B&O Beolab 11 - how does it work?

[natumbri]

Can anyone explain how this subwoofer works?

The specifications say that it has 2 6.5" bass drivers, each in a sealed 2.5l enclosure. The drivers face each other, a couple of centimeters apart.

What is the effect of this? What is the significance of the distance between the two drivers? Would they be in phase or out of phase? Why?

The specifications also mention "Adaptive Bass Linearisation" - anyone know anything about this? After a little searching, I'm imagining a Linkwitz Transform equalised subwoofer but with a response curve that varies depending on how loud the speaker is playing: the louder the music plays, the higher the roll-off frequency. Where there is extra amplifier power available, that power is used to extend the bass response. Just a guess - I'd be interested to know what the actual answer is.

I have a couple of Tang Bang W4-992sd drivers sitting around and am trying to think of something interesting to do with them.

Cheers,
Nik

[chris661]

Hi,

- the drivers would be wired electrically in phase. Acoustically, they'd also be in phase. Because they're facing opposite directions, there should be little cabinet vibration.

- the adaptive bass thingy would have some kind of high pass filter to cut off the really low stuff. The louder the volume, the higher the cutoff. This saves the drivers from moving too far. You're right in your imaginings... I think.

If I was to clone it, I think I'd use the 6.5" TB subs. That said, if they're lying around, it would be easy enough to put 2 sealed cabinets facing each other, mechanically couple them to reduce vibrations and see where you end up.

Chris

[planet10]

The slot loads the front of the drivers, spacing will change performance

dave

[natumbri]

Originally Posted by planet10

The slot loads the front of the drivers, spacing will change performance

dave

Thanks dave. Is there any way for me to simulate different configurations to see what happens?

Is it accurate to say that design is a variation on a bandbass reflex design and that it will will lower the box Fb while (dramatically) raising the system Q?

Cheers,
Nik.

[MaVo]

I think you can model this with hornresp.

[planet10]

Originally Posted by natumbri

Is it accurate to say that design is a variation on a bandbass reflex design and that it will will lower the box Fb while (dramatically) raising the system Q?

More like mass-loading the driver from the front and getting a bit better impedance match with the air outside.

dave

[Studio Au]

Just wanted to point you to my newly started post with the idea to create a great sounding subwoofer, based very loosely on the Beolab 11. Concept, two sketches on paper, and a quick crude sketch up model so far.

http://www.diyaudio.com/forums/subwoofers/215003-concept-beolab-11-style-isobaric-sub-using-ikea-blanda-metal-bowls.html

[natumbri]

Thanks for the heads-up. I'll watch your project with interest.

When I wrote the first post in this thread, back in Nov 2010, I actually had purchased ... 2 IKEA Blanda metal bowls, with a view to using them exactly as you have proposed! I never got around to doing anything and still have the bowls - perhaps I'll dig them out and see how I go.

I don't really understand push-push v push-pull etc [as discussed in the other thread], but I was thinking 'facing each other, in phase' - probably means 'push-push' - with a Linkwitz transform. Anyway, if I do anything more, I'll post in your other thread.

Cheers,
Nik

[planet10]

Originally Posted by natumbri

I don't really understand push-push v push-pull etc [as discussed in the other thread], but I was thinking 'facing each other, in phase' - probably means 'push-push' - with a Linkwitz transform. Anyway, if I do anything more, I'll post in your other thread.

Yes. With face-to-face it is more dofficult to get really tight coupling between the 2 drivers.

dave