Interesting video about designing out speaker shortcomings

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vinylnvalves
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#1 Interesting video about designing out speaker shortcomings

Post by vinylnvalves »

An interesting 2hr video from the designer behind the purifi drivers design rational and innovation... to produce their acclaimed midrange driver.
https://m.youtube.com/watch?v=o90AYycea ... e=youtu.be
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#2 Re: Interesting video about designing out speaker shortcomings

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Looks very interesting - will have a proper view later.
Good link here too on Troels Gravensen's site -
http://www.troelsgravesen.dk/Purifi.htm
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#3 Re: Interesting video about designing out speaker shortcomings

Post by vinylnvalves »

I didn’t realise Troels has had a play with these drivers too. It just doesn’t go high enough for me, to be tempted to try them. My midrange ribbon drivers cover upto 5k, I feel not having a crossover between 300hz and 5k hz will be more beneficial than the IM distortion reduction they claim for this driver to justify me buying a pair to try.
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#4 Re: Interesting video about designing out speaker shortcomings

Post by vinylnvalves »

The adding of the additional magnet to the pole piece is very clever, and will be copied no doubt by others in the future. Fostex had a very similar surround on some studio monitors a few years back.
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#5 Re: Interesting video about designing out speaker shortcomings

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I haven't got to that bit yet.
I think I've watched just under an hour of the film, and I'm already so interested in the driver that I'm plotting a project for a work friend, so I can get a chance to hear a pair.
Anybody who is interested in loudspeakers should make some time to watch this vid, it's both educational and inspiring.
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#6 Re: Interesting video about designing out speaker shortcomings

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Gawd knows they will now cost to import from the EU now. There is a long thread on DIYaudio about people’s designs using the driver.
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#7 Re: Interesting video about designing out speaker shortcomings

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For those who don’t want to watch the 2hr video... this link highlights the timings for parts of the videohttps://www.diyaudio.com/forums/multi-way/35206 ... ds-65.html
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#8 Re: Interesting video about designing out speaker shortcomings

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I just emailed somebody that a few of us know.
I asked if he'd ever mentioned the Purifi drivers, or had seen the vid with Lars Risbo.

He said "I've got a pair here, sat next to me"
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#9 Re: Interesting video about designing out speaker shortcomings

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These are smart - and l'll bet they sound good, with J.G.'s experience -
https://www.monoandstereo.com/2020/08/n ... rhard.html
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#10 Re: Interesting video about designing out speaker shortcomings

Post by vinylnvalves »

Another speaker design, using its LF capability. https://josephcrowe.com/blogs/news/puri ... -enclosure I don’t like the idea of using it for LF duties, it will have a nice decay in a sealed cabinet, that it could be married with a subwoofer easily without a filter at the bottom end.
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#11 Re: Interesting video about designing out speaker shortcomings

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Yes, I was wondering about that. Just not sure you're missing out on some of its capabilities by having the bass roll off as much as it does sealed.
To that end, I was thinking about MLTL, and how I liked the results with the FE103e that I did about 6 years ago . So, I got working on Hornresp and scaled it up and did a few experiments.
I'm not sure I can believe the results, but here it is, looks amazing :
Pure_MLTL_setup.JPG
Pure_MLTL_section.JPG
SPL for 1W - flat to 20Hz with room gain !
Pure_MLTL_SPL.JPG
Last edited by IslandPink on Mon Feb 08, 2021 10:25 pm, edited 1 time in total.
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#12 Re: Interesting video about designing out speaker shortcomings

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But with that relatively slim port, look at the group delay - only 5.4msec at 40Hz :
Pure_MLTL_GD.JPG
and driver displacement for 1W :
Pure_MLTL_Displ.JPG
I want one !
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#13 Re: Interesting video about designing out speaker shortcomings

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Ah, you're finding ye oft-overlooked facet of vented box loading.

A low-tuned EBS or equivalent thereof can sometimes have a GD as good as a lowish-Q sealed box in the frequency range ~an octave above Fb, so these alignments were sometimes used as an alternative that had a bit of an extra kick in the infrasonic region to fill in. Downside like all vented boxes is you're hitting the point of maximum excursion in roughly the octave above Fb, and if that's your primary target operating region, you can run out of headroom for dynamic peaks in that BW.
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#14 Re: Interesting video about designing out speaker shortcomings

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OK yes, good point.
I think there's more trouble in that I haven't thought about how the 'combined output' is being done on this, there needs to be a delay in there. So probably both the SPL and GD are wrong. I need to look at what I have, and do some more reading. I'll put it on a separate thread at some stage.

Presumably Fb is indicated by the lower resonant peak on the impedance plot ?
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#15 Re: Interesting video about designing out speaker shortcomings

Post by Scottmoose »

Fb for a vented box is shown in the impedance as the minimum between the double-saddle peaking, where enclosure resonance / pressure also holds the cone at minimum motion.

Based on the the plots above looks pretty good; out of interest I'll have a gander myself if I get chance later this afternoon (currently having 5mins from writing a lecture on hydrodynamic history). Should be solid for modest SPLs in a small space. :)
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