Interesting video about designing out speaker shortcomings

[vinylnvalves]

An interesting 2hr video from the designer behind the purifi drivers design rational and innovation... to produce their acclaimed midrange driver.

[IslandPink]

Looks very interesting - will have a proper view later.
Good link here too on Troels Gravensen's site -
http://www.troelsgravesen.dk/Purifi.htm

[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.

[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.

[IslandPink]

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.

[vinylnvalves]

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.

[vinylnvalves]

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

[IslandPink]

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"

[IslandPink]

These are smart - and l'll bet they sound good, with J.G.'s experience -
https://www.monoandstereo.com/2020/08/n ... rhard.html

[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.

[IslandPink]

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 :

SPL for 1W - flat to 20Hz with room gain !

[IslandPink]

But with that relatively slim port, look at the group delay - only 5.4msec at 40Hz :

and driver displacement for 1W :

I want one !

[Scottmoose]

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.

[IslandPink]

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 ?

[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.