BeoVox Penta Center Channel Concept

[Evan]

Hey BeoWorlders, just thought I’d share another whacky idea that has been bouncing around in my head over the last few months.

I have two systems that utilize Pentas as L and R channels. One set up (bedroom) uses a BL4k as a center channel and the other (living room) is not equipped with a center at all so just running in stereo. The situation is that I use both for a ton of movie and TV watching and want to upgrade the center channels in both systems.

After a year of listening to a 3.0 system that had a woefully mismatched and underpowered center speaker, I’ve been on a mission to scheme up a solution to get away from this. Not only do I want a home theater system to match the power and spectral capability from all three front speakers (L/C/R) but I also want to match the Timbre as much as possible. Center channels are usually heavily compromised from my point of view and we all know that the center channel is where a majority of content comes from.

So what have I come up with? Well the concept is pretty simple, build an alternative enclosure so that the Penta transducers can be packaged more efficiently as a center channel speaker.

Why redesign the speaker package I hear you say? Why not lay a Penta on its side in front of the telly and call it done?? There are a few reasons. Primarily the need to stand up the center midrange array. Its important to place these midranges vertically so that the array physics appropriately cover the horizontal listening space for various seating areas etc. Secondarily is more of a practical reason – laying a huge Penta on its side in front of the TV is just not going to work from a space perspective.

A few minutes of slideware engineering and here we are:

 

Originally I thought I would 3D print it in sections and then assemble. However I suppose it could be made in wood and CNC’d as well. The advantage to 3D printing is that its very easy to do so once the CAD is finished and it could be potentially styled to match the shape of the Penta cabinet in some interesting, abstract way.

Basically all the transducers would be a carry over from a donor Penta along with the twee-mid module that could essentially just drop in. This arrangement should also keep from having to redesign the crossover but I’m sure the experts among us would say differently.

Let me know what you guys think.

[Ravsted]

I got a BeoLab 7.1 (wired using both left and right channel as center channel).

It is at great center speaker with lot of power and clarity.

If you go for at home-brew solution with a passive speaker I would build something around a non-B&O center speaker … A good second hand B&W or whatever you prefer. I believe that will give you a way better acoustic result.

You can still modify the speaker cabinet to match the Pentas in some way.

[Die_Bogener]

A Penta is way to big… a simple Redline 40/60/120 will do the job.

The important thing is: the speaker must fit to human voice. Too much bass will destroy the effect… and a standard Penta will not work, you must first remove the bubble wrap foil in it’s sound way.

[Glitch]

Evan wrote:

et me know what you guys think.

From a general sound perspective, I don’t see any reason why it wouldn’t work. As long as you keep the cabinet volume and reflex tube length/diameter the same you will, in general, have a similar frequency response. Even if you mess up the very low frequency response, this won’t be critical for voices since they don’t contain those frequencies.

Would you actually be happy with the form factor? I’m having a hard time imagining what this would look like under a TV.

Did you plan to have the bottom-most mid-range close to the floor? Not having the tweeter and mids at ear level may mess with the vertical dispersion. I don’t know if this is a better or worse trade-off versus having the mid-range array horizontal.

Have you considered using a (well matched) pair of Pentas (in the original configuration) placed tight to sides of the TV? The mono pair would provide the a solid centered image and the apparent sweet spot could be roughly controlled by the angle. The other “surround” speakers could also be Pentas for the full overkill effect. 😉

Glitch

 

[Millemissen]

Unfortunately you do not write anything about how you want to connect the ‘new speaker’ – do you use an A/V receiver or will it be connected to a Beovision…..in which case, what is the amplifier?
Apart from the physical drivers in the ‘new speaker’ there are multiple things that can influence the sound.

I would do as Ravsted….get a BL7.1 – alternatively/or even better a BL7.4, if you have room for it below the tv.

MM

[Evan]

Thanks for the replies everyone! Nice to do some brainstorming among the like-minded. This is still a thought experiment for now (many other projects still in flight, as usual). I don’t like to keep crazy ideas to myself just in case there is someone else out there who wants to join in on the fun and build this stuff along with me.

Just for context, I have a BL10. Yes, it should do the job and sometimes did deliver the power it contained (mostly in gaming situations) but the overall sound character (timbre) was very very mismatched. Basically ended up not using it most of the time. Vocals are always the focus of the center channel but there is often times far more content coming through than just voice. Also this isn’t the only experience driving this project, many systems I have heard are usually weakest in the center channel for various reasons, but usually packaging related.

[Evan]

Ravsted wrote:

I got a BeoLab 7.1 (wired using both left and right channel as center channel). It is at great center speaker with lot of power and clarity. If you go for at home-brew solution with a passive speaker I would build something around a non-B&O center speaker … A good second hand B&W or whatever you prefer. I believe that will give you a way better acoustic result. You can still modify the speaker cabinet to match the Pentas in some way.

I’m quite satisfied by the performance of the Penta, its an amazingly capable speaker to my ears. The mission here is to take the capability and repackage to suit the placement more efficiently, technically correct and maybe even elegantly.

I’m chasing down the exact same speakers because I want to keep the timbre between channels as close to each other as possible. Going outside B&O would miss the objective.

[Evan]

Die_Bogener wrote:

A Penta is way to big… a simple Redline 40/60/120 will do the job. The important thing is: the speaker must fit to human voice. Too much bass will destroy the effect… and a standard Penta will not work, you must first remove the bubble wrap foil in it’s sound way.

I hear you. Many speakers fit the role but the objective here is to match as closely as possible the sound of the left and right speakers.

[Evan]

Glitch wrote:

Evan wrote:

et me know what you guys think.

From a general sound perspective, I don’t see any reason why it wouldn’t work. As long as you keep the cabinet volume and reflex tube length/diameter the same you will, in general, have a similar frequency response. Even if you mess up the very low frequency response, this won’t be critical for voices since they don’t contain those frequencies. Would you actually be happy with the form factor? I’m having a hard time imagining what this would look like under a TV. Did you plan to have the bottom-most mid-range close to the floor? Not having the tweeter and mids at ear level may mess with the vertical dispersion. I don’t know if this is a better or worse trade-off versus having the mid-range array horizontal. Have you considered using a (well matched) pair of Pentas (in the original configuration) placed tight to sides of the TV? The mono pair would provide the a solid centered image and the apparent sweet spot could be roughly controlled by the angle. The other “surround” speakers could also be Pentas for the full overkill effect. ? Glitch

Yeah, seems like it, right? I know it will be impossible to match the cabinet coloration but hopefully in normal listening that isn’t such a huge issue.

I’m going to take some impedance measurements of each subsystem (woofer and mid) to find the critical tuning for the cabinet volumes etc. and use that as reference in the build later on.

As for form factor that is still TBD. It should be able to fit inside an Ikea Kallax unit (height-wise). We use a 2×4 kallax shelf for the under-tv area in the bedroom and I have removed one vertical piece to open up the middle area a bit. I’ll add a picture soon to make this all a little easier to explain. The living room setup is a little more difficult and I might have to put it on a stand in front of the TV unit as it is far less accommodating. Let’s be honest, this isn’t a project for the space-conscious!

I really want to print it so that it has the aesthetic of the original Penta geometry. But if it gets made from wood it will likely sound far far superior than a plastic cabinet.

The problem with putting the same signal through both speakers is that you only serve a listener exactly in-between them. My goal is to build the center channel so that it serves all listeners, even those sat to sides etc.

My vision is that this becomes repeatable. I want to be able to share this with those who may be interested enough so that they can build their own.

[Evan]

Millemissen wrote:

Unfortunately you do not write anything about how you want to connect the ‘new speaker’ – do you use an A/V receiver or will it be connected to a Beovision…..in which case, what is the amplifier? Apart from the physical drivers in the ‘new speaker’ there are multiple things that can influence the sound. I would do as Ravsted….get a BL7.1 – alternatively/or even better a BL7.4, if you have room for it below the tv. MM

Hey MM, I left that out almost intentionally as those items are basically equal between both systems. They both have an excellent foundation 🙂

Living room: JBL Synthesis SDP-40 with Emotiva XPA-2 (Gen3)
Bedroom: Lexicon MC-12B with another Emotiva XPA-2 (Gen3)

Of course adding another amp channel will be necessary. So I will either expand the XPA to a three channel unit or swap in a new amp. They will all have equal power.

[Glitch]

Evan wrote:

The problem with putting the same signal through both speakers is that you only serve a listener exactly in-between them.

This is only true if the radial dispersion is constant, which is not the case for the higher frequencies.  This explanation isn’t quite correct. What I meant to say is something more along the lines of… This does not have to be the case if the system was designed to not have a small, narrow sweet spot.

Consider the sound system in your car. The driver is much closer to the driver’s side speaker than the passenger side speaker, and vice versa for the passenger. Despite this, both driver and passenger can simultaneously experience a (mostly) centered image. The car audio engineers achieve this by carefully manipulating the dispersion fields of the higher frequency drivers. An overly simplified explanation is that a speaker is louder on-axis than off-axis. The speakers are arranged such the the far speaker is on-axis and the closer on is off-axis by the exact amount that it needs to be to get an equal sound level at the listener’s position. Look up some of the papers from Dr. Bose for a detailed explanation of the theory behind this.

It would be awesome of Geoff Martin could chime in and provide the dispersion data for the Pentas. I have to believe that B&O has this, but is likely wishful thinking on my part that they would make it available.

Glitch

 

[Millemissen]

Glitch wrote:

….Despite this, both driver and passenger can simultaneously experience a (mostly) centered image.

 

Not in my car!

MM

[Evan]

Glitch wrote:

Evan wrote:

The problem with putting the same signal through both speakers is that you only serve a listener exactly in-between them.

This is only true if the radial dispersion is constant, which is not the case for the higher frequencies. This explanation isn’t quite correct. What I meant to say is something more along the lines of… This does not have to be the case if the system was designed to not have a small, narrow sweet spot. Consider the sound system in your car. The driver is much closer to the driver’s side speaker than the passenger side speaker, and vice versa for the passenger. Despite this, both driver and passenger can simultaneously experience a (mostly) centered image. The car audio engineers achieve this by carefully manipulating the dispersion fields of the higher frequency drivers. An overly simplified explanation is that a speaker is louder on-axis than off-axis. The speakers are arranged such the the far speaker is on-axis and the closer on is off-axis by the exact amount that it needs to be to get an equal sound level at the listener’s position. Look up some of the papers from Dr. Bose for a detailed explanation of the theory behind this. It would be awesome of Geoff Martin could chime in and provide the dispersion data for the Pentas. I have to believe that B&O has this, but is likely wishful thinking on my part that they would make it available. Glitch

Yeah I am familiar with this implementation but it still is an exploitation of generally known locations of the listeners. I think for home theater it is best that there is a dedicated center channel physically centered below the screen.  This will anchor the sound stage and center channel content to the image really well.

[Glitch]

Evan wrote:

I think for home theater it is best that there is a dedicated center channel physically centered below the screen. This will anchor the sound stage and center channel content to the image really well.

Yep, I understand why most people like the “centered below the screen” location. I like the center of my TV screen to be below eye level, which keeps the TV low. The center speaker is almost on the floor. Now the sound is coming from well below the actors faces (which are usually higher on the screen) and things like coffee tables are in the direct path to the speaker. The bigger the TV’s get, the worse this problem becomes. The “dual mono on the side” addresses some of these issues, but admittedly causes other issues.

The good thing about the lack of a perfect solution is that it opens the door for experimentation.

Have you thought about mocking up your original concept? Possibly something like pulling the tweeter/mid module and pairing it with a couple of conventional speakers as surrogates for the woofers?

Glitch

 

[Evan]

Another configuration I briefly considered was this one: a 2×2 woofer arrangement to try and avoid any comb filtering that could come from the woofer pairs being so far apart.

 

One additional idea to consider – arranging the woofers so that they are in a force-cancelling configuration to reduce rattles in the gear / tv unit where this thing will eventually live.

[Evan]

Glitch wrote:

Evan wrote:

I think for home theater it is best that there is a dedicated center channel physically centered below the screen. This will anchor the sound stage and center channel content to the image really well.

Yep, I understand why most people like the “centered below the screen” location. I like the center of my TV screen to be below eye level, which keeps the TV low. The center speaker is almost on the floor. Now the sound is coming from well below the actors faces (which are usually higher on the screen) and things like coffee tables are in the direct path to the speaker. The bigger the TV’s get, the worse this problem becomes. The “dual mono on the side” addresses some of these issues, but admittedly causes other issues. The good thing about the lack of a perfect solution is that it opens the door for experimentation. Have you thought about mocking up your original concept? Possibly something like pulling the tweeter/mid module and pairing it with a couple of conventional speakers as surrogates for the woofers? Glitch

The distance-to-floor problem will definitely be a thing for me in the living room. I have a 75″ panel sitting on an already low tv unit. I’m imagining this might have to be put on its own pedestal in front of the tv + tv unit. Pedestal could be tilted etc.

In the bedroom the TV is mounted fairly high up on the wall to make viewing from the bed easier.

In my experience it seems our human listening isn’t mega sensitive to height, more so side to side. I’m thinking it shouldn’t be a huge issue to place the center relatively low. Not to invalidate your experience at all, Glitch. I have a colleague who has a pair of center channels, one above and one below and he has tuned the [acoustic] image between them.

As for mocking it up, no probably won’t get around to it until I get my hands on another set of Pentas. However this really means I need to clear the project queue of some other big projects. So much going on as usual!

[Glitch]

Evan wrote:

In my experience it seems our human listening isn’t mega sensitive to height, more so side to side. I’m thinking it shouldn’t be a huge issue to place the center relatively low. Not to invalidate your experience at all, Glitch. I have a colleague who has a pair of center channels, one above and one below and he has tuned the [acoustic] image between them.

Different people are sensitive to different things. What one person doesn’t notice, really bothers another. Room acoustics can be quite different also. I could see where the bottom-center location would work someone with a dead floor and a live ceiling. The stronger reflection from ceiling would move the apparent image upward.

I’ve considered the over-under setup. I just can’t figure out a way to make it look “right enough” to be a permanent solution.

Glitch

 

[Die_Bogener]

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?

[pepps]

In my living room I currently have Penta L&R, BL7.4 C and Beovox 3000 (flat panel) LR RR.
I have written on here before about my surprise and delight at how perfectly matched the Beovox 3000 are to the Penta mains. Tonally they are a match made in heaven, so to speak.

Julian

[Evan]

Just adding a photo for context. The BS4500 and BL4ks to either side of the Lexicon are a standalone system. That was brought in to service for light CD listening.

One day I’ll get all my Penta amps running reliably. Currently 2/4 are operational hence why the Emotiva amp has been brought in.

Eventually the Lexicon will move down a level and the Emotiva will go somwhere else so that this Penta center channel can go in the upper middle unit of the shelf.

[Author]

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