audio-talk

I've managed to capture a pretty accurate reconstruction of a half-section of the Lii speaker pear-shape. The light blue line is made up of a couple of elipse arcs and is the outer profile of the speaker (Lii use 15mm side panels).
In theory it's pretty simple to mirror the other half and produce offset lines for the inside and outside edges of the ribs but I've needed to seek some CAD expertise before I progress this further.

Here's the jpg section that I used as the starting point;

That cross-section reminds me of this early 70s classic: the Jordan Watts ‘Flagon’. That shape; once seen never forgotten.
A single Jordan Watts ‘Module’ driver, in a ceramic enclosure. The perfect accessory for your shag pile pad.
Also it inspired me, at age 17, way back in 1975, to start designing speakers.

I more or less finished the CAD drawing for the Lii speaker cross section last evening. Heres the end result showing the rib sections;



With a little more work I'll be able to derive all the parts that would need to be CNC routed for a build.

Just need to decide whether its this one or the SLOB now.

Scottmoose wrote: ↑Wed Jan 01, 2020 3:29 pmWithout accurate dimensions, it's a bit difficult assessing the box, but curved sides apart it appears to be akin to a classic bass reflex alignment (closest to, say, an Ultraflex or Onken). The curve to the rear will provide some of the desired length for the ducting...

I've been asked if I would share the CAD file with my 'pear' shaped cross section approximating to the Lii design - no problem with that - but also a follow on question; to keep the build simple, could the arrangement of port slots shown on the Lii plans be replaced with conventional ports (of similar total area (210sqq cm) and length (6cm)). The idea is to retain the 'stalk' of the pear at the back, but make it solid and then bore holes for a number of ports. I'm not sure it is that simple as the ports on the Li plans are tapered because of the shape of the pear section (and I'm not convinced it would simplify the build much either).

Thoughts?

I think that I would either stick close to the Lii design, or knock up a quick 'box with a port' and do some experiments before building the final enclosure

Depends on the specific dimensions. On the face of it, given the sizing I wouldn't expect Fb to shift more than, say, a few Hz, but if you can let me know I'll take a quick gander for you if you like.

Scottmoose wrote: ↑Sun Jan 19, 2020 7:24 pm Depends on the specific dimensions. On the face of it, given the sizing I wouldn't expect Fb to shift more than, say, a few Hz, but if you can let me know I'll take a quick gander for you if you like.

Hi Scott, just resurrecting this topic and continuing on the theme of changing the ports, the whole thing would be simpler to build if the stalk extension was removed and the back of the speaker simply continued the elipses in a fair curve with the ports changed to a more conventional tube arrangement on the front panel - thoughts?

I have seen it suggested that the 10in Lii Fast-10S drivers would be well suited to an Onken project - a not so mini version of the Planet 10 miniOnken designs;

https://www.diyaudio.com/forums/planet- ... tions.html

What does the panel think?

I've played with this calculator;

http://www.mh-audio.nl/Calculators/Onken.html

and it all looks good except the overall efficiency calculated is an SPL of only 93.6 (dB 1W/1mtr), which is fine except when one factors in my flea-power amps. The bottom end -3dB point is calculated to be at around 30Hz.

Ray P wrote: ↑Sun Mar 01, 2020 12:30 amHi Scott, just resurrecting this topic and continuing on the theme of changing the ports, the whole thing would be simpler to build if the stalk extension was removed and the back of the speaker simply continued the elipses in a fair curve with the ports changed to a more conventional tube arrangement on the front panel - thoughts?

It would certainly be simpler. Wouldn't necessarily sound identical but depends on the CSA of the vent[s] and position thereof (as the latter alters room interaction a bit). Done well, should be fine.

Ray P wrote: ↑Mon Mar 02, 2020 7:06 am I have seen it suggested that the 10in Lii Fast-10S drivers would be well suited to an Onken project - a not so mini version of the Planet 10 miniOnken designs;

What does the panel think?

Despite appearances Dave's boxes are functionally almost the reverse of an Onken, which traces its origins back to the Ultraflex & classical reflex design rather than current Small (via Thiele and Novak) derived vented boxes. Dave is using high aspect ratio vents to provide a degree of resistive loading and create a moderately - well damped alignment. The Onken (& especially its predecessors) were designed to use a massive vent system for optimal efficiency at Fb. Whether you actually want that or not is another matter -the Onken being later exploits T/S filter theory so adjusting the alignment in advance is arguably a bit more straightforward.

I've played with this calculator;

http://www.mh-audio.nl/Calculators/Onken.html

and it all looks good except the overall efficiency calculated is an SPL of only 93.6 (dB 1W/1mtr), which is fine except when one factors in my flea-power amps. The bottom end -3dB point is calculated to be at around 30Hz.

Overall sensitivity / SPL for any back-loaded box is ultimately defined by the drive unit, except in cases of high Q peaking at Fb. To increase overall system sensitivity requires a wide BW front horn.

As a general note -watch the duct length with Onkens. Vents are 1/2 wave resonators (just a law of physics) & if they get too long their self-resonant modes can start combing with the driver's output unless a little extra damping is added.

Scottmoose wrote: ↑Mon Mar 02, 2020 5:49 pm

Ray P wrote: ↑Sun Mar 01, 2020 12:30 amHi Scott, just resurrecting this topic and continuing on the theme of changing the ports, the whole thing would be simpler to build if the stalk extension was removed and the back of the speaker simply continued the elipses in a fair curve with the ports changed to a more conventional tube arrangement on the front panel - thoughts?

It would certainly be simpler. Wouldn't necessarily sound identical but depends on the CSA of the vent[s] and position thereof (as the latter alters room interaction a bit). Done well, should be fine.

Thank you Scott.

CSA - I'm assuming cross sectional area?

Any pointers to resources for sizing/positioning vents? The pear-shaped design has vents that total 210sq cms.

I remembered that the Lii Audio site has a simple box design along these lines;

Scottmoose wrote: ↑Mon Mar 02, 2020 5:59 pm Despite appearances Dave's boxes are functionally almost the reverse of an Onken, which traces its origins back to the Ultraflex & classical reflex design

Thanks Scott. I did post on Dave's Planet 10 forum over at DIY Audio but he doesn't have any miniOnken designs large enough...

Looks like the simplified bass reflex is the more practical option.

Ray P wrote: ↑Mon Mar 02, 2020 7:06 am I have seen it suggested that the 10in Lii Fast-10S drivers would be well suited to an Onken project - a not so mini version of the Planet 10 miniOnken designs;

https://www.diyaudio.com/forums/planet- ... tions.html

What does the panel think?

The first thing I built in 2008, for bass, with the 285GMF, was an Onken.
Like any big box ( even the one above ) it will have reverb energy that clouds things like piano notes. That was why I eventually rejected it.
So, I guess sit depends on whether you want a simple solution...

Ray P wrote: ↑Mon Mar 02, 2020 7:00 pmCSA - I'm assuming cross sectional area?

Right.

Any pointers to resources for sizing/positioning vents? The pear-shaped design has vents that total 210sq cms.

Depends on the overall [internal] box dimensions to be honest, and how many vents you're planning on using for the desired CSA / tuning frequency. If it's a single large vent, somewhere on an uneven multiple or odd harmonic and relatively near the floor for optimal boundary coupling.

I remembered that the Lii Audio site has a simple box design along these lines;[/quote]

Nearer a QW than a pure Helmholtz. I'll have a look at it.

IslandPink wrote: ↑Mon Mar 02, 2020 10:39 pm The first thing I built in 2008, for bass, with the 285GMF, was an Onken.
Like any big box ( even the one above ) it will have reverb energy that clouds things like piano notes. That was why I eventually rejected it.
So, I guess sit depends on whether you want a simple solution...

I suspect some of that was the combing / interference of vent modes that many Onkens with lengthy ducts have. Some like it, some don't, but it's one reason I tend to avoid them myself, older Ultraflex &c. aside, which is of limited use today.