Thank you for the suggestion. I did simulations of all of the RS270 series drivers. Both of the advantages you list are true, and are valuable in a passive design.
In an active design, the behavior of the driver above the pass band in not as important, and DSP can be used to mitigate a big high frequency resonance.
The 2 dB higher sensitivity applies to the range above 100 Hz. Below that, the driver is limited by Xmax, and all of these RS270 drivers have very similar Sd and Xmax. At 40 Hz, they all top out at about 99 dB SPL@1m, and it usually takes only about 20 W to do it. So after the LT EQ, they all have the same headroom.
j.
Yeah it really is a lower mid. driver; even in an MTM bass reflex its bass is sort of absent.
Begs for a Burmester-looking design.
As a general trend I have noticed that when a driver series is offered in paper, polymer, and aluminum cone materials, the aluminum drivers usually have the lowest distortion. I noticed it on ScanSpeak, SBA, and Dayton.
I am not aiming to undershoot my budget target. The price of the RS270-4 is acceptable. The driver budget was 250/side when this was an 8" 3way. Now that it is a 10" 3-way, the budget for the mid+ tweeter is 150... which basically means the overall driver budget is 280/side.
If I spend less I don't view that as a positive, rather I see it as a missed opportunity.
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I concur I have never seen a soft cone with lower nonlinear distortion than a hard cone.
In fact, the opposite tends to be true. Hard cones tends to have lower-non linear distortion than soft cones. The downside is the fierce resonances. Which was resolved a decade or so ago with the use of geometrically furrowed grooves ala SBA, KEF etc.
My hypothesis is that the soft cone, driven from the centre via the voice coil, suspended at the periphery via the surround, is resonating more, at a micro level, than the stiff cone. The ability to measure it is quite difficult with windowed measurements (a 10ms window is only 100Hz), but you can certainly see it another way- by peeking at the impedance traces- you can zoom in as far as you like in the vertical scale.
On the other hand, the the stiff cone is better behaved. But then all hell breaks loose when it resonates!
I’m not a materials scientist/engineer so I’m likely wrong about this.
@lrisbo
Why do hard cone drivers tend to have lower non linear distortion than the soft cones?
PS. I see the PTT10.0X is now available for pre-order!! Less than the Accuton pricing!
In fact, the opposite tends to be true. Hard cones tends to have lower-non linear distortion than soft cones. The downside is the fierce resonances. Which was resolved a decade or so ago with the use of geometrically furrowed grooves ala SBA, KEF etc.
My hypothesis is that the soft cone, driven from the centre via the voice coil, suspended at the periphery via the surround, is resonating more, at a micro level, than the stiff cone. The ability to measure it is quite difficult with windowed measurements (a 10ms window is only 100Hz), but you can certainly see it another way- by peeking at the impedance traces- you can zoom in as far as you like in the vertical scale.
On the other hand, the the stiff cone is better behaved. But then all hell breaks loose when it resonates!
I’m not a materials scientist/engineer so I’m likely wrong about this.
@lrisbo
Why do hard cone drivers tend to have lower non linear distortion than the soft cones?
PS. I see the PTT10.0X is now available for pre-order!! Less than the Accuton pricing!
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I like that. I think I'm inherently thrifty so always taking cost into consideration. But I'm going to use that with my wife the next time I get some premium drivers. If I don't post for a long time, you'll know how that turned out. 😂If I spend less I don't view that as a positive, rather I see it as a missed opportunity.
In the past a mathematical model of straight cones was published by Philips, it correlated well and from that you could see it is the material properties. Paper is ok up to the point / frequency it cannot hold the the forces acting on the cone. Aluminium etc is better. Non straight cones makes it actually worse.
When the accuton's appeared (then called thiele), it was the fist time a tin cone and a very frequency high breakup.
At around the same time the sandwich cones cwme on the market. Ok for bass, but in the midrange something funny was audible , loss of resolution and a sort of double sound, like in a television then a second image just a little bit shifted. We then attributed that to the thick cone.
As far as i understand Purifi has used FEA etc to find a shape that holds up and gives a more controlled breakup.
In the past the first breakup mode appearance in the response actually is a strong and steep dip. I do not see that anymore.
Just sharing details of a 3-way project from the past that used a similar Dayton woofer in a similar-sized cabinet:
https://www.humblehomemadehifi.com/download/Humble Homemade Hifi_Black Box.pdf
https://www.humblehomemadehifi.com/download/Humble Homemade Hifi_Black Box.pdf
I think this rule of thumb pertains to an acoustic LR4 crossover. I’m not sure how valid it is for other crossovers.
A couple of decades ago when @john k... developed the NaO dipole speakers, he was already doing this.
He crossed a pair of 6.5” middriver to a 1” dome tweeter in an MTM format, and use a large CTC spacing of 6.5”, which was against the trend at the time.
When you have a chance @john k... , would you please remind us of the rationale behind this decision?
Linking the more recent explanation (than the similar explanations spread out over pages on VituixCAD thread here on diyaudio) about the driver spacing rule of thumb from Kimmosto here:
https://www.htguide.com/forum/missi...niques/42827-vituixcad-v2?p=835533#post835533
https://www.htguide.com/forum/missi...niques/42827-vituixcad-v2?p=835533#post835533
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Than you assume that more expensive is always better.
Which is definitely not always the case.
Maybe it's a cultural thing, but for me it's a sport to minimize the price as much as possible when I know I can get the same performance.
Can always use that money for something else or another project
With the assumption that it's actually practically beneficial.
I don't agree with the idea that "it's only needed in a commercial world".
I don't know about you, but my bank account and wallet are limited.
You can spend 150 bucks extra on a speaker, or maybe evaluate if that is really necessary and invest it in something else.
Could be even audio/acoustics related.
Maybe even more so if you want to make something that you want to be available for other people as well.
That has zero to do with being commercial or not.
Let's hold off on making it a sticky until we know that this project is a success. I would be annoyed if an unsuccessful project is forever immortalized as a sticky... an homage to Jim's POS Screw Up...
Even then, how many stickies to we need in a forum? Too many and it gets hard to navigate... We already have five.
Watching and waiting, and trying to learn more from you knowledgeable fellows! This is one that I may want to build. Jim, do you think that this project would be good as a midfield monitor for mix/ playback/comparison usage? That's what I've been thinking about as I've followed this thread. Glenn.