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Beolab 19 very special

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wonderfulelectric
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wonderfulelectric Posted: Mon, Nov 11 2013 10:43 PM

I just found out after reading the site info of the Beolab 19 in detail that the two opposing drivers are sealed from each other. That's completely unique! I wonder what gains does that approach yield?

kuyttendaele
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It's not completely unique.. The technique is also implemented on the BeoLab 11... but there the drivers are positioned towards each other.. also canceling out the vibrations of the sub itself. 

Geoff Martin
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wonderfulelectric:

I just found out after reading the site info of the Beolab 19 in detail that the two opposing drivers are sealed from each other. That's completely unique! I wonder what gains does that approach yield?

If you put two drivers in the same enclosure, unless they are ABSOLUTELY identical in every respect, at all levels and temperatures, they will get into a fight and one of them will win.

As part of the development, we tried putting the woofers in a single enclosure, and we found that we get much more control over the woofers, particularly in their temporal response (you can read that as "more punch" if you like - since that's the most obvious audible difference) when they are in separate enclosures. As a result, the acoustic design required that we put an airtight bulkhead down the middle of the the enclosure to keep things behaving properly.

Cheers

-geoff

wonderfulelectric
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Geoff Martin:

wonderfulelectric:

I just found out after reading the site info of the Beolab 19 in detail that the two opposing drivers are sealed from each other. That's completely unique! I wonder what gains does that approach yield?

If you put two drivers in the same enclosure, unless they are ABSOLUTELY identical in every respect, at all levels and temperatures, they will get into a fight and one of them will win.

As part of the development, we tried putting the woofers in a single enclosure, and we found that we get much more control over the woofers, particularly in their temporal response (you can read that as "more punch" if you like - since that's the most obvious audible difference) when they are in separate enclosures. As a result, the acoustic design required that we put an airtight bulkhead down the middle of the the enclosure to keep things behaving properly.

Cheers

-geoff

I thought so as much. All the gains of an opposing driver configuration approach without its real downside. 

Thanks Geoff

Ps. To be honest I had always wanted to know the benefits of this novel implantation of isolated push push configuration but never gotten a chance. But wouldn't this approach essentially halves the volume available for each driver and put further strain on both the amplifier and driver?

Geoff Martin
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wonderfulelectric:

I thought so as much. All the gains of an opposing driver configuration approach without its real downside. 

The advantage of putting woofers back-to-back is almost only the reduction of vibration in the entire device. At a higher frequency, you might make some arguments about the "acoustic centre" of the device, but this would not apply to the BeoLab 19 due to the relationship between the frequency limitations and the total size of the device.
I'm not sure what you mean by the "real downside".

 

wonderfulelectric:

Ps. To be honest I had always wanted to know the benefits of this novel implantation of isolated push push configuration but never gotten a chance. But wouldn't this approach essentially halves the volume available for each driver and put further strain on both the amplifier and driver?

The isolation of woofers and the fact that they are placed back-to-back are two independent things. In other words, they are not isolated because they are back-to-back. If the BeoLab 19 had been designed as a small tower with two woofers on the front, we would still have had to isolate them from each other. Such a design (all other things being equal) would probably have sounded exactly the same - but it would vibrate more, and thus probably make your floor vibrate more - which would contribute a sound of its own.
Of course putting a bulkhead inside the subwoofer cuts the volume in half, but this does not mean that each woofer now "sees" half of the volume it would have seen, since, without the bulkhead, each driver "sees" the other driver, which has an impact on the influence the volume has on the woofer's behaviour. In essence, the question is not one of volume, but of total compliance (the reciprocal of "springiness") of each of the two systems - but that's probably getting too deep into the details. However, since putting the bulkhead in there changes the compliance of each driver from one arbitrary value to another arbitrary value, I wouldn't say that this is a problem.
The advantage of separating them is that the compliance is no longer dynamic with signal. Put a woofer in a box and you get the same compliance all the time (sort of…). Put a woofer in a box with another woofer and Woofer #2 modulates the total compliance of Woofer #1 - and the modulation may result in an audible effect.
As for a "strain on the amplifier and driver" - I'm not sure what you mean by this either. If the amplifier is operating within its limits (i.e. it's behaving linearly) then the current it has to deliver to the driver (which is defined by the voltage it is asked to deliver and the impedance of the driver loading its output) will also, by definition, be behaving (if it weren't, it would be outside its limits). This is basically the same for the driver - as long as you're within the linear behaviour region of the driver. If both the amplifier and the driver are operating linearly (however we may define the threshold of "linearity" ) then the amount of "strain" on the system is not an issue. If we go beyond the linear region for either the amplifier or the driver, then of course, things will sound worse, however the ABL and thermal protection of the system is designed and tuned to keep the subwoofer from straying outside the that region - so it should behave.
Cheers
-geoff
Jeff
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Jeff replied on Wed, Nov 13 2013 3:18 PM

I've seen double woofer setups where one was mounted facing out, the other facing in, allegedly to cancel out certain distortion products inherent in the drivers. Always wondered how much distortion that actually canceled, it seems to me that it'd make more sense to find a woofer with lower mechanical distortion products. 

I have seen DIY speakers where the builder chose not to use a sub chamber for his cone midrange, always fun to watch the woofer modulate the midrange. Especially when at loud volumes a big bass drum whack caused the midrange to push out and stick when the voice coil got misaligned. Suddenly there's a huge suckout in the mids for some odd reason! 

Jeff

I'm afraid I'm recovering from the BeoVirus. Sad

wonderfulelectric
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Thanks for the explanation Geoff. 

And of course the opposing driver configuration is everywhere now, it's great marketing and yields good performance bug I didn't get the isolating the drivers are each other. But Geoff's explanation makes sense. 

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