BeoVox Penta Center Channel Concept

[Evan]

Die_Bogener wrote:

If you use Penta for Left&Right channel and a TV for the Center, then this setup was pretty good with a MX8000 and the DolbyDigital5.1 System. In the background are 2 BL8000… The Pentas are listed in the MX8000 system software, also the BL8000 and the distance to the listener. There is also an option for a subwoofer. The Center speaker of the MX8000 (2x 2way system) is good enough for small/middle size rooms. Surprisingly the option “subwoofer” is not a good selection, it is way to much. Just the opposite is the better solution: switch subwoofer to on, but dont use the subwoofer. The sound is better. The same will happen if you use the Penta as a center. Way to big. Or do we talk about a room with 120qm oder bigger? Have you already tried a Penta in real life as a center?

I’ll admit I get carried away sometimes but this project is more about matching the tonal characteristics between L, C and R (read: “timbre”) and less about overall SPL. The question [here] isn’t “will it center channel?” but more trying to remove the compromises that seem to affect center channel loudspeakers in general.

The idea isn’t far off from what most mastering studios implement. Three large full-range loudspeakers that are all identical.

I suppose it affects music listening more than movie/tv but I’m sure there will be an improvement across all use cases.

Consider it a thought experiment for now as the time when I actually start to make dust is far in the future!

[Evan]

Hey everyone – excited to share some recent thoughts on the center channel idea. I think its time this concept finally turn into a project.

Recently my partner and I moved to a new house and our new AV room could really use a nice center channel. I have a few extra Pentas kicking around so I think its time to start building one of these.

I plan on designing this to fit a pair of cells(?) in the Ikea Kallax shelf (4×2 unit). This spot used to be occupied by the AVP and BL4K that I previously used as a center channel. I don’t think its going to take up the entire 690*335mm opening (although it could!) but it will probably take up most of it.

Before I start modeling the 3D on this, I wanted to open it up for a discussion. I want to design something to share, hopefully something that could be replicated by others interested in this project (first as CAD and then likely a 2D drawing pack).

In my mind there are two ways this could go:

1. Traditional wooden box architecture, cloth fret.
2. A more penta-like solution. Something 3D printed (sturdily) that has the spirit of the Penta cabinet geometry baked into its industrial design.

Both of these ideas have there advantages and disadvantages but I wanted to open it up here for a discussion as I want this to benefit as many people as possible. I think many B&O fans would enjoy having such a speaker in their system. Maybe two variants get designed after all? My dream is that it is eventually driven by a remote BL Penta (150/200 style) amp that sits in one of the other shelf cells.

I was brainstorming all of this and doodled this in my sketchbook today. I hope it inspires you to share some of your thoughts.

[DT79]

That already looks great!

Evan wrote:

Hey everyone – excited to share some recent thoughts on the center channel idea. I think its time this concept finally turn into a project. Recently my partner and I moved to a new house and our new AV room could really use a nice center channel. I have a few extra Pentas kicking around so I think its time to start building one of these. I plan on designing this to fit a pair of cells(?) in the Ikea Kallax shelf. This spot used to be occupied by the AVP and BLK that I previously used as a center channel. I don’t think its going to take up the entire 690*335mm opening (although it could!) but it will probably take up most of it. Before I start modeling the 3D on this, I wanted to open it up for a discussion. I want to design something to share, hopefully something that could be replicated by others interested in this project (first as CAD and then likely a 2D drawing pack). In my mind there are two ways this could go:

1. Traditional wooden box architecture, cloth fret.
2. A more penta-like solution. Something 3D printed (sturdily) that has the spirit of the Penta cabinet geometry baked into its industrial design.

Both of these ideas have there advantages and disadvantages but I wanted to open it up here for a discussion as I want this to benefit as many people as possible. I think many B&O fans would enjoy having such a speaker in their system. Maybe two variants get designed after all? My dream is that it is eventually driven by a remote BL Penta (150/200 style) amp that sits in one of the other shelf cells. I was brainstorming all of this and doodled this in my sketchbook today. I hope it inspires you to share some of your thoughts.

[Evan]

Ok I guess the first step (in the modeling domain) is to get the Kallax into Solidworks. I’ll build the Penta-C(?) / Center Penta(?) What should we name this thing?? …into the Kallax for reference along the way.

[Stereomensch]

I think B&O used speakers that were designed for the use of being a car hifi speaker.

The idea is simple, if we do have a speaker with a limited space, an ordinary speaker wouldn’t perform in an apropiate way. That’s why they used speakers, that were intended as car speakers. Haas was the manufacture of these speakers and they were known for car Hifi systems. Later Haas was a part of IT&T. IT&T was bought by Nokia in the late ninetees.

[Glitch]

Cool.  I appreciate seeing data even if I don’t understand exactly what it is saying. 😉

Is the testing a driver easy enough where it is possible to test multiple drivers?

I’d be curious about the driver uniformity, especially the refoamed mid-ranges. With some measure of “sameness” you could either pick the best of the batch for your project or sort for best matched pairs.

Glitch

[Evan]

A semi-relevant example for you all: The dust cap isn’t the most critical part of the speaker (acoustically) but you can see here how different drivers can be when they are hand built.

[Glitch]

Evan,

I use something similar to clamp the surround. Depending on the particular driver, I’ll run some tests with just the clamp. Once I’m happy with the performance, the surround gets some glue. Sometimes, a segmented clamp is needed so that the surround can be glued a section at a time with a thin needle applicator syringe.

I’m not too surprised to hear that much of this is being done by hand. I’m guessing that the difference between the higher and lesser quality parts has to do with the “end of line” testing and sorting.

Glitch

 

[Evan]

Finished modeling the woofer (basket and motor) so I can begin to design them into a baffle. Most importantly I tried my best to capture the basket’s very poor brownish-green e-coat finish 😛

[Evan]

Finished modeling the woofer (basket and motor) so I can begin to design them into a baffle. Most importantly I tried my best to capture the basket’s very poor brownish-green e-coat finish 😛

[Evan]

Glitch wrote:

Evan, I use something similar to clamp the surround. Depending on the particular driver, I’ll run some tests with just the clamp. Once I’m happy with the performance, the surround gets some glue. Sometimes, a segmented clamp is needed so that the surround can be glued a section at a time with a thin needle applicator syringe. I’m not too surprised to hear that much of this is being done by hand. I’m guessing that the difference between the higher and lesser quality parts has to do with the “end of line” testing and sorting. Glitch

Indeed. End-of-line testing is paramount. From what I hear, 100% of parts are gauged by this process.

Thanks for the tips! I am considering doing something similar, my colleagues are highly recommending I just go all-in and remove the dust cap and do it properly. Beginning to lean in this direction but I have so many of these things to do!

[Evan]

A quick sketch after drafting in a basic twee-mid baffle to start to package everything. Interestingly I had planned in my head that the twee-mid baffle would live on top of the main baffle surface but in reality the pentas see a baffle step in the other direction (duh). May have to rise the woofers up to match. We will see.

Also contemplating printing my own twee-mid chassis as the original is just so hard to seal. Has very thin geometries at various points and is pretty ugly if left uncovered.

This baffle uses a golden ratio factor but the long axis of the twee-mid module seems to be dominating the baffle shape. Tons of space left over around the woofers. This would be good if I planned on keeping the ports but right now I am planning on ditching them, this is plan of record right now but subject to change once I get into some simulations and measurements.

[Evan]

A quick sketch after drafting in a basic twee-mid baffle to start to package everything. Interestingly I had planned in my head that the twee-mid baffle would live on top of the main baffle surface but in reality the pentas see a baffle step in the other direction (duh). May have to rise the woofers up to match. We will see.

Also contemplating printing my own twee-mid chassis as the original is just so hard to seal. Has very thin geometries at various points and is pretty ugly if left uncovered.

This baffle uses a golden ratio factor but the long axis of the twee-mid module seems to be dominating the baffle shape. Tons of space left over around the woofers. This would be good if I planned on keeping the ports but right now I am planning on ditching them, this is plan of record right now but subject to change once I get into some simulations and measurements.

[Evan]

First sketch of the box. Plenty of room to spare, inside volume is 43L at the moment. According the BeoWorld the Penta has a “net volume of 32L”.

Not including the tweemid sticking out, the box dimensions are 534W*319L*330H. It will shrink in the next few iterations as I learn more about the original but I’d love to hear if it should morph one way or the other proportionally (for non Ikea Kallax applications for example).

[Evan]

Flipping the tweemid module over I can get that misalignment to 120-ish mm. Seems pretty reasonably to me.

Also I recently learned that the crossovers are 700Hz and 3kHz. 700Hz is pretty high (for voice) so the 2×2 woofer config is here to stay I think.

[Evan]

Flipping the tweemid module over I can get that misalignment to 120-ish mm. Seems pretty reasonably to me.

Also I recently learned that the crossovers are 700Hz and 3kHz. 700Hz is pretty high (for voice) so the 2×2 woofer config is here to stay I think.

[Evan]

Die_Bogener wrote:

Make it more symmetric, move 2 of the woofers to the other side.

If this is of interest, to anyone reading this, I will offer this design configuration separately.

[Author]

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