[Bobby]

I contacted Dave via email yesterday asking him his thoughts on digital room correction (TACT, DEQX, Behringer, etc.).  One of the reasons why I would like to hear Dave's opinion on this subject is because he seems to back up his beliefs/designs with sound reasoning  (speaker measurements are available, etc.) and not "slick" dialog (let me tell you how great my product sounds but please don't ask for any design details or response plots).  Dave requested that I post this question on his forum so that others could participate in the discussion. 

[David Ellis]

I... remain on the fence with regard to digital room correction.  This a huge topic, but I will convey my thoughts briefly herein. I will address this topic in 3 areas:  advantages, the frequency impact, and what isn't commonly stated my purveyors of digital room correction gear.

First, there are a many folks who really love the advantage of digital room correction. The signal amplitude for the listening location can be corrected, a flat response is obviously more idea.

I have learned that in many rooms the frequency response above 300hz is generally flat.  When comparing an in room sweep response to a gated response there are extreme similarities.  While a detailed in room sweep will be very ragged due to reflections, the 1/3 octave average is generally flat, and matches the gated response from that speaker. 

Below 300hz, the matters is very different.  Due to the very long waveform and room interaction, there are significant modes and cancellations in most rooms.  This is "impossible" to avoid.  Only digital correction will alleviate this for the 1 listening position used for analysis.  In all other positions, the "correction" remains present.  The problems will remain present or be exaggerated.  So, while the digital correction might do a dandy job in the intended listening position, the remainder of the room may/will actually become worse due to the correction.

There are 2 things NOT stated by those conveying digital correction gear.  First, the gear DOES add processing.  Second, room reflections are not magically alleviated/eliminated by this gear.  Regarding the former, I am not an expert in digital processing, but those who are will happily convey the effects of digital problems such as jitter.  I believe that not all digital is created equal.  Some digital gear is better.  Some digital gear is worse.  Modifying the digital section of source components is alive and well.  I believe it is foolish to think that adding digital signal processing will have no impact on overall sound quality.  This difference may be small, but it is present.  Caveat: I have NOT done a focused a/b session with a piece of more common digital processing gear.  I have, however, done a solid a/b test with an active/passive crossover using 2 very similar and exceptionall good speakers.

The common conception is that an Active Crossover eliminates those nasty passive crossover components and will sound superior.  The result was that John K's active NAO didn't sound better than Jim Salk's passive HT3.  In fact, the performance of the SALK HT3 narrowly edged out the NAO in an audience of @ 20 gents.  Hmmmmm.

The other part of unmentionable information among digital processing propaganda is reflected waves.  While the digital processing gear will equalize the signal, it does not alleviate the reflections from the back wall, side walls, ceiling, or floor.  These do have an impact.

My CURRENT summary is this.

My system is very good.  I can easily discern the impact of a volume pot versus a stepped attenuator in my system. I will not add digital processing to fix the response level below 300hz to the marginal detriment of sound quality above 300hz. 

My opinion may change, but this is where it currently stands.

If someone wants to send me a piece of digital processing gear, I'd be happy to pay the shipping, and provide an appropriate response.

Also, I must convey that Jim Salk is probably a better source of information regarding the impact of using digital room correction.  Jim HAS fiddled with this gear, and can provide some input.  I do have a guess regarding his general response, but it would be better to read his comments directly.

I am sorry that my insight on this subject remains limited.  I... simply don't have the funds $$ to experiment with everything.  With many issues, I have to read between the lines, and make educated guesses.  This is obviously one of those areas.  My opinion on this matter should be taken as non-authoritative comments from a guy with some undersanding of the issues.

On a similar issue, I recently tried to implement a Cary 572MK2 SE into my system.  The balance of instruments and spl were fine, but... this is a very mediocre sounding amplifier when compared to the better stuff from the DIY folks.  My Golden Tube SE40SE (heavily modified) is considerably more expensive, but also sounds commensurately better.  My VanAlstine Ultimate 70 also sounds better than the 572.  I was hoping there might be a positive impact by using the Cary 572 SET at lower volume levels.  It didn't happen.  I was surprised.

Dave

[JoshK]

Philisophically I agree with Dave (phillisophically because I haven't tested it yet, but the math predicts that he is about right) that below 300hz it makes a difference, above 300, well...  Read Dr. Geddes' white paper on Summas and he talks about his belief that human hearing perception isn't as affected by modes >500 (iirc) as it is below.  He recommends dampening the first (lowest) mode, treating first reflections and then controlling directivity.  It seems he isn't in favor of a lot of action to treat >500hz. 

I think the real power of room correction is below 300hz or thereabouts.  But we don't all have similar rooms.  My room is super leaky with huge 9' tall by 14' wide archways into the next rooms, so bass SPL and overloading is quite different in my room then in most.  I actually need more bass power then most.  I still have standing wave issues but frequency sweeps show that it isn't like other rooms I have had.  Midrange is my problem since my room is too reflective. 

[DARTH AUDIO]

Hey Dave, I'm about to try the TacT 2.2 XP To see if it corrects the sound in my room. I can tell the difference going from a dedicated room with treatments to a condo living room with little treatments. The bass is boomy(is that a word?), the imaging isn't as precise. But I don't want foam and bass traps all over my room. I'll see first hand if the TacT works in my situation. BTW, the sweet spot always rules with or without room correction. I've had several conversations with the guys at TacT. It's worth a try since I can get my money back if I don't like it

But my question is what room correction devices have you tried to come up with your explanation? I'm not doubting your technical skill. Just wondering what room correction devices have you had in your system? I look forward to hearing more on this subject. I think Zybar(George) could add a lot of info on this topic??

Thanks,

Gary

[jsalk]

Dave asked me to comment on this thread, so here goes...

As some of you may be aware, our Veracity HT3's are normally set up with passive crossovers.  But I also have a version available for use in an active set-up (and have set up some pairs for customers using an passive/active option so they can use passive now and later move to active). 

I personally use DEQX and am quite pleased with the results.

First, the DEQX unit will correct for minor anomalies in the frequency response of the drivers.  Of course, the drivers we use are very accurate to begin with.  So the impact of this correction is probably not that significant (although the results are audible).

DEQX will also adjust phase response and "time align" the drivers.  This can be useful in enhancing imaging.  But, again, the passively-crossed HT3's do a good job in this regard to begin with.

The third area where DEQX comes in handy is tailoring bass response to the room.  This has been extremely beneficial for me personally, especially at audio shows where the rooms tend to be very poor acoustically.  While my personal listening space has nothing in terms of room treatments, but it is not too bad to begin with and I do not hesitate to demo the HT3's with passive crossovers.

The bottom line is that DEQX does provide some advantages over a passive crossover when used with the HT3's. 

I am often asked whether it is worth the investment in the DEQX unit and a 6-channel amplifier to drive a pair of HT3's.  This is a question I cannot answer for anyone but myself.  I just don't feel comfortable spending someone else's money. 

Going active will, at a minimum, double or triple the cost of an HT3 setup.  Does the improvement in performance justify the cost delta?  I am happy I have done it.  But I will not recommend it to others.  I will leave the answer up to each individual as their fiscal philosophies and budgets probably differ from mine.

I hope this helps.

- Jim

[fred]

I added a Behringer DEQ2496 a few months ago, and have been pleased with the results.  My equipment: 1801b speakers, Aksa-100 N+, Aksa GK-1R, and perpetual technologies P3A DAC. I have a very problematic room, with a brick wall & fireplace 3 feet away on the left, and an open area to the bar and kitchen on the right; windows directly behind the couch - my listening position; walls are hardwood panel, 8' ceiling.  My motivation for trying DEQ was that the bass (< 350 Hz) was very asymmetric - left side significantly louder than the right because of the closer wall (I assume).  The DEQ cured this.  If it did any damage to the sound, it isn't apparent - and I've done a number of A/B tests.  Oh yes, I also found it very helpful for blending in my subwoofers.

[meby]

Don't mean to high jack the thread.  But Fred have you used the DAC in the 2496?  How does it compare to the P3A?

[fred]

Meby - No, I haven't used the internal DAC - simply because others have said the stock DAC within it wasn't very good, and I already owned the P3A. There are some mods available that are supposed to improve it.  It should nevertheless be an interesting comparison - I'll give it a try when I have a chance.