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Active crossover question
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audiolabtower
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PostPosted: Thu Dec 02, 2010 5:07 pm    Post subject: Reply with quote

They are the same, the sensitivity is set by the chosen bass extension point in the chosen enclosure for this type of bextrene driver, the passive crossover cannot boost bass above that efficiency, it cuts the mid to get a flat response, and this is what the active curve is emulating, compensating the mid to get a flat response.

Efficiency is not a consideration in the active because once each driver is equalised flat an overall flatness is easily achieved by adjusting the gain of each of the 3 amplifiers as long as you are within the power handling capability.

Different amplifiers have different electrical phase responses, ie the delay between input and output at different frequencies is not constant from 20Hz to 20kHz but varies with design and bandwidth, particularly in negative feedback amps. This is not the same as absolute acoustic phase. Since the 105 is a "minimum phase design" with in line driver acoustic phase at crossover using identical amps is even more important than usual I would say.

Incidentally the 105 has a linear acoustic phase plot (which most speakers do not have) from +180 deg at 20Hz to -900 deg at 20kHz as shown in the KefTopics design leaflet Vol 3 No 1.
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BobL
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Joined: 27 Jan 2004
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Location: West Midlands, UK

PostPosted: Thu Dec 02, 2010 7:02 pm    Post subject: Reply with quote

audiolabtower wrote:
They are the same, the sensitivity is set by the chosen bass extension point in the chosen enclosure for this type of bextrene driver, the passive crossover cannot boost bass above that efficiency, it cuts the mid to get a flat response, and this is what the active curve is emulating, compensating the mid to get a flat response.
I have no argument with that.
audiolabtower wrote:
Efficiency is not a consideration in the active because once each driver is equalised flat an overall flatness is easily achieved by adjusting the gain of each of the 3 amplifiers as long as you are within the power handling capability.
If you are talking about the whole speaker system then to some extent I agree, it isn't useful in deciding how much amplifier power you need. However, I wasn't, I was talking about 1 drive unit in 1 box as part of a system. The reason the response correction is there in either a passive or active system is to compensate for the different efficiency the transducer has at different frequencies. So to say it's not a consideration is to say you don't need correction in the xover passive or active.
audiolabtower wrote:
Different amplifiers have different electrical phase responses, ie the delay between input and output at different frequencies is not constant from 20Hz to 20kHz but varies with design and bandwidth, particularly in negative feedback amps.
You're telling me that you can show me a class A or class B amplifier with a phase shift inside 20Hz to 20KHz that is significant when compared to mechanic shift of a drive unit? Please show me one.
audiolabtower wrote:
This is not the same as absolute acoustic phase. Since the 105 is a "minimum phase design" with in line driver acoustic phase at crossover using identical amps is even more important than usual I would say.

Incidentally the 105 has a linear acoustic phase plot (which most speakers do not have) from +180 deg at 20Hz to -900 deg at 20kHz as shown in the KefTopics design leaflet Vol 3 No 1.
No problem with that either.
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audiolabtower
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PostPosted: Thu Dec 02, 2010 8:26 pm    Post subject: Reply with quote

I'll leave it at that. This is obvioulsy not a serious discussion when all you want to do is pick apart every sentence giving it a slant that was not there in the first place, and I have to repeat everything ad nauseam.
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audiolabtower
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PostPosted: Mon Nov 28, 2011 9:31 pm    Post subject: Reply with quote

As a postscript to this thread the new Kef History site has updated the 105.2 details and the spec shows a 400Hz crossover.
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