About 18 months ago I bought a pair of Kef 104/2 speakers from "Spider". They are an early model.
I played about quite a bit with their placement and with use of the included KUBE. Also measuring them in comparison to my B&W DM2a speakers in the same room. Here's the thread from mid-2017:
https://hifiwigwam.com/forum/topic/125677-measurement-of-kef-1042
I enjoyed the Kefs for about a year but this summer I moved the B&W back -- and despite the fact that they have a less flat response than the Kefs, there's something about their presentation that I just seem to prefer, though it's a very close thing.
I've decided to have a go at converting the Kef 104/2 to active crossovers. If I get it done and it's a success I might move on and convert the B&W DM2a.
I've done some reading here:
- starting with Serge's B&W 801 project
https://hifiwigwam.com/forum/topic/47853-a-winters-project/
- general discussion of crossovers
https://hifiwigwam.com/forum/topic/124334-crossover-design/
- candidates for active conversion
https://hifiwigwam.com/forum/topic/125091-what-speakers-to-turn-active/
- "MF 1000"'s recent 104/2 conversion
https://hifiwigwam.com/forum/topic/129572-kef-1042-restoration-conversion-to-3-way-active-build/
and abroad:
- MiniDSP's intro to active crossovers
https://www.minidsp.com/applications/digital-crossovers/digital-crossover-basics
- Active Crossover Design toolkit in Excel
http://audio.claub.net/software/ACD/ACD.html
- Measuring driver timing offsets
https://app.box.com/s/ouxjjsx0m8bs00cil5iq
Based on this reading, never having tried one of these conversions before, my plan so far is:
1) measure them unchanged with their original passive crossovers, both in the room and outdoors (for a near-anechoic meaurement) so that I know what I'm trying to improve on.
2) remove crossovers and measure each set of drivers (tweeter, pair of mids, pair of woofers) individually outdoors and in the room so that I have the characteristics of each driver and also their relative timings
3) load this response and timing information into miniDSP
4) programme the miniDSP to reproduce the original passive crossovers (frequencies, slopes) with a view to measuring the anticipated superiority of the active crossover implementation
5) explore improved crossover designs to implement in the miniDSP software
Crossover
It seems like the best way for me to implement the crossovers will be using a miniDSP 4x10-hd (https://www.minidsp.com/products/minidsp-in-a-box/minidsp-4x10-hd) which takes analogue input and has up to 8 analogue outputs.
Amplification
Whilst it might be fun to put together two 3-channel 'backplate' style amps using ready-made D-class boards, this sounds like unwise complexity for a first attempt. I will have enough on my plate getting the crossover, timing and polarity issues solved without introducing the factor of a possibly flaky DIY amp. So in terms of using a pre-built amp I think the choice is either:
- 3 x stereo amp, e.g. like Serge's trio of Behringer A500 which he noted had the benefit of being dual-mono design, i.e. with very little chance of cross-channel distortion
- a multi-channel amp like the Rotel RB-976 which has 3 pairs of inputs and outputs and is rated at 60W per channel in 8 ohms. Should be more than adequate given the 104/2 is a sensitive speaker and removal of the passive crossovers is going to make it still easier to drive?
One piece of information which I don't have -- and perhaps someone here can help with is: what is the precise design of the original passive crossover in the 104/2? At what frequencies are they set? What type of filters are they? (e.g. Linkwitz-Riley, Butterworth etc)
Apart from getting an answer to this specific question, I will be most grateful for general comments and advice on the above.
Many thanks
I played about quite a bit with their placement and with use of the included KUBE. Also measuring them in comparison to my B&W DM2a speakers in the same room. Here's the thread from mid-2017:
https://hifiwigwam.com/forum/topic/125677-measurement-of-kef-1042
I enjoyed the Kefs for about a year but this summer I moved the B&W back -- and despite the fact that they have a less flat response than the Kefs, there's something about their presentation that I just seem to prefer, though it's a very close thing.
I've decided to have a go at converting the Kef 104/2 to active crossovers. If I get it done and it's a success I might move on and convert the B&W DM2a.
I've done some reading here:
- starting with Serge's B&W 801 project
https://hifiwigwam.com/forum/topic/47853-a-winters-project/
- general discussion of crossovers
https://hifiwigwam.com/forum/topic/124334-crossover-design/
- candidates for active conversion
https://hifiwigwam.com/forum/topic/125091-what-speakers-to-turn-active/
- "MF 1000"'s recent 104/2 conversion
https://hifiwigwam.com/forum/topic/129572-kef-1042-restoration-conversion-to-3-way-active-build/
and abroad:
- MiniDSP's intro to active crossovers
https://www.minidsp.com/applications/digital-crossovers/digital-crossover-basics
- Active Crossover Design toolkit in Excel
http://audio.claub.net/software/ACD/ACD.html
- Measuring driver timing offsets
https://app.box.com/s/ouxjjsx0m8bs00cil5iq
Based on this reading, never having tried one of these conversions before, my plan so far is:
1) measure them unchanged with their original passive crossovers, both in the room and outdoors (for a near-anechoic meaurement) so that I know what I'm trying to improve on.
2) remove crossovers and measure each set of drivers (tweeter, pair of mids, pair of woofers) individually outdoors and in the room so that I have the characteristics of each driver and also their relative timings
3) load this response and timing information into miniDSP
4) programme the miniDSP to reproduce the original passive crossovers (frequencies, slopes) with a view to measuring the anticipated superiority of the active crossover implementation
5) explore improved crossover designs to implement in the miniDSP software
Crossover
It seems like the best way for me to implement the crossovers will be using a miniDSP 4x10-hd (https://www.minidsp.com/products/minidsp-in-a-box/minidsp-4x10-hd) which takes analogue input and has up to 8 analogue outputs.
Amplification
Whilst it might be fun to put together two 3-channel 'backplate' style amps using ready-made D-class boards, this sounds like unwise complexity for a first attempt. I will have enough on my plate getting the crossover, timing and polarity issues solved without introducing the factor of a possibly flaky DIY amp. So in terms of using a pre-built amp I think the choice is either:
- 3 x stereo amp, e.g. like Serge's trio of Behringer A500 which he noted had the benefit of being dual-mono design, i.e. with very little chance of cross-channel distortion
- a multi-channel amp like the Rotel RB-976 which has 3 pairs of inputs and outputs and is rated at 60W per channel in 8 ohms. Should be more than adequate given the 104/2 is a sensitive speaker and removal of the passive crossovers is going to make it still easier to drive?
One piece of information which I don't have -- and perhaps someone here can help with is: what is the precise design of the original passive crossover in the 104/2? At what frequencies are they set? What type of filters are they? (e.g. Linkwitz-Riley, Butterworth etc)
Apart from getting an answer to this specific question, I will be most grateful for general comments and advice on the above.
Many thanks