances in (in particular) the output of the tweeter and the port.

Now I’m not saying this is a bad speaker at all. It ticks most of the basic boxes, and it has low distortion, great bass extension for its size, and is capable of high output.

But I still feel that it’s a SOTA woofer being showcased in a significantly-less-than SOTA design.

Anyway I’ll bow out now I don’t want to give the impression I’m bashing this speaker, or even that I don’t think it’s a decent design. I’m just a little disappointed/underwhelmed.

 

[HooStat]

I don't see anything any more sophisticated in the design of the Selah implementation which is also just a box.

Well, the most obvious difference is in the use of a passive radiator instead of a port. And I am sure the cross-over is different, but he would have to comment on that.

 

[Deleted member 14468]

I think what's happening here at my end is that I'm struggling to understand why a merely rudimentary design the was chosen to demonstrate what is apparently a SOTA component. It seems the woofer, if anything, is being done a mild injustice here.

I was one of the first reviewers to actually ask for an receive an SPK5. I don't know if it was in their plan to do that originally. My experience with Purifi goes back to November 2019, when I sat down with Peter Lyngdorf. See this link: https://www.soundstageglobal.com/in...oland/888-avs-2019-coffee-with-peter-lyngdorf

After I received the speaker, I found out some designers already had it and they were satisfied with what they got. They could see the woofer in action, then take it out and do what they wanted to with it.

So understand this was more or less just a demo thing so people could get a handle on what it's about -- and for that it's great. Same with the demo amps they've been sending out. Amps, however, unlike loudspeakers, don't vary so wildly in terms of implementation.

Doug
SoundStage!

 

[andreasmaaan]

Thanks @Doug Schneider for all the input on this. I appreciate that maybe my assumptions about the purpose of this thing are misguided.

Anyway, I’m curious, did you also listen to the speaker? If so, what were your thoughts on how it sounded? Thx

 

[Deleted member 14468]

Anyway, I’m curious, did you also listen to the speaker? If so, what were your thoughts on how it sounded? Thx

Hi,

First thing I did -- always before measuring: https://www.soundstagehifi.com/index.php/opinion/1420-purifi-audios-pint-sized-powerhouses

Doug
SoundStage!

 

[Massimo]

When I called the design somewhat “primitive” and “rudimentary”, this was not directed primarily at the shape of the box (FWIW, my view on box shape is that by the time you’ve built any kind of rudimentary box that is sufficiently bevelled at the edges of the baffle and is adequately stiff and damped, the law of diminishing returns has already kicked in).

Rather, the elements of this design I find unbefitting of a demonstration design for a woofer of this class are primarily:

• Use of a low-order XO frequency, resulting in a wide band of vertical off-axis cancellation.
• Placement of the XO at a frequency of wavelength significantly longer than the drivers’ centre-to-centre distance (which - especially in conjunction with the previous point - will lead to a particularly poor vertical dispersion characteristic).
• Failure to address resonances in (in particular) the output of the tweeter and the port.

Now I’m not saying this is a bad speaker at all. It ticks most of the basic boxes, and it has low distortion, great bass extension for its size, and is capable of high output.

But I still feel that it’s a SOTA woofer being showcased in a significantly-less-than SOTA design.

Anyway I’ll bow out now I don’t want to give the impression I’m bashing this speaker, or even that I don’t think it’s a decent design. I’m just a little disappointed/underwhelmed.

OK. I was under the impression you were responding to the post with images which referred to the design as a rudimentary plywood box.

 

[andreasmaaan]

Hi,

First thing I did -- always before measuring: https://www.soundstagehifi.com/index.php/opinion/1420-purifi-audios-pint-sized-powerhouses

Doug
SoundStage!

Many thanks Doug. Seems like you enjoyed the speaker and found that the drivers integrate well. Also provides some additional context and clarifies that it’s a rough-around-the-edges design at this stage.

Incidentally, I wonder if the midrange congestion you noticed might have had more to do with what appears to be a pipe resonance in the port around ~450Hz?

 

[Deleted member 14468]

Incidentally, I wonder if the midrange congestion you noticed might have had more to do with what appears to be a pipe resonance in the port around ~450Hz?

It could be. They're actually investigating. But that was at EXTRAORDINARILY high SPLs. Not normal listening.

Doug
SoundStage!

 

[CDMC]

Great distortion performance as expected, but little else to get excited about.

I am having a flashback to the early 90s:

https://www.stereophile.com/content/velodyne-df-661-loudspeaker

 

[mitchco]

I listened to and measured the Purifi SPK4 eval kit: https://audiophilestyle.com/ca/revi...and-1et400a-amplifier-technology-review-r866/

From the SPK4 application note:

"SPK4 is intended as demonstration platform for the PTT6.5W04-01A transducer.The design is deliberately kept very simple: a small ported wooden box, traditionally shaped with no particular management of edge diffraction, and a passive cross over at ~2.5kHz. Although extremely simple, with
numerous possibilities for enhancement by the skilled speaker designer, the SPK4 design very successfully demonstrates the tremendous improvements in sound quality which is possible to achieve when using the longstroke ultra-low-distortion PTT6.5W04 woofer from PURIFI Transducer Technology."

Having listened to them quite a bit, I think they were pretty successful as a demonstration platform for the PTT6.5.
The lack of distortion and outstanding low frequency extension (32 Hz) from this 6.5” (sub)(mid)woofer sets a new standard to these ears. The clarity is stunning. PTT6.5 does not break up like a regular driver. Long past the point of where my Kef LS50's have given up, the PTT6.5 keeps going without a hint of distortion until it physically bottoms out. If you back it off a bit, crystal clear. I have not heard any other transducer like that.

There are a number of diyAudio Purifi builds: https://www.diyaudio.com/forums/multi-way/352063-exploring-purifi-woofer-speaker-builds.html

What I am surprised about is there does not seem to be a cardioid/DSP build like the 8c or Kii THREE... These PTT6.5 drivers would make a perfect candidate for a loudspeaker like that.

 

[Ericglo]

It is great to see how a ported design measures, but I thought a PR was a better implementation.