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Romy the Cat wrote:

For a casual observer it might appear that I am constantly fought with my ULF, finding and loosing better and worse configurations.  It might be so but I have a very strong sense of objective of what I would like to accomplish. I want to reinstate that Sound in my room what I was injecting +20dB at sub 20Hz in my room. However, I would like to do it in a way that under any circumstances would smear my midbass. Ironically to raise the order of ULF filter and to add volume does not work. It has to be, for some reasons, 18dB per octave and the key is to control the slop of that roll of. This is what I will be experimenting now, I know that I will find the solution as I have very strong visualization of what I need to get as the result. I have much option on the table. The DSP is one of them. I have Velodyne SMS-1 and I need to do the action only on one channel, so I might use it. I have another digital parametric EQ that I might use. I might implement notch filter and correct the slope’ bump. (Here is a homework for you: why I religiously against notch filters but feel that it will work fine in my case). There is a few other options, I will examine them. Actually the bigger question to me is why I like the Sound after my tube active crossover more than with line-level passive filter. The ULF IS better quality with line-level passive filter – I can testify it. But the ULF after the 4 stages of active tube filter make the ULF to sound that same as it come from the rest of the system – lash, measured and super polite. It does not have that thrilling ULF slam but it does not exist in real life ad well and I am trying to run as far from it as I can.  The ULF after that tube crossover is very pleasurable and listening I would quests that I have SS amp doing bass.  In way the tube crossover as my SS Yamaha B2 amp make the ULF amp to sound more similar to Milq. I personally feel that it has to do with characteristic distortions of 12AX4 in tube crossover – I happened to LOVE it in my “End of the Life Phonostage”. It will be VERY funny if I decide to stay with this tube active crossover as final version. For now, after a few day of listening with line-level passing I voluntary took it off and switched to tube active. It gives me a feeling as I am sitting at the table and do something and somebody performs a foot massage on me…  I am listening now the live broadcast from Symphony Hall with full production of Berlioz‘s Roméo et Juliette, Charles Dutoit leads BSO and Tanglewood Festival Chorus. I did not have time to calibrate my active crosier and set it up by pure intuition. I know that upperbass a bit eaten by my phase bitterly on right channel but the whole sound of the Symphony Hall is amazing.  With this ULF injection the whole room is breathing with sounds and I have absolutely no feelings of bass excessiveness. Just wonderful! I raise my glass to Karl Leonhard!

For now, without going digital, I have settled with 3rd order filter on left and 4th the order on right. I also run the right ULF 2dB louder then left.  To use different filter on right and left channel sound logical to address the ULF asymmetry of my room but it was a bit strange sounding at beginning. Eventually, when I discovered the need to drive the channel with higher order hotter it straights itself up.

So, I am taking that I can run ULF 10dB up and down and had not much impact to sound and at the same time I am very picky about 2dB right channel to be louder then left. What I am talking about then?

Well, this is the tricky part.  ULF serves not only lower extension of my Sound but also is acts almost as a delay channels, extending the reverberation time in my room. If the contribution of ULF in auditable sound might be very much tolerated to a large degree then the moderation of reverberation time is in my view need to be set more or less accurately.

Listening how ULF deal with decays in my room requires totally different type of listening. The room might dissipate only so much bass and so much infra bass. Pumping the room with ULF a create a critical mass of infra bass and further increased of it has no positive effect to auditable sound. This ULF level of saturation is very important as my ULF channels is NOT true ULF but it has SOME touch in auditable bass. So, the objective is to set the right level of auditable lower octave but in the same time to pump the room with max amount of ULF, under the level of room ULF saturation. This is what the slope of the filters and volume controls at each ULF channel become the tools of action. It is VERY interestingly that the “right level of auditable lower” with tube crossover is flexible but the right level of ULF saturation is very picky. With line-level passive filter and only SS amp it was in reverse: the “right level of auditable lower” was very demanding but ULF saturation level was very flexible. It is very interesting phenomena, read again to understand is and do not ask me about the reason – I do not know the reason.

So, what to listen while adjust the critical level of ULF saturation, or effectively the reverberation time on listening room? This is very good question. You will not always will be able to do it by the ambient sound of recording, even if you know the recording very well. What I suggest to do is to use tempo as the reference for reverberation time. Get a good recording of a good organist that you trust playing let say Bach. Max out your ULF and play Bach. The room will be too “long” and soon you will feel ( if your organist is a good one) that Back is being played slower than it has to be for the sound of your room. Close your eyes and listed the tempo with witch the notes are opening up. Pretend that you are the one who play it. Continue music to play but stop listening it and set your own tempo in your head with the respect to the reverberation in your room. Not begin to shorten your ULF output db by dB until your own feeling of right tempo will be absolutely identical to the tempo your organist. You need to be able to spell out loud the Bach notes with no timing discrepancies between the expressed tempo of your organist and your own feeling of tempo in your listening room. If you have a mute switch then it is very convenient to mute the sound, to continue with Back in your own tempo and then bring sound back. If you have good listening expertise then you do not need mute switch and can do it by singing the notes louder then sound of recording, or juts do the exercise in your mind.

Your objective shall be your absolute agreement with tempo of your organist.  You might disagree with his tempo but you need to have your own reasons why you or him did what you both did.  You might use not organ but a well recording piano but with piano recording there is a danger. Many piano recordings are vandalized by idiots sound engineer who inject into recording artificial sound reverberations and a mix from microphones installed inside the piano deck. It is bad as it is but the idiots do all of it after the pianist played, so those recordings has no human-induced and artistically-measured relation between reverberation and tempo.  It looks to me that the idiots do not temper so much with recordings of organs.

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