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Best way to hook up subs?

Discussion in 'audio' started by sonddek, Mar 6, 2023.

  1. sonddek

    sonddek Trade: SUPATRAC

    I got fed up with Linn Akurate subs failing on me so I bought a KEF KC62 because it's really small, and then another one.

    I can't help suspecting that the AD-DSP-DA path through these subs has some kind of compromising effect on a good vinyl signal. Some kind of freshness, presence or credibility seems to get lost when I feed speakers from the high pass output of the KC62. Consequently I started feeding them only with the lower bass output from my active crossovers, which seemed to give a better result, but I'm now unsure whether there is some kind of delay in the KC62's high pass digital circuit.

    Would I be better off making a custom interconnect which splits the lower bass output to both lower bass driver and KC62 so that the KC62's DSP doesn't feed the lower bass amp? What's the downside to driving two 'amps' from a single RCA line output?

    Does anybody have views about the different ways to feed signal to a sub alongside other speakers? Is there a significant delay in a DSP sub like a KC62 which affects correct phase alongside a crisp analogue signal?
  2. moo-fi

    moo-fi pfm Member

    Interesting that you are not the first to be searching about delay time in KEF subs, there appear to be a few values floating about. Darko suggests 0,5m/s and Kef in one answer 0m/s and in the same answer then goes on to talk about 0.4m/s. Is this significant, perhaps?

    In any signal processing you have to like what comes out the other end, and in this case this would seem not to be the case. In work we always use the minimum possible, although it still shed loads to be truthful. In an ideal world you would only process the sound which is affected by the room, so typically around 300k and below, which then leads to a time delay between processed and unprocessed sound and this is something humans are very sensitive too.

    How does this help you, firstly you could try different processing/sub combination (we prefer outboard processing) as this gives more options to getting the sound right (and wrong).
  3. sonddek

    sonddek Trade: SUPATRAC

    Very interesting information. If I fork the active (analogue) crossover's lower bass output to the sub and lower bass driver, I can set crossover at the lowest point - 40Hz, with a period of 25ms, so 0.4ms represents a phase lag of only 6º at worst. That should be bordering on the inaudible at those frequencies, and certainly dwarfed by room reactions. I'm going to give it a try. These LS50 Metas are sounding superb on their own now, obviously without an abundance of very deep bass, but deep enough for quite rich orchestral and piano and very tuneful in the deep notes. I really bought the KC62s to go with my active Linn 242s, so I'm now going to compare the LS50s tout seul against KC62-boosted active 242s. That might seem like an unfair fight, but I don't need excessive volume and there's a lot to be said for simplicity.

    There's also an argument for leaving out the 242s' lower bass driver altogether. I was advised to crossover to the sub at 100Hz, but if I raise the cut-off to 140Hz it might sound good, albeit with a dip between 140Hz and 225Hz. Probably better to keep it in and crossover to the sub at 40Hz though. Time for a bit of Heath Robinson soldering.
  4. sonddek

    sonddek Trade: SUPATRAC

    Right now I'm taking sub input from the lower bass output of the 242 crossovers and then feeding the subs' high pass outputs to the lower bass amps. Subs are set to crossover at 40Hz. It's not bad at all. I'm not sure I prefer it to the Linn Akurate subs, but the KC62s are really small and I expect they'll be more reliable than the Linn Akurate subs. I can live with this. The LS50 Metas are on Ebay.
  5. Purité Audio

    Purité Audio Trade: Purite Audio

    I have asked KEF’s technical support, as soon as I hear.
  6. sonddek

    sonddek Trade: SUPATRAC

    Thanks - very helpful!
  7. Purité Audio

    Purité Audio Trade: Purite Audio

    Well we will see!

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