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Old 27th November 2010, 11:47 AM   #1
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Default B&O Beolab 11 - how does it work?

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
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Old 27th November 2010, 06:32 PM   #2
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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
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Old 27th November 2010, 06:41 PM   #3
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The slot loads the front of the drivers, spacing will change performance

dave
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Old 30th November 2010, 11:15 AM   #4
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Quote:
Originally Posted by planet10 View Post
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.
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Old 30th November 2010, 05:53 PM   #5
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I think you can model this with hornresp.
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Old 30th November 2010, 08:00 PM   #6
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Quote:
Originally Posted by natumbri View Post
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
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Old 25th June 2012, 09:33 PM   #7
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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
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Old 26th June 2012, 12:07 PM   #8
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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
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Old 26th June 2012, 03:14 PM   #9
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Quote:
Originally Posted by natumbri View Post
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
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Old 20th August 2013, 06:06 AM   #10
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Quote:
Originally Posted by natumbri View Post
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
Here's some advantages of doing this:

1) it looks different
2) two 6.5" drivers have a surface area that's similar to a 10" woofer
3) Based on some measurements I've done, and what I've read, slot loading will lower the FS a little, and raise the QTS. For instance, if you have a 6.5" woofer with an FS of 40hz, if you slot load it you might see the FS drop to 38 or even 36hz, and the QTS will go up a little. The net effect is that you end up with parameters that are similar to a larger driver.
4) Probably the biggest advantage is that the slot will act as a low pass filter. If you make it big enough, and size it carefully, it will act similar to a bandpass subwoofer. This is a method to reduce harmonic distortion physically, as the physical lowpass filter that's formed by the slot will reduce everything above a certain frequency. (Not just the fundamental, but also the harmonic distortion.)

Long story short - it's a clever way to make a couple of small drivers sound like a bigger driver.

There are some drawbacks:

1) it's more complex than a simple sealed box with a 10"
2) Two 6.5" drivers have an SD that's similar to a 10" driver, but most 10" drivers have more xmax. Therefore, a single 10 will typically have more displacement.

Of course, Beolabs aren't cheap, so they may be using some high displacement 6.5" woofers.
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