Phono Stage upgrade to complement Dohmann Helix One Mk 2

drbond, In most cases both the HPF and the LPF built in to a high grade commercial sub would be ACTIVE filters, not the same as just inserting a capacitor in series with your main ampifier, which is a PASSIVE filter. The difference is that in an active or electronic crossover, usually there are some active gain components that correct for insertion loss (remember insertion loss from way back up this thread?). A side benefit of an active (electronic) crossover is you don’t have to be concerned too much about the input and output impedance of the driven and driving devices. In other words, you don’t have to worry about the input Z of the amplifier you are connecting to. Remember I mentioned that your amp with a 22K ohm input impedance needs about 0.1uF capacitance to roll off below 80Hz? With an active crossover set at 80Hz, you could buy a new amplifier with a very different input Z and not have to change anything. Also, you can just twist a knob to experiment with a lower or higher HPF point, if 80Hz is not satisfying. With a passive filter, you would have to re-calculate the capacitance and install the new value.

Also, your thinking about the cello frequencies as you outlined it in your post at 12:47 pm today is a bit off target. If the main speaker and subwoofer are well adjusted, then you will not hear a problem. Of course, that takes some thought and effort to get right, since as you say the cello operates right at the crossover frequencies one is most likely to use with a full range speaker + sub, 60 to 80Hz. Like everything else in life, there is no free lunch, which is why I have resisted subwoofers with my SLs even though I acknowledge the potential benefits. (I’m rethinking the issue as a result of this thread.) One point to consider is that subs are very re-sale-able, if you end up disappointed. There is a big market among home theater gurus. Finally, with a passive 6db filter, the chosen crossover point represents a frequency where the attenuation is -3db; it’s not flat down to the crossover point. Thus, another octave down is -9db, not -6db. Not so with most active crossovers.

@rauliruegas , if you listen to any modern music of course you do. It is all digitally recorded. I record other people's special records to my hard drive in 24/192. You can easily AB the recording with the original and nobody can tell the difference. In other words the full characteristics of my turntable playing a record are 100% maintained even after all this digital monkey business. It is also a lot of fun getting cool free music! 

@lewm , the problem is most commercial subs do not have any HPF. Yes, the LPF is always active. Analog crossovers add distortion and phase shifts. Some can shift phase 180 degrees with a knob but only by ear which is a trial and error nightmare. The crossover you are thinking about is too low. You should be up around 100 Hz to get the maximum benefit in terms of lowering distortion in the SLs. The problem is the subs have to be in time and phase with the SLs or you will hear them. this is true at 80 Hz also. I have listened to every crossover point and slope you can think of between 40 and 150 Hz 1 to 10th order slopes. As I have said before I can change crossovers on the fly from my listening chair. My Acoustats did better at 125 Hz. For some reason the SLs do better at 100 Hz. My guess is it is more surface area. Below that you start to loose headroom and increase distortion. Another issue is a subwoofer array for your system would be more involved than dr bond. He has 7 foot SLs with a high ceiling so below 200 Hz he is point source. You have 8 footers and if you have 8 or nine foot ceilings you are line source. In order to match the power projection of a line source speaker you have to have a line source sub array. This mean subwoofers at up to 6 foot intervals from wall to wall, corner to corner. I operate mine in stereo due to the high crossover point. Obviously, this is a more expensive set up but you are very clever and capable of building your own. 

@lewm , sorry I forgot to mention. At this moment I am using my outdated TacT 2.2X. I have a DEQX Pre 8 on order. It has a much faster processor so you do not have to worry about digital volume. When you lower volume in the digital domain you loose bits. With my Tact at low volumes you are worse than a CD about 12 bits. With the Pre 8 you are still above 24 bits. The Pre 8 also has four crossovers so I can see what a ribbon or horn tweeter will do above 12 kHz. There is the Pre 4 which is essentially the same unit as the 8 but with only one crossover for your subwoofers. You manage the units with your computer and a dedicated program. You can design any target curve equalizing the system any way you want. I keep mine dead flat until 100 hz where I increase the bass at about 3 dB.oct down to 20 Hz were I roll off steeply at 80 dB/oct creating a digital rumble filter. It also prevents launching your subwoofer cones across the room when you drop the tonearm:-)

If you look at the Stereophile review of even the old SoundLab A1, they measured the panel as flat out past 20kHz, so the need for a super tweeter escapes me. But of course ESLs do beam at HF. Depends where you sit, and your hearing acuity. Your present digital volume control would seem to be wanting in fidelity. Ok if you can run wide open.

@mijostyn  : " It is all digitally recorded.  "

For many years many of us knowed that and so what?. I can't control recording proccess. Can you?

R.