[ekovalsky]

24dB/octave digital crossovers (simulated Linkwitz-Riley) @ 60hz, 400hz, 2700hz are implemented, along with correction, by the S2150 amps using the freeware TACS program.  TACS runs great under Windows Vista.  I was plagued by com errors with XP and these don't happen with Vista.  I do not use the TacT software for the 2.2X or 2150 amps; it is not even installed on my laptop.

The RCS 2.2X used in bypass mode and is functionality is limited to digital signal distribution among the amps and generation of test tones for the Audiocontrol microphone.  The latter is a less expensive alternative to the Earthworks and does not require any calibration file.  The RCS 2.2X also acts as a digital volume control, but I have the amps set so that I usually have the 2.2X at 0dB i.e. no digital attenuation.  There is no loss of bits when controlling volume in the amps, as attenuation is achieved by lowering voltage on the output stage.  Of course some bits are inevitably lost in the correction process, but this is only a few dB (except in the woofers which lose up to 9dB at some frequencies where there is room reinforcement).  Not only is this insignificant with the 24 bit words used internally by the TacT equipment, but some digital attenuation is actually beneficial for most modern non-classical recordings.  While this may be counter-intuitive it reflects the typically too high levels used in modern recording, with potential clipping when reconstructing the analog signal from the digital samples.  Basically, clipping can potentially occur in the DAC even when the recording does not surpass 0dB.

By the way I have not and will not 'upgrade' the amps to the newer X series.  In many ways the X series is downgrade since the newer DSP boards cannot perform correction and crossover simultaneously.  Also they will not work with TACS software which is leaps and bounds ahead of anything TacT Audio has provided to its customers.  I believe the main benefit of the newer TacT equipment is ease of use and setup, as use of a PC is no longer obligatory.  For many customers and installers this is a good thing and will give good sound in minimal time, but as those with TacT and DeqX know achieving optimum results takes a lot of time with the PC and measuring equipment.  Also my amps and the 2.2X have been fully upgraded to eliminate issues with jitter and noise, in addition to the more typical capacitor, inductor, and transformer upgrades.

I remain completely satsified with the system and these ears have yet to hear anything that can really compare, save for the top of the line McIntosh setup which I felt on par (without correction but in a much larger room) in terms of quality, with dynamics that far exceed anything else on the market.  Alas that system costs more than most people's homes.

[95bcwh]

wow...pretty flat response..impressive..

But..I have no clue what the 1st graph and the 3rd graph means.. care to provide some eduction to newbies like me?

cheers

[ctviggen]

The first graph is a so-called "impulse response" graph. In theory, an "impulse" in the time domain has infinite height but no width and consequently has flat frequency response in the frequency domain.  (Infinite in one domain = finite in another domain.) What these programs do is send a signal out and measure that signal.  The measured signal is meant to be as close as possible to an impulse response.  In order to get an impulse response in the time domain, you must send out all frequencies equally.  So, they use a wide-frequency-band signal.  In particular, they use a maximum likelihood signal that is wide-frequency-band but also repeats.  This way, they can match up data coming back with data that was sent.  This way, they know when "zero" occurs. 

So, the first figure is a graph of the time domain response that occurs at a microphone in response to a wide frequency band signal played by the speakers.  You'll note that there's no undershoot before the main hump, which is good.  There's also not a lot of ringing (ringing would be bad).

A detriment to using MLS is that it's not good at under about 300Hz or so.  An ETF response curve, which uses steady-state frequency signals, would look different in the low frequency region.

The third graph is a graph of phase.  This one, I'm not too sure of, so I'll let someone else discuss this.

[Carlman]

Eric,
It's mighty impressive what you've done to get the most out of the TacT gear.  I use my 2.0S in bypass mode now all the time.  I feel the room is good enough now to go correctionless.  However, I think if I knew a bit more about how to employ the curves I'd be in better shape still.  So, thanks for leading the front on this.
-C

[ekovalsky]

wow...pretty flat response..impressive..

But..I have no clue what the 1st graph and the 3rd graph means.. care to provide some eduction to newbies like me?

cheers

The graphs reflect a full range test, in which three separate pulses (low, mid, high) are sent the speakers. 

First graph is the impulse/time response just as ctviggen mentioned, with only the HF pulse shown.  The x axis is time, showing 19-21 ms for a range of 2 ms, while amplitude in mV is on the y axis.  There are clearly two superimposed waves, the larger and faster one coming from the ribbon tweeters and the smaller and slower one coming from the midranges.  I use the 10% value of max amplitude for time alignment.  So at about 19.75 ms the tweeter and midrange drivers are both at 10% of maximum amplitude following the test pulse.  Digital filter latency is most pronounced with low pass filters and is inversely proportional to frequency.  So the subwoofer has the longest lag, making it the reference driver.  Progressive delays must be added to woofer, midrange, and tweeter groups to time align the system.  TACS allows you to select which pulse(s) to send to which driver group(s) and the most recent version somewhat automates the process, although I get better results doing it manually.  In the time alignment process, I use the HF pulse to align the tweeter and midrange, the MF pulse to align the midrange and woofer, and the LF pulse to align the woofer and subwoofer.  Since the speaker placement is exactly mirror imaged about the listening position, I only need to do the alignment process for one speaker as the values will be the same for the other. 

The middle graph is frequency response, which is derived from the impulse/time data via an FFT algorithm.  Note how symmetric the channel tracking is across the whole frequency band.  The few discrepancies reflect some asymmetric framing elements behind the room's symmetric walls; three walls are exterior and covered with stucco, while one is interior with a sliding door.  Unlike TacT's 2.2X software, with TACS you can measure the system after correction and that is what you see in this graph.  The resulting frequency spectrum exactly reflects the target curve I have programmed, which has a modest boost in the bass below 300hz, a minimal cut in the two octaves centered aroun 2.5khz, and a slight drop off at the high frequencies.  Low bass output is maintained to well below 20hz resulting in a palpable listening experience with appropriate program.

Bottom graph shows overall phase behavior.  The x axis is frequency and the y axis is phase in radians.  FIR or IIR filters are available on the tweeters.  Zero phase FIR filters inevitably are plagued by pre-ringing so I avoid them.  I feel that minimum phase IIR filters are a much better choice.  Overall the phase and group response are near ideal, deviating only in the bass which is related to the correction filter itself.  All the drivers run in the same electrical polarity; the stock passive filters invert polarity to the midrange which is quite common among three way speakers. 

[brj]

Very nice work, Eric!  You've obviously put a lot of work into getting such a balanced response!

three walls are exterior and covered with stucco, while one is interior with a sliding door.

Do you have a different audio room now than you did a year ago?  If so, and the new room is larger than the old, how much easier was it to dial in the system?

Thanks!

[Brucemck]

Ecovalsky ... can you post a link to information about the TACS software?

Thanks

[zybar]

Do you have a different audio room now than you did a year ago?  If so, and the new room is larger than the old, how much easier was it to dial in the system?

Thanks!

I believe Eric's room remains unchanged from a year ago.

George

[ekovalsky]

brj,

George is correct, there has been no change to the room.  There are/were plans to build it out but they are on hold for various reasons:

• I'm completely satisfied with the sound
• We may possibly buy or build another house in the near future
• Other projects (most recently a reef tank) have been absorbing resources i.e. time and $
  

...

Bruce, here is some background and some links about the TACS software

http://www.dirac.fr/tacs/

Look under the "Version francaise" header for documentation.  It is in French but you can still follow it pretty well by recognizing some words and particularly studying the pictures.  Or you can try Babelfish.  A pretty good tutorial is "TACS for Dummies" which has been translated into English as an Acrobat (pdf) file.  Alas it was written using a now outdated version of TACS so some of the recent feature additions are not mentioned.  The Release history section is quite thorough so you can see what exactly has been changed, omitted, or added with each new version.  The software has gotten progressively easier to use and more powerful.  Most recent download is from 8/2006 and is nearly feature complete.  TACS is totally free and is worth downloading even if just to play around if you do't have one or more 2150 amps.  Please realize that TACS will only cooperate with the original 2150 amps --  it does not work at all with the newer X versions, Millenium, Boz, Lyngdorf, etc. which have a totally redesigned DSP section.  The newer amps have some advantages and disadvantages, if anyone wants I can go into that in more detail.

I have uninstalled all the software provided by TacT Audio for the 2150 and 2.2X from my laptop as it is no longer needed -- not only is TACS far superior and sophisticated but TacT Audio has done a miserable/negligent job of updating their own software and correcting well documented bugs.  Hopefully they will do better with the newer product line since there are no 3rd party alternatives, at least yet.