You might want to look into the TacT gear.
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I've been bi-amping with a TacT RCS2.2X for 3 years. The previous format was a Placette passive Linestage and a modded Dahlquist DQ-LP1, which combo proved extremely transparent. What very slight loss of transparency was experienced has been more than compensated for by the ability to make room/speaker/woofer corrections in the time domain, choose a 60db/oct slope w/o phase shift, and smooth my low end frequency response(in the room) to with +/- 2db from 20 to 250hz. No losses whatever in sound staging, imaging, immediacy, or timbre, but rather a much greater sense of being present in the recording venue. Some of which I have(as a reference).
These are good up to a certain level. Once you get beyond a certain price point the built-in DAC's in these units are not as good as aftermarket DAC's. The other disadvantage is that these are PCM only, so no DVD-A or SACD. Also, if you want to use an analog source, you will have to run the signal through an ADC.
The advantage is the very steep crossover slopes you can achieve - up to 300dB/octave with no phase issues. Such steep slopes are unheard of in the analog crossover world ... well not without major problems.
You can also correct room anomalies digitally. This works by finding the null point in your room and subtracting all other frequencies to match the null point. In some cases you may find that you do not have enough gain, but I have been told that on some units it is possible to modify the op-amps in the output stage of the DAC to provide higher output if necessary.
I wish I could remember who it was but about 2 years ago at RMAF there was a guy that was demonstrating an open baffle 3 way kind of home brew loudspeaker. Well--sort of. What he was really demonstrating was a computer based digital crossover and eq system. He had relatively inexpensive amps and these reasonably priced drivers and then basically just crossed them over and did correction for the space he was in (completely untreated too). He was playing files off i-tunes and I thought he had a really nice demonstration. This was not high end, more high achievement for really pretty inexpensive components and I thought a really cool demonstration of what can be done digitally. If anyone knows who he was or his company name--please add it to this thread.
Selah Audio, which has a forum at audiocircle, can custom build a system using the DEQX. That's probably who Rives mentioned. Wouldn't surprise me that he wasn't trying to impress at a show.
If I was DIY'ing or doing a kit, I would go with a DEQX, with the exception of the BG ribbons, where the Wisdom DCAB is probably better suited.
The DEQX gives you what I call "lowest common denominator" sound. I was able to borrow a friend's DEQX and try it in my system since people think it is the audio equipment of The Second Coming. Even on straight through settings (no correction applied) the system took a big performance hit. The DAC's are just not as good as my CDP.
Although the DEQX can be used as a preamp, it is not a good preamp. The version I got to try had the optional analog volume control, and this was MUCH better than the digital volume control. You can easily hear the loss of resolution with the digital volume control - the sound was decimated and the quality is even worse than an iPod.
Another person tried running an analogue signal from a turntable into the DEQX and reported that the T/T sounded no better than CD. There are too many variables at play to definitively say if it was the DEQX which was blenderizing the sound but I suspect the ADC had a lot to answer for.
Digital crossovers are a very purist approach but you have to understand that it does come with certain limitations. No analogue sources for you - it will work, but whether it works well is another matter. Also, the DAC's in this particular DEQX iteration is no better than a low level CD player. If you have anything better than a mid-market CD player the DAC's are definitely better.
As with any hi-fi it is not a perfect solution. You get a performance benefit in some areas, but you also get a performance hit in others, and it suits certain types of consumer better than others. Good luck with your decision.
No, it wasn't DEQX. This was more or less home brewed off a PC. The PC had the crossover and all curves (which could be manipulated by the user) built in. It did correction for driver problems as well as room. I think the entire system probably cost a little more than a single DEQX unit.
Oh yeah--PC stands for "personal computer" here, not Power Cord!
Martykl don't get me wrong, the DEQX is a very good product. However the benefits of a unit like this has to be weighed against the losses that you get from the ADC (if used), the "not quite there" DAC's, and the digital processing. The controversy arises when people disagree on the weighting that should be given to the benefits and the losses.
The cons (as mentioned) are loss of resolution and an overly digitized sound. This is not so much of a problem when competing with low-end CD players or when the machine is inserted into a not-very-resolving signal chain. The signal still contains more resolution than most low to mid end speakers can handle - so the losses are masked, if you like.
However, the benefits of room correction, active crossovers with extremely steep slopes, group delay correction, phase control, etc. etc. are all there for the taking.
Do not underestimate the stunning results you can get from 300dB crossover slopes. I have heard the difference between the shallower slopes and the steep slopes, and the improvement in clarity is breathtaking. You can do things which are impossible with analog crossovers - for example, tweeters are typically crossed over at 3kHz with 12dB slopes to protect it from bass frequencies (meaning, -12dB at 1.5kHz, -24dB at 750Hz). With a 300dB slope, you could cross the tweeter over at 1.5kHz and still enjoy the same protection. There will also be no overlap with the midwoofer, since you can bring that up to 1.5kHz too.
IF you are like me and have a "finished" speaker with internal crossovers, you will not be able to exploit some of the best features of the DEQX so the balance changes markedly to the negative. Using the DEQX for room correction only is not worth the performance hit I get with the loss of resolution.
However, if you are a DIY enthusiast, or you can bypass the internal crossovers and are willing to purchase seperate amps for each driver, OR if the designer of your speaker did an incompetent job with the crossover or design, then the DEQX makes much more sense. In such a case the benefits will outweigh the cost.
Another thing. There have been a few threads on Audiogon recently about the evils of digital volume controls. This is because bits are thrown away prior to analog conversion - you lose resolution AND the signal goes closer to the noise floor. Room correction works by finding the null point in your room and subtracting other freq's to match the null point. So you can not get away from the digital volume control. If you are interested in room correction ONLY I would investigate an analog unit. I believe that Rives (who has posted above) makes one.
Disclaimer: no association with Rives, DEQX, TaCT, or any company.
I agree with Amfibius. The rate limiting step with the DEQX and other similar products is the DA conversion, which I find atrocious....it totally degrades the sound.
People are screwing around with new ways of doing this....one approach, taken by Clayton Shaw, at Spatial Computing, is to do all manipulation in the true digital domain (computer), including the x-over, room correction, etc. Time will tell.