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SpeakerTalk This forum has been set up to facilitate discussion of 1970s KEF speakers and drive units. The owner of the Forum has no connection with KEF Audio.
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clubsport911 Senior Contributor 100+
Joined: 26 Aug 2012 Posts: 165 Location: Cheltenham, UK
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Posted: Mon Jan 09, 2023 1:51 pm Post subject: Reference Three's |
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Good afternoon folks.
As a satisfied owner of 105/3's, and listened to Reference 4's & Blade Meta's at my mates house, I have decided to move into Reference Three's - I was tempted by Fours (4.2's) but they are a touch too large.
Three's seem to offer me a little "more" of what I want - a few more Hz in the lower registers etc. I'm aware that Andrew (on the KEF design team ) used to post here and I think he moved to Elac ? If he is still on-line and active, I'd love to deep dive a little into the ethos of these designs as they have some slightly difference design concepts compared to the 105/3's.
Needless to say, my 105/3's will be up for sale soon as Director of Domestic operations has a limit to the number of boxes allowed in the AV room.
Any other Reference Three owners here ? |
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speakerguru Über Contributor 1000+
Joined: 18 Nov 2005 Posts: 1192 Location: Green Hut, Tovil
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Posted: Fri Jan 13, 2023 11:29 am Post subject: |
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Andrew Jones left KEF in the 90s when he moved to the USA to join Pioneer, if I remember correctly.
That was around the time before we'd even started work on the Ref Series 1, 2, 3 and 4. I don't think he had much input on that series before he left. AFAIC recall. most of the work was done by myself and Richard Hunter.
At LF, I think they all used the double coupled cavity configuration, where a reflex box feeds a second ported cavity and it's this second cavity which ports to the outside.
Advantages; more extension and excursion reduction
Disadvantages: higher order cut off.
Earlier coupled cavity designs had a closed box feedning into the second cavity. |
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clubsport911 Senior Contributor 100+
Joined: 26 Aug 2012 Posts: 165 Location: Cheltenham, UK
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Posted: Sat Jan 14, 2023 12:46 am Post subject: |
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Thanks. Yes, I have (over the years) become very familiar with the CC bass system on 104/2, 105/3 etc.
The Newer Reference One, Two, Three and Four had the so-called interport as you mentioned. On the KEF enthusiasts FaceBook page, I have documented the dissassembly of the Three's comparing them to the 105/3's I have. I was surprised (but not really in fact) to see just how much cheaper the modern speakers were compared to the earlier designs and it shows up in so many ways. I also noticed the Three crossover is much simpler which surprised me as from a post by Andrew, he mentioned just how hard it was to align the crossover on the interported design.
More thoughts ?
Welcome ! |
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speakerguru Über Contributor 1000+
Joined: 18 Nov 2005 Posts: 1192 Location: Green Hut, Tovil
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Posted: Tue Jan 17, 2023 12:27 pm Post subject: |
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It's too long ago for me to remember much detail. I don't recall the crossovers being simple.
WHat I can say is that compared to a reflex's two impedance peaks, a raw interport (or double coupled cavity) design has three peaks in the impedance curve as well as the usual hf rise due to the voice coil semi-inductance. This is a difficult load for any passive filter to "see" when designing a xo.
In order to get the LF section of the crossover to converge to a target response, with this load, the upper peaks would have to be, at least, partially reduced with conjugate networks (like the 104|2 which ended up as a substantially resistive load).
Can you provide a schematic of the Three's XO? |
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clubsport911 Senior Contributor 100+
Joined: 26 Aug 2012 Posts: 165 Location: Cheltenham, UK
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Posted: Tue Jan 17, 2023 11:52 pm Post subject: |
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Yes, I do have a cct diagram for my Reference Three's. Interestingly, the speakers are labelled as "Three's" but have the boundary layer compensation device and the "5th wire" to a low value resistor in the crossover. As far as I can ascertain, if you short out the resistor, bass is flat (but speakers need to be away from walls / corner). If you leave it open circuit, bass is reduced for boundary placement.
How can i attach a picture on this forum ? |
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audiolabtower VIP Contributor 500+
Joined: 06 Jan 2009 Posts: 686
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Posted: Wed Jan 18, 2023 4:48 pm Post subject: |
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Upload the pic to a site like Flickr which will give a url to the picture direct. That url will work in a post using the IMG links in the posting box. Google photos tend to be a pain to get to actually display. |
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