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Kef b300 in smaller enclosures
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SimplySound
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Joined: 08 May 2012
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Location: Albuquerque, NM

PostPosted: Wed Mar 27, 2013 4:42 am    Post subject: Reply with quote

clubsport911 wrote:
As a student of matters "coupled cavity bass" I keep returning to the same question. If truth is universal, and the twin coupled cavity bass is so "clever" why do more people not use it now?.


Not sure but my opinion is that it is pretty expensive and to a certain degree very complex to pull off. Remember the cross overs and KUBE are all part of the package that delivers a true 20hz at +/- 2db and is hitting 18Hz at 3db down!!!

As an owner of the R107, I can tell you that the quality of Bass Reproduction from these is probably second to none. Detail and presense is a hard thing to describe. As a reference, my IMF TLS-50MkII's can't touch the quality of the Big KEF Bass response.

So it isn't because the couple-cavity design doesn't work!
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Kef 107's-"One of the few full-range loudspeakers that I have experienced to touch the soul—not just of the music, but of the listener."—John Atkinson
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clubsport911
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Joined: 26 Aug 2012
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Location: Cheltenham, UK

PostPosted: Wed Mar 27, 2013 9:25 am    Post subject: Reply with quote

Surely the main costs were time in researching the optimum design ? There is perhaps some increased complexity in component count for the crossovers, but computers solve the former and the real costs of a few more caps and inductors for these kinds of speakers is negligable.

No, I'm not buying the cost or complexity reason for 2013.

I think you have nailed it well. It needs equalisation to make it perform and this does add. Few modern speakers except active studio monitors contain in built correction (and of course, subwoofers).

Interested that a lot of car subs are cavity coupled bandpass designs.

There is another reason ?
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SaSi
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Joined: 24 Aug 2008
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PostPosted: Thu Mar 28, 2013 2:40 am    Post subject: Reply with quote

The 4th order bandbass enclosure is a design that trades frequency response for efficiency. It gives much higher output for a limited frequency range. Provided it's coupled with a capable mid/bass to cater for frequencies above 60-80Hz it's a decent tradeoff.

In some older threads it was described how difficult it was to model and then finetune (by testing and modification) the bandpass tuning.

For several years (perhaps decades) KEF was constantly producing at least one such design. There are several different products employing this principle (104/2, 105/3, 107, 107/2, etc).

I am guessing that the difficulty in finetuning the design would have implications on how these systems aged. Surround and spider drift in characteristics over years could alter the tuning and perhaps make these systems age less gracefully than other designs.

Additionally, KEF switched priorities and looks like they now focus on concentric drivers that reduce lobbing between mid range and tweeter.
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speakerguru
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PostPosted: Thu Mar 28, 2013 9:58 am    Post subject: Reply with quote

SaSi wrote:
The 4th order bandbass enclosure is a design that trades frequency response for efficiency. It gives much higher output for a limited frequency range.
This is true of closed box, reflex and any loudspeaker design. Most commercial designers do everything they can to keep the box size sensible while extracting the most bass.
SaSi wrote:
In some older threads it was described how difficult it was to model and then finetune (by testing and modification) the bandpass tuning.
It is self-evidently more complex to optimise and more expensive to manufacture a multi-cavity box. Some say it is more difficult to sell because people have been prejudiced or indoctrinated into believing that you have to be able to see the bass drivers to get real bass.
SaSi wrote:
I am guessing that the difficulty in finetuning the design would have implications on how these systems aged. Surround and spider drift in characteristics over years could alter the tuning and perhaps make these systems age less gracefully than other designs.
No. The design is much more robust to driver ageing than a reflex design.
SaSi wrote:

Additionally, KEF switched priorities and looks like they now focus on concentric drivers that reduce lobbing between mid range and tweeter.
KEF changed ownership in 1991 and changed a lot of personnel in the following 10 years.
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SimplySound
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Joined: 08 May 2012
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Location: Albuquerque, NM

PostPosted: Thu Mar 28, 2013 3:19 pm    Post subject: Reply with quote

speakerguru wrote:
SaSi wrote:
In some older threads it was described how difficult it was to model and then finetune (by testing and modification) the bandpass tuning.
It is self-evidently more complex to optimise and more expensive to manufacture a multi-cavity box. Some say it is more difficult to sell because people have been prejudiced or indoctrinated into believing that you have to be able to see the bass drivers to get real bass.


Thanks SASI and Guru... I think that gets to the point. Again, it isn't because Coupled Cavity does work, it's just an expensive solution!
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Kef 107's-"One of the few full-range loudspeakers that I have experienced to touch the soul—not just of the music, but of the listener."—John Atkinson
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SaSi
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PostPosted: Sat Apr 13, 2013 10:26 am    Post subject: Reply with quote

It's very interesting to see that the ported design is more sensitive to aging than 4th order bandpass.

I mean, I know that a ported speaker design is hard to tune - at least compared to a sealed box - but I didn't realize it's also sensitive to aging.

One thing that makes me wonder is refoaming (in a broader sense to cover rubber surrounds as well). Perhaps the spider is much stiffer than the surrounds but I'm guessing that changing the original surround to an unknown - generic - version should alter the characteristics of the driver, hence possibly bring the system out of tune.

But going back to the original comment; a ported system is a 3rd order system and a bandpass system is a 4th order system. Isn't it logical to assume that the higher order system is easier to bring out of tune?
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speakerguru
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PostPosted: Mon Apr 15, 2013 10:35 pm    Post subject: Reply with quote

The alignment of a woofer system is dominated by the moving masses of driver and ports (if present) and the compliance of the box volumes. These are normally very stable with time.

If the system has been designed sensibly the compliance of the driver and passive radiators (if present) which do age will be swamped by the box cavity compliances which do not.
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