Non-linear distortion is only really caused by the motor and at low frequencies compliant parts (spider, surround) also. Rarely does a rigid cone produce significant nonlinearity by itself.
Linear (only impacting amplitude/phase response) distortion is caused by the cone, interface with compliant parts, reflections (Inc enclosure) and so forth.
Where they interact is that the nonlinear distortion is shaped by the linear distortion. If the cone/dome rings/breaksup at +20db at a certain frequency, non linear distortion components at that frequency produced by say the motor are increased by 20db too.
A good example as the rs52a where you have that 13khz breakup spike. The 3rd harmonic is increased at 4.3khz (3*4.3=13) because while the motor only produces it at a low level, the dome absolutely sings when excited by a 13khz component. That's why I like metal drivers because the breakup is pushed to higher frequencies therefore the HD stays lower up to a higher frequency. Paper drivers have their breakup energy dispersed over a wider range of frequencies but it begins at a lower frequency so the HD on an equivalent paper driver starts creeping up sooner.
If the motor is insanely linear this can be practically avoided, like you're not going to care that -110db became -90.
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Thank you for this. Based on your review, I tracked down a pair in Purifi's SPK4 demo kit to give a listen:
Purifi PTT6.5 Woofer and 1ET400A Amplifier Technology Review - Reviews - Audiophile Style
Mitch, that was a great write up and review. It made me get up and play the Madonna track through my JBL's, while I finished reading, and wishing that I could have been in the listening room with you! Lol. I'm a huge fan of the punch of 15's mated with horns, and your subjective praise for the Purifi is remarkable. Technology, brilliant design, and a bunch of cash.............rabbit holes of danger that can jack up the bank account ��. Glenn.
Yes, very likely that is caused by cone breakup around 6.5kHz.
That driver is also a prime example of non-linear distortion which isn't caused by the motor. The big spike of all harmonics simultaneously showing up around 1kHz is caused by a resonance. Perhaps the cone, spider, surround, basket or some interaction between any of those components. When you see all orders coming up like that at the same frequency you often also see a wiggle in the frequency response, and we see that here too. I'm actually surprised that SB even shipped them like that, because it (IMO) prevents what is otherwise a very high performance driver from being used in a 2-way. You don't often see an issue like that and I see that all of the Satori mids/woofers do it to some degree, which indicates some sort of design flaw. Perhaps the issue wasn't as severe in pre-production units and it was too late to fix once they went into mass production.
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Somewhere Ulrik Schmidt told about his decisions when designing Satori midwoofer. The 1.2 kHz problem is an only compromise they took to get a speaker with very extended and even frequency response, very low distortion and very GOOD sounding. It was inevitable compromise for a soft cone speaker. They could use a high loss surround and easy decrease that problem but at cost of sounding.
BTW, is there any soft cone speaker with better performance at such a price?
Thank you, Mitch, for very good and interesting review![emoji846]
At this time I'm designing my version of 2way bookshelf speaker based on PTT6.5W04-01A and BlieSMa T25B-6 in waveguide. I will try the both option for the enclosures - bass reflex and passive radiator.
If the project turns out successful it can get the name "Pure Bliss"[emoji3]
The T25B-6 in a waveguide ? This is very interesting, I look forward to see how that project will turn out.
It reminds me of this build with the T34B-4 in a waveguide : Build therad: OLA-WG 2.5 - a 2.5way with SB midwoofers and a Bliesma tweeter
Exactly my thoughts how to use those drivers. As T25 surround outer diameter should be very close to 30mm it will fit my 5"WG.
To compete with the MW16P, how about the Vifa NE180W or ScanSpeak 18W8531G? Motors are slightly less linear but soft parts are more well behaved. For the MW19P, perhaps the NE225W - I haven't seen any measurements of this one but I'm hopeful. It's comically marketed as a 'subwoofer' - I suspect it's a little more capable than for just subwoofer use 😉
Thanks Glenn! I was evaluating Dirac Live 2.0 on these yesterday with a -3 dB point of 25 Hz in-room response. Still blows my mind how much low frequency energy these put out yet the lower mids and mids sound perfectly clear, right up until the woofer bottoms out 🙂
Thank you! That looks like a very interesting design - Pure Bliss is right 😉 Will be curious to hear your thoughts on the SQ once the project is complete.
Happy New Year!
Purifi "secretly" released a PR 🙂
PTT6.5PR-01A - PURIFI
I to have to say I am curious, curious enough to do a "Pure Bliss" loudspeaker.
PTT6.5PR-01A - PURIFI
I to have to say I am curious, curious enough to do a "Pure Bliss" loudspeaker.
7.5" looks better than 6.5" in some ways - ie dip above 1khz isnt a deal breaker and looks worse as the driver is so well behaved everywhere else. Looking at where -3db is at 30 degrees off axis, a 2.3khz crossover is doable. Viawave territory.
Two very new drivers, but both look to be outstanding performers. I'm looking forward to seeing what you come up with.