Ralf, the evidence that matters is how the built unit sounds. The Purifi designed bookshelf speakers with AMT driver has been auditioned by many people, all positive and some glowing, with none of the issues you claim as evidence of poor design. I appreciate what you are saying but the end result is what counts. Mitch Barnett auditioned the SPK4 which has been further refined in the SPK5 design. He said it was fantastic and it measured superbly and you do a disservice to the highly regarded engineers involved (Bruno Putzeys, Lars Risbo and Peter Lyngdorf) by inferring that their design is poorly conceived and driven by marketing.
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Any speaker that uses a 6.5" driver up to 3.2kHz with a standard tweeter is poorly conceived for the reasons already mentioned.
Don't like it? Tough. The physics says that it's poorly conceived.
Does this mean the speaker will sound bad? Far from it and there are loads of designs out there that do a similar thing. They are all poorly conceived too but most review very well. This does not mean they couldn't be improved.
The point is the design is flawed. You can do a much better job. A different tweeter, a 1.8kHz cross and you're half way there.
Even better would be a 6" waveguide but that complicates things.
Just because the guys who designed them are highly regarded engineers doesn't mean that they are free from prejudice. Someone at Purifi clearly has a thing for AMTs otherwise this speaker wouldn't use one.
We all know Bruno takes a different opinion with his Kii speakers. Using a waveguide tweeter and appropriate crossover frequency. Those speakers are a lesson in excellent engineering and are an example in how to design a speaker both in terms of how it's designed and how the budget has been allocated.
The spk4 was obviously designed by someone more concerned with appeal than perfect engineering. The first time I saw the spk4 I thought what are they doing. That tweeter is not something an engineering focused person would pick and is a compromise on the design. Bruno would never have picked it if the Kii is anything to go by. That guy is pure engineering and choosing that AMT, in this design, is suboptimal on a few levels. The DXT tweeter, used in the Kii, would have been a much better choice. Far less expensive than the AMT and would allow the design to perform significantly better.
Don't like it? Tough. The physics says that it's poorly conceived.
Does this mean the speaker will sound bad? Far from it and there are loads of designs out there that do a similar thing. They are all poorly conceived too but most review very well. This does not mean they couldn't be improved.
The point is the design is flawed. You can do a much better job. A different tweeter, a 1.8kHz cross and you're half way there.
Even better would be a 6" waveguide but that complicates things.
Just because the guys who designed them are highly regarded engineers doesn't mean that they are free from prejudice. Someone at Purifi clearly has a thing for AMTs otherwise this speaker wouldn't use one.
We all know Bruno takes a different opinion with his Kii speakers. Using a waveguide tweeter and appropriate crossover frequency. Those speakers are a lesson in excellent engineering and are an example in how to design a speaker both in terms of how it's designed and how the budget has been allocated.
The spk4 was obviously designed by someone more concerned with appeal than perfect engineering. The first time I saw the spk4 I thought what are they doing. That tweeter is not something an engineering focused person would pick and is a compromise on the design. Bruno would never have picked it if the Kii is anything to go by. That guy is pure engineering and choosing that AMT, in this design, is suboptimal on a few levels. The DXT tweeter, used in the Kii, would have been a much better choice. Far less expensive than the AMT and would allow the design to perform significantly better.
Another aspect of the port is consistency. Take a rear or bottom ported box that is dependent on how close you get it to the wall. You have to measure while you move it around. The internal port might move and it may also vibrate. It's difficult to reach to adjust. It may want to be fixed to the front or top to keep it still. You'd have to make a removable top panel, or stuff the port instead.
To be honest, I am rather puzzled by Mitchba's rave review of the Purify. First of all, I was always under the impression Mitchba was pretty much a Uniform Directivity adept, which the Purify's conceptually are clearly not with their extreme 3.2 kHz x/o.
Closely spaced 5 degree off axis measurements are sorely missing in the review: I am in full agreement with Geralfino and 5th that some nasties would show up then. I would like to see a full heatmap for these speakers.
What I find surprising is that the Purify is designed on a hardware-only-philosophy plainly against the Harman/Toole/Olive design guideliness, and is yet claimed to be one of the best. Hmm.
Maybe Mitchba can shed some light on this matter: @Mitch: are you converted to a non Uniform Directivity listener (given the small listening room) and may we state from now on the Toole c.s.design guidleines no longer apply to on-axis semi nearfield (2 metres) listening in our average listening rooms? I am highly intrigued.
Eelco
Closely spaced 5 degree off axis measurements are sorely missing in the review: I am in full agreement with Geralfino and 5th that some nasties would show up then. I would like to see a full heatmap for these speakers.
What I find surprising is that the Purify is designed on a hardware-only-philosophy plainly against the Harman/Toole/Olive design guideliness, and is yet claimed to be one of the best. Hmm.
Maybe Mitchba can shed some light on this matter: @Mitch: are you converted to a non Uniform Directivity listener (given the small listening room) and may we state from now on the Toole c.s.design guidleines no longer apply to on-axis semi nearfield (2 metres) listening in our average listening rooms? I am highly intrigued.
Eelco
I hope people do realise that Mitchba reviewed a version of the purifi speaker that crossed over at 2.5khz, and had a shorter port with no bends for a 5hz higher F3, the SPK4.
Wobba is referring to the SPK5, which was 'refined (see:changed)' to have a supposed 30hz F3 and a crossover of 3.2khz.
Now, keen eyed viewers would also read in those two speaker papers that the first paragraph contains information stating that the speaker design is purely to show off the ability of the 6.5" driver, and changes should be made by DIYers as they see fit.
So changed: the SPK5 is using a rather ridiculously high 3.2khz crossover and 30hz bottom end to show off the woofers capabilities of wide FR response without breakup first. Cabinet design was second and tweeter selection third, imo.
I have two purifi woofers here on my desk and also have the two AMTs from the SPK4/5 and would have them in a cabinet measured and rockin' if it wasn't for COVID (hope everyones doin okay btw), as we are locked in and hardware stores aren't open. Im out of materials.
Ive also ordered some wavecor tweeters to experiment with getting the crossover nice and low. For now I will go with the SPK4 2.5khz crossover just as a baseline and probably do a slot port as I can't get that snakey SPK5 tube port with my limited gear.
Wobba is referring to the SPK5, which was 'refined (see:changed)' to have a supposed 30hz F3 and a crossover of 3.2khz.
Now, keen eyed viewers would also read in those two speaker papers that the first paragraph contains information stating that the speaker design is purely to show off the ability of the 6.5" driver, and changes should be made by DIYers as they see fit.
So changed: the SPK5 is using a rather ridiculously high 3.2khz crossover and 30hz bottom end to show off the woofers capabilities of wide FR response without breakup first. Cabinet design was second and tweeter selection third, imo.
I have two purifi woofers here on my desk and also have the two AMTs from the SPK4/5 and would have them in a cabinet measured and rockin' if it wasn't for COVID (hope everyones doin okay btw), as we are locked in and hardware stores aren't open. Im out of materials.
Ive also ordered some wavecor tweeters to experiment with getting the crossover nice and low. For now I will go with the SPK4 2.5khz crossover just as a baseline and probably do a slot port as I can't get that snakey SPK5 tube port with my limited gear.
Hey guys, I hope everyone is doing well.
As @mainframe99 indicated, the SPK4's I reviewed had this in the app 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."
If you look at the PTT6.5 Purifi Audio PTT6.5W04-01A midwoofer | HiFiCompass off axis frequency response measurements, does a pretty good job out to 3.5 kHz - even flat response 30 degrees off axis at that XO point. From @hificompass, "Off-axis frequency responses are just as good as axial frequency response, there’s nothing to add. No hidden resonances were found."
My rave review is about the woofer. My only comment about the AMT was good transient response and low distortion. The speakers were pointed on axis as you can see in my review. The AMT's could have been padded down just a bit more as there was a bit of excess energy in the 3 kHz to 10 kHz range to my ears and measurements. Maybe -2dB over all in that range. Easy enough with some broad band eq.
Personally, if I had a pair of the PTT6.5, like @5th element says, the DXT tweeter would be high on my list as I also reviewed the Kii THREE's. If I could do it, I would use a compression driver and constant directivity waveguide combo with digital XO and time alignment. Maybe an OS waveguide or something like on the new JBL HDI speakers. Yah, @Boden, I am still uniform directivity, Harman target kind a guy. My review of the SPK4 is predominantly about the woofer in the demo eval kit. If you read the subjective listening section in my review, all of my comments are about the PTT6.5.
Good luck with your builds. PTT6.5 is one smokin (sub)woofer(mid) driver!
As @mainframe99 indicated, the SPK4's I reviewed had this in the app 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."
If you look at the PTT6.5 Purifi Audio PTT6.5W04-01A midwoofer | HiFiCompass off axis frequency response measurements, does a pretty good job out to 3.5 kHz - even flat response 30 degrees off axis at that XO point. From @hificompass, "Off-axis frequency responses are just as good as axial frequency response, there’s nothing to add. No hidden resonances were found."
My rave review is about the woofer. My only comment about the AMT was good transient response and low distortion. The speakers were pointed on axis as you can see in my review. The AMT's could have been padded down just a bit more as there was a bit of excess energy in the 3 kHz to 10 kHz range to my ears and measurements. Maybe -2dB over all in that range. Easy enough with some broad band eq.
Personally, if I had a pair of the PTT6.5, like @5th element says, the DXT tweeter would be high on my list as I also reviewed the Kii THREE's. If I could do it, I would use a compression driver and constant directivity waveguide combo with digital XO and time alignment. Maybe an OS waveguide or something like on the new JBL HDI speakers. Yah, @Boden, I am still uniform directivity, Harman target kind a guy. My review of the SPK4 is predominantly about the woofer in the demo eval kit. If you read the subjective listening section in my review, all of my comments are about the PTT6.5.
Good luck with your builds. PTT6.5 is one smokin (sub)woofer(mid) driver!
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