I'm planning to extend my stereo setup to a 2.1 system and I'm looking for opinions / suggestions about how to handle the signal conversion from full range stereo channels to high-frequency stereo plus mixed low frequency. I've built my entire setup (digital source, stereo amp) from scratch so I have quite a lot of freedom as to how to process the signal, and I use a relay attenuator that can easily support 3 channels. As I see it I could:
1. Do it all in the digital domain. Mix the stereo channels into a third mono channel then HF pass the stereo channels and LF pass the mono. Then pass all 3 channels to 3 channels of a 4-channel DAC and amplify as required.
2. Take the existing stereo output from the DAC and do the mixing to mono and HF and LF filtering in hardware at the line level. There's a PCB available from KMount on eBay that does this - I've used it before and it works fine, I've never taken any measurements though.
3. Take the existing stereo output and just mix to mono but no HF or LF filtering. Amplify all 3 full-range channels and then filter the signals sent to each speaker.
I think I've probably ruled out 1 at the moment, the commonly available SBCs don't support 4 channels over I2S and I'm not convinced there aren't too many timing issues around the signal processing and USB audio interfaces. So it's between line level and speaker level crossovers - what are the pros and cons of each?
1. Do it all in the digital domain. Mix the stereo channels into a third mono channel then HF pass the stereo channels and LF pass the mono. Then pass all 3 channels to 3 channels of a 4-channel DAC and amplify as required.
2. Take the existing stereo output from the DAC and do the mixing to mono and HF and LF filtering in hardware at the line level. There's a PCB available from KMount on eBay that does this - I've used it before and it works fine, I've never taken any measurements though.
3. Take the existing stereo output and just mix to mono but no HF or LF filtering. Amplify all 3 full-range channels and then filter the signals sent to each speaker.
I think I've probably ruled out 1 at the moment, the commonly available SBCs don't support 4 channels over I2S and I'm not convinced there aren't too many timing issues around the signal processing and USB audio interfaces. So it's between line level and speaker level crossovers - what are the pros and cons of each?
Do the mixing to mono and HF and LF filtering in hardware at the line level sounds like a better choice to me.
The third is a possibility that can turn expensive to have a good bass cut.
The first choice involve digital degeneration of mixing and filtering algorithms. Probably acceptable for the most of applications especially with the newer technology but, in my experience, it always been a less natural and less detailed configuration.
The third is a possibility that can turn expensive to have a good bass cut.
The first choice involve digital degeneration of mixing and filtering algorithms. Probably acceptable for the most of applications especially with the newer technology but, in my experience, it always been a less natural and less detailed configuration.
Many years ago I built a Linkwitz 3way active system. The LFs used a pair of Kef B139 built into a large coffee table and the mid/hf units (using Kef 110 & T27) suspended from the ceiling on chains.
His Linkwitz Riley active filters, with delay compensation and LF correction were a pain to build but the results were superb, especially the bass which could shake the house.
A few years later, I built a dipole system based on his design and this resulted in my liking for electrostatics (ESL 63 and Martin Logan Aeons)
Worth a read.
Linkwitz Lab - Loudspeaker Design
But I agree with others - do it in hardware.
Also I am puzzled why you want to convert to mono and then filter it. Why not just create a mono side chain and then low pass filter it for the sub and separate high pass filter the stereo for the mid/hf?
His Linkwitz Riley active filters, with delay compensation and LF correction were a pain to build but the results were superb, especially the bass which could shake the house.
A few years later, I built a dipole system based on his design and this resulted in my liking for electrostatics (ESL 63 and Martin Logan Aeons)
Worth a read.
Linkwitz Lab - Loudspeaker Design
But I agree with others - do it in hardware.
Also I am puzzled why you want to convert to mono and then filter it. Why not just create a mono side chain and then low pass filter it for the sub and separate high pass filter the stereo for the mid/hf?
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