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Old 23rd June 2008, 01:32 AM   #211
Salas is offline Salas  Greece
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Quote:
Originally posted by Joe Rasmussen
The renegade theory allows me to get that comfortably without going to extremes as has been the need in the past.
Joe R.

KEF in the Calinda and Cantata papers (late 70s) used 18 db AcButterworth in physically reversed vertical mid tweeter arrangement. Along saying that it erected the lobe back, they also said that the also electrically reversed polarity tweeter spread the phase much better in the all pass.

90deg phase difference for 3rd order also for them, and a deliberate electrical inversion again. But they did not think of using those seeds of evidence for minimum phase.

Time synchronization wasn't a goal or a legend back then. At least in the UK.
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Old 23rd June 2008, 10:52 PM   #212
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Quote:
Originally posted by salas



KEF in the Calinda and Cantata papers (late 70s) used 18 db AcButterworth in physically reversed vertical mid tweeter arrangement. Along saying that it erected the lobe back, they also said that the also electrically reversed polarity tweeter spread the phase much better in the all pass.

90deg phase difference for 3rd order also for them, and a deliberate electrical inversion again. But they did not think of using those seeds of evidence for minimum phase.

Time synchronization wasn't a goal or a legend back then. At least in the UK.
It rings a bell... sort of?

I don't remember the model numbers/names (I thought KEF 104 something was one of them?) and it was adjusting crossover values to get a particular curve on the tweeter. I don't remember the details but a friend had built a pair of 104 clones. It was an early example of setting a target acoustic curve and matching it as closely as possible. Is this the same that you are referring to? I don't specifically remember whether the tweeter was in or out of phase.

Joe R.
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Old 23rd June 2008, 11:03 PM   #213
Salas is offline Salas  Greece
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KEF Cantata

Rings a bell?
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Old 23rd June 2008, 11:10 PM   #214
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I googled Kef 104 and found this blurb on 104aB, this is what my friend at the time was attempting to clone:

http://www.hifiloudspeakers.info/Ana...Kef104abXO.pdf

I found that a number papers actually lodged by Dave Dlugos, we are joined by the same umbilical cord called Vacuum State.

http://www.hifiloudspeakers.info/Ana.../pages/p12.htm

The 'net not only makes the world smaller but also a time bubble.

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Old 23rd June 2008, 11:13 PM   #215
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Quote:
Originally posted by salas
KEF Cantata

Rings a bell?
Same website www.hifiloudspeakers.info. When replying I hadn't noticed you'd posted already. I will take a bit more of a look later, just about to fly out of the door.

Joe R.
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Old 23rd June 2008, 11:23 PM   #216
Salas is offline Salas  Greece
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Here you are. Had to scan the original KEF document.
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Old 24th June 2008, 11:47 AM   #217
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Quote:
Originally posted by salas
Here you are. Had to scan the original KEF document.
Thanks. Interesting website (didn't know of it) re KEF , Cooke and Fincham. I recall when they roped in Small, it must have been towards the end of the 80's (he worked at Sydney University). Before he left I had a disagreement with him - alas I now feel he was correct but that the solution would still not be acceptable (so don't tell). He argued Re should be increased externally if the driver was overdamped - erode Qe and then target the alignment - sealed box. I now know a certain local small scale manufacturer who does exactly that with a compact sub-woofer - sworn me not to tell.

The longitudinal bracing used in the Elsinores is very much influenced by Laurie Fincham.

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Old 24th June 2008, 02:23 PM   #218
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In theory that 90deg phase difference (error?) should be constant across the "wide spread" and thus should/ought sum flat in either case, so when they say "but in practice... connected in reverse... because this arrangement gives a smoother" etc, I think this is related to the fact that the drivers are bandpass devices. Try build, in simulation, Butterworth filter/crossover. I did this some time ago. I generated generic responses for both tweeter and midbass (generic 8R Z), got them to sum flat and then reversed the phase on one of them. Should sum the same but no surprises they didn't. Didn't at that point think about optimising the reverse/180deg phase. Should have in hindsight. The advantages they (this is likely Fincham?) spoke about might have emerged. But my focus was elsewhere.

Re your question about Mk3 null at H25deg, it wasn't exactly what I was looking at, at the time. Even though the tweeter was too deep to be absolutely optimised (Mk1/2), at off axis there is a foreshortening of the tweeter, so the time difference is smaller. This is the same as moving the tweeter forward, lessening the error that existed. As a thought experiment, at 90deg the drivers are equidistant. What I am trying to say in a muddled sort of a way, it is that a decent null should be available both on axis as well as off axis, even though there may well be a point where you get that absolute best null. What I will say is this: I believe the best null result all round should appear off axis as it ought to be weighed 2:1 in importance IMO. Also it should be influenced by the fact that I recommend for the Elsinores 10-15deg off axis listening to the system. So, while the null technique is still important, the aim is to find the widest practical window, get close to 100% vector summing and time/phase related properties that are fairly forgiving. My error actually proved just how forgiving this approach really is. If and wherever you get close to 100% summing, the null is at least going to look reasonable.

Need I say that this is also helpful to optimise a consistent power response?

Joe R.
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Old 14th July 2008, 09:20 PM   #219
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Hello, can I use the vifa XT25 tweeter instead of Peerless HDS 810921 in the MK3 laudspeaker version? thank you
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Old 15th July 2008, 09:03 AM   #220
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Quote:
Originally posted by nitronori
Hello, can I use the vifa XT25 tweeter instead of Peerless HDS 810921 in the MK3 laudspeaker version? thank you
I suppose you could, but the highpass to the Tweeter would need to be different. You will need to revert to Mk1 crossover which will still work with the different box construction. Please note that the HDS Tweeter's cutout and flushmount is virtually the same. You can update to HDS Tweeter later and make appropriate Mk3 changes to crossover. The HDS is worth the extra - trust me!

PLEASE NOTE THAT THIS CROSSOVER IS NOT TO BE USED WITH PEERLESS HDS TWEETER - ONLY VIFA XT25:
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