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Multi-Way Conventional loudspeakers with crossovers

B&O Beolab 90 - adjustable directivity by DSP
B&O Beolab 90 - adjustable directivity by DSP
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Old 8th October 2015, 10:09 AM   #1
Quip is offline Quip
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Default B&O Beolab 90 - adjustable directivity by DSP

So B&O just released their funky new flagship. Uses DSP to shape dispersion and yields excellent polar performance.

BeoLab 90: Behind the scenes earfluff and eyecandy

B&O Tech: What is “Beam Width Control”? earfluff and eyecandy

Beamwidth can be switched with a touch on their app, with the ability to configure beamwidth presets that one can switch in between on the fly. Comes with automated room correction and 18 channels of amplification/channel too. Can anyone explain how the unusual driver array works? I'm guessing that some drivers are deliberately aligned out-of-phase digitally to induce cancellation and shape the dispersion pattern that is desired.
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Old 8th October 2015, 10:14 AM   #2
billshurv is offline billshurv  United Kingdom
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B&O Beolab 90 - adjustable directivity by DSP
similar to the kii. Look here for an animation on how they do it acoustics

Last edited by billshurv; 8th October 2015 at 10:14 AM. Reason: spelling
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Old 8th October 2015, 10:37 AM   #3
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Originally Posted by billshurv View Post
similar to the kii. Look here for an animation on how they do it acoustics
I've actually read up on the Kii. Similar tech, but different priorities. Putzey's aim is to use the cancellation to significantly reduce backward radiation below baffle step, giving an effectively cardiod dispersion pattern in the bass, except for the lowest frequencies. The midrange and treble is relatively textbook (for an active) to my understanding. And the dispersion pattern is fixed.

B&O's design is clearly more ambitious. It aims for near-CD performance with variable beamwidth from direct radiators. What I struggle to understand is how the directivity can be varied so much between different DSP profiles?
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Old 8th October 2015, 10:50 AM   #4
billshurv is offline billshurv  United Kingdom
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B&O Beolab 90 - adjustable directivity by DSP
It's a phased array. By driving each unit from a separate amplifier you can vary the phase between them. As its DSP you can then do tricks to change relative phasing against frequency. Not entirely dissimilar to how the Quad ESL 63 replicates a point source from a big flat sheet of cling film.

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Old 8th October 2015, 10:57 AM   #5
manninen is offline manninen  Finland
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if someone wanted to do Kii clone how many channels it needs? simple 2-way i think 4-5 delayed channels?
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Old 8th October 2015, 11:13 AM   #6
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if someone wanted to do Kii clone how many channels it needs? simple 2-way i think 4-5 delayed channels?
4 channels, yeah. 2 side-firing woofers (1 on each side) and 2 at the back. Not cheap, but certainly quite inventive and unique.
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Old 8th October 2015, 11:27 AM   #7
Omholt is offline Omholt  Norway
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B&O Beolab 90 - adjustable directivity by DSP
I fail to understand how the polars can look as constant as it does on page 15 and 16 (narrow and wide) when multiple drivers are used in a cluster. That would normally lead to lobing in both planes. Would be nice to see independent measurements.
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Old 8th October 2015, 11:35 AM   #8
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I fail to understand how the polars can look as constant as it does on page 15 and 16 (narrow and wide) when multiple drivers are used in a cluster. That would normally lead to lobing in both planes. Would be nice to see independent measurements.
Yes! That's what I'm perplexed about. Horizontal directivity, I can understand due to perhaps the properties of the phased array (judicious cancellation and delay to yield smooth directivity characteristics) and B&Os DSP. Vertical directivity? I can only imagine large amounts of lobing.

EDIT: Geoff Martin, the designer, provides further details of the DSP setup:

'The point of the rear-facing drivers is to interfere with the front-firing drivers. However, this is done in a very controlled fashion using an individual FIR filter customised for each driver. Consequently, at one frequency, the back drivers may be cancelling the front in a given direction whereas at another frequency, they are “helping”. The magnitude and phase responses of the filters are the result of the measurements of the drivers in their locations, and an optimisation algorithm designed to find the best possible solution to the target of a given beam width.'

The unique selling point as I see it is how automated the entire process is.

Last edited by Quip; 8th October 2015 at 11:41 AM.
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Old 8th October 2015, 11:38 AM   #9
Juhazi is offline Juhazi  Finland
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^Could be just smoothing, but carefully set crossover frequencies help to minimize lobing in passband. BO90 in ambient mode shows all the lobing, obviously all drivers are in same phase. Other modes are Narrow and Wide.
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Old 8th October 2015, 11:50 AM   #10
Omholt is offline Omholt  Norway
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B&O Beolab 90 - adjustable directivity by DSP
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Originally Posted by Quip View Post
Horizontal directivity, I can understand due to perhaps the properties of the phased array (judicious cancellation and delay to yield smooth directivity characteristics) and B&Os DSP.
Can you explain further how this is accomplished?

I assume the crossover between the tweeters and mids is fairly high. Meaning the spacing between them in this freq. area will cause lobing. Unless you use a very large amounts of drivers (like in a line-array) you will have lobing and comb filtering.

Omni is my opinion a waste to use indoor in a living room. It's more than sufficient to have a wide dispersion which covers all the listeners no matter where they sit. Making it omni only causes unwanted frontwall reflections.
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