[Evan]

Last week (or was it the week before??) I put my BeoSound Century in my office cube as I have no room for it at home currently.

Also needed to dig it out as someone handed me a cassette copy of their latest album they recently recorded so I needed a tape deck to play it and the Century is my only one!

Excuse the non-matching table stand. The Century didn’t come with one when I bought it and I grabbed this one off the ‘bay. Its great to finally put all the bits together. Now to fix the broken antenna and this ‘project’ will be done.

[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!

[Evan]

Either way – let us know how it turns out! For future use it would be good to attach copies of the exact files used. All I could find was the plate with a hole in it.

[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:

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.

[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.

[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]

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]

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]

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]

Happy to help print the parts if you decide to do so, just PM me. Although I can’t verify the fitment as I don’t have a pair of those speakers on hand.

[Evan]

Latest addiction: new-to-me pair of M100-2’s. Have been trying to get my hands on a pair of these for years now.

Swapped them into my humble corner of the office we refer to as the “clubhouse” before they make their journey home. They are effortlessly filling our warehouse with sound. Maybe I will swap them into the listening room if I find the time. They should annoy my colleagues downstairs with ease!

[Evan]

This is sad news indeed! I am very late to this thread but I would be remiss not to acknowledge Peter’s dedication and passion for B&O – both the products and community.

From my earliest years of BeoWorld forum reading/lurking/posting I remember seeing his constant updates and refinements to his system where he built a stand-alone ICEpower amp for his Pentas. As many have said in the posts above, his drawings and diagrams are legendary.

[Evan]

TheFinisher wrote:

they do sound very good , I mean end game speakers.

You’re making me want a pair of M100s even more. Why do you tease us!!

[Evan]

Glad you enjoyed it and found it useful.

I measured a few of them but not all. The ones I had measured were very close to spec. Unfortunately I think I tossed them so I can’t go back and check – sorry!

[Evan]

Glitch wrote:

I just finished a refresh of this Beomaster 4000. This receiver was a good example of why one shouldn’t just grab a spray can of “contact cleaner/lubricant” and spray indeterminately to fix a noisy potentiometer or switch. Whatever product the previous owner used seeped everywhere inside the receiver then turned into a hard waxy substance. Fortunately, I was able to fully disassemble the receiver and clean the “gunk” out of the chassis, sliders and switches. My plan for the receiver is to pair it with four Braun speakers from the same era. Braun speakers are actually somewhat rare in the US. I like to assemble systems with a theme. This will be my “70’s Euro-system”. I’m guessing that most of the forum members would just call it a “70’s system” I’m looking forward to experiencing the Ambiophonic feature. Does anyone have suggestions for era-appropriate recordings that highlight this feature? Glitch

Nice work. Really clean 4k you have there! I can’t wait to work through my BM4k. I have a BG4002 with CD4 built in and can’t wait to get the duo playing together one day.

[Evan]

jesnystrup@gmail.com wrote:

pepps wrote:

Evan wrote:

I’m back in the US for a little while so I’m trying to sort out one of my other previous acquisitions, BL Penta MK2. They need the full overhaul so I bought all 3 cap kits and new foam surrounds. These will be the main L/R channels in the master bedroom and the basis of a surround system (eventually!).

Looking forward to seeing/reading some more on this project.

Thats ALOT of work ..Let us know how it went Jess

Hey Jess – it definitely was a lot of work and still is! The project lives on when I have time for it.

You can find the full write up here: Evan’s MK2 BeoLab Pentas

[Evan]

Great thread, have been wanting to bring up a similar topic as I have contemplated something very similar.

Inspired by a configuration for architectural speakers by Meridian, I wonder if new life could be breathed into BL6000 and BeoLab 8000 speakers by building trios for wall mounting where space might be an issue for some. Meridian offers customers the ability to “array” their in-wall speakers so their customers with very large spaces / longer than usual listening distances (or need much higher SPL in their room). In their demo theater, Meridian uses three sets of three DSP-750 speakers as the L/C/R behind the projection screen. However they are mounted vertically unlike the icon depicts.

 

[Evan]

Hey Bihu – Powerlink signals are single ended, not able to send balanced signals that an XLR connector would usually carry. Of course you can use XLR if you want you will just have to make do with the positive and ground wired only.

Each Powerlink jack/cable/plug will carry both left and right channels.

For more details on the connector, see the Powerlink diagram here.

For a quick solution, visit Steve’s site linked at the bottom of this forum.

[Evan]

Beozip wrote:

But less is more …. so is B&O thinking and had create his own horizontally tablestand. This is very flexible. Do you know this stand?

 

Yes, I knew this stand was out there. I don’t really like the look of the bent wire and didn’t feel like hunting it down.

I enjoy designing things and I’m addicted to 3D printing so it was easy for me to do. Its good to flex the creative muscles every now and then.

Edit: Just checked the analytics and a whopping 7 people have downloaded it so far. Modest take rate but I’m glad a few people out there liked it enough to download 🙂

[Author]

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